Erythropoietin-modulated calcium influx through TRPC2 is mediated by phospholipase Cγ and IP3R

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Abstract
In the present study, we examined the mechanisms through which erythropoietin (Epo) activates the calcium-permeable transient receptor potential protein channel (TRPC)2. Erythroblasts were isolated from the spleens of phenylhydrazine-treated mice, and Epo stimulation resulted in a significant and dose-dependent increase in intracellular calcium concentration ([Ca2+]i). This increase in [Ca2+]iwas inhibited by pretreatment with the phospholipase C (PLC) inhibitor U-73122 but not by the inactive analog U-73343, demonstrating the requirement for PLC activity in Epo-modulated Ca2+influx in primary erythroid cells. To determine whether PLC is involved in the activation of TRPC2 by Epo, cell models were used to examine this interaction. Single CHO-S cells that expressed transfected Epo receptor (Epo-R) and TRPC2 were identified, and [Ca2+]iwas quantitated. Epo-induced Ca2+influx through TRPC2 was inhibited by pretreatment with U-73122 or by downregulation of PLCγ1 by RNA interference. PLC activation results in the production of inositol 1,4,5-trisphosphate (IP3), and TRPC2 has IP3receptor (IP3R) binding sites. To determine whether IP3R is involved in Epo-R signaling, TRPC2 mutants were prepared with partial or complete deletions of the COOH-terminal IP3R binding domains. In cells expressing TRPC2 IP3R binding mutants and Epo-R, no significant increase in [Ca2+]iwas observed after Epo stimulation. TRPC2 coassociated with Epo-R, PLCγ, and IP3R, and the association between TRPC2 and IP3R was disrupted in these mutants. Our data demonstrate that Epo-R modulates TRPC2 activation through PLCγ; that interaction of IP3R with TRPC2 is required; and that Epo-R, TRPC2, PLCγ, and IP3R interact to form a signaling complex.