As SDF 1 also acts on Gi coupled CXCR4 receptor in HeLa cells for PKD activation, we then performed similar knockdown treatment to verify the pos sible PLCB23 dependency. Our result demonstrated that this Gi induced signaling also required the GB�� responsive PLCB23 isoforms to stimulate the PKD activation. Discussion Extending from prior such reports on the regulation of PKD1 by Gq, the present study demonstrates unequivo cally that each and every member of the Gq subfamily are capable of inducing the kinase activity of all PKD isoforms. The ability to B stimulate PKD activity is apparently unique to the Gq members because other G subunits belong ing to the Gi, Gs, or G12 subfamilies all failed to induce PKD phosphorylation or kinase activity.
However, it should be noted that addition of AlF? to cells co expressing PKD and wild type G13 can lead to PKD activation. Such an observation is confounded by the fact that AlF? may activate multiple G proteins simultaneously. The lack of Inhibitors,Modulators,Libraries effect on PKD by the consti tutively active mutant of G13 has in fact been reported. Hence, it is reasonable to conclude that only mem bers Inhibitors,Modulators,Libraries of the Gq subfamily are efficiently linked to PKD activation. Despite the preponderance of Gq in mediating Inhibitors,Modulators,Libraries GPCR induced activation of PKD, stimulation of Gi coupled re ceptors in HeLa cells resulted in PKD phosphorylation. This may be explained by the observation that HeLa cells endogenously express GB�� responsive PLCB23, thereby allowing GB�� released from acti vated heterotrimeric Gi proteins to mediate PKD activa tion through the GB��PLCPKC axis.
One would expect that stimulation of Gi coupled receptors will result in PKD activation in cells endowed with Inhibitors,Modulators,Libraries PLCB23. However, if the endogenous PLCB23 is responsive to GB�� dimers and all active G protein heterotrimers liberate free GB�� dimers, then it remains puzzling why stimulation of Gs coupled receptors cannot activate PKD via PLCB23. A recent report has revealed that differential dissociation may exist among different G proteins, though it has long been thought that active G protein heterotrimers readily dissociate into G GTP subunits and GB�� dimers. Activated GoA heterotrimers can seemingly dissociate more readily than activated Gs heterotrimers, and this may account for G specific acti vation of GB�� sensitive effectors.
Alternatively, the lack of Gs induced PKD activation may be attributed to insufficient release of GB�� dimers as most Inhibitors,Modulators,Libraries GB�� dependent signaling appeared to require substantial amounts of free GB��, which is most often achieved by stimulating the more abundantly expressed Gi proteins. Another interesting selleckchem 17-DMAG observation in the present study pertains to the requirement of PLCB23 for GB�� induced PKD activation. At first sight, our finding seems to suggest a concept different from the previous belief that GB�� dimers alone can activate PKD through interaction with the PH domain.