Remodeling of Store Operated Channels in Colon Cancer

Ponente: Carlos Villalobos Jorge

Institute of Molecular Biology and Genetics (IBGM) [Valladolid, España]

Host: Eugenio Santos/ Rósula García Navas

Fecha: 28/09/2017

Hora: 12:30

Salón de Actos del Centro de Investigación del Cáncer

Intracellular Ca²⁺ regulates multiple processes such as cell proliferation, cell migration and cell death, critically involved in tumor cell growth. Recent evidence indicate that changes in intracellular Ca²⁺ homestasis (Ca²⁺ remodelling) may contribute to cancer hallmarks. We have investigated changes in intracellular Ca²⁺ handling in human colon adenocarcinoma cells. For this end, fluorescence Ca²⁺ imaging, patch-clamp electrophysiology, conventional and quantitative PCR, western-blotting, gene silencing, co-immunoprecipitation assays, next generation sequencing and cell proliferation, invasion and survival assays were used in human colon cancer cells and normal colonic cells. Our results show that store-operated Ca²⁺ entry (SOCE), Ca²⁺ release and Ca²⁺ entry induced by agonists, and Ca²⁺ release-activated Ca²⁺ current (CRAC) are much larger in human adenocarcinoma colon cells (HT29 cells) compared to normal human colonic mucosa cells (NCM460 cells). Furthermore, tumor cells display a nonselective store-operated current (SOC) that is missing in normal cells. Enhanced SOCE correlates with increased cell proliferation and SOCE inhibition prevented cell proliferation and cell invasion. At the molecular level, tumor cells display enhanced expression of TRPC1, ORAI1, ORAI2 and ORAI3, and loss of expression of TRPC7, TRPV6 and TRPM8. In addition, STIM2 protein expression is decreased in tumor cells compared to normal cells. In addition, about 30 genes involved in calcium transport were differentially expressed in tumor vs. normal cells. Gene silencing experiments show that changes in SOCE and CRAC in normal cells could be mediated by differences in ORAI1 expression whilst the change in SOC in tumor cells could be mediated by enhanced expression of TRPC1. Co-immunoprecipitation experiments suggest that SOCE in tumor cells may be due to channel complexes made of Orai1, STIM1 and TRPC1 that are different and/or absent in normal cells. SOCE is also modulated by mitochondria in both normal and colon cancer cells. In normal cells, mitochondria is required for Icrac activation, however CRAC channels inactivate regardless of mitochondrial status leading to transient SOCE. In colon cancer cells, the Warburg effect increases mitochondrial potential, thus empowering cancer cell mitochondria to take up Ca²⁺. In this scenario, mitochondria is able to prevent the slow, Ca²⁺ dependent inactivation of SOCs in tumor cells, leading to a sustained SOC and enhanced SOCE. Mitochondrial depolarization with selected non-steroideal anti-inflammatory drugs (NSAIDs) promote SOC inactivation and inhibit SOCE and tumor cell proliferation, thus providing a rationale for colon cancer chemoprevention by NSAIDs. We conclude that colon cancer cells undergo deep changes in intracellular Ca²⁺ homeostasis including remodelling of store-operated channels that contribute to cancer hallmarks and some of these effects can be counteracted by NSAIDs providing a new target for cancer chemoprevention.