PCR-based analysis of voltage-gated K+ channels in vascular smooth muscle

Peroxisome proliferator-activated receptor alpha and gamma ligands differentially affect smooth muscle cell proliferation and migration

Peroxisome proliferator-activated receptors (PPARs) alpha and gamma are expressed in smooth muscle cells (SMCs). This study was designed to compare the effects of PPARalpha and PPARgamma on SMC proliferation and migration and to determine how they operate. Treatment of SMCs from porcine coronary artery revealed that mitogen-stimulated DNA synthesis was blocked by the PPARalpha ligand 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (WY14,643) and 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)) (a putative PPARgamma agonist) but not by the PPARgamma agonist rosiglitazone or the PPARbeta/delta ligand 2-methyl-4-((4-methyl-2-(4-trifluoromethylphenyl)-1,3-thiazol-5-yl)-methylsulfanyl)phenoxy acetic acid (GW501516). Inhibition of DNA synthesis by clofibrate and 2-(4-(2-(1-cyclohexanebutyl-3-cyclohexylureido)ethyl)phenylthio)-2-methylproprionic acid (GW7647) confirmed that SMC proliferation is affected by PPARalpha. This conclusion was supported by the fact that WY14,643 also inhibited the proliferation of H4IIE hepatoma cells (expressing only PPARalpha) but not A10 SMCs (expressing only PPARgamma1). In contrast, the effective inhibition of all cell types with 15d-PGJ(2) indicated that this compound probably operates via a PPARgamma-independent mechanism. Interestingly, rosiglitazone did not inhibit DNA synthesis of either H4IIE or A10 cells, suggesting that the activation of PPARgamma does not influence cell proliferation. Phosphorylation of cyclin-dependent kinase 2 and expression of proliferating cell nuclear antigen were inhibited by WY14,643 but not by rosiglitazone or 15d-PGJ(2), indicating that PPARalpha prevents progression into S phase. Although rosiglitazone did not block SMC proliferation, it (like WY14,643) reduced neointimal hyperplasia in vitro. This observation can be rationalized by the fact that both WY14,643 and rosiglitazone inhibit SMC migration, probably through matrix metalloproteinase 9. Our study therefore shows that selective interference with mediators of cell cycle progression and cell migration via activation of PPARs may prevent growth-related vascular diseases such as restenosis and atherosclerosis.

PGE(2) stimulates vascular smooth muscle cell proliferation via the EP2 receptor

Prostaglandins released by injured vascular tissue can modulate smooth muscle cell (SMC) proliferation. The mechanism of action of PGE(2) was investigated with porcine coronary artery SMCs obtained by explant culture. DNA and RNA syntheses exhibited a concentration-dependent increase following treatment of quiescent SMCs with PGE(2), while PGI(2) had no effect. PGE(2) also elevated PCNA expression, bromodeoxyuridine incorporation, and cell number, indicative of a hyperplastic growth response. Furthermore, induction of c-fos expression required activation of both phosphatidylinositol 3-kinase and mitogen-activated protein kinase. Contrary to these data, treatment of proliferating cells with PGE(2) caused a reduction in DNA synthesis. A role for PKA in either growth stimulation or inhibition was excluded. Interestingly, only quiescent SMCs expressed EP2 receptors, and the selective EP2 receptor agonist butaprost confirmed that this receptor was essential for growth stimulation and possibly inhibition. These data suggest that the growth state-dependent actions of PGE(2) on SMC proliferation may be mediated via the EP2 receptor.

Endogenous mono-ADP-ribosylation mediates smooth muscle cell proliferation and migration via protein kinase N-dependent induction of c-fos expression

ADP-ribosylation has been coupled to intracellular events associated with smooth muscle cell vasoreactivity, cytoskeletal integrity and free radical damage. Additionally, there is evidence that ADP-ribosylation is required for smooth muscle cell proliferation. Our investigation employed selective inhibitors to establish that mono-ADP-ribosylation and not poly(ADP-ribosyl)ation was necessary for the stimulation of DNA synthesis by mitogens. Mitogen treatment increased concomitantly the activity of both soluble and particulate mono-ADP-ribosyltransferase, as well as the number of modified proteins. Inclusion of meta-iodobenzylguanidine (MIBG), a selective decoy substrate of arginine-dependent mono-ADP-ribosylation, prevented the modification of these proteins. MIBG also blocked the stimulation of DNA and RNA synthesis, prevented smooth muscle cell migration and suppressed the induction of c-fos and c-myc gene expression. An examination of relevant signal transduction pathways showed that MIBG did not interfere with MAP kinase and phosphatidylinositol 3-kinase stimulation; however, it did inhibit phosphorylation of the Rho effector, PRK1/2. This novel observation suggests that mono-ADP-ribosylation participates in a Rho- dependent signalling pathway that is required for immediate early gene expression.

Expression and regulation of the insulin-like growth factor-1 receptor by growing and quiescent H4IIE hepatoma

Recent evidence that insulin-like growth factor-1 (IGF-1) influences certain properties of H4IIE hepatoma cells independent of insulin led us to examine whether H4IIE cells express IGF-1 receptors. Competitive binding experiments demonstrated IGF-1, but not insulin or IGF-II, could compete with [125I]IGF-1. Chemical crosslinking detected a protein with an apparent mass of 175 kDa and its identity as the IGF-1 receptor alpha-subunit was confirmed by Western blotting. The apparent molecular mass of this protein decreased to 135 kDa following deglycosylation. Immunofluorescence microscopy verified that both insulin and IGF-1 receptors were present, although measurement of IGF-1 receptor quantity revealed they were less abundant than insulin receptors. Binding of IGF-1 was low in growing cells and higher in a quiescent cell population. Scatchard analysis confirmed that receptor density was increased in non-growing H4IIE cells while there was no apparent difference in receptor affinity. Western blot analysis and RT-PCR revealed that both protein and mRNA levels were elevated as cell growth ceased. Interestingly, addition of insulin to quiescent H4IIE cells, which stimulates cell proliferation, further increased IGF-1 receptor protein levels with a peak at 12-24 h. Distinct modes of regulating IGF-1 receptor expression are indicated.

Insulin is required for angiotensin II-mediated hypertrophy of smooth muscle cells

The prevalence of hypertension and atherosclerosis among subjects with hyperinsulinemia supports the premise of a direct metabolic link between insulin and angiotensin II at the cellular level. In the present study, the effect of insulin on the angiotensin II-induced growth of A10 smooth muscle cells (SMC) was investigated. Treatment of quiescent A10 cells with angiotensin II caused an increase in RNA synthesis, proto-oncogene c-fos mRNA levels and cell size dependent upon pretreatment with insulin. The insulin requirement was independent of its actions as a growth factor, since a pre-treatment of at least 24 h with insulin was essential for growth stimulation by angiotensin II. Using RT-PCR, insulin was shown to regulate AT2 receptor expression in both quiescent and differentiating cells. These data suggest the AT2 receptor, which mediates the growth effects of angiotensin II in A10 cells, may be the critical target for the effect of insulin.