Biomedical subjects

Kohjiro Ueki

Publications and source records attributed to Kohjiro Ueki.

35 records · Page 2Linked to original sources

PubMed2004

Insulin receptor substrate 2 plays a crucial role in beta cells and the hypothalamus.

We previously demonstrated that insulin receptor substrate 2 (Irs2) KO mice develop diabetes associated with hepatic insulin resistance, lack of compensatory beta cell hyperplasia, and leptin resistance. To more precisely determine the roles of Irs2 in beta cells and the hypothalamus, we generated beta cell-specific Irs2 KO and hypothalamus-specific Irs2 knockdown (betaHT-IRS2) mice. Expression of Irs2 mRNA was reduced by approximately 90% in pancreatic islets and was markedly reduced in the arcuate nucleus of the hypothalamus. By contrast, Irs2 expression in liver, muscle, and adipose tissue of betaHT-IRS2 mice was indistinguishable from that of control mice. The betaHT-IRS2 mice displayed obesity and leptin resistance. At 4 weeks of age, the betaHT-IRS2 mice showed normal insulin sensitivity, but at 8 and 12 weeks, they were insulin resistant with progressive obesity. Despite their normal insulin sensitivity at 8 weeks with caloric restriction, the betaHT-IRS2 mice exhibited glucose intolerance and impaired glucose-induced insulin secretion. beta Cell mass and beta cell proliferation in the betaHT-IRS2 mice were reduced significantly at 8 and 12 weeks but not at 10 days. Insulin secretion, normalized by cell number per islet, was significantly increased at high glucose concentrations in the betaHT-IRS2 mice. We conclude that, in beta cells and the hypothalamus, Irs2 is crucially involved in the regulation of beta cell mass and leptin sensitivity.

Animals↗

PubMed2003

Vascular endothelial growth factor activates PI3K/Akt/forkhead signaling in endothelial cells.

OBJECTIVE: Vascular endothelial growth factor (VEGF) is a potent angiogenic growth factor that promotes endothelial cell (EC) survival, migration, and permeability. The forkhead transcription factors FKHR, FKHRL1, and AFX are mammalian orthologues of DAF-16, a forkhead protein that controls longevity in Caenorhabditis elegans. In this study, we examined whether VEGF is coupled to phosphatidyl inositol 3-kinase (PI3K)/Akt/forkhead in ECs. METHODS AND RESULTS: We demonstrate that human ECs express members of the forkhead family (FKHR, FKHRL1, and AFX) and that VEGF modulates the phosphorylation, subcellular localization, and transcriptional activity of one or more of these isoforms by a PI3K/Akt signaling pathway. VEGF inhibited EC apoptosis, promoted DNA synthesis and the G(1)-to-S transition, and reduced expression of the cyclin-dependent kinase inhibitor p27(kip1). Each of these effects was blocked by the PI3K inhibitor LY294002 or by a phosphorylation-resistant mutant of FKHRL1, but not by wild-type FKHRL1. CONCLUSIONS: These results suggest that VEGF signaling in ECs is coupled to forkhead transcription factors through a PI3K/Akt-dependent pathway.

Active Transport, Cell Nucleus↗

PubMed2003

Reduced beta-cell mass and altered glucose sensing impair insulin-secretory function in betaIRKO mice.

Pancreatic beta-cell-restricted knockout of the insulin receptor results in hyperglycemia due to impaired insulin secretion, suggesting that this cell is an important target of insulin action. The present studies were undertaken in beta-cell insulin receptor knockout (betaIRKO) mice to define the mechanisms underlying the defect in insulin secretion. On the basis of responses to intraperitoneal glucose, approximately 7-mo-old betaIRKO mice were either diabetic (25%) or normally glucose tolerant (75%). Total insulin content was profoundly reduced in pancreata of mutant mice compared with controls. Both groups also exhibited reduced beta-cell mass and islet number. However, insulin mRNA and protein were similar in islets of diabetic and normoglycemic betaIRKO mice compared with controls. Insulin secretion in response to insulin secretagogues from the isolated perfused pancreas was markedly reduced in the diabetic betaIRKOs and to a lesser degree in the nondiabetic betaIRKO group. Pancreatic islets of nondiabetic betaIRKO animals also exhibited defects in glyceraldehyde- and KCl-stimulated insulin release that were milder than in the diabetic animals. Gene expression analysis of islets revealed a modest reduction of GLUT2 and glucokinase gene expression in both the nondiabetic and diabetic mutants. Taken together, these data indicate that loss of functional receptors for insulin in beta-cells leads primarily to profound defects in postnatal beta-cell growth. In addition, altered glucose sensing may also contribute to defective insulin secretion in mutant animals that develop diabetes.

