¹The Ruttenberg Cancer Center, Mount Sinai School of Medicine, New York, NY 10029, USA

²Department of Tumor Biology, Norwegian Radium Hospital, Montebello, Oslo, Norway

Correspondence to: Z Ronai, Ruttenberg Cancer Center, Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1130, New York, NY 10029, USA

Mechanisms underlying radiation and chemotherapy resistance, the hallmark of human melanoma, are not well understood. Here we demonstrate that expression levels of signal adaptor protein TRAF2 coincide with melanoma resistance to UV-irradiation. Altered TRAF2 signaling by a form of TRAF2, which lacks the ring finger domain (TRAF2N), increases activities of p38 MAPK, ATF2, and the level of TNF expression. Forced expression of TRAF2N in HHMSX highly metastatic melanoma cells that lack Fas expression and thus utilize the TNF-TNFR1 as the major apoptotic pathway sensitized cells to UV-induced apoptosis. An over twofold increase in degree of apoptosis was observed in TRAF2N expressing cells that were treated with actinomycin D, anisomycin or with the radiomimetic drug neocarzinostatin. Sensitization by TRAF2N is selective since it was not observed in response to either Taxol or cis-platinum treatment. TRAF2N effects are primarily mediated via p38 since inhibition of p38 reduces, whereas activation of p38 promotes the level of UV-induced apoptosis. Conversely, activation of IKK attenuates the sensitization of melanoma by TRAF2N, indicating that p38-mediated suppression of NF-B activity is among TRAF2N effects. Our finding identifies p38, TNF and NF-B among key players that efficiently sensitizes melanoma cells to UV-, ribotoxic (anisomycin) and radiomimetic chemicals-induced programmed cell death in response to aberrant TRAF2 signaling. Oncogene (2001) 20, 2243-2253.

p38; TRAF2; melanoma; apoptosis; radiation; anisomycin; actinomycin D

AP1, activator protein-1; ATF2, activating transcription factor 2; NF-B, nuclear factor kappa B; IKK, inhibitor nuclear factor kappa B kinase; PI, propidium iodide; TNF, tumor necrosis factor alpha; TNFR, tumor necrosis factor receptor; TRAF2, tumor necrosis factor receptor associated factor 2; GFP, green fluorescent protein; IB, inhibitor NF-B; MAPK, mitogen-activated protein kinase; MFI, medium fluorescence intensity; MKK, MAPK kinase; CHX, cycloheximide; NCS, neocarzinostatin