STORE-OPERATED CALCIUM ENTRY TRIGGERS THE ACTIVATION OF CAMP RESPONSE ELEMENT BINDING PROTEIN THROUGH THE CALCIUM/CALMODULIN-DEPENDENT PROTEIN KINASE PATHWAY IN HUMAN NEURAL PROGENITOR CELLS

In neural progenitor cells (NPCs), intracellular calcium (Ca²⁺) is primarily regulated by store-operated Ca²⁺ entry (SOCE) — a mechanism that promotes Ca²⁺ influx when intracellular Ca²⁺ stores are empty. In addition to the filling of Ca²⁺ stores, SOCE has been implicated as having downstream effects on NPC proliferation and differentiation. Therefore, our lab sought to identify the cellular signalling pathways that connect SOCE to NPC function. We first found that the induction of SOCE in human induced pluripotent stem cell-derived NPCs altered gene expression, especially those related to development. We then probed whether SOCE facilitated the activity of cAMP Response Element-Binding Protein (CREB), a calcium (Ca²⁺)-sensitive transcription factor that regulates NPC function, but has yet to be linked to SOCE in said cells. Indeed, our efforts suggest that SOCE induction results in the phosphorylation of CREB at serine 133, increasing the transciption factor's gene regulatory activity. Next, we established the signaling pathway responsible for this activation of CREB using inhibitors of the ERK1/2, Akt, and CaMK pathways. Only pharmacological inhibition of the CaMK pathway significantly blocked the phosphorylation of CREB, suggesting that this is the main pathway that drives CREB activation following SOCE induction in NPCs. To further confirm this, we created CaMKIV, CaMKIIα, CaMKIIβ knockdowns using a CRISPR-Cas9 system to probe CREB activation following SOCE, and to additionally determine the effect of the CaMKs' absence on NPC proliferation and morphology. Taken together, these findings provide a better understanding of SOCE-activated signaling during the initial stages of neuron growth and differentiation.