Ras-Associated Protein-1 Regulates Extracellular Signal-Regulated Kinase Activation and Migration in Melanoma Cells: Two Processes Important to Melanoma Tumorigenesis and Metastasis

Abstract

Melanoma is one of the most devastating malignances with a rising incidence and lack of effective treatments for advanced disease. Constitutive activation of the mitogen-activated protein kinase (MAPK) pathway and altered expression of A v B 3 integrin are critical for melanoma development and progression. Ras-associated protein-1 (Rap1), a Ras family member of the small GTPases, has emerged as a key mediator in these two important processes. In this study, we have shown Rap1 activation in cells derived from two human metastatic melanomas and also in three of seven cutaneous metastatic melanoma tissues. We found increased extracellular signalregulated kinase (ERK) activity in the tumors with detected Rap1 activity that interestingly harbored neither BRAF nor N-Ras mutation, suggesting a role for Rap1 in ERK activation in vivo. We also showed Rap1 and ERK activation by both hepatocyte growth factor (HGF) and 8CPT-2Me-cAMP (an activator of Epac, a Rap1 guanine nucleotide exchange factor) in two human melanoma cell lines. In addition, the activation of ERK by HGF was reduced, at least in part, by small interfering RNAs against Rap1 and a dominant-negative Rap1. Finally, a functional role for Rap1 activation was shown by Rap1-induced A v B 3 integrin activation and consequent increased melanoma cell migration in vitro. Taken together, these results show that Rap1 is involved in the activation of MAPK pathway and integrin activation in human melanoma and suggest a potential role for Rap1 in melanoma tumorigenesis and metastasis. (Cancer Res 2006; 66(16): 7880-8)

Epac increases melanoma cell migration by a heparan sulfate-related mechanism

“…These reports suggested that the coordination of syndecan-2 and HS plays a role in cell migration; however, little is known about the key molecule that regulates such coordination. In this report, we demonstrate that Epac increases melanoma cell migration using two human melanoma cell lines: SK-Mel-2, which was derived from regional metastasis, and SK-Mel-24, which was derived from lymph node metastasis; both cell lines show potent migratory ability (16,38). We also demonstrated that syndecan-2 translocation and HS production are involved in Epac-induced cell migration.…”

“…Two isoforms of Epac, Epac1 and Epac2, were shown to mediate cAMP signaling to activate a small-molecular-weight G protein Rap1 and to regulate cellular functions, including secretion, Ca 2ϩ signaling, proliferation, and apoptosis (6). Several reports also indicate the involvement of Epac in regulating cell migration (16,28); however, the molecular mechanisms that lead to increased cell migration through Epacs remain unknown.…”

Phosphorylation of Rap1 by cAMP-dependent Protein Kinase (PKA) Creates a Binding Site for KSR to Sustain ERK Activation by cAMP

“…We propose that efficient signaling of Rap1 to ERKs requires multiple events in addition to Rap1 activation, including phosphorylation by PKA and recruitment of KSR. This model may explain why constitutively active Rap1 mutants are poor activators of ERKs in the absence of PKA phosphorylation and may explain why constitutively active Rap1 mutants are rarely seen in human cancers (60). In this regard, it is interesting that the mitogenic actions of constitutively active Rap1 in a model of thyroid follicular cell growth required Rap1 phosphorylation (61).…”

Anaplastic lymphoma kinase activates the small GTPase Rap1 via the Rap1-specific GEF C3G in both neuroblastoma and PC12 cells

“…Further, Rap1 is also involved in the regulation of cell proliferation. When overexpressed, Rap1 induces oncogenic transformation in Swiss-3T3 cells (Altschuler and Ribeiro-Neto, 1998), and has been reported to be activated in metastatic mammary carcinomas, during melanoma tumorigenesis as well as metastasis (Hemmeryckx et al, 2001;Gao et al, 2006). Rap1 also appears to be involved in the process of thyroid mitogenesis and has been suggested to contribute to thyroid-stimulating hormone-stimulated thyroid tumorigenesis Hong et al, 2008).…”