Regulation and compartmentation of PC metabolism

The addition of a-thronibin io quiescent IIC9 cells results in the stimulation of PI and PC metabolism. PC metabolism involves the activation of a PC PI,I) and PLA2 as well as an ''apparent1' PC-PLC activity. We further demonstrated that a PC-PLD ifc activated at the nucleus and this activation is mediated by RhoA. The present studies were designed to examine the molecular mechanisms regulating a-thrombin-induced PC.' metabolism, including those occuring at the nuclear envelope. We demonstrate that one a-thrombin receptor, couples to both PI and PC metabolism but that this occurs via different G proteins. PI metabolism is mediated via a Gq protein while much of the PC metabolism is mediated via betagammadimers associated with Go. The activation of PC-P LI) and PLA2 are mediated by G proteins distinct from Gq or the Go betagamma dimerb. We have cloned a PLO in IIC!) and show that these cells contain both a hamster PLDl that resembles the human PLDlb (hamPLDlb). and a PLD2. Interestingly, while nuclear PLD activity is increased in response to a thrombin, PLD in the Golgi is unaffected even though both fractions contain a hamPLDlb. Taken together, these results indicate that the specificity of PLD activation (and PLA2) is regulated at two levels; (a)by the initial G proteins and {!)) by the immediate downstream activators. Studies to examine other nuclear enzvmrs and regulators are in prepress.