Oncogene database

208

AKT2

v-akt murine thymoma viral oncogene homolog 2;AKT2;v-akt murine thymoma viral oncogene homolog 2

PKB beta|RAC-PK-beta|RAC-beta serine/threonine-protein kinase|murine thymoma viral (v-akt) homolog-2|protein kinase Akt-2|protein kinase B beta|rac protein kinase beta

19q13.1-q13.2

protein-coding

AKT2 is a serine/threonine kinase implicated in human ovarian and pancreatic cancers. AKT2 is activated by a variety of growth factors and insulin via phosphatidylinositol 3-kinase (PI3K). However, its normal cellular role is not well understood. To gain insight into the function of AKT2, we performed yeast two-hybrid system to screen for interacting proteins. Using this technique, we identified a novel interactor, designated APPL, which contains a pleckstrin homology (PH) domain, a phosphotyrosine binding (PTB) domain and a leucine zipper, classes of motifs defined in signaling molecules as functional interaction domains with specific targets. The PH domain of APPL shows similarity to those found in GTPase-activating proteins such as oligophrenin-1 and Graf, whereas its PTB domain exhibits homology with CED-6, an adaptor protein that promotes engulfment of apoptotic cells, and IB1, a transactivator of the GLUT2 gene. APPL is highly expressed in skeletal muscle, heart, ovary and pancreas, tissues in which AKT2 mRNA is abundant. APPL interacts with the inactive form of AKT2; moreover, APPL binds to the PI3K catalytic subunit, p110alpha. These data suggest that APPL is an adaptor that may tether inactive AKT2 to p110alpha in the cytoplasm and thereby may expedite recruitment of AKT2 and p110alpha to the cell membrane upon mitogenic stimulation. Furthermore, the APPL gene was mapped to human chromosome 3p14.3-p21.1, where deletions and other rearrangements have often been reported in a variety of tumor types. The identification of APPL may facilitate further analysis of the physiological and oncogenic activities of AKT2.

The kinases Akt2, Akt3 and their myristylated variants, Myr-Akt2 and Myr-Akt3 were expressed by the RCAS vector in chicken embryo fibroblasts (CEF). Myr-Akt2 and Myr-Akt3 were strongly oncogenic, inducing multilayered foci of transformed cells. In contrast, wild-type Akt2 and Akt3 were only poorly transforming, their efficiencies of focus formation were more than 100-fold lower; foci appeared later and showed less multilayering. Addition of the myristylation signal not only enhanced oncogenic potential but also increased kinase activities. Myr-Akt2 and Myr-Akt3 also induced hemangiosarcomas in the animal, whereas wild type Akt2 and Akt3 were not oncogenic in vivo. Furthermore, Akt2, driven by the lck (lymphocyte specific kinase) promoter in transgenic mice, induced lymphomas. The oncogenic effects of Akt2 and Akt3 described here are indistinguishable from those of Akt1. The downstream targets relevant to oncogenic transformation are therefore probably shared by the three Akt kinases.

The inhibition of apoptosis is a critical event in the development of colorectal malignancies, although the mechanism(s) remain incompletely understood. The anti-apoptotic proto-oncogene, AKT, has been implicated in the molecular pathogenesis of a variety of human malignancies; however, no data exist on the role of AKT in colon carcinogenesis. We therefore evaluated the presence of AKT in human and experimental colon neoplasms by immunohistochemistry. Normal colonic mucosa and hyperplastic polyps exhibited no significant AKT expression, in marked contrast to the dramatic AKT immunoreactivity seen in colorectal cancers (57% positive) and in both human colorectal cancer cell lines examined. Importantly, AKT was also detected in 57% of the adenomas examined, implicating overexpression of this proto-oncogene as an early event during colon carcinogenesis. Moreover, in the rodent-carcinogen model, azoxymethane (AOM)-treatment induced AKT expression in premalignant rat colonocytes. tumors that evolve via different genetic pathways displayed a lower incidence of AKT overexpression. Indeed, only 22% of mismatch repair defective tumors and 42% of AOM-induced rodent tumors upregulated AKT. Staining with an antibody specific for AKT 2 duplicated findings with the AKT 1&2 antibody, suggesting that AKT 2 was the predominant isoform involved in colon carcinogenesis. Furthermore, utilizing an antibody that specifically recognizes the serine-473 phosphorylated form of AKT, we observed that activated AKT was detectable in the neoplastic but not normal epithelium. In summary, our immunohistochemical analysis indicates AKT overexpression occurs frequently during human colon carcinogenesis, but is less common in colon cancers with microsatellite instability. The early inhibition of apoptosis during sporadic colon carcinogenesis may be related, at least partly, to the overexpression of AKT.

