11156

PTP4A3

protein tyrosine phosphatase type IVA, member 3;PTP4A3;protein tyrosine phosphatase type IVA, member 3

potentially prenylated protein tyrosine phosphatase|protein tyrosine phosphatase type IVA 3|protein-tyrosine phosphatase 4a3|protein-tyrosine phosphatase of regenerating liver 3

8q24.3

protein-coding

PURPOSE: The aim of this study was to investigate the expression of the PRL-3 in human invasive breast cancer and to evaluate its clinical and prognostic significance. Its potential role in the invasive-metastatic properties of invasive breast cancer was also investigated. METHODS: Protein expression of PRL-3 was evaluated by immunohistochemistry for a consecutive series of 82 invasive human breast cancer tissues and 63 matched lymph node metastases, including PRL-3 mRNA expression analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) in malignant, nonmalignant breast tissue samples and lymph node metastases. We investigated the correlation of PRL-3 with clinicopathologic features, Overall and recurrence-free survival distribution curves were assessed using the Kaplan-Meier test and log-rank statistics, followed by Cox proportional hazards regression model. RESULTS: We found that 70.7% patients expressed a high level of PRL-3 protein in their tumors, and its over expression was positive correlated with lymph node metastasis (LNM) (P = 0.011). Moreover, The PRL-3 mRNA expression was significantly higher in malignant compared to benign breast tissue, while increased expression of PRL-3 mRNA was significantly associated with LNM (P = 0.002). Univariate analysis showed that the positive expression of PRL-3 was a poor risk prognostic factor (OS, P = 0.045; RFS, P = 0.034). Multivariate analysis using the Cox regression model indicated that high PRL-3 expression was an independent unfavorable prognostic factor for RFS. CONCLUSIONS: These results strongly suggest that PRL-3 expression can indicate the potential role of LNM to some extent. Increasing the risk of tumor metastasis (OR = 3.889). Our results also imply that PRL-3 might be a novel molecular marker for predicting relapse of invasive breast cancer.

To gain insights into the molecular basis for metastasis, we compared the global gene expression profile of metastatic colorectal cancer with that of primary cancers, benign colorectal tumors, and normal colorectal epithelium. Among the genes identified, the PRL-3 protein tyrosine phosphatase gene was of particular interest. It was expressed at high levels in each of 18 cancer metastases studied but at lower levels in nonmetastatic tumors and normal colorectal epithelium. In 3 of 12 metastases examined, multiple copies of the PRL-3 gene were found within a small amplicon located at chromosome 8q24.3. These data suggest that the PRL-3 gene is important for colorectal cancer metastasis and provide a new therapeutic target for these intractable lesions.

PURPOSE: Overexpression of PRL-3 has been implicated in colorectal cancer metastases. We investigated the significance of PRL-3 expression in the progression and development of colorectal cancer. EXPERIMENTAL DESIGN: We transfected PRL-3-specific small interfering RNA into human colon cancer DLD-1 cells and analyzed its effect on proliferation, motility, and hepatic colonization. Using an in situ hybridization method, we examined the levels of PRL-3 expression in both primary (177 cases) and metastatic (92 cases) human colorectal cancers and elucidated the relationships with clinicopathological parameters including the incidence of metachronous liver and/or lung metastasis after curative surgery for primary tumor. RESULTS: Transient down-regulation of PRL-3 expression in DLD-1 cells abrogated motility (in vitro) and hepatic colonization (in vivo), but no effect on the proliferation of these cells was observed. In human primary colorectal cancers, the frequency of up-regulated PRL-3 expression in cases with liver (84.4%) or lung (88.9%) metastasis was statistically higher than that in cases without either type of metastasis (liver, 35.9%; lung, 42.3%). In metastatic colorectal cancer lesions, high expression of PRL-3 was frequently detected (liver, 91.3%; lung, 100%). Interestingly, metachronous metastasis was observed more frequently in the cases with high PRL-3 expression (P < 0.0001). CONCLUSIONS: These results indicate that PRL-3 expression in colorectal cancers may contribute to the establishment of liver metastasis, particularly at the step in which cancer cells leave the circulation to extravasate into the liver tissue. In addition, PRL-3 is expected to be a promising biomarker for identifying colorectal cancer patients at high risk for distant metastases.

