Cellular dynamics are controlled by key signaling molecules such as cAMP-dependent protein kinase (PKA) and protein kinase C (PKC). AKAP12/SSeCKS/Gravin (AKAP12) is a scaffold protein for PKA and PKC which controls actin-cytoskeleton reorganization in a spatiotemporal manner. AKAP12 also acts as a tumor suppressor which regulates cell-cycle progression and inhibits Src-mediated oncogenic signaling and cytoskeletal pathways. Reexpression of AKAP12 causes cell flattening, reorganization of the actin cytoskeleton, and the production of normalized focal adhesion structures. Downregulation of AKAP12 induces the formation of thickened, longitudinal stress fibers and the proliferation of adhesion complexes. AKAP12-null mouse embryonic fibroblasts exhibit hyperactivation of PKC, premature cellular senescence, and defects in cytokinesis, relating to the loss of PKC scaffolding activity by AKAP12. AKAP12-null mice exhibit increased cell senescence and increased susceptibility to carcinogen-induced oncogenesis. The paper describes the regulatory and scaffolding functions of AKAP12 and how it regulates cell adhesion, signaling, and oncogenic suppression. 1. Introduction The actin cytoskeleton plays an essential role in numerous aspects of cell biology such as cell adhesion, cell morphology, cytokinesis, and migration. Cell migration machinery is regulated by signaling intermediates that can be activated by diverse stimuli and that can exert control over a large number of downstream target molecules, all with temporal and spatial specificity [1, 2]. PKA, PKC, and C a 2 + -binding proteins are examples of cellular regulators that mediate diverse effects on cytoskeletal dynamics, cell adhesion, and cell migration [3, 4]. Control of the subcellular localization of PKA and PKC activities in a temporal manner by A-Kinase-Anchoring Proteins (AKAP) has emerged as a pivotal mechanism to control cell migration [2]. For instance, AKAP12/SSeCKS/Gravin (AKAP12) is thought to control a number of cellular events by scaffolding key signaling molecules such as cyclin D1, calmodulin, PKA, and PKC (Figure 1) [5]. Figure 1: AKAP12 binds to key signaling molecules. AKAP12 contains various demonstrated protein binding domains as well as PKC phosphorylation sites (pS) and a tyrosine phosphorylation site (pY). NLS, nuclear localization signals (at least 4 T ag motifs); CaM, calmodulin; GalTase, β1,4-galactosyltransferase; Myr, N-terminal myristoylation. SSeCKS (rodent AKAP12), the Src-Suppressed-C-Kinase-Substrate, was originally identified in a screen for genes severely downregulated by
References
[1]
M. L. Gardel, I. C. Schneider, Y. Aratyn-Schaus, and C. M. Waterman, “Mechanical integration of actin and adhesion dynamics in cell migration,” Annual Review of Cell and Developmental Biology, vol. 26, pp. 315–333, 2010.
[2]
W. Wong and J. D. Scott, “AKAP signalling complexes: focal points in space and time,” Nature Reviews Molecular Cell Biology, vol. 5, no. 12, pp. 959–970, 2004.
[3]
A. K. Howe, “Cross-talk between calcium and protein kinase A in the regulation of cell migration,” Current Opinion in Cell Biology, vol. 23, no. 5, pp. 554–561, 2011.
[4]
C. Larsson, “Protein kinase C and the regulation of the actin cytoskeleton,” Cellular Signalling, vol. 18, no. 3, pp. 276–284, 2006.
[5]
I. H. Gelman, “The role of SSeCKS/gravin/AKAP12 scaffolding proteins in the spaciotemporal control of signaling pathways in oncogenesis and development,” Frontiers in Bioscience, vol. 7, pp. d1782–1797, 2002.
[6]
B. J. Frankfort and I. H. Gelman, “Identification of novel cellular genes transcriptionally suppressed by v-src,” Biochemical and Biophysical Research Communications, vol. 206, no. 3, pp. 916–926, 1995.
[7]
X. Lin, P. J. Nelson, B. Frankfort, E. Tombler, R. Johnson, and I. H. Gelman, “Isolation and characterization of a novel mitogenic regulatory gene, 322, which is transcriptionally suppressed in cells transformed by src and ras,” Molecular and Cellular Biology, vol. 15, no. 5, pp. 2754–2762, 1995.
