9788

MTSS1

metastasis suppressor 1;MTSS1;metastasis suppressor 1

metastasis suppressor YGL-1|metastasis suppressor protein 1|missing in metastasis protein

8p22

protein-coding

Using a modified version of the mRNA differential display technique, five human bladder cancer cell lines from low grade to metastatic were analyzed to identify differences in gene expression. A 316-bp cDNA (C11-300) was isolated that was not expressed in the metastatic cell line TccSuP. Sequence analysis revealed that this gene was identical to KIAA 0429, has a 5.3-kb transcript that mapped to 8q24.1. The protein is predicted to be 356 amino acids in size and has an actin-binding WH2 domain. Northern blot revealed expression in multiple normal tissues, but none in a metastatic breast cancer cell line (SKBR3) or in metastatic prostatic cancer cell lines (LNCaP, PC3). We have named this gene Missing in metastasis (MIM) and our data suggest that it may be involved in cytoskeletal organization.

We previously identified MIM-A (missing in metastasis, MTSS1) by differential display techniques as missing in invasive, metastatic bladder cancer cell lines and suggested that MIM-A is a novel putative metastasis suppressor gene. Characterization of the MIM gene revealed a WH2 (Wiskott-Aldrich syndrome protein homology 2) domain in the C-terminus that is known to bind actin monomers and regulate organization of the actin cytoskeleton. Here, we further describe two alternatively splice variants of MIM-A, called MIM(12del) and MIM-B, which share > 50% amino acid sequence homology with MIM-A in the C-terminal domain. We show that expression of all three transcripts is down-regulated in prostate cancer cell lines and tumor samples from patients. In addition, we generated stably-transfected PC-3 cells overexpressing MIM-A to evaluate the importance of MIM-A in prostate cancer biology. The initial experiments show that expression of MIM decreased the number of actin filaments and was associated with a decrease in the G:F actin ratio. Overexpression of MIM-A had no effect on PC-3 cell adhesion to extracellular matrices, as well as no effect on PC-3 motility. Further, overexpression of MIM-A reduced the rate of PC-3 cell proliferation. These results support the hypothesis that MIM-A is an actin-binding protein and implicate a role of MIM-A in the regulation of cellular proliferation. These data suggest that the reduction of MIM-A gene expression in prostate cancer and other cancers may contribute to tumor growth and development, as well as metastasis.

MIM/MTSS1 was initially described as a gene missing in invasive bladder cancer cell lines. Functional analysis revealed that MIM is an actin binding protein involved in the regulation of actin cytoskeleton dynamics. MIM was shown to be sonic hedgehog (Shh) signaling dependent and synergizes with the effects of Gli transcription factors. Overexpression of MIM in cell lines leads to the inhibition of cell proliferation. In this study, we showed that the inhibition of cell growth by MIM is anchorage independent. We identified and cloned the promoter region of MIM and located the main promoter activity to 276 bp of 5' flanking sequence sited within a CpG island. Analysis of DNA methylation using bisulphite sequencing revealed that MIM promoter is methylated in its 5' region in cells and tissue samples with reduced endogenous MIM expression. Using luciferase reporter assay, we demonstrated that nonmethylated MIM promoter has a similar activity in cell lines with different endogenous MIM expression. Inhibition of DNA methylation by 5-Aza-2'-deoxycytidine led to upregulation of MIM expression in a low expressing cell line. In conclusion, we clearly demonstrate here that the expression of metastasis suppressor MIM is regulated by DNA methylation of a CpG island within its promoter region.

MTSS1 (metastasis suppressor-1) was first identified as a metastasis suppressor missing in metastatic bladder carcinoma cell lines. The down-regulation of MTSS1 that may be caused by DNA methylation was also observed in many other types of cancer. While accumlating evidence for the function of MTSS1 support the concept that it is unlikely to be a metastasis suppressor, but actually acts as a scaffold protein that interacts with multiple partners to regulate actin dynamics. It has also been demonstrated that MTSS1 is involved in the Shh signaling pathway in the developing hair follicle and in basal cell carcinomas of the skin. Such evidence indicates that MTSS1 as a multiple functional molecular player and has an important role in development, carcinogenesis and metastasis. However, the biochemical mechanisms by which MTSS1 functions in cells and the physiological role of this protein in animals remain largely unknown. In this review, we will discuss the current knowledge of MTSS1's role in cancer metastasis, carcinogenesis, and development. The clinical significance of MTSS1 will also be discussed.