PURPOSE: The PRL-3 mRNA is consistently elevated in metastatic samples derived from colorectal cancers. We sought to generate a specific PRL-3 monoclonal antibody (mAb) that might serve as a potential diagnostic marker for colorectal cancer metastasis. EXPERIMENTAL DESIGN: PRL-3 is one of three members (PRL-1, PRL-2, and PRL-3) in a unique protein-tyrosine phosphatase family. Because the three PRLs are 76% to 87% identical in their amino acid sequences, it poses a great challenge to obtain mAbs that are specific for respective phosphatase of regenerating liver (PRL) but not for the other two in the family. We screened over 1,400 hybridoma clones to generate mAbs specific to each PRL member. RESULTS: We obtained two hybridoma clones specifically against PRL-3 and another two clones specifically against PRL-1. These antibodies had been evaluated by several critical tests to show their own specificities and applications. Most importantly, the PRL-3 mAbs were assessed on 282 human colorectal tissue samples (121 normal, 17 adenomas, and 144 adenocarcinomas). PRL-3 protein was detected in 11% of adenocarcinoma samples. The PRL-3- and PRL-1-specific mAbs were further examined on 204 human multiple cancer tissues. The differential expressions of PRL-3 and PRL-1 confirmed the mAbs specificity. CONCLUSIONS: Using several approaches, we show that PRL-3- or PRL-1-specific mAbs react only to their respective antigen. The expression of PRL-3 in >10% of primary colorectal cancer samples indicates that PRL-3 may prime the metastatic process. These mAbs will be useful as markers in clinical diagnosis for assessing tumor aggressiveness.

BACKGROUND: Human phosphatases of regenerating liver (PRLs) can induce cell growth, differentiation, and malignant transformation. In this study, we used specific polyclonal antibodies against PRLs to investigate their expression in colonic adenocarcinomas and its correlation with patient gender, age, tumor differentiation, localization, invasion, and metastasis. MATERIALS AND METHODS: The polyclonal antibodies against PRL-1, PRL-2, and PRL-3 were produced and purified. The expression of PRLs in human colorectal carcinoma cell lines (SW480 and SW620) was examined by Western blotting. We also examined their expression in normal and pathologic tissues from the human colon. The tissues included 49 primary colonic adenocarcinomas, 14 cases with lymph node metastases, 15 colonic adenomas, and 12 normal colon samples. Hematoxylin and eosin staining, immunohistochemistry, and semiquantitative morphological analysis were used to evaluate the sections. RESULTS: PRLs were widely expressed in SW480 and SW620. PRL-1, PRL-2, and PRL-3 were expressed, respectively, in 16, 10, and 16% of primary colonic adenocarcinomas. In contrast, PRLs were strongly expressed in all lymph node metastases. There were no significant correlations between the expression of PRLs and patient gender, age, tumor differentiation, depth of invasion, or localization of tumor within the different sections of the colon. PRLs were not expressed in normal colon tissues or in colonic adenomas. PRLs were mainly expressed in the cytoplasm and at the cytoplasmic membranes of the colonic adenocarcinoma cells as well as in the endothelial cells and the surrounding smooth muscle cells of larger vessels in the lymph node metastases. CONCLUSION: Colonic adenocarcinoma cells have the ability to produce PRLs, which may relate to the lymph node metastasis of colonic adenocarcinoma.

