Targeted overexpression of protein kinase C β2 isoform in myocardium causes cardiomyopathy

Self Cite

The expression of the basic helix-loop-helix transcription factor c-Myc is induced in pancreatic islets of several different diabetic model animals and is possibly involved in suppression of the insulin gene transcription. In this study, we found that activity of protein kinase C is increased by high glucose, preceding the induction of c-myc expression and that PKC ␤2 specifically regulates c-myc expression in pancreatic ␤-cells. Since PKC ␣, ␤2, ␦, ⑀, and were expressed in rat pancreatic islets, we prepared each wild type (WT) and dominant negative type (DN) PKC isoform (␣, ␤2, ␦, ⑀, and )-expressing adenovirus to examine the effect of each PKC isoform on c-myc expression. In isolated rat pancreatic islets, adenovirus-mediated overexpression of WT PKC ␤2, but not other PKC isoforms, markedly increased c-myc expression. Moreover, c-myc induction by high glucose was suppressed by adenovirus-mediated overexpression of DN PKC ␤2 but not by other DN PKC isoforms. Finally, adenovirus-mediated overexpression of WT PKC ␤2, but not of other PKC isoforms, leads to suppression of the insulin gene transcription in pancreatic islets. These results suggest that at least some of the reduction of insulin gene transcription found in the diabetic state is mediated by PKC ␤2 regulation of c-myc expression.

Section: Discussionsupporting

confidence: 79%

Section: Induction Of C-myc Gene Expression In Rat Pancreatic Islets supporting

confidence: 80%

supporting

confidence: 49%

See 1 more Smart Citation

Involvement of Protein Kinase C β2 in c-mycInduction by High Glucose in Pancreatic β-Cells

Kaneto

Suzuma

Sharma

et al. 2002

Self Cite

“…In addition, the calcium-regulated actin-binding protein gelsolin accumulates and redistributes in the dilated TOT heart (data not shown). Chronic elevation of intracellular calcium in TOT cardiomyocytes (6) is likely responsible for activation of calciumdependent protein kinase C isoforms (data not shown) associ- ated with hypertrophy and dilation (3,4). Multiplex signaling occurring in TOT cardiomyopathy may have relevance for end stage human heart failure characterized by activation of numerous reactive pathways (33), as well as elevation of intracellular calcium levels leading to activation of calcium-dependent signaling (1,2).…”

Section: Discussionmentioning

confidence: 99%

Activation of pyk2/Related Focal Adhesion Tyrosine Kinase and Focal Adhesion Kinase in Cardiac Remodeling

Meléndez

Welch

Schaefer³

et al. 2002

Cellular remodeling during progression of dilation involves focal adhesion contact reorganization. However, the signaling mechanisms and structural consequences leading to impaired cardiomyocyte adhesion are poorly defined. These events were studied in tropomodulinoverexpressing transgenic mice that develop dilated cardiomyopathy associated with chronic elevation of intracellular calcium. Analysis of tropomodulin-overexpressing transgenic hearts by immunoblot and confocal microscopy revealed activation and redistribution of signaling molecules known to regulate adhesion. Calcium-dependent pyk2/related focal adhesion tyrosine kinase (RAFTK) showed changes in expression and phosphorylation state, similar to changes observed for a related downstream target molecule of pyk2/RAFTK termed focal adhesion kinase. Paxillin, the target substrate molecule for focal adhesion kinase phosphorylation, was redistributed in tropomodulin-overexpressing transgenic hearts with enhanced paxillin phosphorylation and cleavage. Certain aspects of the in vivo signaling phenotype including increased paxillin phosphorylation could be recapitulated in vitro using neonatal rat cardiomyocytes infected with recombinant adenovirus to overexpress tropomodulin. In addition, increasing intracellular calcium levels with ionomycin induced pyk2/ RAFTK phosphorylation, and adenovirally mediated expression of wild-type pyk2/RAFTK resulted in increased phospho-pyk2/RAFTK levels and concomitant paxillin phosphorylation. Collectively, these results delineate a cardiomyocyte signaling pathway associated with dilation that has potential relevance for cardiac remodeling, focal adhesion reorganization, and loss of contractility.Altered intracellular calcium handling is characteristic of heart failure, presumably as a compensatory mechanism to stimulate contractile function and signal transduction (1, 2). Chronic elevation of diastolic calcium level consequently activates calcium-dependent signal transduction pathways. Calcium-activated pathways regulate cardiac function, and disruption of calcium-responsive signaling has been associated with cardiomyopathic changes in experimental transgenic mouse models. Myocardium-specific transgenic overexpression of calcium-activated enzymes such as protein kinase C ␤2 (3, 4) or calcineurin (5) cause hypertrophy. Calcineurin activation, hypertrophic remodeling, and elevation of intracellular calcium are associated with heart failure in a cardiomyopathic transgenic mouse model created by overexpression of tropomodulin (Tmod), 1 a regulatory component of the sarcomere (6). Tmodoverexpressing transgenic (TOT) hearts are characterized by a combination of increased intracellular calcium levels, myofibril degeneration, loss of systolic function, and inability to hypertrophy. This constellation of features is reminiscent of degenerative changes associated with heart failure (1, 7, 8), making the TOT mouse a useful model for studying structural and signaling changes occurring in myocardial decompensation.TOT hearts dilate rapidl...