[8]
S. B. Cohen, A. Waha, I. H. Gelman, and P. K. Vogt, “Expression of a down-regulated target, SSeCKS, reverses v-Jun-induced transformation of 10T1/2 murine fibroblasts,” Oncogene, vol. 20, no. 2, pp. 141–146, 2001.
[9]
C. Chapline, B. Mousseau, K. Ramsay et al., “Identification of a major protein kinase C-binding protein and substrate in rat embryo fibroblasts: decreased expression in transformed cells,” Journal of Biological Chemistry, vol. 271, no. 11, pp. 6417–6422, 1996.
[10]
W. Xia, P. Unger, L. Miller, P. J. Nelson, and I. H. Gelman, “The Src-suppressed C kinase substrate, SSeCKS, is a potential metastasis inhibitor in prostate cancer,” Cancer Research, vol. 61, no. 14, pp. 5644–5651, 2001.
[11]
P. J. Nelson, K. Moissoglu, J. Vargas Jr., P. E. Klotman, and I. H. Gelman, “Involvement of the protein kinase C substrate, SSeCKS, in the actin-based stellate morphology of mesangial cells,” Journal of Cell Science, vol. 112, no. 3, pp. 361–370, 1999.
[12]
S. R. Coats, J. W. Covington, M. Su et al., “SSeCKS gene expression in vascular smooth muscle cells: regulation by angiotensin II and a potential role in the regulation of PAI-1 gene expression,” Journal of Molecular and Cellular Cardiology, vol. 32, no. 12, pp. 2207–2219, 2000.
[13]
P. J. Nelson and I. H. Gelman, “Cell-cycle regulated expression and serine phosphorylation of the myristylated protein kinase C substrate, SSeCKS: correlation with culture confluency, cell cycle phase and serum response,” Molecular and Cellular Biochemistry, vol. 175, no. 1-2, pp. 233–241, 1997.
[14]
I. H. Gelman, E. Tombler, and J. Vargas Jr., “A role for SSeCKS, a major protein kinase C substrate with tumour suppressor activity, in cytoskeletal architecture, formation of migratory processes, and cell migration during embryogenesis,” Histochemical Journal, vol. 32, no. 1, pp. 13–26, 2000.
[15]
W. Xia and I. H. Gelman, “Mitogen-induced, FAK-dependent tyrosine phosphorylation of the SSeCKS scaffolding protein,” Experimental Cell Research, vol. 277, no. 2, pp. 139–151, 2002.
[16]
X. Lin, E. Tombler, P. J. Nelson, M. Ross, and I. H. Gelman, “A novel src- and ras-suppressed protein kinase C substrate associated with cytoskeletal architecture,” Journal of Biological Chemistry, vol. 271, no. 45, pp. 28430–28438, 1996.
[17]
J. B. Nauert, T. M. Klauck, L. K. Langeberg, and J. D. Scott, “Gravin, an autoantigen recognized by serum from myasthenia gravis patients, is a kinase scaffold protein,” Current Biology, vol. 7, no. 1, pp. 52–62, 1997.
[18]
L.-W. Guo, L. Gao, J. Rothschild, B. Su, and I. H. Gelman, “Control of protein kinase C activity, phorbol ester-induced cytoskeletal remodeling, and cell survival signals by the scaffolding protein SSeCKS/GRAVIN/AKAP12,” Journal of Biological Chemistry, vol. 286, no. 44, pp. 38356–38366, 2011.
[19]
C. Chapline, J. Cottom, H. Tobin, J. Hulmes, J. Crabb, and S. Jaken, “A major, transformation-sensitive PKC-binding protein is also a PKC substrate involved in cytoskeletal remodeling,” Journal of Biological Chemistry, vol. 273, no. 31, pp. 19482–19489, 1998.
[20]
X. Lin and I. H. Gelman, “Reexpression of the major protein kinase C substrate, SSeCKS, suppresses v-src-induced morphological transformation and tumorigenesis,” Cancer Research, vol. 57, no. 11, pp. 2304–2312, 1997.
