SUMMARY Transforming growth factor beta (TGF-β) family ligands are pleotropic proteins with diverse cell type-specific effects on growth and differentiation. For example, PAK2 activation is critical for the proliferative/pro-fibrotic action of TGF-β on mesenchymal cells, and yet is not responsive to TGF-β in epithelial cells. We therefore investigated the regulatory constraints that prevent inappropriate PAK2 activation in epithelial cultures. The results show that the epithelial-enriched protein Erbin controls the function of the NF2 tumor suppressor Merlin by determining the output of Merlin's physical interactions with active PAK2. While mesenchymal TGF-β signaling induces PAK2-mediated inhibition of Merlin function in the absence of Erbin, Erbin/Merlin complexes bind and inactivate GTPase-bound PAK2 in epithelia. These results not only identify Erbin as a key determinant of epithelial resistance to TGF-β signaling, but also show that Erbin controls Merlin tumor suppressor function by switching the functional valence of PAK2 binding.

Miller. Differential effects of 17␤-estradiol, conjugated equine estrogen, and raloxifene on mRNA expression, aggregation, and secretion in platelets. Am J Physiol Heart Circ Physiol 288: H2355-H2362, 2005. First published January 14, 2005 doi:10.1152/ajpheart.01108.2004.-Changes in platelet functions could contribute to thrombotic risk associated with estrogen treatments. This study was designed to test the hypothesis that three clinically relevant estrogenic treatments affect platelet function comparably. Adult female pigs were ovariectomized and randomized to either no treatment or treatment with oral 17␤-estradiol (2 mg/day), conjugated equine estrogen (0.625 mg/day), or raloxifene (60 mg/day) for 4 wk. Platelet turnover, aggregation, and secretion were assessed before and after treatment. Platelet turnover and mRNA increased significantly only in pigs treated with 17␤-estradiol. Expression of estrogen receptors increased with ovariectomy and decreased with all treatments. Platelet aggregation and secretion of ATP, platelet-derived growth factor, and matrix metalloproteinase-2 increased with ovariectomy. All treatments reduced both aggregation and secretion. Expression of mRNA for constitutive endothelial nitric oxide synthase (eNOS), but not eNOS protein, increased with ovariectomy. Only eNOS mRNA decreased with all treatments, but only treatment with 17␤-estradiol increased secretion of nitric oxide from intact platelets. Platelets from 17␤-estradiol-treated animals caused relaxation of coronary arteries, which was sensitive to inhibition of nitric oxide. Although three different estrogenic treatments reversed increases in platelet aggregation caused by ovariectomy, only 17␤-estradiol increased platelet RNA and release of plateletderived nitric oxide. These differences reflect transcriptional and posttranscriptional regulation of protein synthesis in bone marrow megakaryocytes and circulating platelets.hormones; matrix metalloproteinase; nitric oxide; thrombosis ESTROGEN TREATMENTS, including selective estrogen receptor modulators (SERMs) like raloxifene, increase risk of venous thrombosis in postmenopausal women (2, 11, 12, 14 -17, 25, 42). In addition, in older women, treatment with conjugated equine estrogen (CEE) but not raloxifene increases arterial thrombotic events such as stroke (41). More information is needed regarding mechanisms by which estrogenic compounds affect thrombosis. Hormones affect the blood vessel wall but also elements of the blood, such as platelets.Platelets contribute to thrombosis in several ways. They provide the membrane surface for the generation of thrombin, express membrane receptors that affect platelet-platelet and platelet-vessel wall interactions, and release vasoactive substances affecting vascular tone, which in turn affect retention of a platelet plug. Platelets and their precursors, megakaryocytes, contain both estrogen receptor (ER)␣ and ER␤ (21,22,26,40). Therefore, the concentration of circulating hormones, i.e., hormonal status defined by the loss or replaceme...

In humans, cardiovascular disease begins in young adulthood and is more prevalent in males than females. However, little is known about vascular function during transition to adulthood in males. The aim of this study was to define changes in production of endothelium-derived nitric oxide (NO) and coronary arterial responses during puberty. Plasma was collected from juvenile (2-3 mo of age) and adult (5-6 mo of age) male pigs (n = 8/group) for measurement of NO, and aortic endothelial cells were collected for measurement of mRNA and protein for endothelial NO synthase (eNOS). Although plasma NO was higher in juvenile (67.0 +/- 25.6 microM) than in adult (15.0 +/- 7.1 microM) male pigs, eNOS protein was similar in both groups. However, levels of mRNA for eNOS were lower in aortic endothelial cells from juvenile pigs. In rings of coronary arteries suspended in organ chambers for measurement of isometric force and contracted with PGF2alpha, relaxations to an alpha2-adrenergic agonist were significantly inhibited by indomethacin only in juvenile pigs [EC50 (-log M), 6.7 +/- 0.3 with indomethacin and 7.7 +/- 0.3 under control conditions]. NG-monomethyl-l-arginine (l-NMMA) inhibited relaxations in both groups. On the contrary, in the presence of indomethacin, relaxations to bradykinin were inhibited by l-NMMA only in arteries from adult pigs [EC50 (-log M), 8.9 +/- 0.3 with indomethacin and 8.6 +/- 0.3 with addition of l-NMMA]. These results suggest that hormonal changes associated with sexual maturity may affect posttranscriptional and/or translational regulation of eNOS protein and result in lower plasma NO in adult male pigs. In addition, endothelium-derived inhibitory cyclooxygenase products seem to predominate in juveniles.

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