Physiological control of receptor-activated Ca²⁺ signaling by TRP channels

Abstract

Physiological functions of transient receptor potential (TRP) Ca²⁺-permeable cation channels must be studied in "contexts" of dominant signaling pathways. In non-excitable cells, receptor-activated Ca²⁺ signalling comprises initial transient responses followed by a Ca²⁺ entry-dependent sustained and/or oscillatory phase. Here, we describe the molecular mechanism underlying the second phase linked to signal amplification. An in vivo inositol 1,4,5-trisphosphate (IP₃) sensor revealed that in B lymphocytes, receptor-activated and store-operated Ca²⁺ entry greatly enhanced IP₃ production, which terminated in phospholipase Cγ2 (PLCγ2)-deficient cells. Association between receptor-activated TRPC3 Ca²⁺ channels and PLCγ2, which cooperate in potentiating Ca²⁺ responses, was demonstrated by coimmunoprecipitation. PLCγ2-deficient cells displayed diminished Ca²⁺ entry-induced Ca²⁺ responses. However, this defect was canceled by suppressing IP₃-induced Ca²⁺ release, implying that IP₃ and IP₃ receptors mediate the second Ca²⁺ phase. Furthermore, confocal visualization of PLCγ2 mutants demonstrated that Ca²⁺ entry evoked a C2 domain-mediated PLCγ2 translocation toward the plasma membrane in a lipase-independent manner to activate PLCγ2. Strikingly, Ca²⁺ entry-activated PLCγ2 maintained Ca²⁺ oscillation and extracellular signal-regulated kinase activation downstream of protein kinase C. We suggest that coupling of Ca²⁺ entry with PLCγ2 translocation and activation controls the amplification and coordination of receptor signalling. [Jpn J Physiol 54 Suppl:S37 (2004)]