OBJECTIVE: To investigate the expression of phosphatase of regeneration liver-3(PRL-3) protein and its relationship with tumor invasion and metastasis in human colorectal carcinoma,and elucidate prognostic value. METHODS: Immunohistochemistry method was applied to detect the PRL-3 expression in the primary tumor specimens and paired paratumor normal tissues from 46 colorectal carcinoma patients, the adenoma tissues from 6 patients with colorectal adenoma, all the metastatic lymph nodes from 29 cases and the metastatic liver lesions from 6 cases. The relationship between PRL-3 expression and clinicopathologic parameters was analyzed and a survival curve was achieved according to Kaplan-Meier method. RESULTS: No or weak PRL-3 protein expression was detected in normal colorectal mucosa and colorectal adenoma. In colorectal carcinoma tissues, PRL-3 expression was confirmed in 26 of 46 cases (56.5%) of primary colorectal carcinomas (with lymph node metastasis 63.0%, without lymph node metastasis 37.0%, P=0.001), 26 of 29 (89.7%) lymph node metastases, and 5 of 6 liver metastases. The expression of PRL-3 was assembled in the cytoplasm of carcinoma cells and more intensively on the cell membrane.Analysis of the relationship between PRL-3 expression and the clinicopathologic features showed that PRL-3 expression was closely associated with tumor stage (P=0.019), lymph node metastasis (P=0.026), but no relationship with age, sex, tumor size, degree of differentiation was founded (P<0.05). The mean follow-up time was 41.4 months and results showed that patients with positive expression of PRL-3 had a significantly poorer prognosis than those with negative PRL-3 expression group(P=0.032). CONCLUSIONS: PRL-3 protein plays a novel role in tumor progression and metastasis of colorectal carcinoma. PRL-3 can be expected to be a potential predictive biomarker for identifying the prognosis in colorectal carcinoma patients.

Phosphatase of regenerating liver (PRL)-3 was identified as a molecule associated with liver metastasis in colorectal cancer (CRC), although its precise causative role in distant metastasis remains elusive from a clinical point of view. The aim of this study was to promote the mechanistic insight of PRL-3 involvement in liver metastasis in CRC. One hundred and seven CRC patients with resection of the primary lesions were studied for clinicopathological and prognostic association with PRL-3 and were evaluated by immunohistochemistry in univariate and multivariate analyses. Intense immunostaining of PRL-3 was found in Dukes' A (0/26), Dukes' B (0/30), Dukes' C (18/30) and Duke's D (20/21) although the PRL-3 expression could not predict metachronous liver metastasis (MLM) in Dukes' C patients. PRL-3 expression showed an inverse correlation of prognosis in a univariate prognostic analysis (P<0.0001), though a multivariate assay failed to demonstrate PRL-3 relevance as an independent prognostic factor. PRL-3 expression was closely associated with classic prognostic factors such as the pN factor (P<0.0001), H factor-synchronous liver metastasis (SLM) (P<0.0001), pT factor (P=0.0002), preoperative CEA (P<0.0001) and preoperative CA19-9 (P<0.0001). Multivariate logistic regression analysis of PRL-3 expression revealed that the pN factor (P<0.0001), CEA (P<0.0001) and CA19-9 (P<0.0001) were finally remnant as an independent association with PRL-3. However, the H factor (SLM) was eliminated. Our data suggested that liver metastasis by PRL-3 is putatively mediated through lymph node metastasis and elevated tumor markers in the serum and the PRL-3 expression may not represent a direct causative mechanism of liver metastasis.

Phosphatase of regenerating liver-3 (PRL-3) is a member of the PRL protein tyrosine phosphatase family and has been proposed to promote the invasiveness and metastastic capability of colorectal cancers (CRCs); however, the underlying mechanisms and target molecules of PRL-3 protein remain unknown. On the basis of the biological significance of PRL-3 phosphatase activity confirmed by the catalytically inactive PRL-3 mutant (C104S) and a PRL-3 inhibitor in CRC-derived SW480 cells, we performed protein expression profiling to search for PRL-3-mediated effector proteins. By a comparative study of phosphorylated proteins that differentially expressed in wild type and C104S mutant PRL-3-transfected SW480 cells; the cytoskeletal intermediate filament keratin 8 (KRT8) was identified as a physiological PRL-3-interacting protein. Indeed, treatment with the PRL-3 inhibitor effectively suppressed the phosphorylation of KRT8 at S73 and S431. Moreover, we detected the physiological interaction between PRL-3 and KRT8 and their colocalization at cellular lamellipodias and ruffles in vivo. In CRC tissue samples, tumor cells with high PRL-3 expression showed reduction or loss of phosphorylated KRT8 expression, particularly at the invasive front and in the liver metastases. In conclusion, our results indicate that PRL-3 may play an important role for the promotion of CRC cell migration and metastatic potential through direct KRT8 dephosphorylation.

