Dysfunction of the endoplasmic reticulum (ER) has been reported in a variety of human pathologies, including cancer. However, the contribution of the ER to the early stages of normal cell transformation is largely unknown. Using primary human melanocytes and biopsies of human naevi (moles), we show that the extent of ER stress induced by cellular oncogenes may define the mechanism of activation of premature senescence. Specifically, we found that oncogenic forms of HRAS (HRASG12V) but not its downstream target BRAF (BRAFV600E), engaged a rapid cell-cycle arrest that was associated with massive vacuolization and expansion of the ER. However, neither p53, p16INK4a nor classical senescence markers - such as foci of heterochromatin or DNA damage - were able to account for the specific response of melanocytes to HRASG12V. Instead, HRASG12V-driven senescence was mediated by the ER-associated unfolded protein response (UPR). The impact of HRAS on the UPR was selective, as it was poorly induced by activated NRAS (more frequently mutated in melanoma than HRAS). These results argue against premature senescence as a converging mechanism of response to activating oncogenes and support a direct role of the ER as a gatekeeper of tumour control.
|Original language||English (US)|
|Number of pages||11|
|Journal||Nature Cell Biology|
|State||Published - Oct 2006|
Bibliographical noteFunding Information:
We are grateful to A. Bengtson, T.P. Miller and W.-H. Tang for technical support; K. Zhang for advice with UPR-related dominant-negative constructs; J. Martens for help with the time-lapse microscopy; S. Núñez, E. de Stanchina and S. Lowe for p16 shRNA lentiviral vector and AKT-DN retroviral constructs; K. Guan and A. Vojtek for HA-tagged BRAF pcDNA; D. Peeper for pBabe-puro-BRAF; and W. Tirasophon and T. Ruthowski for ATF-6 and IRE1 antibodies. We also thank G. Núñez, J.A. Esteban, M. Serrano, G. Ferbeyre and A. Dlugosz for helpful suggestions and critical reading of this manuscript. This work was supported by a postdoctoral fellowship from La Ligue Contre le Cancer (C.D); Career Development Awards from the Dermatology Foundation to M.S.S. and M.A.N.; the Elsa U. Pardee Foundation (M.S.S); and National Institutes of Health grants CA107237 (M.S.S), R33 CA95300 (B.C.B.), DK42394 (R.J.K) and A112243 and U01CA83180 (S.B.G). M.S.S. is a V Foundation for Cancer Research Scholar.