Gα12 Directly Interacts with PP2A

Abstract

in ϳ300% stimulation of PP2A activity that was not detected with other G␣ subunits and was similar with GTP␥S-and GDP-liganded G␣ 12 . When tau and active kinase (Cdk5 and p25) were cotransfected in to COS cells, there was robust tau phosphorylation. Co-expression of wild type or QL␣ 12 with tau and the active kinase resulted in 60 ؎ 15% reductions in tau phosphorylation. In primary cortical neurons stimulated with lysophosphatitic acid, a 50% decrease in tau phosphorylation was observed. The G␣ 12 effect on tau phosphorylation was inhibited by the PP2A inhibitor, okadaic acid (50 nM), in COS cells and neurons. Taken together, these findings reveal novel, direct regulation of PP2A activity by G␣ 12 and potential in vivo modulation of PP2A target proteins including tau.Heterotrimeric G proteins 1 regulate many fundamental cellular responses, and the canonical receptor-G protein-effector paradigm has become significantly more complex in recent years. G protein signaling is modulated through interactions with families of regulatory proteins that affect nucleotide binding and hydrolysis. These include the RGS (regulators of G protein signaling) protein family that stimulate G␣ GTPase activity (reviewed in Ref. 1), and the GPR (G protein regulatory) protein family that share a conserved motif that inhibits GDP release from the G␣ i /␣ o families of G␣ subunits (2-4). G␣ 12/13 have multiple cellular functions including regulation of the actin cytoskeleton (5) and many functions are shared by both G␣ 12 and G␣ 13 subunits. G␣ 12/13 regulation of the actin cytoskeleton and stress fiber formation occurs through direct interactions with Rho regulatory proteins (6, 7), and other aspects of G␣ 12 /␣ 13 signaling are regulated through specific interactions with membrane or scaffolding proteins. For example, the binding of G␣ 12 and G␣ 13 to the C terminus of E-cadherin displaces ␤-catenin permitting it to signal (8, 9). We identified direct binding of both wild type and constitutively active (QL)␣ 12 to ZO-1 and regulation of paracellular permeability of Madin-Darby canine kidney cells (10,11). In addition, G␣ 12 interacts with AKAP-lbc, a scaffolding molecule that organizes components of cAMP signaling and Rho signaling machinery (12). Here, we have identified the A␣ subunit of Ser/ Thr phosphatase PP2A as another "scaffolding" protein that selectively interacts with G␣ 12 .Tau is a microtubule-associated protein that is predominantly expressed in neurons and functions to stabilize the cytoskeleton. Tau phosphorylation is necessary for microtubule binding and other protein interactions, but hyperphosphorylated tau is the predominant component of neurofibrillary tangles, a pathologic hallmark finding found in several neurodegenerative disorders including Alzheimer disease and FTDP-17 (frontotemporal dementia and Parkinson's disease linked to chromosome 17; reviewed in Ref. 13). Several kinases phosphorylate tau including mitogen-activated protein kinase (MAP), glycogen synthase 3␤ (GSK-3␤), tau-tubulin kinase, and cyclindepe...

Gα12 Stimulates Apoptosis in Epithelial Cells through JNK1-mediated Bcl-2 Degradation and Up-regulation of IκBα

“…G␣ 12 binds PP2A and stimulates phosphatase activity (20), and the binding domains were recently identified (21). The current results extend these observations and reveal regulation of apoptosis through PP2A using at least 2 different pathways: G␣ 12 dependent activation of JNK and a G␣ 12 -independent pathway.…”

“…However, there is very little known about the role of G␣ 12 in regulating apoptosis in non-transfected cells, and few studies have investigated G protein regulation of apoptosis in epithelial cells. Recently, we identified an interaction of G␣ 12 with the regulatory subunit of the serine/threonine phosphatase protein phosphatase 2A (PP2A) and demonstrated that G␣ 12 stimulated PP2A activity in vitro and in MDCK cells (20,21). PP2A is implicated in many of the same cellular processes that have been described for G␣ 12 (reviewed in Ref.…”

Gα12 Interaction with αSNAP Induces VE-cadherin Localization at Endothelial Junctions and Regulates Barrier Function

“…Both activated and nonactivated forms of G␣ 12 were found to be competent for the interaction with ␣SNAP. This is similar to the binding of G␣ 12 to Hsp90 (22) and to the scaffolding subunit of PP2A (21), which also occurs independently of the activation state of G␣ 12 . We found that among several G␣ subunits tested the interaction with ␣SNAP was specific for G␣ 12 .…”

“…The complex roles of G␣ 12 and G␣ 13 may reflect their ability to interact with many protein partners, such as several RhoGEFs (14,17,18), radixin (19), the protein Ser/Thr phosphatase PP5 (20), the scaffolding subunit of another protein Ser/ Thr phosphatase PP2A (21), and the chaperone Hsp90 (22), which can mediate a variety of responses (23). Some of these interacting partners bind both G␣ 12 and G␣ 13 , whereas others are specific for one of them.…”

Polymeric alkylpyridinium salts permit intracellular delivery of human Tau in rat hippocampal neurons: requirement of Tau phosphorylation for functional deficits

“…Kinase-mediated Tau phosphorylation is opposed by phosphatases, of which protein phosphatase 2A (PP2A) principally regulates Tau phosphorylation in vivo [14,24,25], though in vitro Tau is a suitable substrate for PP1, PP2A, PP2B and PP5 [26][27][28][29][30]. In AD brains, there is strong evidence for impaired phosphatase activity, primarily due to a reduction in PP2A expression and activity, but also as a consequence of up-regulation of the endogenous inhibitor of PP2A (I 1 PP2A ), alongside a modest decrease in PP5 activity [30][31][32][33].…”