BACKGROUND: metastasis suppressor 1 (MTSS1) is proposed to function as a cytoskeletal-associated protein, which may play a role in the aggressiveness of cancer cells. Recent studies have demonstrated a clinical significance of MTSS1 in certain types of cancer, but its role in bladder cancer remains unknown. We investigated the expression of MTSS1 in normal and malignant human bladder tissues and its molecular interaction within bladder cancer cells. MATERIALS AND METHODS: The expression of MTSS1 in human bladder tissues and bladder cancer cell lines was assessed at both the mRNA and protein levels using reverse transcription-PCR (RT-PCR) and immunohistochemistry, respectively. Full-length MTSS1 cDNA was amplified from normal mammary tissues. The effect of MTSS1 overexpression on cellular functions was examined in bladder cancer cells using a variety of in vitro assays. RESULTS: Transitional cells of bladder tissues stained positively for MTSS1. However, cancer cells from tumour tissues did not stain for MTSS1. Similarly, in bladder cancer cell lines, MTSS1 was almost absent from T24 and RT112 cells, and the EJ138 cell line expressed a very low level of MTSS1. Overexpression of MTSS1 reduced the growth and adhesion of bladder cell lines in vitro. However, overexpression of MTSS1 had no bearing on the invasion and migration of bladder cell lines in vitro. CONCLUSION: MTSS1 is expressed at low levels or is absent from human bladder cancer cells. MTSS1 levels are inversely correlated with the growth and adhesion of bladder cancer cells in vitro. MTSS1 appears to be a potential tumour suppressor in human bladder cancer.

metastasis suppressor 1 (MTSS1) may play an important role in cancer metastasis. Firstly, this study assessed MTSS1 expression levels within breast cancer patients to reveal any clinical relevance. Secondly, we aimed to clarify the cellular function of MTSS1 in breast cancer cells. MTSS1 expression levels were assessed in a cohort of breast cancer specimens (normal n=33; cancer n=127), through quantitative PCR analysis and immuno-histochemical techniques. The influence of MTSS1 was further examined via biological overexpression and knockdown within breast cancer cell lines. We report that patients with tumours expressing reduced levels of MTSS1 had a poorer prognosis (p=0.042). High levels of MTSS1 correlated with an increased patient overall survival (p=0.0108) and disease-free survival (p=0.012). Furthermore, overexpression of MTSS1 significantly suppressed (p<0.01) the invasive, migratory, growth and adherence properties of a human breast cancer cell line. In contrast, knockdown of MTSS1 dramatically enhanced these properties. We conclude that MTSS1 is a prognostic indicator of disease-free survival in breast cancer patients and demonstrates the ability to play a role in governing the metastatic nature of breast cancer cells.

Molecular pathogenesis of high-grade serous ovarian carcinoma (HG-SOC) is poorly understood. Recent recognition of HG-SOC precursor lesions, defined as serous tubal intraepithelial carcinoma (STIC) in fimbria, provides a new venue for the study of early genetic changes in HG-SOC. Using microRNA profiling analysis, we found that miR-182 expression was significantly higher in STIC than in matched normal Fallopian tube. Further study revealed that miR-182 was significantly overexpressed in most HG-SOC cases. To test whether miR-182 plays a major role in early tumourigenesis of HG-SOC, we overexpressed miR-182 in immortalized ovarian surface, Fallopian tube secretory cells and malignant ovarian cell lines, and found that miR-182 overexpression resulted in increased tumour transformation in vitro, and enhanced tumour invasiveness in vitro and metastasis in vivo. Mechanistically, we demonstrated that the oncogenic properties of miR-182 in ovarian cancer were mediated in part by its impaired repair of DNA double-strand breaks and negative regulation of breast cancer 1 (BRCA1) and metastasis suppressor 1 (MTSS1) expression as well as its positive regulation of the oncogene high-mobility group AT-hook 2 (HMGA2). Our findings suggest that miR-182 dysregulation confers powerful oncogenic potential in the tumourigenesis of HG-SOC. Copyright (c) 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

