Abstract
Activation of PLCβ enzymes by G(iβγ) and G(αq/11) proteins is a common mechanism to trigger cytosolic Ca(2+) increase. We and others reported that G(αq/11) inhibitor FR900359 (FR) can inhibit both G(αq)- and, surprisingly, G(iβγ)-mediated intracellular Ca(2+) mobilization. Thus, the G(αi)-G(βγ)-PLCβ-Ca(2+) signaling axis depends entirely on the presence of active G(αq), which reasonably explained FR-inhibited G(iβγ)-induced Ca(2+) release. However, the conclusion that G(iβγ) signaling is controlled by G(αq) derives mostly from HEK293 cells. Here we show that indeed in HEK293 cells both G(αq/11) siRNA and G(αq/11) inhibitors diminished Ca(2+) increase triggered by native G(q)-coupled P2Y(1) receptors, or by transfected G(i)-coupled A(1)- or G(s)-coupled A(2B) adenosine receptors (ARs). However, in T24 bladder cancer cells, G(i) inhibitor PTX, but not G(αq/11) inhibitors, FR, YM254890 (YM) or G(q/11) siRNA, inhibited Ca(2+) increase triggered by native A(2B)AR activation. Simultaneous inactivation of G(i) and G(s) further suppressed A(2B)AR-triggered Ca(2+) increase in T24 cells. The G(αq/11) inhibitor YM fully and partially inhibited endogenous P2Y(1)- and β(2)-adrenergic receptor-induced Ca(2+) increase in T24 cells, respectively. PKC activator PMA partially diminished A(2B)AR-triggered but completely diminished β(2)-adrenergic receptor-triggered Ca(2+) increase in T24 cells. Neither β-arrestin1 nor β-arrestin2 siRNA affected A(2B)AR-mediated Ca(2+) increase. Unlike in T24 cells, YM inhibited native A(2B)AR-triggered calcium mobilization in MDA-MB-231 breast cancer cells. Thus, G(αq/11) is vital for Ca(2+) increase in some cell types, but G(iβγ)-mediated Ca(2+) signaling can be Gα(q/11)-dependent or independent based on cell type and receptor activated. Besides G proteins, PKC also modulates cytosolic Ca(2+) increase depending on cell type and receptor.