BACKGROUND: Phosphatase of regenerating liver-3 (PRL-3) plays a causative role in tumor metastasis, but the underlying mechanisms are not well understood. In our previous study, we observed that PRL-3 could decrease tyrosine phosphorylation of integrin beta1 and enhance activation of ERK1/2 in HEK293 cells. Herein we aim to explore the association of PRL-3 with integrin beta1 signaling and its functional implications in motility, invasion, and metastasis of colon cancer cell LoVo. METHODS: Transwell chamber assay and nude mouse model were used to study motility and invasion, and metastsis of LoVo colon cancer cells, respectively. Knockdown of integrin beta1 by siRNA or lentivirus were detected with Western blot and RT-PCR. The effect of PRL-3 on integrin beta1, ERK1/2, and MMPs that mediate motility, invasion, and metastasis were measured by Western blot, immunofluorencence, co-immunoprecipitation and zymographic assays. RESULTS: We demonstrated that PRL-3 associated with integrin beta1 and its expression was positively correlated with ERK1/2 phosphorylation in colon cancer tissues. Depletion of integrin beta1 with siRNA, not only abrogated the activation of ERK1/2 stimulated by PRL-3, but also abolished PRL-3-induced motility and invasion of LoVo cells in vitro. Similarly, inhibition of ERK1/2 phosphorylation with U0126 or MMP activity with GM6001 also impaired PRL-3-induced invasion. In addition, PRL-3 promoted gelatinolytic activity of MMP2, and this stimulation correlated with decreased TIMP2 expression. Moreover, PRL-3-stimulated lung metastasis of LoVo cells in a nude mouse model was inhibited when integrin beta1 expression was interfered with shRNA. CONCLUSION: Our results suggest that PRL-3s roles in motility, invasion, and metastasis in colon cancer are critically controlled by the integrin beta1-ERK1/2-MMP2 signaling.

To better understand the role of PRL-3 in progression and metastasis of colorectal cancer (CRC), we searched for PRL-3 associated proteins using proteomic methods. We identified 39 PRL-3 associated proteins based on proteomic strategy. Stathmin, a key oncoprotein, was proved to be a new PRL-3 associated protein. Notably, co-immunoprecipitation assays in both endogenous CRC cell lines and CRC tissues indicated that PRL-3 could interact with stathmin. And, both stathmin and PRL-3 contributed to microtubule (MT) destabilization of CRC cells. Moreover, gain-of-function and loss-of-function analyses revealed that stathmin promoted proliferation, cell adhesion, and migration of human CRC cells. Immunohistochemical analysis of 149 colorectal tumor samples showed that overexpression of stathmin was strongly correlated with tumor differentiation (P = 0.035), tumor invasion (P = 0.024), lymph node status (P < 0.001), Dukes classification (P < 0.001), and TNM staging (P < 0.001) of CRC patients. Univariate and multivariate survival analyses further supported that overexpression of stathmin protein was a potential independent poor prognostic factor for CRC. Our results reveal many PRL-3 associated proteins for the first time. The oncoprotein stathmin plays a key role in CRC as a new target of PRL-3. Interaction between PRL-3 and stathmin leads to MT destabilization of CRC cells, which contributes to progression and metastasis of CRC.