Animals↗

PubMed2003

Positive and negative roles of p85 alpha and p85 beta regulatory subunits of phosphoinositide 3-kinase in insulin signaling.

Class IA phosphoinositide (PI) 3-kinase is composed of a p110 catalytic subunit and a p85 regulatory subunit and plays a pivotal role in insulin signaling. To explore the physiological roles of two major regulatory isoforms, p85 alpha and p85 beta, we have established brown adipose cell lines with disruption of the Pik3r1 or Pik3r2 gene. Pik3r1-/- (p85 alpha-/-) cells show a 70% reduction of p85 protein and a parallel reduction of p110. These cells have a 50% decrease in PI 3-kinase activity and a 30% decrease in Akt activity, leading to decreased insulin-induced glucose uptake and anti-apoptosis. Pik3r2-/- (p85 beta-/-) cells show a 25% reduction of p85 protein but normal levels of p85-p110 and PI 3-kinase activity, supporting the fact that p85 is more abundant than p110 in wild type. p85 beta-/- cells, however, exhibit significantly increased insulin-induced Akt activation, leading to increased anti-apoptosis. Reconstitution experiments suggest that the discrepancy between PI 3-kinase activity and Akt activity is at least in part due to the p85-dependent negative regulation of downstream signaling of PI 3-kinase. Indeed, both p85 alpha-/- cells and p85 beta-/- cells exhibit significantly increased insulin-induced glycogen synthase activation. p85 alpha-/- cells show decreased insulin-stimulated Jun N-terminal kinase activity, which is restored by expression of p85 alpha, p85 beta, or a p85 mutant that does not bind to p110, indicating the existence of p85-dependent, but PI 3-kinase-independent, signaling pathway. Furthermore, a reduction of p85 beta specifically increases insulin receptor substrate-2 phosphorylation. Thus, p85 alpha and p85 beta modulate PI 3-kinase-dependent signaling by multiple mechanisms and transmit signals independent of PI 3-kinase activation.

Adenoviridae↗

PubMed2003

Characterization of multiple signaling pathways of insulin in the regulation of vascular endothelial growth factor expression in vascular cells and angiogenesis.

The effects of insulin on vascular endothelial growth factor (VEGF) expression in cultured vascular cells and in angiogenesis were characterized. Insulin increased VEGF mRNA levels in mouse aortic smooth muscle cells from 10(-9) to 10(-7) m with an initial peak of 3.7-fold increases at 1 h and a second peak of 2.8-fold after 12 h. The first peak of VEGF expression was inhibited by LY294002, an inhibitor of phosphatidylinositol (PI) 3-kinase, and by the overexpression of dominant negative forms of p85 subunit of PI 3-kinase or Akt. Inhibitors of MEK kinase, PD98059, or overexpression of dominant negative forms of Ras was ineffective. In contrast, the chronic effect of insulin on VEGF expression was partially inhibited by both LY294002 or PD98059 as well as by the overexpression of dominant negatives of PI 3-kinase or Ras. The importance of PI 3-kinase-Akt pathway on VEGF expression was confirmed in mouse aortic smooth muscle cells isolated from insulin receptor substrate -1 knockout (IRS-1-/-) mice that showed parallel reductions of 46-49% in insulin-stimulated VEGF expression and PI 3-kinase-Akt activation. Insulin-induced activation of PI 3-kinase-Akt on hypoxia-induced VEGF expression and neovascularization was reduced by 40% in the retina of neonatal hypoxia model using IRS-1-/- mice. Thus, unlike other cells, insulin can regulate VEGF expression by both IRS-1/PI 3-kinase-Akt cascade and Ras-MAPK pathways in aortic smooth muscle cells. The in vivo results provide direct evidence that insulin can modulate hypoxia-induced angiogenesis via reduction in VEGF expression in vivo.

Animals↗

PubMed2003

Evidence that phosphatidylinositol 3-kinase- and mitogen-activated protein kinase kinase-4/c-Jun NH2-terminal kinase-dependent Pathways cooperate to maintain lung cancer cell survival.

