Phospholipase C-γ1 is required for the activation of store-operated Ca²⁺ channels in liver cells

Repetitive hormone-induced changes in concentration of free cytoplasmic Ca²⁺ in hepatocytes require Ca²⁺ entry through receptor-activated Ca²⁺ channels and SOCs (store-operated Ca ²⁺ channels). SOCs are activated by a decrease in Ca²⁺ concentration in the intracellular Ca²⁺ stores, but the molecular components and mechanisms are not well understood. Some studies with other cell types suggest that PLC-γ (phospholipase C-γ) is involved in the activation of receptor-activated Ca²⁺ channels and/or SOCs, independently of PLC-γ-mediated generation of IP₃ (inositol 1,4,5-trisphosphate). The nature of the Ca²⁺ channels regulated by PLC-γ has not been defined clearly. The aim of the present study was to determine if PLC-γ is required for the activation of SOCs in liver cells. Transfection of H4IIE cells derived from rat hepatocytes with siRNA (short interfering RNA) targeted to PLC-γ1 caused a reduction (by approx. 70%) in the PLC-γ1 protein expression, with maximal effect at 72-96 h. This was associated with a decrease (by approx. 60%) in the amplitude of the I _SOC (store-operated Ca²⁺ current) developed in response to intracellular perfusion with either IP₃ or thapsigargin. Knockdown of STIM1 (stromal interaction molecule type 1) by siRNA also resulted in a significant reduction (approx. 80 % at 72 h post-transfection) of the I _SOC amplitude. Immunoprecipitation of PLC-γ1 and STIM1, however, suggested that under the experimental conditions these proteins do not interact with each other. It is concluded that the PLC-γ1 protein, independently of IP₃ generation and STIM1, is required to couple endoplasmic reticulum Ca²⁺ release to the activation of SOCs in the plasma membrane of H4IIE liver cells.