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The transcription factor activating transcription factor 2 (ATF2) has been shown to be associated with melanocytic oncogenesis and melanoma tumor proliferation in preclinical models. The clinical significance of ATF2 expression is unknown. To determine the prognostic value of ATF2 in melanoma, we evaluated the pattern and level of ATF2 expression in a large cohort of melanoma specimens. Immunohistochemical staining was performed on a tissue microarray representing 544 patients with a mean follow-up time of 60 months. Expression was evaluated semiquantitatively and correlated with overall survival and other clinicopathological data. Strong cytoplasmic ATF2 expression was associated with primary specimens rather than metastases (P < 0.0001) and with better survival (P = 0.0003). Strong nuclear ATF2 expression was associated with metastatic specimens (P < 0.0001) and with poor survival (P = 0.0008). Patients who had both weak cytoplasmic and strong nuclear ATF2 staining had the worst outcome, both among the full cohort of patients (P < 0.0001) and among the patients with localized disease (n = 269; P < 0.0001). On multivariate analysis of the primary cutaneous specimens, weak cytoplasmic staining and strong nuclear staining was an independent predictor of poor outcome, as was Clark level. Nuclear ATF2 is likely to be transcriptionally active, whereas cytoplasmic ATF2 probably represents an inactive form. These findings support other preclinical findings in which transcriptionally active ATF2 is involved in tumor progression-proliferation in melanoma. Moreover, our findings suggest that ATF2 might be a useful prognostic marker in early-stage melanoma.

Constitutive cell surface receptor kinase signaling and persistent phosphorylation/inactivation of the retinoblastoma (pRb) family of proteins (pRb, p107 and p130, known as pocket proteins) have been implicated in conferring uncontrolled growth to melanoma cells. However, the signals linking receptor kinase activity to neutralization of pocket proteins have not yet been fully elucidated. We therefore used specific chemical inhibitors to examine pRb regulation in melanoma cells. The most efficient agent, AG1024, known as an inhibitor of insulin-like growth factor 1 receptor and insulin receptor, arrested melanoma cell growth in vitro at nanomolar concentrations within 24 h of application. AG1024 inhibited the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway and restored pRb tumor suppressive function. The latter was observed by the reduction in the phosphorylated forms of pRb, p107 and p130, and the formation of growth suppressive DNA binding complexes consisting of pRb and E2F1 or E2F3. The loss of phosphorylated forms of pRb at early time points after AG1024 application was not associated with suppression of cyclin-dependent kinases 2 and 4 activity but rather with proteasomal and nonproteasomal degradation. Thus, inhibition of melanoma cell proliferation by AG1024 is mediated by inhibition of mitogen-activated protein kinase/extracellular signal-regulated kinase 2 signaling and activation of pRb by a mechanism involving protein degradation.