CONTEXT: Phosphatase of regenerating liver (PRL) 3 messenger RNA (mRNA) was reported to express in human colorectal, gastric, ovarian, breast, and hepatic cancers. OBJECTIVE: To examine the expression of PRL-1 and PRL-3 mRNAs in human esophageal squamous cell carcinoma (ESCC). DESIGN: expression of PRL-1 and PRL-3 mRNA was examined with reverse transcriptase-polymerase chain reaction in fresh tissue collected from 40 cases of ESCC with matched lymph node metastasis in 21 cases. The association of expression of PRL-1 and PRL-3 mRNAs with clinicopathologic parameters was analyzed. RESULTS: The frequencies of PRL-1 and PRL-3 mRNA expression were significantly higher in ESCC than in normal esophageal tissue (P = .001; P = .01) and also significantly higher in ESCC with lymph node metastasis than in those without lymph node metastasis (P = .01; P = .03). The levels of PRL-1 and PRL-3 mRNA expression were significantly higher in ESCC with lymph node metastasis than in those without lymph node metastasis (P = .04; P = .04). The frequencies and levels of PRL-1 and PRL-3 mRNA expression were correlated with the later stages but not with tumor differentiation, tumor location in the esophagus, patient's sex, and age. CONCLUSIONS: PRL-1 and PRL-3 mRNAs may be involved in and used to predict the metastasis of ESCC. The possibility of using PRL-1 and PRL-3 as the therapeutical target is also discussed.

Phosphatase of regenerating liver (PRL)-3, encoding a 22-kD low molecular weight tyrosine phosphatase, has been reported to be associated with metastasis of colorectal carcinoma. We assessed the levels of PRL-3 mRNA expression to know whether its up-regulation was involved in progression and metastasis of gastric carcinoma. Levels of PRL-3 expression in 94 human gastric adenocarcinomas and 54 matched lymph node metastases were detected by in situ hybridization and compared with clinicopathological characteristics including prognosis. High PRL-3 expression was detected in 36.2% of primary gastric carcinoma (with nodal metastasis, 55.6%; without nodal metastasis, 10%; P < 0.001) and in 74.1% of lymph node metastases. The incidence of high PRL-3 expression in lymph node metastasis was significantly higher than in primary tumors (P < 0.044). Moreover, high expression of PRL-3 was closely associated with tumor size, lymphatic invasion, venous invasion, extent of lymph node metastasis, and tumor stage. These results suggest that high PRL-3 expression may participate in the progression and metastasis of gastric carcinoma. PRL-3 might be a novel molecular marker for aggressive gastric cancer.

High PRL-3 expression had been reported to have close association with lymph node metastasis (LNM) of gastric cancer. However, the prognostic significance of highly expressing PRL-3 in LNM of human gastric cancer and the role in the metastasis remain unclear. Our study examined PRL-3 expression both in the LNM (n = 107) and in the primary lesion (n = 137) of gastric cancer, and compared the overall survival rates. RNA interference, induced by recombinant plasmid pcDNA.rPRL3-miR expressing artificial PRL-3 miRNA, was employed to knockdown PRL-3 expression in human SGC7901 gastric cancer cells. Invasion assay and migration assay in vitro were conducted to determine the role of PRL-3 in the metastasis. The role of PRL-3 in the proliferation of SGC7901 cells and tumor growth were also determined. We observed that high PRL-3 expression was more frequently detected in the LNM than in the matched primary lesion (72.9 vs. 47.7%, p < 0.001). Furthermore, the overall survival rate of the patients with high expression of PRL-3 in the LNM was significantly less than those with moderate/low expression (p = 0.003). Importantly, knockdown of PRL-3 can significantly reduce both invasion and migration potencies of SGC7901 cells (p < 0.001), and significantly suppressed the proliferation of SGC7901 cells and slowed down the tumor growth (p < 0.001). It was concluded that high expression of PRL-3 in the LNM had a negative impact on the prognosis of the patients, and plays important roles in LNM of gastric cancer and the tumor growth, which can be a potential therapeutic target and a prognostic factor.

OBJECTIVE: Overexpression of phosphatase of regenerating liver-3 (PRL-3) has been implicated in tumor progression and metastasis of gastric carcinoma. Here we examined what alterations occur in the phenotype of gastric cancer cells in vitro and in vivo when PRL-3 expression is knocked down. METHODS: We constructed a small interfering RNA (siRNA)-expressing vector which stably interfered with PRL-3 expression and was transfected into SH101-P4 cells, which express the highest PRL-3 mRNA levels among 13 gastric cancer cell lines. The new SH101-P4 subclones, in which PRL-3 was stably reduced, were established and their in vitro growth, motility and abilities of liver metastasis from the injected spleen were analyzed in vivo. RESULTS: PRL-3 knockdown effectively suppressed invasion and growth of SH101-P4 cells in vitro. Liver metastasis in vivo was significantly decreased when PRL-3 expression was suppressed. The primary tumor size in the injected spleen tended to be smaller in PRL-3 knockdown clones than in the controls. These findings suggest that PRL-3 expression may contribute not only to the establishment of metastasis but also to the growth of primary foci of human gastric cancer. Therefore, PRL-3 may be one of the target molecules in gastric cancer therapy.

