Elucidation of physiological significance of direct Ca^<2+> channel-phospholipase coupling in cell fate control

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TRP superfamily proteins form plasma membrane cation channels acting as ‘sensors' for diverse cellular stimuli. TRPM2 is a Ca^<2+> permeable channel activated by redox statue changes such as oxidative stress. Although it has been suggested that Ca^<2+> influx via TRPM2 mediate cell death, its physiological significance is still elusive. TRPM2 is expressed in immunocytes such as monocytes and lymphocytes. In monocytic cell line U937, it is known that hydrogen peroxide (H_2O_2) induces chemotactic cytokine interleukin-8 (IL-8) production via Erk/NF-κB pathway and that IL-8 is produced via intracellular Ca^<2+> increases. Here, we reveal that oxidative stress-sensitive TRPM2 Ca^<2+> channels are crucial for H_2O_2-induced IL-8 production in U937. We also report physiological significance of the TRPM2 in vivo with regard to the above biological response by utilizing TRPM2 knockout mice.We also demonstrate a novel activation mechanism mediated by cysteine S-nitrosylation in TRP channels. TRPC1, C4, C5, V1, V3, and V4 of TRPC and TRPV families, commonly classified as receptor-activated channels and thermosensor channels, show prominent responses to nitric oxide (NO) to elicit Ca^<2+> entry in HEK293 cells. TRPC5 cysteine mutants, examined for NO responsiveness and susceptibility to S-nitrosylation, have revealed Cys553 and Cys558 as modification sites essential for the NO sensitivity. The responsive TRPs harbor conserved cysteines on the same N-terminal side of the pore region. Strikingly, membrane sidedness of reactive disulfide-induced activation via Cys553 modification suggests cytoplasmic accessibility to Cys553. Thus, multidisciplinary approach based upon chemical biology and physiology identifies the structural motif for NO-sensitive activation gate in TRP channels, establishing ‘NO sensors' as a new functional category extending over different TRP subfamilies.