Cancer cells in which the PTEN lipid phosphatase gene is deleted have constitutively activated phosphatidylinositol 3-kinase (PI3K)-dependent signaling and require activation of this pathway for survival. In non-small cell lung cancer (NSCLC) cells, PI3K-dependent signaling is typically activated through mechanisms other than PTEN gene loss. The role of PI3K in the survival of cancer cells that express wild-type PTEN has not been defined. Here we provide evidence that H1299 NSCLC cells, which express wild-type PTEN, underwent proliferative arrest following treatment with an inhibitor of all isoforms of class I PI3K catalytic activity (LY294002) or overexpression of the PTEN lipid phosphatase. In contrast, overexpression of a dominant-negative mutant of the p85alpha regulatory subunit of PI3K (Deltap85) induced apoptosis. Whereas PTEN and Delta85 both inhibited activation of AKT/protein kinase B, only Deltap85 inhibited c-Jun NH2-terminal kinase (JNK) activity. Cotransfection of the constitutively active mutant Rac-1 (Val12), an upstream activator of JNK, abrogated Deltap85-induced lung cancer cell death, whereas constitutively active mutant mitogen-activated protein kinase kinase (MKK)-1 (R4F) did not. Furthermore, LY294002 induced apoptosis of MKK4-null but not wild-type mouse embryo fibroblasts. Therefore, we propose that, in the setting of wild-type PTEN, PI3K- and MKK4/JNK-dependent pathways cooperate to maintain cell survival.

Apoptosis↗

PubMed2003

Impact of genetic background on development of hyperinsulinemia and diabetes in insulin receptor/insulin receptor substrate-1 double heterozygous mice.

Type 2 diabetes is a complex disease in which genetic and environmental factors interact to produce alterations in insulin action and insulin secretion, leading to hyperglycemia. To evaluate the influence of genetic background on development of diabetes in a genetically susceptible host, we generated mice that are double heterozygous (DH) for knockout of the insulin receptor and insulin receptor substrate-1 on three genetic backgrounds (C57BL/6 [B6], 129Sv, and DBA). Although DH mice on all backgrounds showed insulin resistance, their phenotypes were dramatically different. B6 DH mice exhibited marked hyperinsulinemia and massive islet hyperplasia and developed early hyperglycemia, with 85% overtly diabetic by 6 months. By contrast, 129Sv DH mice showed mild hyperinsulinemia and minimal islet hyperplasia, and < 2% developed diabetes. DBA mice had slower development of hyperglycemia, intermediate insulin levels, and evidence of islet degeneration, with 64% developing diabetes. Thus, mice carrying the same genetic defects on different backgrounds exhibited the full spectrum of abnormalities observed in humans with type 2 diabetes, which allowed for identification of potential loci that promote development of the diabetic phenotype.

Animals↗

PubMed2002

Lipoatrophic diabetes in Irs1(-/-)/Irs3(-/-) double knockout mice.

Based on the phenotypes of knockout mice and cell lines, as well as pathway-specific analysis, the insulin receptor substrates IRS-1, IRS-2, IRS-3, and IRS-4 have been shown to play unique roles in insulin signal transduction. To investigate possible functional complementarity within the IRS family, we generated mice with double knockout of the genes for IRS-1/IRS-3 and IRS-1/IRS-4. Mice with a combined deficiency of IRS-1 and IRS-4 showed no differences from Irs1(-/-) mice with respect to growth and glucose homeostasis. In contrast, mice with a combined deficiency of IRS-1 and IRS-3 developed early-onset severe lipoatrophy associated with marked hyperglycemia, hyperinsulinemia, and insulin resistance. However, in contrast to other models of lipoatrophic diabetes, there was no accumulation of fat in liver or muscle. Furthermore, plasma leptin levels were markedly decreased, and adenovirus-mediated expression of leptin in liver reversed the hyperglycemia and hyperinsulinemia. The results indicate that IRS-1 and IRS-3 play important complementary roles in adipogenesis and establish the Irs1(-/-)/Irs3(-/-) double knockout mouse as a novel model of lipoatrophic diabetes.

Adenoviridae↗

PubMed2002

Altered signaling and cell cycle regulation in embryonal stem cells with a disruption of the gene for phosphoinositide 3-kinase regulatory subunit p85alpha.

