Activation of Jun Kinase/Stress-activated Protein Kinase by GTPase-deficient Mutants of Gα12 and Gα13

Abstract

Signal transduction pathways regulated by G12 and G13 heterotrimeric G proteins are largely unknown. Expression of activated, GTPase-deficient mutants of alpha 12 and alpha 13 alter physiological responses such as Na+/H+ exchanger activity, but the effector pathways controlling these responses have not been defined. We have found that the expression of GTPase-deficient mutants of alpha 12 (alpha 12Q229L) or alpha 13 (alpha 13Q226L) leads to robust activation of the Jun kinase/stress-activated protein kinase (JNK/SAPK) pathway. Inducible alpha 12Q229L and alpha 13Q226L expression vectors stably transfected in NIH 3T3 cells demonstrated JNK/SAPK activation but not extracellular response/mitogen-activated protein kinase activation. Transient transfection of alpha 12Q229L and alpha 13Q226L also activated the JNK/SAPK pathway in COS-1 cells. Expression of the GTPase-deficient mutant of alpha q (alpha qQ209L) but not alpha i (alpha iQ205L) or alpha s (alpha sQ227L) was also able to activate the JNK/SAPK pathway. Functional Ras signaling was required for alpha 12Q229L and alpha 13Q226L activation of the JNK/SAPK pathway; expression of competitive inhibitory N17Ras inhibited JNK/SAPK activation in response to both alpha 12Q229L and alpha 13Q226L. The results describe for the first time a Ras-dependent signal transduction pathway involving JNK/SAPK regulated by alpha 12 and alpha 13.

The G12 coupled thrombin receptor stimulates mitogenesis through the Shc SH2 domain

“…Thus, like many growth factors, Ga 12 can communicate to the JNK pathway through a Ras dependent mechanism (Minden et al, 1995;Vara Prasad et al, 1995;Collins et al, 1996). Dominant negative proteins in the JNK pathway are e ective inhibitors of AP-1 mediated gene expression by Ga 12 , while this response is insensitive to the MEK inhibitor PD090859 (our unpublished observations).…”

“…It is also important to note that while Ga 12 activates Ras, it stimulates the activity of the JNK but not the ERK family of MAP kinases Vara Prasad et al, 1995). Thus, like many growth factors, Ga 12 can communicate to the JNK pathway through a Ras dependent mechanism (Minden et al, 1995;Vara Prasad et al, 1995;Collins et al, 1996).…”

The ras-related GTPase rac1 regulates a proliferative pathway selectively utilized by G-protein coupled receptors

“…The response was dose-dependent, and was greater for rac* than rac. For comparison, wild-type and activated versions of the heterotrimeric G-protein Ga13, which is oncogenic (Dhanasekaran and Dermott, 1996;VoynoYasenetskaya et al, 1994) and is thought to regulate rac-dependent signaling pathways (Voyno-Yasenetskaya et al, 1996;Vara Prasad et al, 1995), were also tested. Ga13* induced a response very similar in magnitude to rac*.…”

“…The heterotrimeric G-proteins Gaq, Ga12 and Ga13 are each capable of transforming NIH3T3 cells (Dhanasekaran and Dermott, 1996;Voyno-Yasenetskaya et al, 1994;Chan et al, 1993;Xu et al, 1993;Jiang et al, 1993;Kalinec et al, 1992) and we have previously shown that Gaq but not Ga12 is responsible for transducing m5-induced proliferative responses in NIH3T3 cells (Burstein et al, 1995b;. It has been recently shown that GTPase de®cient mutants of Gaq, Ga12 and Ga13 activate the JNK pathway (VoynoYasenetskaya et al, 1996;Vara Prasad et al, 1995) and we have found that Gaq, Ga12 and Ga13 can each induce proliferative responses in R-SAT TM (Figure 1 and see Burstein et al, 1997). Thus, although bg subunits have been implicated in MAP kinase pathway activation (Crespo et al, 1994), the available evidence suggests that the Ga subunit probably transduces proliferative responses along the signaling pathway regulated by rac.…”

Oncogenic mutant of Gα12 stimulates cell proliferation through cycloxygenase-2 signaling pathway

“…Furthermore, the expression of the Ga 12 QL has been shown to stimulate DNA synthesis in several other cell-types such as 1321N1 astrocytoma cells (Aragay et al, 1995). Studies from several laboratories including ours have shown that the proliferative pathway regulated by Ga 12 includes the Ras/Rac mediated activation of JNKs (Vara Prasad et al, 1995;Collins et al, 1996;Voyno-Yasenetskaya et al, 1996), Rho-dependent activation of cytoskeletal changes (Buhl et al, 1995;Hooley et al, 1996;Needham and Rozengurt, 1998), Rho-dependent activation of speci®c transcription factors (Fromm et al, 1997), Rac/MEKK1-mediated activation of AP-1 complex (Collins et al, 1996), and Ras/Rac/Rhodependent cell transformation (Zhang et al, 1996;Tolkacheva et al, 1997;Fromm et al, 1997). In addition, it has been shown that serum-induced phospholipase A 2 (PLA 2 ) activity was potentiated by Ga 12 QL in NIH3T3 cells, suggesting a role for eicosanoids in Ga 12 QL signaling (Xu et al, 1993).…”