Selective G Alpha(I) Subunits As Novel Direct Activators Of Trpc4 And Trpc5 Channels

The Transient Receptor Potential, Canonical (TRPC) channels function as non-selective, Ca2+-permeable channels and mediate numerous cellular functions. It is commonly assumed that TRPC channels are activated by stimulation of Gαq coupled receptors. However, whether the Gαq-PLC pathway regulates the TRPC4/5 channels and how these channels are regulated by other Gα proteins is unknown.Here, we discovered that Gαi subunits, rather than Gαq, are the primary and direct activators of TRPC4 and TRPC5. These channels were activated by the stimulation of Muscarinic receptor 2 that regulated by pertusis toxin sensitive manner in the activation process of channel.The expression of the constitutively active Gαi mutants selectively activates TRPC4 and TRPC5 channels. TRPC4 is activated by several Gαi subunits, most prominently by Gαi2 and TRPC5 is activated primarily by Gαi3. On the other hand, to investigate the effect of Gβγ on the activation process of TRPC4/5, we used Gβ mutants (Gβ1W99A and Gβ1I80A). The result from these mutants does not suggest the role of Gβγ subunit as a key modulator for TRPC4/5 activation. Finally, to check out that the mechanism of TRPC4 activation by Gαi2, we expressed TRPC4 C-terminus deletion and truncation mutants in HEK293 cells. When the region from 700 to 720 in C-terminal region of TRPC4 channel was deleted, electrophysiological activity did not elicited by Gαi2 QL and infused GTPγS. Also co-IP between TRPC4 and Gαi2 QL was altered by the deleted c-terminal region (700-720).These findings indicate an essential role of Gαi proteins as novel activators for TRPC4/5 and reveal the molecular mechanism by which G proteins activate the channels.∗ This research was supported by the National Research Foundation of Korea (NRF) funded by the Korea government (MEST) (2008-2005948 and 2010-0019472).