metastasis suppressor 1 (MTSS1) is an important tumor suppressor protein, and loss of MTSS1 expression has been observed in several types of human cancers. Importantly, decreased MTSS1 expression is associated with more aggressive forms of breast and prostate cancers, and with poor survival rate. Currently, it remains unclear how MTSS1 is regulated in cancer cells, and whether reduced MTSS1 expression contributes to elevated cancer cell proliferation and migration. Here we report that the SCFbeta-TRCP regulates MTSS1 protein stability by targeting it for ubiquitination and subsequent destruction via the 26S proteasome. Notably, depletion of either Cullin 1 or beta-TRCP1 led to increased levels of MTSS1. We further demonstrated a crucial role for Ser322 in the DSGXXS degron of MTSS1 in governing SCFbeta-TRCP-mediated MTSS1 degradation. Mechanistically, we defined that Casein Kinase Idelta (CKIdelta) phosphorylates Ser322 to trigger MTSS1's interaction with beta-TRCP for subsequent ubiquitination and degradation. Importantly, introducing wild-type MTSS1 or a non-degradable MTSS1 (S322A) into breast or prostate cancer cells with low MTSS1 expression significantly inhibited cellular proliferation and migration. Moreover, S322A-MTSS1 exhibited stronger effects in inhibiting cell proliferation and migration when compared to ectopic expression of wild-type MTSS1. Therefore, our study provides a novel molecular mechanism for the negative regulation of MTSS1 by beta-TRCP in cancer cells. It further suggests that preventing MTSS1 degradation could be a possible novel strategy for clinical treatment of more aggressive breast and prostate cancers.

metastasis suppressor 1 (MTSS1) is a novel metastasis suppressor gene in a variety of cancers. This study aimed to detect MTSS1 expression in normal and cancerous tissue specimens from Chinese patients with hilarcholangiocarcinoma to determine the association with clinicopathological parameters and survival. Tissue microarrays containing normal and tumor specimens were constructed using paraffin blocks from 61 patients for immunohistochemical analysis of MTSS1 expression. A subgroup of these tissues was verified by Western blot analysis. MTSS1 protein was expressed in 24 of 61 cases (39.3 %) of tumor tissues, compared to that in 22 of 26 (84.6 %) of non-neoplastic bile duct epithelium and in 26 of 26 (100 %) of adjacent normal liver cells. Loss of MTSS1 expression was associated with lymph node metastases of cholangiocelluarcarcinoma and tumorcellde-differentiation.MTSS1 expression inversely associated with tumor recurrence and overall survival of the patients by univariate and multivariate analyses. MTSS1 expression was significantly decreased in human hilarcholangiocarcinoma and lost MTSS1 expression was associated with pooroverall survival and tumor recurrences in cholangiocarcinoma patients. Thus, MTSS1 expression represents an independent predictor for tumor recurrence and overall survival in patients with cholangiocarcinoma.

OBJECTIVE: To investigate the expression of miR-23a and metastasis suppressor 1 (MTSS1) and their clinical significance in colon carcinoma. METHODS: A total of 92 cases of colon carcinomas were collected with both the tumor and paired normal tissue samples for the study. The miR-23a targeting MTSS1 was evaluated by luciferase reporter vector. Cell invasion potential was evaluated by trans-well invasion assay. In-situ hybridization and immunohistochemistry were used to detect miR-23a and MTSS1 expression. RESULTS: MiR-23a downregulated the expression of MTSS protein and enhanced the invasiveness of colon carcinoma. The expression rates of miR-23a and MTSS1 were 87.0% (80/92) and 17.4% (16/92) in colon carcinoma cases, respectively (P < 0.01). The up-regulation of miR-23a expression was associated with an advanced clinical stage (P = 0.029) and depth of invasion (P = 0.000). The expression of miR-23a was higher in the tumors with lymph node metastasis than those without (P = 0.041). Down-regulation of MTSS1 expression was associated with an advanced clinical stage (P = 0.027) and depth of invasion (P = 0.017). The expression of MTSS1 was lower in the tumors with lymph node metastasis than those without (P = 0.009). The expression of miR-23a had significantly negative correlation with that of MTSS1 (r = -0.594, P = 0.013). CONCLUSIONS: MiR-23a expression promotes colon carcinoma cell growth, invasion and metastasis through inhibition of MTSS gene. Both the low expression of MTSS1 and high expression of miR-23a may serve as important biological markers for the malignant phenotypes of colon cancer, such as invasion and metastasis.

