Abstract 896: Knocking out the gene (SNCA) that codes for the Parkinson’s disease-related protein alpha-synuclein in SK-Mel-28 melanoma cells significantly retards tumor growth in SCID mice

The Parkinson’s disease-associated protein alpha-synuclein (α-syn) is often highly expressed in melanoma. α-Syn appears to exert a pro-survival function in melanoma cells, possibly by maintaining autophagy homeostasis. The long-term goal of our work is to determine the mechanism by which α-syn confers survival in melanoma cells. Herein, we used CRISPR (clustered regularly interspaced short palindromic repeats) to disrupt SNCA, the gene that codes for α-syn, in the melanoma cell line SK-Mel-28. Western blotting and real-time-qPCR verified that we generated four α-syn knockout (KO) clones. Three clones showed no expression of α-syn, whereas one had about 50% less α-syn than the control cells. DNA sequencing is consistent with three of the clones having both alleles of SNCA knocked out, whereas one clone has only one allele knocked out. α-Syn KO clones were tested in a variety of assays to ascertain the function of α-syn. First, the percentage of cells with exofacial phosphatidylserine (PS) was determined by annexin V-FITC/PI staining in conjunction with fluorescence-activated cell sorting. On average, there was a statistically significant 50% increase in exofacial PS (annexin V+/PI-) in three of the four α-syn KO clones compared to control cells. Exofacial PS was increased in the α-syn KO clones without a concomitant increase in apoptotic cells (annexin V+/PI+). Second, the clones were tested for growth in vivo using SCID mice. All four clones showed a ~65% reduction in the rate of tumor growth, followed over 12 weeks. Third, immunohistochemical staining of excised tumors from the SCID mice showed that the proliferation marker Ki-67 was significantly (p< 0.0001) lower in the tumors generated from the KO clones compared to tumors from control cells. In conclusion, given that α-syn avidly binds to PS, one possibility is that α-syn is like molecular Velcro that binds to PS molecules embedded in the inner leaflet, and this binding helps ATP-driven flippases keep PS in the inner leaflet. Loss α-syn then increases exofacial PS, which is a marker of senescence. Our working model is that α-syn is an anti-senescence protein, and that the α-syn KO clones grow slower than control cells in vivo because the clones have entered a senescent state. Citation Format: Sahar Shekoohi, Santhanasabapathy Rajasekaran, Shu Yang, Sureshbabu Nagarajan, Dhaval Patel, Xiuping Yu, Stephan N. Witt. Knocking out the gene (SNCA) that codes for the Parkinson’s disease-related protein alpha-synuclein in SK-Mel-28 melanoma cells significantly retards tumor growth in SCID mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 896.