We isolated cDNA clones containing the entire coding region of the putative oncogene AKT2. Sequence analysis and in vitro translation demonstrated that AKT2 encodes a 56-kDa protein with homology to serine/threonine kinases; moreover, this protein contains a Src homology 2-like domain. AKT2 was shown to be amplified and overexpressed in 2 of 8 ovarian carcinoma cell lines and 2 of 15 primary ovarian tumors. AKT2 was mapped to chromosome region 19q13.1-q13.2 by fluorescence in situ hybridization. In the two ovarian carcinoma cell lines exhibiting amplification of AKT2, the amplified sequences were localized within homogeneously staining regions. We conclude that AKT2 belongs to a distinct subfamily of protein-serine/threonine kinases containing Src homology 2-like domains and that alterations of AKT2 may contribute to the pathogenesis of ovarian carcinomas.

We investigated gene expression profiles of non-small cell lung carcinomas (NSCLC) to screen candidate molecules that might be useful as diagnostic markers or for development of novel molecular-targeting therapies. Here we report evidence that a member of the armadillo protein family, plakophilin 3 (PKP3), is a potential molecular target for treatment of lung cancers and might also serve as a prognostic indicator. We documented elevated expression of PKP3 in the great majority of NSCLC samples examined. Treatment of NSCLC cells with small interfering RNAs of PKP3 suppressed growth of the cancer cells; on the other hand, induction of exogenous expression of PKP3 conferred growth-promoting activity on COS-7 cells and enhanced their mobility in vitro. To investigate its function, we searched for PKP3-interacting proteins and identified dynamin 1-like, which was also activated in NSCLC. In addition, a high level of PKP3 expression was associated with poor survival as well as disease stage and node status for patients with lung adenocarcinoma, suggesting an important role of the protein in development and progression of this disease. As our data imply that up-regulation of PKP3 is a frequent and important feature of lung carcinogenesis, we suggest that targeting the PKP3 molecule might hold promise for development of a new therapeutic and diagnostic strategy for clinical management of lung cancers.

OBJECTIVE: To investigate the expression and clinical significance of oncogene AKT2 in laryngeal squamous cell carcinoma (LSCC). METHOD: The expression of AKT2 protein was measured with immunohistochemistry (Elivision two steps) in 60 cases of LSCC tissue, 28 cases of peri-cancer tissue and 16 cases of normal laryngeal epithelium, the relationship between AKT2 expression and clinical pathologic factors in LSCC was also analyzed. RESULT: The positive rates of AKT2 protein expression in LSCC and peri-cancer tissue were 56.7% (34/60), 14.3% (4/28) respectively. There was no expression of AKT2 in normal laryngeal epithelium. The positive rate of AKT2 protein expression in LSCC was significantly higher than that in peri-cancer tissue and normal laryngeal epithelium (P < 0.05, respectively). The positive rate of AKT2 was correlated with tumor site, lymph node metastasis and clinical stage of LSCC (P < 0.05, respectively), but wasn t correlated with patient s age, sex, and T stage (P > 0.05, respectively). CONCLUSION: AKT2 might play an important role in the tumorigenesis and development of LSCC, and it was suggested that AKT2 could be a useful marker for predicting tumorigenesis, invasion and metastasis potential of LSCC.

The signaling network of protein kinase B(PKB)/Akt has been implicated in survival of lung cancer cells. However, understanding the relative contribution of the different isoform of Akt network is nontrival. Here, we report that Akt2 is highly expressed in human lung adenocarcinoma cell line A549 cells. Suppression of Akt2 expression in A549 cells results in notable inhibition of cell poliferation, soft agar growth, and invasion, accompanying by a decrease of nucleophosmin/B23 protein. Overexpression of Akt1 restores cancerous growth of A549 cells in B23-knockdown (KD) cells while Akt2 overexpression did not restore proliferating potential in cells with downregulated B23, thus suggesting Akt2 requires B23 to drive proliferation of lung cancer cell. Loss of functional Akt2 and B23 has similar defects on cell proliferation, apoptotic resistance and cell cycle regulation, while loss of Akt1 has less defects on cell proliferation, survival and cell cycle progression in A549 cells. Moreover, overexpression of B23 rescues the proliferative block induced as a consequence of loss of Akt2. Thus our data suggest that Akt2/B23 functions as an oncogenic unit to drive tumorigenesis of A549 lung cancer cells.

A previous report described the isolation of a directly transforming retrovirus, AKT8, from a spontaneous thymoma of an AKR mouse. The AKT8 provirus has now been molecularly cloned from a transformed, nonproducer cell line. The virus genome contains both viral and nonviral, cell-related sequences; the nonviral sequence has been designated v-akt, the presumed viral oncogene of the AKT8 virus. This gene lacks homology to the 16 other oncogenes tested. The cloned provirus has undergone a partial deletion, during cell passage in vitro, that prevents direct demonstration of the transforming ability of this molecular clone. Two human homologues of the v-akt oncogene, AKT1 and AKT2, were cloned. A survey of 225 human tumors for changes involving AKT1 led to the discovery of a 20-fold amplification of this gene in one of the five gastric adenocarcinomas tested. The results demonstrate that AKT8 has the characteristic structure of a directly transforming retrovirus and that it contains a gene derived from highly conserved cellular sequences that may be involved in the pathogenesis of some human malignancies.