[21]
B. Su, Y. Bu, D. Engelberg, and I. H. Gelman, “SSeCKS/gravin/AKAP12 inhibits cancer cell invasiveness and chemotaxis by suppressing a protein kinase C Raf/MEK/ERK pathway,” Journal of Biological Chemistry, vol. 285, no. 7, pp. 4578–4586, 2010.
[22]
H. Busch, D. Camacho-Trullio, Z. Rogon et al., “Gene network dynamics controlling keratinocyte migration,” Molecular Systems Biology, vol. 4, article 199, 2008.
[23]
J. Piontekt and R. Brandt, “Differential and regulated binding of cAMP-dependent protein kinase and protein kinase C isoenzymes to gravin in human model neurons. Evidence that gravin provides a dynamic platform for the localization of kinases during neuronal development,” Journal of Biological Chemistry, vol. 278, no. 40, pp. 38970–38979, 2003.
[24]
X. Yan, M. Walkiewicz, J. Carlson, L. Leiphon, and B. Grove, “Gravin dynamics regulates the subcellular distribution of PKA,” Experimental Cell Research, vol. 315, no. 7, pp. 1247–1259, 2009.
[25]
I. H. Gelman, K. Lee, E. Tombler, R. Gordon, and X. Lin, “Control of cytoskeletal architecture by the src-suppressed C kinase substrate, SSeCKS,” Cell Motility and Cytoskeleton, vol. 41, pp. 1–17, 1998.
[26]
S. Akakura, R. Bouchard, W. Bshara, C. Morrison, and I. H. Gelman, “Carcinogen-induced squamous papillomas and oncogenic progression in the absence of the SSeCKS/AKAP12 metastasis suppressor correlate with FAK upregulation,” International Journal of Cancer, vol. 129, pp. 2025–2031, 2011.
[27]
S. Akakura, P. Nochajski, L. Gao, P. Sotomayor, S. I. Matsui, and I. H. Gelman, “Rb-dependent cellular senescence, multinucleation and susceptibility to oncogenic transformation through PKC scaffolding by SSeCKS/AKAP12,” Cell Cycle, vol. 9, no. 23, pp. 4656–4665, 2010.
[28]
X. Lin, P. J. Nelson, and I. H. Gelman, “SSeCKS, a major protein kinase C substrate with tumor suppressor activity, regulates progression by controlling the expression and cellular compartmentalization of cyclin D,” Molecular and Cellular Biology, vol. 20, no. 19, pp. 7259–7272, 2000.
[29]
X. Lin and I. H. Gelman, “Calmodulin and cyclin D anchoring sites on the Src-suppressed C kinase substrate, SSeCKS,” Biochemical and Biophysical Research Communications, vol. 290, no. 5, pp. 1368–1375, 2002.
[30]
M. C. Choi, Y. U. Lee, S. H. Kim et al., “A-kinase anchoring protein 12 regulates the completion of cytokinesis,” Biochemical and Biophysical Research Communications, vol. 373, no. 1, pp. 85–89, 2008.
[31]
J. R. A. Hutchins, Y. Toyoda, B. Hegemann et al., “Systematic analysis of human protein complexes identifies chromosome segregation proteins,” Science, vol. 328, no. 5978, pp. 593–599, 2010.
[32]
R. Kittler, L. Pelletier, A. K. Heninger et al., “Genome-scale RNAi profiling of cell division in human tissue culture cells,” Nature Cell Biology, vol. 9, no. 12, pp. 1401–1412, 2007.
[33]
M. Werner and M. Glotzer, “Control of cortical contractility during cytokinesis,” Biochemical Society Transactions, vol. 36, no. 3, pp. 371–377, 2008.
[34]
I. H. Gelman and L. Gao, “SSeCKS/Gravin/AKAP12 metastasis suppressor inhibits podosome formation via RhoA- and Cdc42-dependent pathways,” Molecular Cancer Research, vol. 4, no. 3, pp. 151–158, 2006.
[35]
A. T. Saurin, J. Durgan, A. J. Cameron, A. Faisal, M. S. Marber, and P. J. Parker, “The regulated assembly of a PKCε complex controls the completion of cytokinesis,” Nature Cell Biology, vol. 10, no. 8, pp. 891–901, 2008.
