Abstract 3474: Depletion of SPECC1L inhibits colorectal cancer cell proliferation

• Published in: Cancer research (Chicago, Ill.) Ill.), 2017-07, Vol.77 (13_Supplement), p.3474-3474
• Main Authors: Bhattacharya, Rajat, Xia, Ling, Fan, Fan, Wang, Rui, Boulbes, Delphine, Ye, Xiang-Cang, Hawke, David, Ellis, Lee
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2017-3474

Introduction: Despite the numerous drugs available for patients with metastatic colorectal cancer (mCRC), median overall survival for this group of patients remains at ~20-24 months, with no significant advances in the last 7 years. In the US ~50,000 patients die each year from mCRC refractory to systemic therapy. Inhibiting angiogenesis as a therapy has led to a great deal of enthusiasm. However, the overall benefit of classical-antiangiogenic therapy remains modest and has not lived up to their expectations in treating CRC. Our recent studies suggest that VEGF intracrine signaling, rather than autocrine/paracrine signaling, regulates cell survival in CRC cells. Further studies to understand the significance and mechanisms of this novel function have led us to identify factors that intracellularly interact with VEGF. Our studies further indicate that one such interacting protein, SPECC1L, may have a significant role in CRC cell proliferation and may be a potential target in mCRC therapy. Methods: Lysates from CRC cells expressing Myc-tagged VEGF protein were immunoprecipitated and analyzed by mass spectrometry to identify VEGF-interacting protiens. SPECC1L was identified as a co-precipitated protein with high level of confidence. SPECC1L was depleted using siRNA and effects of such depletion on CRC cell growth and morphology were measured by cell growth assays (MTT), microscopy, FACS and western blot analyses. Localization of the protein and its interaction with microtubules and actin were visualized by immunostaining of FLAG-tagged recombinant SPECC1L protein. Results: SPECC1L was identified as a protein that co-immunoprecipitated with Myc-tagged VEGF in CRC cells using mass spectroscopy. Previous literature suggests a role for SPECC1L in cell division. As a fraction of VEGF overexpressing CRC cells have a large multinucleated phenotype, likely arising due to defects in cell division, it was hypothesized that a VEGF mediated regulation of SPECC1L may lead to such phenotype. Depletion of SPECC1L by siRNAs in multiple CRC cell lines led to strong defects in cell division. The effects of SPECC1L depletion were manifested as accumulation of doublet-cells failing to complete cytokinesis following mitosis and resulted in reduced cell proliferation. Failure to complete cell division also led to the formation of multinucleated cells and enhanced cell death. Conclusions: Inhibition of SPECC1L strongly inhibits CRC cell proliferation and enhances cell death. Thus