“…Mechanical stimuli (87,88) and hypoxia (89) also activate PK-C. The pathophysiologic consequences of excessive PK-C ␤II activation in myocardium, as occurs in diabetes (63,65) and congestive cardiomyopathies (58), is supported by transgenic mouse models in which myocardial PKC ␤II overexpression leads to a fatal postnatal cardiomyopathy (90). Although our studies demonstrate the involvement of PK-C ␤II in phosphorylation of the VLDL-R, however, they do not exclude the possibility that other PK-C isoforms such as PK-C ␦ may also mediate this activity (91).…”

Section: Activation Of Pk-c By Elevated Glucose Concentrations Leads mentioning

confidence: 99%

Regulation of the Ligand Binding Activity of the Human Very Low Density Lipoprotein Receptor by Protein Kinase C-dependent Phosphorylation

Sakthivel¹,

Zhang²,

Strickland³

et al. 2001

The very low density lipoprotein receptor (VLDL-R) binds and internalizes several ligands, including very low density lipoprotein (VLDL), urokinase-type plasminogen activator:plasminogen activator inhibitor type 1 complexes, lipoprotein lipase, and the 39-kDa receptor-associated protein that copurifies with the low density lipoprotein receptor-related protein/␣ 2 -macroglobulin receptor. Although several agonists regulate VLDL-R mRNA and/or protein expression, post-transcriptional regulation of receptor activity has not been described. Here, we report that the ligand binding activity of the VLDL-R in THP-1 monocytic cells, endothelial cells, smooth muscle cells, and VLDL-R-transfected HEK 293 cells is diminished after treatment with phorbol 12-myristate 13-acetate. This response was blocked by inhibitors of protein kinase C (PK-C), including a specific inhibitor of the PK-C ␤II isoform, and was associated with phosphorylation of serine residues in the cytoplasmic domain of the receptor. Culture of endothelial cells in the presence of high glucose concentrations, which stimulate diacylglycerol synthesis and PK-C ␤II activation, also induced a PK-C-dependent loss of VLDL-R ligand binding activity. Taken together, these studies demonstrate that the ligand binding activity of the VLDL-R is regulated by PK-C-dependent phosphorylation and that hyperglycemia may diminish VLDL-R activity. The very low density lipoprotein receptor (VLDL-R)1 is a member of the low density lipoprotein receptor (LDL-R) family, which encompasses several structurally related proteins such as the LDL receptor-related protein/␣ 2 -macroglobulin receptor, gp330 (megalin), and apoE receptor 2 (1-4) among others. Members of this family are characterized by a cytoplasmic domain NPXY sequence that mediates ligand internalization through clathrin-coated pits (5) and an extracellular domain comprised of cysteine-rich complement-type and epidermal growth factor precursor-like repeats that regulate ligand binding specificity (2). Except for the presence of an additional complement-type repeat in its extracellular domain, the domain structure of the VLDL-R is identical to that of the LDL-R (6 -8). Despite this homology, however, the ligand binding specificity of these receptors differs. Though both receptors bind apoE-containing lipoproteins (6, 7, 9, 10), only the LDL receptor binds lipoproteins containing apoB-100 (6, 7), whereas the VLDL-R binds several additional ligands such as lipoprotein lipase (9), (11) urokinase-type plasminogen activator:plasminogen activator inhibitor type 1 (u-PA:PAI-1) complexes (11,12), and Lp(a) (13). Finally, the 39-kDa receptor-associated protein (RAP), which co-purifies with (14, 15) and binds with high affinity to the LDL receptor-related protein/␣ 2 -macroglobulin receptor (16 -18), binds tightly to the VLDL-R (19) but with only low affinity to the 20).Differences in the tissue distribution of the LDL and VLDL receptors also suggest non-overlapping physiologic functions. Although the LDL-R is highly expressed in liver...