The p85alpha regulatory subunit of class I(A) phosphoinositide 3-kinases (PI3K) is derived from the Pik3r1 gene, which also yields alternatively spliced variants p50alpha and p55alpha. It has been proposed that excess monomeric p85 competes with functional PI3K p85-p110 heterodimers. We examined embryonic stem (ES) cells with heterozygous and homozygous disruptions in the Pik3r gene and found that wild type ES cells express virtually no monomeric p85alpha. Although, IGF-1-stimulated PI3K activity associated with insulin receptor substrates was unaltered in all cell lines, p85alpha-null ES cells showed diminished protein kinase B activation despite increased PI3K activity associated with the p85beta subunit. Furthermore, p85alpha-null cells demonstrated growth retardation, increased frequency of apoptosis, and altered cell cycle regulation with a G(0)/G(1) cell cycle arrest and up-regulation of p27(KIP), whereas signaling through CREB and MAPK was enhanced. These phenotypes were reversed by re-expression of p85alpha via adenoviral gene transfer. Surprisingly, all ES cell lines could be differentiated into adipocytes. In these differentiated ES cells, however, compensatory p85beta signaling was lost in p85alpha-null cells while increased signaling by CREB and MAPK was still observed. Thus, loss of p85alpha in ES cells induced alterations in IGF-1 signaling and regulation of apoptosis and cell cycle but no defects in differentiation. However, differentiated ES cells partially lost their ability for compensatory signaling at the level of PI3K, which may explain some of the defects observed in mice with homozygous deletion of the Pik3r1 gene.

Animals↗

PubMed2002

Differential roles of insulin receptor substrates in the anti-apoptotic function of insulin-like growth factor-1 and insulin.

Insulin-like growth factor-1 (IGF-1) and insulin are known to prevent apoptosis. The signaling network of IGF-1 and insulin occurs via multiple pathways involving different insulin receptor substrates (IRSs). To define their roles in the anti-apoptotic function of IGF-1 and insulin, we established brown pre-adipocyte cell lines from wild-type and IRS knockout (KO) animals. In response to 16 h of serum deprivation, IRS-1-deficient cells showed a significant decrease in response to IGF-1 protection from apoptosis, whereas no changes were observed in the IRS-2, IRS-3, or IRS-4 KO cells. Five hours after serum withdrawal, cells already began to undergo apoptosis. At this early time point, IGF-1 and insulin were able to protect both wild-type and IRS-1 KO cells from death by 85-90%. After a longer period of serum deprivation, the protective ability of insulin and IGF-1 was decreased, and this was especially reduced in the IRS-1 KO cells. Reconstitution of these cells with IRS-1, IRS-2, IRS-3, or IRS-1/IRS-2 chimeras restored the anti-apoptotic effects of IGF-1, whereas overexpression of IRS-4 had no effect at long time points and actually reduced the effect of IGF-1 at the short time point. The biochemical basis of the defect in anti-apoptosis was not dependent on phosphorylation of mitogen-activated protein kinase; whereas phosphoinositide 3-kinase activity was decreased by 30% in IRS-1 KO cells. Akt phosphorylation was slightly reduced in these cells. Phosphorylation of the transcription factors cAMP response element-binding protein and FKHR by IGF-1 and insulin was markedly reduced in IRS-1 KO cells. In addition, both IGF-1 and insulin prevented caspase-3 cleavage in the wild-type cells, and this effect was greatly reduced in the IRS-1-deficient cells. These findings suggest that the IRS proteins may play differential roles in the anti-apoptotic effects of IGF-1 and insulin in brown pre-adipocytes, with IRS-1 being predominant, possibly acting through caspase-3-, CREB-, and FKHR-dependent mechanisms.

Animals↗

PubMed2002

Characterization of protein kinase C beta isoform's action on retinoblastoma protein phosphorylation, vascular endothelial growth factor-induced endothelial cell proliferation, and retinal neovascularization.

Retinal neovascularization is a major cause of blindness and requires the activities of several signaling pathways and multiple cytokines. Activation of protein kinase C (PKC) enhances the angiogenic process and is involved in the signaling of vascular endothelial growth factor (VEGF). We have demonstrated a dramatic increase in the angiogenic response to oxygen-induced retinal ischemia in transgenic mice overexpressing PKC beta 2 isoform and a significant decrease in retinal neovascularization in PKC beta isoform null mice. The mitogenic action of VEGF, a potent hypoxia-induced angiogenic factor, was increased by 2-fold in retinal endothelial cells by the overexpression of PKC beta 1 or beta 2 isoforms and inhibited significantly by the overexpression of a dominant-negative PKC beta 2 isoform but not by the expression of PKC alpha, delta, and zeta isoforms. Association of PKC beta 2 isoform with retinoblastoma protein was discovered in retinal endothelial cells, and PKC beta 2 isoform increased retinoblastoma phosphorylation under basal and VEGF-stimulated conditions. The potential functional consequences of PKC beta-induced retinoblastoma phosphorylation could include enhanced E2 promoter binding factor transcriptional activity and increased VEGF-induced endothelial cell proliferation.