BACKGROUND: The putative tumor metastasis suppressor 1(MTSS1) is an actin-binding scaffold protein that has been implicated to play an important role in carcinogenesis and cancer metastasis, yet its role in the development of gastric cancer has not been well illustrated. In this study, we detected MTSS1 expression and explored its clinical significance in gastric cancer. METHODS: Immunohistochemistry was performed using tissue microarrays containing gastric adenocarcinoma specimens from 1,072 Chinese patients with normal adjacent mucosa, primary gastric cancer and lymph node (LN) metastasis and specific antibody against MTSS1. MTSS1 mRNA and protein expression were detected by reverse transcription-polymerase chain reaction and Western blotting. The clinical follow-up was done in the 669 patients living in Shanghai that was chose from the 1072 cases. RESULTS: Complete loss of MTSS1 expression was observed in 751 cases (70.1%) of the 1,072 primary tumors and 103 (88%) of 117 nodal metastases; and loss of MTSS1 expression was significantly associated with poorly differentiated tumors, large tumor size, deep invasion level, the presence of nodal metastases and advanced disease stage. Moreover, multivariate analysis demonstrated that loss of MTSS1 expression correlated significantly with poor survival rates (RR = 0.194, 95% CI = 0.144-0.261, P < 0.001). CONCLUSIONS: MTSS1 expression decreased significantly as gastric cancer progressed and metastasized, suggesting MTSS1 may serve as a useful biomarker for the prediction of outcome of gastric cancer.

Mtss1 is located within chromosomal region 8q23-24, which is one of the three most commonly amplified regions in head and neck squamous cell carcinoma (HNSCC). Mtss1 is lost in metastatic cells, but confusingly is commonly overexpressed in primary tumors. Here we address possible reasons why Mtss1 is positively selected for in primary tumors. We find that Mtss1 enhances the localization of the epidermal growth factor (EGF) receptor to the plasma membrane, prolonging EGF signaling and resulting in enhanced proliferation in HNSCC. Depletion of Mtss1 results in decreased EGF receptor levels and decreased phosphorylation of Erk1/2 and Akt. However, when cells are at high density and adherent to each other, analogous to conditions in a solid tumor, Mtss1 does not confer any growth advantage, either in basal conditions or following EGF stimulation. This could indicate why Mtss1 might be lost in metastases, but preserved in early primary tumors. This is supported by an organotypic assay showing that Mtss1-expressing cells display a less proliferative more epithelial-like morphology on top of a collagen matrix. Furthermore, xenograft tumors expressing Mtss1 initially grow more rapidly, but later show less proliferation and more differentiation. Mtss1 positively modulates EGF signaling at low cell densities to promote proliferation and, therefore, may be beneficial for the early stages of primary HNSCC tumor growth. However, at high cell densities, Mtss1 impacts negatively on EGF signaling and this suggests why it inhibits metastasis.

OBJECTIVE: To investigate the effects of lentivirus mediated siRNA targeting human metastasis suppressor 1 (MTSS1, MIM-B gene) gene on the invasive and metastatic potentials of hepatocellular carcinoma (HCC) MHCC97H cells. METHODS: The siRNA targeting MTSS1 was cloned into one lentivirus work vector. The work vector and three package plasmids were co-transfected into 293T cells with the help of lipefeetamine 2000. Lentivirus was collected in 72 hours and was added to the cultured MHCC97H cells. The total cell MIM-B mRNA and MIM-B protein were extracted and underwent real-time PCR and western-blot test respectively. Boden chamber assay was used to evaluate the invasive potential of MHCC97H cells. Gelatin zymography was used to detect matrix metalloproteinase-2 (MMP2) activity. metastatic human HCC nude mice models were established by orthotopic implantation with a high metastatic potential human HCC cell line MHCC97H. Twenty-four nude mice bearing orthotopic xenografts were randomized into black control group, Lenti-GFP group and intervention group (Lenti-MTSS1 group) 14 days after orthotopic implantation (8 per group). The ultrasound-guided multi-point injection was performed on mice with borate buffered saline, Lenti-GFP and Lenti-MTSS1 respectively. Mice were sacrificed on day 35 for the examination of pulmonary metastasis. The SPSS 13.0 soft ware was applied to data analysis. RESULTS: The small interfering RNA targeting MTSS1 was constructed successfully with a transfection efficiency of 97.0%, which produced a marked inhibition of invasive ability of MHCC97H cells through Matrigel, being 37.9+/-4.4, 37.4+/-5.3 and 26.6+/-4.6 in the black control group, Lenti-GFP group and Lenti-MTSS1 group (F = 26.695, P value is less than 0.01), respectively. MIM-B expression and MMP2 activity of intervention group were also significantly down-regulated as compared to the control group. The results of in vivo studies showed that the numbers of lung metastatic nodules were 6.5+/-2.6, 6.4+/-2.7 and 3.8+/-1.3 in the black control group, Lenti-GFP group and intervention group respectively with significant statistical difference (F = 3.637, P value is less than 0.05), accorded with tumor tissue MIM-B mRNA expression of 0.39+/-0.19, 0.38+/-0.10 and 0.16+/-0.11 respectively (F = 11.644, P value is less than 0.01) when comparison was made between control group and therapy group. CONCLUSION: Small interfering RNA mediated by lentivirus inhibited MIM-B expression and resulted in inhibition of the invasive and metastatic potentials of MHCC97H cells, which may attributed, in part, the down regulation of MMP2 activity, and thus may provide a new molecular targeted therapy for HCC patients in the future.