Phosphatase of regenerating liver (PRL)-3 is involved in the metastasis of various tumors, but the expression of PRL-3 and its possible role in primary intrahepatic cholangiocarcinoma (ICC) has not been reported yet. In this study, we assessed the expression levels of PRL-3 by immunohistochemistry in 102 primary ICC samples, 62 matched lymph node metastases (LNM) and 102 adjacent normal liver tissues. Then we investigated the relationship between PRL-3 expression and clinicopathologic factors. Survival analysis was performed to determine the prognostic significance of PRL-3 expression in ICC. Immunochemistry results suggested PRL-3 expression was negative or weak in non-neoplastic intrahepatic bile ducts of adjacent liver tissue. In primary lesion and LNM high PRL-3 expression was frequently detected. Furthermore, the rate of high PRL-3 expression in LNM was higher than that in primary lesion (80.6% vs. 47.1%, P < 0.05). High expression of PRL-3 in primary tumors was significantly associated with TNM (P < 0.001), T stage (P < 0.001), vascular invasion (P = 0.002), and LNM (P < 0.001). Survival analysis results with Kaplan-Meier method and Cox proportional hazard model indicated high expression of PRL-3 was correlated with decreased overall survival and was an independent prognostic marker of overall survival. Thus, our results suggested high expression of PRL-3 was correlated with progression and metastasis of ICC and indicated negative prognostic impact. PRL-3 might serve as a novel prognostic marker for patients with ICC.

BACKGROUND: Phosphatase of the regenerating liver (PRL)-3 protein tyrosine phosphatase gene is expressed in colon cancer metastasis. To investigate the role of this gene in metastatic lung cancer, we compared PRL-3 gene expression between primary cancers, metastatic lung cancer, and normal lung tissue. MATERIALS AND METHODS: Five metastatic tumor and normal samples from non-small cell lung cancer patients were obtained at the National Hospital Organization Kumamoto Medical Center (Kumamoto, Japan). For a quantitative evaluation of RNA expression by PCR, we used Taqman PCR methods. RESULTS: Although PRL-3 gene expression levels in the primary lesions were slightly decreased compared with those in the normal tissues, those in the metastatic lesions were extremely down-regulated in the synchronous metastatic case. In 2 of these 3 cases, the metastatic tumors showed down-regulated PRL-3 gene expression at 10 times less than that of the normal tissue, and the other tumor showed a slightly weaker expression. CONCLUSION: These data suggest that a down-regulation of the PRL-3 gene is important in lung cancer metastasis and provide a new hypothesis of lung cancer metastases.

BACKGROUND: Phosphatase of regenerating liver-3 (PRL-3) is a member of the novel phosphatases of regenerating liver family, characterized by one protein tyrosine phosphatase active domain and a C-terminal prenylation (CCVM) motif. Though widely proposed to facilitate metastasis in many cancer types, PRL-3's cellular localization and the function of its CCVM motif in metastatic process remain unknown. METHODOLOGY/PRINCIPAL FINDINGS: In the present study, a series of Myc tagged PRL-3 wild type or mutant plasmids were expressed in B16F1 melanoma cells to investigate the relationship between PRL-3's cellular localization and metastasis. With immuno-fluorescence microcopy and cell adhesion/migration assay in vitro, and an experimental passive metastasis model in vivo, we found that CCVM motif is critical for the localization of PRL-3 on cell plasma membrane and the lung metastasis of melanoma. In particular, Cystine170 is the key site for prenylation in this process. CONCLUSIONS/SIGNIFICANCE: These results suggest that cellular localization of PRL-3 is highly correlated with its function in tumor metastasis, and inhibition of PRL-3 prenylation might be a new approach to cancer therapy.

