Store-operated Ca²⁺ entry in hippocampal neurons: Regulation by protein tyrosine phosphatase PTP1B

Store operated Ca²⁺ entry (SOCE) replenishes intracellular Ca²⁺ stores and activates a number of intracellular signalling pathways. Whilst several molecular components forming store operated Ca²⁺ channels (SOCC) have been identified, their modulation in neurons remains poorly understood. Here, we extend on our previous findings and show that neuronal SOCE is modulated by tyrosine phosphorylation. Cyclopiazonic acid induced SOCE was characterised in hippocampal cultures derived from forebrain specific protein tyrosine phosphatase 1B knockout (PTP1B KO) mice and wild type (WT) litter mates using Fura-2 Ca²⁺ imaging. PTP1B KO cultures expressed elevated SOCE relative to WT cultures without changes in cytoplasmic Ca²⁺ homeostasis or depolarisation-induced Ca²⁺ influx. WT and PTP1B KO cultures displayed similar pharmacological sensitivities towards the SOCE inhibitors gadolinium and 2-aminoethoxydiphenyl borate, as well as the tyrosine kinase inhibitor Ag126 indicating an augmentation of native SOCCs by PTP1B. Following store depletion WT culture homogenates showed heightened phospho-tyrosine levels, an increase in Src tyrosine kinase activation and two minor PTP1B species. These data suggest tyrosine phosphorylation gating SOCE, and implicate PTP1B as a key regulatory enzyme. The involvement of PTP1B in SOCE and its relation to SOCC components and mechanism of regulation are discussed.