BACKGROUND: miR-182 is one of the most significantly up-regulated miRNAs in hepatocellular carcinoma (HCC). metastasis suppressor 1 (MTSS1), one target gene of miR-182, plays an important role in the metastasis of cancers. However, it remains unclear what role does function and mechanism of miR-182 and MTSS1play in HCC. METHODS: miR-182 expression was tested in 86 cases of paired HCC and normal tissues by real-time PCR and the relationships between miR-182 expression and clinicopathological parameters were analyzed. The expression of MTSS1 was evaluated by immunohistochemistry and western blot in the above tissues and its correlation with miR-182 expression was analyzed. Moreover, western blot and invasion assays were performed after transfection of pre-miR-182 or anti-miR-182 to HCC cell lines. In addition, luciferase assays was performed to confirm the regulation of miR-182 on MTSS1. RESULTS: Compared with normal tissue, miR-182 was up-regulated and MTSS1 was down-regulated in HCC tissues. Moreover, the over-expression of miR-182 was correlated with intrahepatic metastasis (p = 0.034) and poor prognosis (p = 0.039) of HCC patients. There was a negative correlation between miR-182 and MTSS1 expression in both HCC tissues (r = -0.673, p < 0.01) and HCC cell lines (r = -0.931, p = 0.021). Furthermore, the up-regulation of miR-182 resulted in the down-regulation of MTSS1 and increased invasive potential of HUH-1, and reverse results were also confirmed when the expression of miR-182 was inhibited. In addition, the results of the luciferase assay demonstrated the targeted regulation of miR-182 on MTSS1. CONCLUSIONS: miR-182 could promote metastasis of HCC and inhibit the expression of MTSS1. miR-182 and MTSS1 are potential prognostic markers and/or therapeutic targets in HCC.

In cancers with a highly altered genome, distinct genetic alterations drive subsets rather than the majority of individual tumours. Here we use a sequential search across human tumour samples for transcript outlier data points with associated gene copy number variations that correlate with patient's survival to identify genes with pro-invasive functionality. Employing loss and gain of function approaches in vitro and in vivo, we show that one such gene, MTSS1, promotes the ability of melanocytic cells to metastasize and engages actin dynamics via Rho-GTPases and cofilin in this process. Indeed, high MTSS1 expression defines a subgroup of primary melanomas with unfavourable prognosis. These data underscore the biological, clinical and potential therapeutic implications of molecular subsets within genetically complex cancers.

Insulin receptor tyrosine kinase substrate p53 (IRSp53) has been identified as an SH3 domain-containing adaptor that links Rac1 with a Wiskott-Aldrich syndrome family verprolin-homologous protein 2 (WAVE2) to induce lamellipodia or Cdc42 with Mena to induce filopodia. The recruitment of these SH3-binding partners by IRSp53 is thought to be crucial for F-actin rearrangements. Here, we show that the N-terminal predicted helical stretch of 250 amino acids of IRSp53 is an evolutionarily conserved F-actin bundling domain involved in filopodium formation. Five proteins including IRSp53 and missing in metastasis (MIM) protein share this unique domain and are highly conserved in vertebrates. We named the conserved domain IRSp53/MIM homology domain (IMD). The IMD has domain relatives in invertebrates but does not show obvious homology to any known actin interacting proteins. The IMD alone, derived from either IRSp53 or MIM, induced filopodia in HeLa cells and the formation of tightly packed parallel F-actin bundles in vitro. These results suggest that IRSp53 and MIM belong to a novel actin bundling protein family. Furthermore, we found that filopodium-inducing IMD activity in the full-length IRSp53 was regulated by active Cdc42 and Rac1. The SH3 domain was not necessary for IMD-induced filopodium formation. Our results indicate that IRSp53, when activated by small GTPases, participates in F-actin reorganization not only in an SH3-dependent manner but also in a manner dependent on the activity of the IMD.

