PHYSIOLOGICAL IMPLICATIONS AND MOLECULAR INSIGHTS INTO CA2+ ENTRY AND CLEARANCE MECHANISMS

Abstract

My studies seek to understand how Ca2+ signals are controlled by entry and clearance mechanisms, leading to pluripotent changes in cell fate. The Ca2+-dependent activity of transcription factor NFAT, which drives many changes in gene expression, was examined. Remarkably, overexpression of Ca2+-extruder PMCA4 increased NFAT activation in a splice variant-dependent manner. Partner of STIM1 (POST), rather than facilitating STIM1-mediated inhibition of PMCA4, accelerated clearance via close associations with PMCA4b and Orai1. Furthermore, it was found that PMCA4b markedly depressed near-PM Ca2+ while raising global levels. These observations define the role of POST in facilitating sustained SOCE and spontaneous Ca2+ oscillations by coupling PMCA4 and Orai1 activity. EGR4 was found to upregulate POST during T cell activation, and knocking out Egr4 resulted in dysregulated Ca2+ oscillations. Moreover, knockout of Egr4 induced strong IFN-γ expression independent of T cell polarization. The dysregulation of Ca2+ signals and cytokine production support a new role for EGR4 in T cell differentiation. Finally, SOCE was found to be reduced in invasive melanoma cell lines. Correlation of diminished SOCE with increased invasiveness support a model in which invasiveness can be driven by reduced SOCE downstream of non-canonical Wnt5a signaling. These novel findings present new mechanisms governing sustained Ca2+ responses, and their ramifications on T cell development and progression of neoplastic disease.