Animals↗

PubMed2002

Tumstatin, an endothelial cell-specific inhibitor of protein synthesis.

Tumstatin is a 28-kilodalton fragment of type IV collagen that displays both anti-angiogenic and proapoptotic activity. Here we show that tumstatin functions as an endothelial cell-specific inhibitor of protein synthesis. Through a requisite interaction with alphaVbeta3 integrin, tumstatin inhibits activation of focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3-kinase), protein kinase B (PKB/Akt), and mammalian target of rapamycin (mTOR), and it prevents the dissociation of eukaryotic initiation factor 4E protein (eIF4E) from 4E-binding protein 1. These results establish a role for integrins in mediating cell-specific inhibition of cap-dependent protein synthesis and suggest a potential mechanism for tumstatin's selective effects on endothelial cells.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Adipose tissue selective insulin receptor knockout protects against obesity and obesity-related glucose intolerance.

Insulin signaling in adipose tissue plays an important role in lipid storage and regulation of glucose homeostasis. Using the Cre-loxP system, we created mice with fat-specific disruption of the insulin receptor gene (FIRKO mice). These mice have low fat mass, loss of the normal relationship between plasma leptin and body weight, and are protected against age-related and hypothalamic lesion-induced obesity, and obesity-related glucose intolerance. FIRKO mice also exhibit polarization of adipocytes into populations of large and small cells, which differ in expression of fatty acid synthase, C/EBP alpha, and SREBP-1. Thus, insulin signaling in adipocytes is critical for development of obesity and its associated metabolic abnormalities, and abrogation of insulin signaling in fat unmasks a heterogeneity in adipocyte response in terms of gene expression and triglyceride storage.

Adipocytes↗

PubMed2002

Molecular balance between the regulatory and catalytic subunits of phosphoinositide 3-kinase regulates cell signaling and survival.

Class Ia phosphoinositide (PI) 3-kinase is a central component in growth factor signaling and is comprised of a p110 catalytic subunit and a regulatory subunit, the most common family of which is derived from the p85alpha gene (Pik3r1). Optimal signaling through the PI 3-kinase pathway depends on a critical molecular balance between the regulatory and catalytic subunits. In wild-type cells, the p85 subunit is more abundant than p110, leading to competition between the p85 monomer and the p85-p110 dimer and ineffective signaling. Heterozygous disruption of Pik3r1 results in increased Akt activity and decreased apoptosis by insulin-like growth factor 1 (IGF-1) through up-regulated phosphatidylinositol (3,4,5)-triphosphate production. Complete depletion of p85alpha, on the other hand, results in significantly increased apoptosis due to reduced PI 3-kinase-dependent signaling. Thus, a reduction in p85alpha represents a novel therapeutic target for enhancing IGF-1/insulin signaling, prolongation of cell survival, and protection against apoptosis.

Animals↗

PubMed2002

Reduced expression of the murine p85alpha subunit of phosphoinositide 3-kinase improves insulin signaling and ameliorates diabetes.

A critical component of insulin action is the enzyme phosphoinositide (PI) 3-kinase. The major regulatory subunits of PI 3-kinase, p85alpha and its splice variants, are encoded by the Pik3r1 gene. Heterozygous disruption of Pik3r1 improves insulin signaling and glucose homeostasis in normal mice and mice made insulin-resistant by heterozygous deletion of the Insulin receptor and/or insulin receptor substrate-1 (IRS1) genes. Reduced expression of p85 modulates the molecular balance between this protein, the p110 catalytic subunit of PI 3-kinase, and the IRS proteins. Thus, despite the decrease in p85alpha, PI 3-kinase activation is normal, insulin-stimulated Akt activity is increased, and glucose tolerance and insulin sensitivity are improved. Furthermore, Pik3r1 heterozygosity protects mice with genetic insulin resistance from developing diabetes. These data suggest that regulation of p85alpha levels may provide a novel therapeutic target for the treatment of type 2 diabetes.

