Abstract 3868: Identification of PHLPP1 as a novel metastasis suppressor in melanoma .

Abstract

Abstract Metastatic dissemination is the cause of nearly all melanoma-related deaths. Despite an improving understanding of genetic lesions present in human melanomas, how these alternations relate to the metastatic process is not well understood. Previously, we found that activation of the PI3K/Akt pathway is a driving force in metastatic melanomas. Here we identify PHLPP1 as a novel metastasis suppressor in melanoma. PHLPP1 was recently identified as a Ser/Thr-specific phosphatase, belonging to pleckstrin homology (PH) domain leucine-rich repeat protein phosphatase family. The two isoforms of this family, PHLPP1 and PHLPP2 control kinase signaling in the AKT family by catalyzing the dephosphorylation of the hydrophobic phosphorylation motif. PHLPP1 can specifically dephosphorylate AKT2 and AKT3, whereas PHLPP2 dephosphorylates AKT1 and AKT3. To study the role of PHLPPs in metastatic melanoma, we first examined the expression of PHLPPs in 30 melanoma metastases, 30 primary melanomas, and 9 normal skin tissues using tissue microarray analysis. We found that PHLPP1 was significantly downregulated or lost in metastatic melanoma samples, but not PHLPP2. Moreover, analysis of various human melanoma cell lines (12 highly metastatic, 14 poorly metastatic melanoma cell lines and 1 normal melanoctye cell line) demonstrated that PHLPP1 expression correlated with metastatic behavior, supporting the notion that PHLPP1 is involved in the metastatic regulation of melanoma. To confirm a functional role for PHLPP1 in metastasis, we forced the expression of PHLPP1 and PHLPP2 in B16 and A375sm melanoma cell lines. Overexpression of PHLPP1 dramatically inhibited metastasis in both cell lines. Unexpectedly, the PHLPP2 isoform had little influence on metastatic ability in both cell lines in vivo, despite the fact that both PHLPP1 and PHLPP2 were able to inhibit in vitro cell proliferation, motility, migration as well as colony formation in soft agar. Notably, introduction of PH mutant forms of PHLPP1 still blunted the metastatic potential of both cell lines, whereas a phosphatase-deficient C-terminal mutant did not affect metastasis. Interestingly, transfected AKT2 active form could rescue PHLPP1-mediaed inhibition of metastasis. Our data demonstrate at the first time that PHLPP1 plays a critical role in inhibiting metastasis through its phosphatase activity, and suggest that PHLPP1 could be a diagnostic marker and therapeutic target for metastatic melanoma. Citation Format: Yanlin Yu, Andrew Lu, Meng Dai, Glenn Merlino. Identification of PHLPP1 as a novel metastasis suppressor in melanoma . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3868. doi:10.1158/1538-7445.AM2013-3868