[36]
S. Akakura, C. Huang, P. J. Nelson, B. Foster, and I. H. Gelman, “Loss of the ssecks/gravin/akap12 gene results in prostatic hyperplasia,” Cancer Research, vol. 68, no. 13, pp. 5096–5103, 2008.
[37]
M. Collado and M. Serrano, “The power and the promise of oncogene-induced senescence markers,” Nature Reviews Cancer, vol. 6, no. 6, pp. 472–476, 2006.
[38]
J. H. Rhim, I. S. Jang, E. J. Yeo, K. Y. Song, and S. C. Park, “Role of protein kinase C-dependent A-kinase anchoring proteins in lysophosphatidic acid-induced cAMP signaling in human diploid fibroblasts,” Aging Cell, vol. 5, no. 6, pp. 451–461, 2006.
[39]
C. M. Perou, T. S？rile, M. B. Eisen et al., “Molecular portraits of human breast tumours,” Nature, vol. 406, no. 6797, pp. 747–752, 2000.
[40]
A. Rosenwald, A. A. Alizadeh, G. Widhopf et al., “Relation of gene expression phenotype to immunoglobulin mutation genotype in B cell chronic lymphocytic leukemia,” Journal of Experimental Medicine, vol. 194, no. 11, pp. 1639–1647, 2001.
[41]
P. N. Tonin, T. J. Hudson, F. Rodier et al., “Microarray analysis of gene expression mirrors the biology of an ovarian cancer model,” Oncogene, vol. 20, no. 45, pp. 6617–6626, 2001.
[42]
W. Liu, M. Guan, B. Su et al., “Quantitative assessment of AKAP12 promoter methylation in colorectal cancer using methylation-sensitive high resolution melting: correlation with dukes' stage,” Cancer Biology and Therapy, vol. 9, no. 11, pp. 862–871, 2010.
[43]
M. Hayashi, S. Nomoto, M. Kanda, et al., “Identification of the A kinase anchoring protein 12 (AKAP12) gene as a candidate tumor suppressor of hepatocellular carcinoma,” Journal of Surgical Oncology, vol. 105, pp. 381–386, 2012.
[44]
G. W. McLean, K. Brown, M. I. Arbuckle et al., “Decreased focal adhesion kinase suppresses papilloma formation during experimental mouse skin carcinogenesis,” Cancer Research, vol. 61, no. 23, pp. 8385–8389, 2001.
[45]
H. S. Lee, J. Han, H. J. Bai, and K. W. Kim, “Brain angiogenesis in developmental and pathological processes: regulation, molecular and cellular communication at the neurovascular interface,” FEBS Journal, vol. 276, no. 17, pp. 4622–4635, 2009.
[46]
B. Su, Q. Zheng, M. M. Vaughan, Y. Bu, and I. H. Gelman, “SSeCKS metastasis-suppressing activity in MatLyLu prostate cancer cells correlates with vascular endothelial growth factor inhibition,” Cancer Research, vol. 66, no. 11, pp. 5599–5607, 2006.
[47]
B. Burnworth, J. Pippin, P. Karna, et al., “SSeCKS sequesters cyclin D1 in glomerular parietal epithelial cells and influences proliferative injury in the glomerulus,” Laboratory Investigation, vol. 92, pp. 490–510, 2012.
[48]
H. Y. Wang, J. Tao, E. Shumay, and C. C. Malbon, “G-protein-coupled receptor-associated A-kinase anchoring proteins: AKAP79 and AKAP250 (gravin),” European Journal of Cell Biology, vol. 85, no. 7, pp. 643–650, 2006.
[49]
F. Lin, H. Y. Wang, and C. C. Malbon, “Gravin-mediated formation of signaling complexes in β2-adrenergic receptor desensitization and resensitization,” Journal of Biological Chemistry, vol. 275, no. 25, pp. 19025–19034, 2000.
[50]
S. W. Lee, W. J. Kim, Y. K. Choi et al., “SSeCKS regulates angiogenesis and tight junction formation in blood-brain barrier,” Nature Medicine, vol. 9, no. 7, pp. 900–906, 2003.
[51]
H. B. Kwon, Y. K. Choi, J. J. Lim, et al., “AKAP12 regulates vascular integrity in zebrafish,” Experimental Molecular Medicine, vol. 44, pp. 225–235, 2012.
