Inactivation of RASA1 promotes melanoma tumorigenesis via R-Ras activation

// Hyeran Sung 1, 2 , Krishna L. Kanchi 3 , Xue Wang 1, 2 , Kristen S. Hill 1, 2 , Jane L. Messina 2, 4, 5 , Ji-Hyun Lee 6 , Youngchul Kim 7 , Nathan D. Dees 3 , Li Ding 3, 8, 9 , Jamie K. Teer 7 , Shengyu Yang 2, 10 , Amod A. Sarnaik 2, 4 , Vernon K. Sondak 2, 4 , James J. Mule 2, 4 , Richard K. Wilson 3, 9 , Jeffrey S. Weber 11 , Minjung Kim 1, 2, 4 1 Department of Molecular Oncology, Moffitt Cancer Center, Tampa, FL, USA 2 Comprehensive Melanoma Research Center, Moffitt Cancer Center, Tampa, FL, USA 3 The Genome Institute, Washington University, St. Louis, MO, USA 4 Department of Cutaneous Oncology, Moffitt Cancer Center, Tampa, FL, USA 5 Department of Pathology, Moffitt Cancer Center, Tampa, FL, USA 6 Department of Internal Medicine, University of New Mexico Comprehensive Cancer Center, Albuquerque, NM, USA 7 Department of Biostatistics and Bioinformatics, Moffitt Cancer Center, Tampa, FL, USA 8 Department of Medicine, Washington University, St. Louis, MO, USA 9 Department of Genetics, Washington University, St. Louis, MO, USA 10 Department of Tumor Biology, Moffitt Cancer Center, Tampa, FL, USA 11 Department of Medicine, NYU Langone Medical Center, New York, NY, USA Correspondence to: Minjung Kim, e-mail: Minjung.kim@moffitt.org Keywords: melanoma, RASA1, RasGAP, R-Ras, whole genome sequencing Received: January 15, 2016      Accepted: February 28, 2016      Published: March 16, 2016 ABSTRACT Inactivation of Ras GTPase activating proteins (RasGAPs) can activate Ras, increasing the risk for tumor development. Utilizing a melanoma whole genome sequencing (WGS) data from 13 patients, we identified two novel, clustered somatic missense mutations (Y472H and L481F) in RASA1 (RAS p21 protein activator 1, also called p120RasGAP). We have shown that wild type RASA1, but not identified mutants, suppresses soft agar colony formation and tumor growth of BRAF mutated melanoma cell lines via its RasGAP activity toward R-Ras (related RAS viral (r-ras) oncogene homolog) isoform. Moreover, R-Ras increased and RASA1 suppressed Ral-A activation among Ras downstream effectors. In addition to mutations, loss of RASA1 expression was frequently observed in metastatic melanoma samples on melanoma tissue microarray (TMA) and a low level of RASA1 mRNA expression was associated with decreased overall survival in melanoma patients with BRAF mutations. Thus, these data support that RASA1 is inactivated by mutation or by suppressed expression in melanoma and that RASA1 plays a tumor suppressive role by inhibiting R-Ras, a previously less appreciated member of the Ras small GTPases.