MTSS1 (metastasis suppressor-1) was first identified as a metastasis suppressor missing in metastatic bladder carcinoma cell lines. The down-regulation of MTSS1 that may be caused by DNA methylation was also observed in many other types of cancer. While accumlating evidence for the function of MTSS1 support the concept that it is unlikely to be a metastasis suppressor, but actually acts as a scaffold protein that interacts with multiple partners to regulate actin dynamics. It has also been demonstrated that MTSS1 is involved in the Shh signaling pathway in the developing hair follicle and in basal cell carcinomas of the skin. Such evidence indicates that MTSS1 as a multiple functional molecular player and has an important role in development, carcinogenesis and metastasis. However, the biochemical mechanisms by which MTSS1 functions in cells and the physiological role of this protein in animals remain largely unknown. In this review, we will discuss the current knowledge of MTSS1's role in cancer metastasis, carcinogenesis, and development. The clinical significance of MTSS1 will also be discussed.

BACKGROUND: metastasis suppressor-1 (MTSS1) has been proposed to function as a cytoskeletal protein with a role in cancer metastasis. Recent studies have demonstrated the clinical significance of MTSS1 in certain type of cancers, yet the clinical relevance of MTSS1 in oesophageal squamous cell carcinoma (ESCC) has not been reported. METHODS: In this study, we assessed the expression levels of MTSS1 in tumours and its matched adjacent non-tumour tissues obtained from 105 ESCC patients. We also used ESCC cells with differing MTSS1 expression and assessed the influence of MTSS1 on ESCC cells. RESULTS: Down-regulation of MTSS1 expression was observed both in oesophageal tumour tissues and ESCC cancer cell lines. We also reported that MTSS1 expression was associated with tumour grade (p = 0.024), lymph node metastasis (p = 0.010) and overall survival (p = 0.035). Patients with high levels of MTSS1 transcripts had a favorable prognosis in comparison with those who had reduced or absent expression levels. Using over-expression and knockdown approach, we created sublines from ESCC cells and further demonstrated that MTSS1 expression in ESCC cells significantly influenced the aggressiveness of the oesophageal cancer cells, by reducing their cellular migration and in vitro invasiveness. CONCLUSION: MTSS1 serves as a potential prognostic indicator in human ESCC and may be an important target for cancer therapy.

metastasis suppressor 1 (MTSS1) is an important tumor suppressor protein, and loss of MTSS1 expression has been observed in several types of human cancers. Importantly, decreased MTSS1 expression is associated with more aggressive forms of breast and prostate cancers, and with poor survival rate. Currently, it remains unclear how MTSS1 is regulated in cancer cells, and whether reduced MTSS1 expression contributes to elevated cancer cell proliferation and migration. Here we report that the SCFbeta-TRCP regulates MTSS1 protein stability by targeting it for ubiquitination and subsequent destruction via the 26S proteasome. Notably, depletion of either Cullin 1 or beta-TRCP1 led to increased levels of MTSS1. We further demonstrated a crucial role for Ser322 in the DSGXXS degron of MTSS1 in governing SCFbeta-TRCP-mediated MTSS1 degradation. Mechanistically, we defined that Casein Kinase Idelta (CKIdelta) phosphorylates Ser322 to trigger MTSS1's interaction with beta-TRCP for subsequent ubiquitination and degradation. Importantly, introducing wild-type MTSS1 or a non-degradable MTSS1 (S322A) into breast or prostate cancer cells with low MTSS1 expression significantly inhibited cellular proliferation and migration. Moreover, S322A-MTSS1 exhibited stronger effects in inhibiting cell proliferation and migration when compared to ectopic expression of wild-type MTSS1. Therefore, our study provides a novel molecular mechanism for the negative regulation of MTSS1 by beta-TRCP in cancer cells. It further suggests that preventing MTSS1 degradation could be a possible novel strategy for clinical treatment of more aggressive breast and prostate cancers.