CAPN1 is a novel binding partner and regulator of the tumor suppressor NF1 in melanoma

Abstract

// Michal Alon 1 , Rand Arafeh 1 , Joo Sang Lee 2, 3 , Sanna Madan 2, 3 , Shelly Kalaora 1 , Adi Nagler 1 , Tereza Abgarian 1 , Polina Greenberg 1 , Eytan Ruppin 2, 3 and Yardena Samuels 1 1 Molecular Cell Biology Department, Weizmann Institute of Science, Rehovot, Israel 2 Center for Bioinformatics and Computational Biology, The University of Maryland, College Park, Maryland, USA 3 Cancer Data Science Lab, National Cancer Institute, National Institute of Health, Bethesda, Maryland, USA Correspondence to: Yardena Samuels, email: [e-mail] Keywords: melanoma; NF1; CAPN1; degradation; combination therapy Abbreviations: NF1: Neurofibromin 1; CAPN1: Calpain1 Received: March 07, 2018     Accepted: July 05, 2018     Published: July 27, 2018 ABSTRACT Neurofibromin 1 (NF1), a tumor suppressor that negatively regulates RAS through its GTPase activity, is highly mutated in various types of sporadic human cancers, including melanoma. However, the binding partners of NF1 and the pathways in which it is involved in melanoma have not been characterized in an in depth manner. Utilizing a mass spectrometry analysis of NF1 binding partners, we revealed Calpain1 (CAPN1), a calcium-dependent neutral cysteine protease, as a novel NF1 binding partner that regulates NF1 degradation in melanoma cells. ShRNA-mediated knockdown of CAPN1 or treatment with a CAPN1 inhibitor stabilizes NF1 protein levels, downregulates AKT signaling and melanoma cell growth. Combination treatment of Calpain inhibitor I with MEKi Trametinib in different melanoma cells is more effective in reducing melanoma cell growth compared to treatment with Trametinib alone, suggesting that this combination may have a therapeutic potential in melanoma. This novel mechanism for regulating NF1 in melanoma provides a molecular basis for targeting CAPN1 in order to stabilize NF1 levels and, in doing so, suppressing Ras activation; this mechanism can be exploited therapeutically in melanoma and other cancers.