AKAP-Lbc Anchors Protein Kinase A and Nucleates Gα12-selective Rho-mediated Stress Fiber Formation

Abstract

The transmission of information from the plasma membrane to the actin cytoskeleton is essential to control a variety of dynamic cellular processes including cell shape, motility, and adherence (1). Critical mediators of these events are the Rho family small molecular weight GTPases, Rho, Rac, and Cdc42, which regulate distinct actin remodeling events. Rho is primarily responsible for the assembly of actin stress fibers and focal adhesions, and Rac controls the formation of lamellipodia, while Cdc42 induces filopodial formation (1, 2). In addition to these effects, Rho has also been implicated in a variety of other critical cellular functions including gene transcription (3,4) and progression through the cell cycle (5).Lysophosphatidic acid (LPA) and thrombin are the extracellular ligands that induce Rho signaling events (2). Binding of either ligand to distinct classes of cell surface receptors triggers a series of events that mobilize the pertussis toxin-insensitive heterotrimeric G protein subunits G␣ 12 and G␣ 13 (6, 7). The intracellular targets for either G␣ subunit are a growing family of guanine nucleotide exchange factors (GEFs) (8). These exchange factors dock with activated G␣ 12 and G␣ 13 and facilitate GTP loading of Rho. Individual cells express several Rho-GEFs, which activate distinct Rho signaling pathways (9). For example, p115 Rho-GEF interacts with G␣ 13 through a regulator of G protein signaling (RGS) domain located in the amino-terminal region of the exchange factor (10, 11). Likewise, a related module, the Lsc homology domain, governs docking of G␣ 13 to exchange factors such as PDZ Rho-GEF, KIAA0380,.A universal hallmark of exchange factors that activate GTPases of the Rho family is a conserved region of ϳ250 residues that contains a Dbl homology (DH) domain followed by a pleckstrin homology domain (9). The DH domain contains the nucleotide exchange activity, whereas the pleckstrin homology domain is thought to be involved in the subcellular localization of GEFs (2). GTPase selectivity is governed by determinants located within the DH domain that discriminate Rho-specific from Rac or Cdc42-specific exchange factors. Several families of Rho-specific exchange factors have been recognized. Members of the Lbc family were originally identified in a screen for transforming genes from human myeloid leukemias (15). OncoLbc is a 424-residue oncogenic protein with unregulated exchange factor activity that transforms NIH-3T3 cells in a Rhodependent manner (16). Subsequently, a proto-oncogenic form has been isolated with a COOH-terminal region that attenuates its transforming potential (17). More recently, a splice variant called Brx has been identified that is specifically expressed in testis and estrogen-sensitive tissues (18). Interestingly, Lbc does not possess RGS-like domains, suggesting that different mechanisms might be involved in its activation in response to extracellular signals.In this study, we demonstrate that a novel Lbc splice variant, AKAP-Lbc, is also an A-kinase-anchoring protein (...

Bioinformatic design of A-kinase anchoring protein- in silico : A potent and selective peptide antagonist of type II protein kinase A anchoring

“…This 24-residue peptide is derived from human anchoring protein AKAP-Lbc and binds RII with a K d of 2-4 nM (18,50). Our biochemical studies show that AKAP-IS binds RII with a 5-fold higher affinity (K d ϭ 0.4 nM), and our cell-based experiments confirm that it is a more effective inhibitor of PKA anchoring in vivo.…”

An entirely specific type I A-kinase anchoring protein that can sequester two molecules of protein kinase A at mitochondria

“…Thus, the PKA anchoring and sphingosine kinase 1 binding may represent independent aspects of SKIP function that reside within the same polypeptide chain. This concept is reminiscent of how other cardiac PKA anchoring proteins such as AKAPLbc and PI3 kinase γ seem to operate as they also encode catalytic units for guanine nucleotide exchange and lipid kinase activity, respectively (57,58). Alternatively, our MS evidence that SKIP is recruited into higher order macromolecular complexes within the mitochondrial intermembrane space could enhance PKA phosphorylation of ChChd3 (43) and accommodate an antiapoptotic role for sphingosine kinase 1 (53).…”

A regulatory SNP in AKAP13 is associated with blood pressure in Koreans

“…AKAP13 binds to the regulatory subunit of protein kinase A, anchoring it to discrete areas within cells. AKAP13 also binds RhoA to activate the Rho family GTPase; [17][18][19] the GTPase is a mediator of cardiac hypertrophy, and AKAP13 is upregulated in hypertrophic cardiomyocytes. 20 Moreover, cardiomyocytes in AKAP13-null mice have impaired sarcomere formation, causing 21 Therefore, we speculate that rs11638762, an SNP of AKAP13, alters AKAP13 expression levels, leading to variations in wall thickness in the heart, which might influence blood pressure, secondary to the pumping capacity of the heart.…”

“…The longest transcript contains at least five domains, such as an ankyrinrepeat domain, a PKA-anchoring domain, a protein kinase C-like diacyglycerol consensus binding site, a dbl oncogene homology domain, and a pleckstrin homology domain; a dbl oncogene homology-pleckstrin homology domain acts as a guanine nucleotide exchange factor for the Rho GTPase. 17 rs11638762 is located upstream of three AKAP13 transcripts (ENST00000452008, ENST00000426424 and ENST00000394510), 2682 bp upstream of ENST00000452008 (Figure 2). However, the SNP located on intron of the other AKAP13 transcript.…”