A high percentage of uveal melanoma patients develop metastatic tumors predominantly in the liver. We studied the molecular profiles derived from gene expression microarrays and comparative genomic hybridization microarrays, to identify genes associated with metastasis in this aggressive cancer. We compared 28 uveal melanomas from patients who developed liver metastases within three years of enucleation with 35 tumors from patients without metastases or who developed metastases more than 3 years after enucleation. Protein tyrosine phosphatase type IV A member 3 (PTP4A3/PRL3), was identified as a strong predictor of metastasis occurrence. We demonstrated that the differential expression of this gene, which maps to 8q24.3, was not merely a consequence of 8q chromosome overrepresentation. PTP4A3 overexpression in uveal melanoma cell lines significantly increased cell migration and invasiveness in vivo, suggesting a direct role for this protein in metastasis. Our findings suggest that PTP4A3 or its cellular substrates could constitute attractive therapeutic targets to treat metastatic uveal melanomas.

PURPOSE: expression of the PRL-3 tyrosine phosphatase is elevated in liver metastases derived from colorectal cancer (CRC). We sought to determine the cellular basis of this elevation and assess the expression of PRL-3 in metastatic lesions derived from cancers of the colon and other tissues. EXPERIMENTAL DESIGN: We developed modifications of in situ hybridization methods that facilitated the study of paraffin-embedded sections. We also evaluated PRL-3 gene copy numbers using fluorescence in situ hybridization and developed antibodies to assess PRL-3 subcellular localization. RESULTS: PRL-3 mRNA expression was elevated in nearly all metastatic lesions derived from CRCs, regardless of the site of metastasis (liver, lung, brain, or ovary). expression was found in neoplastic cells, although tumor endothelium also expressed the gene. In contrast, little or no PRL-3 expression was observed in normal colon, nonmetastatic primary cancers, or metastatic lesions derived from cancers other than those of the colon (pancreas, stomach, or esophagus). Interphase fluorescence in situ hybridization confirmed that gene amplification was not the major cause of PRL-3 overexpression. Immunohistochemical analysis with anti-PRL-3 antibodies showed a cell membrane localization, consistent with the predicted isoprenylation of the protein. CONCLUSIONS: These studies establish an unexpected and unprecedented specificity in metastatic gene expression profiles: PRL-3 is apparently expressed in CRC metastases to any organ but is not expressed in metastases of other cancers to the same organs or in nonmetastatic CRCs. PRL-3 is also expressed in tumor vasculature, regardless of the tumor source. These data raise intriguing questions about the role of protein phosphorylation in angiogenesis and cell-type-specific metastatic processes.

PRL-3 protein belongs to the family of protein tyrosine phosphatases with unique COOH-terminal prenylation motif, which determines the functions of this protein and its location in the cell. Numerous research studies revealed that apart from performing the poorly investigated physiological role, PRL-3 takes part in the process of carcinogenesis. Specifically, it is involved in reconstructing of the cytoskeleton, regulating adhesion and cell cycle of the cancer cells, and in epithelial-mesenchymal transition. Through these mechanisms PRL-3 protein participates in invasion, migration, metastasis and angiogenesis. Numerous studies indicate that PRL-3 expression is particularly important in colorectal, as well as in gastric, ovarian and breast carcinomas. Recently, several studies on PRL-3 protein in other types of cancer have been published. They reveal a significant role of this protein in the process of angiogenesis and metastasis. It has been proven that a higher expression of PRL-3 correlates with tumor progression and its severity. While the degree of overexpression of PRL-3 varies in different types of tumors, most research shows that in the metastases of these tumors, whether to the lymph nodes or to other organs, the level of expression is extremely high. Overexpression of PRL-3 protein was repeatedly confirmed in metastases, but not with primary tumors. PRL-3 seems to be an adequate marker in diagnosing the stage of tumor advancement for various types of carcinomas, especially for colorectal carcinoma investigated thoroughly in this study. PRL-3 overexpression predicts poor prognosis in patients with various carcinomas and is a promising target in the cancer treatment.