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

Michal Alon,Rand Arafeh,Polina Greenberg,Shelly Kalaora,Yardena Samuels,Adi Nagler,Joo Sang Lee,Tereza Abgarian,Eytan Ruppin,Sanna Madan

doi:10.18632/oncotarget.25805

Michal Alon, Rand Arafeh + Show 8 more

Open Access

https://doi.org/10.18632/oncotarget.25805

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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.

Highlights

Melanoma is the deadliest form of human skin cancer for which the incidence rate continues to increase [1]
Mass spectrometry was performed on endogenous Neurofibromin 1 (NF1) coimmunoprecipitates that were generated from two melanoma cell lines: A375, a commercial melanoma cell line, and 74T, a cell line derived from a melanoma patient
Both cell lines are NF1 wild-type, with A375 containing a BRAFV600E mutation and 74T, an NRASQ61K mutation, which allowed us to screen for NF1 interactions in the two major mutational backgrounds of melanoma [2]

Summary

Introduction

Melanoma is the deadliest form of human skin cancer for which the incidence rate continues to increase [1]. The genetic landscape of melanoma has been extensively studied [2,3,4], which has enabled the development of highly effective targeted therapies [5,6,7]. Unraveling the mechanisms by which cancer cells become resistant to drugs and developing new agents to target the relevant pathways represent the logical steps in personalized cancer treatment. One approach to tackle these challenges in melanoma is to characterize the drivers’ protein interactions by unbiasedly investigating driver protein’s binding partners. These proteomic investigations might provide novel molecules that can serve as biomarkers for cancer diagnosis, prognosis or therapy [13, 14]

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