Although median survival was not notably different (median survival 21.6 vs. and promote metastasis. Correspondingly, gain- and loss-of-function studies established that Pten loss increases invasion and migration of melanoma cells and non-transformed melanocytes, and that such biological activity correlates with a shift to phosphorylation of AKT2 isoform and E-cadherin down-regulation. Thus, Pten inactivation can drive the genesis and promote the metastatic progression of RAS activated Ink4a/Arf deficient melanomas. Keywords:melanoma, PTEN, RAS, E-cadherin, AKT2, mouse model == Introduction == RAS activation is a common and potent oncogenic event in human solid tumors, including melanoma. The relevance of RAS-RAF-MAPK pathway in melanoma pathogenesis is evidenced by high frequency BRAF mutations (Davieset al., 2002) and less common yet reciprocal NRAS mutations (Tsaoet al., 2004). Activating mutations of NRAS are found in as many as 56% of congenital nevi, 33% of primary and 26% of metastatic melanoma samples (Chinet al., 2006). Although, NRAS is the most commonly mutated RAS family member, mutations on KRAS (2%) and HRAS (1%) are also observed in human melanomas (Forbeset al., 2008). In particular, HRAS mutation was reported to be found in 7.7% of the nodular melanoma subtype (Jafariet al., 1995). Genetic evidence of a pathogenetic Nadolol role for the RAS-RAF-MAPK pathway in melanoma derives from a melanoma-prone condition in mice transgenic for melanocyte-directed HRASV12Gor NRASQ61Kalleles and null forp16INK4aand/orp19ARFtumor suppressors (Ackermannet al., 2005;Chinet al., 1997;Chinet al., 1999;Sharplesset al., 2003). Additionally, BRAF, a key effector of RAS signaling, is the most frequently mutated Nadolol gene in human melanocytic neoplasms with frequencies of 82% of benign nevi and 66% in melanomas (Davieset al., 2002;Pollocket al., 2003). Melanocyte-directed expression of BRAFV600Ecan induce nevoid hyperpigmentation phenotype in mice (Dankortet al., 2009;Dhomenet al., 2009;Goelet al., 2009) with rare progression to melanoma (Dhomenet al., 2009;Goelet al., 2009). While activation of the RAS-RAF signaling cascade has been recognized as an obligate event in melanocyte transformation, Khavari and colleagues have demonstrated that activation of BRAF MAPK requires concomitant AKT activation to effect melanoma development (Chudnovskyet al., 2005). Consistent with importance of the PI3K-AKT pathway, over 60% of human melanomas exhibit activated AKT (Dhawanet al., Rabbit Polyclonal to ABHD12 2002), and mutational inactivation and/or deletion of the PI3K negative regulator, PTEN, occurs in 5-15% of uncultured melanoma specimens and metastasis, 17% of melanoma short-term cultures, and 30-40% of established melanoma cell lines (Bircket al., 2000;Guldberget al., 1997;Linet al., 2008;Tsaoet al., 2004). Nadolol Mouse modeling has also demonstrated thatPten+/-Ink4a/Arf+/-mice do succumb to melanoma at low frequency (Youet al., 2002) and robust melanoma formation and metastases can occur upon combination with activated BRAF (Dankortet al., 2009). The PI3K-AKT signaling pathway can be activated by receptor tyrosine kinases. Active PI3K phosphorylates and converts the lipid phosphatidylinositol (4,5) bisphosphate (PIP2) into PIP3, which in turn activates AKT through PDK1 mediated phosphorylation. PTEN negatively regulates PI3K signaling by dephosphorylating PIP3, converting it back to PIP2. Therefore, deletion or inactivation of PTEN results in constitutive AKT activation (Cullyet al., 2006;Salmenaet al., 2008). On the other hand, RAS proteins can positively regulate the PI3KAKT pathway by direct binding of RAS to the p110 catalytic subunit (Guptaet al., 2007) or by activating an autocrine signaling pathway involving EGFR family ligands (Bardeesyet al., 2005). Since PTEN inactivation and RAS activating mutation can both target the PI3K pathway to drive constitutive AKT activation, it has been proposed that RAS mutation and PTEN inactivation are redundant events in tumorigenesis, as suggested by a reciprocal trend of their mutations in human melanoma and endometrial carcinoma (Ikedaet al., 2000;Tsaoet al., 2000). However, constitutive AKT1 activation in mouse has resulted in a milder cancer phenotype than complete PTEN inactivation (Maet al., 2005;Majumderet al., 2003;Stambolicet al., 2000;Trotmanet al., 2003;Wanget al., 2003), pointing to AKT independent activities of PTEN in tumorigenesis (Blanco-Aparicioet al., 2007). Similarly, while expression of oncogenic K-RAS or conditional PTEN deletion in the ovarian epithelium gives rise to preneoplastic ovarian lesions, the combined effect of these two mutations in the ovary leads to invasive and widely metastatic endometrioid ovarian adenocarcinomas with complete penetrance and a disease latency of only 7 weeks (Dinulescuet al., 2005). In this study, we addressed the potential collaborative interactions between RAS activation and PTEN inactivation on the genetic level. == Results == == Pten inactivation cooperates with HRASV12Gin melanoma genesisin vivo == We had previously shown thatTyr-HRASV12GInk4a/Arf-/-compound mutant mice (hereafter RAS-Ink4a/Arf) developed non-metastatic cutaneous melanomas with short latency and high penetrance (Chinet al., 1997;Chinet al., 1999;Kimet al., 2006). The occurrence of PTEN loss.