1. ¹Department of Dermatology, School of Medicine, University of Colorado Denver, Aurora, Colorado, USA
2. ²US Department of Veterans Affairs Medical Center, Dermatology Section, Denver, Colorado, USA

Correspondence: Dr Yiqun G. Shellman, Department of Dermatology, University of Colorado Denver, School of Medicine, Mail Stop no. 8127, PO Box 6511, Aurora, Colorado 80010, USA. E-mail: Yiqun.Shellman@uchsc.edu

³These authors contributed equally to this work

Received 15 January 2008; Revised 23 April 2008; Accepted 15 June 2008; Published online 31 July 2008.

Abstract

B-Raf and N-Ras proteins are often activated in melanoma, yet their roles in producing inherent survival signals are not fully understood. In this study, we investigated how N-RAS^Q61K and B-RAF^V600E contribute to melanoma's resistance to apoptosis induced by detachment from the extracellular matrix (anoikis). We found that expression of constitutively active N-RAS^Q61K and B-RAF^V600E downregulated the proapoptotic Bim protein in an immortalized melanocyte cell line. Bim is one of the main proapoptotic mediators of anoikis. Western blot analysis showed that detachment increased Bim expression in melanocytes, and Annexin V staining indicated that detachment induced cell death significantly in melanocytes. Blocking Bim expression by using RNAi vectors or by expressing N-RAS^Q61K significantly inhibited anoikis in melanocytes. In summary, this report indicates that N-RAS^Q61K and B-RAF^V600E contribute to melanoma's resistance to apoptosis in part by downregulating Bim expression, suggesting that Bim is a possible treatment target for overriding melanoma's inherent defenses against cell death.