We isolated mouse cDNA clones containing the entire coding region of the putative oncogene Akt2. Sequence analysis revealed that, like its human homolog, Akt2 encodes a protein-serine/threonine kinase containing a pleckstrin homology domain at its amino terminus. Fluorescence in situ hybridization of the mouse cDNA to rodent metaphase spreads demonstrated that the Akt2 gene maps to mouse chromosome band 7B1 and rat chromosome 1q22. expression levels of mouse Akt2 mRNA and Akt2 protein varied among tissues, with the highest levels in skeletal muscle. Akt2 expression was low in a multipotent fibroblast cell line, but it was upregulated when these cells were transformed with Myod and induced to differentiate into myocytes. These data demonstrate that Akt2 expression is activated during cellular differentiation and suggest that it functions in the signaling pathways of some adult tissues.

The AKT2 gene is one of the human homologues of v-akt, the transduced oncogene of the AKT8 virus, which induces lymphomas in mice. In previous studies, AKT2, which codes for a serine-threonine protein kinase, was shown to be amplified and overexpressed in some human ovarian carcinoma cell lines and amplified in primary tumors of the ovary. To confirm and extend these findings, we conducted a large-scale, multicenter study of AKT2 alterations in ovarian and breast cancer. Southern-blot analysis demonstrated AKT2 amplification in 16 of 132 (12.1%) ovarian carcinomas and in 3 of 106 (2.8%) breast carcinomas. No AKT2 alteration was detected in 24 benign or borderline tumors. Northern-blot analysis revealed overexpression of AKT2 in 3 of 25 fresh ovarian carcinomas which were negative for AKT2 amplification. The difference in the incidence of AKT2 alterations in ovarian and breast cancer suggests a specific role for this gene in ovarian oncogenesis. No significant association was found between AKT2 amplification and amplification of the proto-oncogenes MYC and ERBB2, suggesting that amplification of AKT2 defines an independent subset of breast and ovarian cancers. Ovarian cancer patients with AKT2 alterations appear to have a poor prognosis. Amplification of AKT2 was especially frequent in undifferentiated tumors (4 of 8, p = 0.019), suggesting that AKT2 alterations may be associated with tumor aggressiveness.

The AKT2 oncogene encodes a protein-serine/threonine kinase containing a pleckstrin homology domain characteristic of many signaling proteins. Recently, it was shown that AKT2 kinase activity can be induced by platelet-derived growth factor through phosphatidylinositol-3-OH kinase, suggesting that AKT2 may be an important signal mediator that contributes to the control of cell proliferation. We previously reported amplification and overexpression of AKT2 in human cancers. To investigate the transforming activity of AKT2, we used a retrovirus-based construct to express AKT2 in NIH3T3 cells. Overexpression of AKT2 was found to transform NIH3T3 cells, as determined by growth in soft agar and tumor formation in nude mice. The oncogenic activity of AKT2 was diminished by truncation of a 70-amino acid proline-rich region at the carboxyl-terminus. To facilitate the characterization of AKT2, we generated monoclonal and polyclonal antibodies against this protein. AKT2 was localized to the cytoplasm by cell fractionation experiments, immunocytochemistry, and immunofluorescence. Protein levels were more abundant in mitotic cells than in interphase cells. Western blot analysis of synchronized pancreatic cancer cells demonstrated that the expression level of AKT2 protein in mitotic cells is three to fivefold higher than in their interphase counterparts. A time-course study of phytohemagglutinin-stimulated lymphocytes revealed that AKT2 mRNA and AKT2 protein levels are highest 48-72 h after addition of mitogen, when cells are actively dividing. These data suggest that AKT2 could play a significant role in cell cycle progression and that the oncogenic activity of overexpressed AKT2 may be mediated by aberrant regulation of cellular proliferation.

AKT2, an oncogene encoding a protein serine-threonine kinase implicated in phosphatidylinositol-3-OH kinase signaling, is amplified in some human ovarian and pancreatic carcinomas. We previously demonstrated that the tumorigenicity and invasiveness of pancreatic ductal adenocarcinoma (PDAC) cell lines with amplified AKT2 could be markedly reduced by transfection with antisense AKT2 constructs. To evaluate further the extent of AKT2 alterations in PDAC, DNA and immunohistochemical analyses were performed to assess amplification or overexpression of AKT2, respectively, in 72 PDACs. Thirty-five PDACs were subjected to Southern analyses, and AKT2 amplification was detected in seven tumors (20%). Forty-one formalin-fixed PDAC specimens were examined immunohistochemically with an anti-AKT2 monoclonal antibody, and moderate to intense staining was observed in eight tumors (20%). AKT2 immunostaining paralleled AKT2 genomic status in each of four cases in which both Southern and immunohistochemical analyses were performed. No obvious relationship was observed between AKT2 status and tumor TNM stage or grade. These observations suggest the utility of immunohistochemical analysis in assessing alterations of AKT2 in human cancers. Furthermore, the role played by the AKT2 kinase in the signaling pathways of various mitogenic growth factors implicated in the development of pancreatic cancer suggests that alteration of AKT2 may be an important component in the pathogenesis of a substantial subset of PDACs.