Alleles↗

PubMed2001

Increased insulin sensitivity in mice lacking p85beta subunit of phosphoinositide 3-kinase.

On the basis of ex vivo studies using insulin-responsive cells, activation of a Class IA phosphoinositide 3-kinase (PI3K) seems to be required for a wide variety of cellular responses downstream of insulin. The Class IA PI3K enzymes are heterodimers of catalytic and regulatory subunits. In mammals, insulin-responsive tissues express both the p85alpha and p85beta isoforms of the regulatory subunit. Surprisingly, recent studies have revealed that disruption of the p85alpha gene in the mouse (p85alpha(-/-) mice) results in hypoglycemia with decreased plasma insulin, and the p85alpha(+/-) mice exhibit significantly increased insulin sensitivity. These results suggest either that p85alpha negatively regulates insulin signaling, or that p85beta, which mediates the major fraction of Class IA PI3K signaling in the absence of p85alpha, is more efficient than p85alpha in mediating insulin responses. To address this question, we have generated mice in which the p85beta gene is deleted (p85beta(-/-) mice). As with the p85alpha(-/-) mice, the p85beta(-/-) mice showed hypoinsulinemia, hypoglycemia, and improved insulin sensitivity. At the molecular level, PI3K activity associated with phosphotyrosine complexes was preserved despite a 20-30% reduction in the total protein level of the regulatory subunits. Moreover, insulin-induced activation of AKT was significantly up-regulated in muscle from the p85beta(-/-) mice. In addition, insulin-dependent tyrosine phosphorylation of insulin receptor substrate-2 was enhanced in the p85beta(-/-) mice, a phenotype not observed in the p85alpha(-/-) mice. These results indicate that in addition to their roles in recruiting the catalytic subunit of PI3K to the insulin receptor substrate proteins, both p85alpha and p85beta play negative roles in insulin signaling.

Animals↗

PubMed2001

Stretch-induced retinal vascular endothelial growth factor expression is mediated by phosphatidylinositol 3-kinase and protein kinase C (PKC)-zeta but not by stretch-induced ERK1/2, Akt, Ras, or classical/novel PKC pathways.

Stretch-induced expression of vascular endothelial growth factor (VEGF) is thought to be important in mediating the exacerbation of diabetic retinopathy by systemic hypertension. However, the mechanisms underlying stretch-induced VEGF expression are not fully understood. We present novel findings demonstrating that stretch-induced VEGF expression in retinal capillary pericytes is mediated by phosphatidylinositol (PI) 3-kinase and protein kinase C (PKC)-zeta but is not mediated by ERK1/2, classical/novel isoforms of PKC, Akt, or Ras despite their activation by stretch. Cardiac profile cyclic stretch at 60 cpm increased VEGF mRNA expression in a time- and magnitude-dependent manner without altering mRNA stability. Stretch increased ERK1/2 phosphorylation, PI 3-kinase activity, Akt phosphorylation, and PKC-zeta activity. Signaling pathways were explored using inhibitors of PKC, MEK1/2, and PI 3-kinase; adenovirus-mediated overexpression of ERK, PKC-alpha, PKC-delta, PKC-zeta, and Akt; and dominant negative (DN) mutants of ERK, PKC-zeta, Ras, PI 3-kinase and Akt. Although stretch activated ERK1/2 through a Ras- and PKC classical/novel isoform-dependent pathway, these pathways were not responsible for stretch-induced VEGF expression. Overexpression of DN ERK and Ras had no effect on VEGF expression in these cells. In contrast, DN PI 3-kinase as well as pharmacologic inhibitors of PI 3-kinase blocked stretch-induced VEGF expression. Although stretch-induced PI 3-kinase activation increased both Akt phosphorylation and activity of PKC-zeta, VEGF expression was dependent on PKC-zeta but not Akt. In addition, PKC-zeta did not mediate stretch-induced ERK1/2 activation. These results suggest that stretch-induced expression of VEGF involves a novel mechanism dependent upon PI 3-kinase-mediated activation of PKC-zeta that is independent of stretch-induced activation of ERK1/2, classical/novel PKC isoforms, Ras, or Akt. This mechanism may play a role in the well documented association of concomitant hypertension with clinical exacerbation of neovascularization and vascular permeability.

Animals↗