Integrins contribute to progression in many cancers, including breast cancer. For example, the interaction of ␣ 5 ␤ 1 with plasma fibronectin causes the constitutive invasiveness of human prostate cancer cells. Inhibition of this process reduces tumorigenesis and prevents metastasis and recurrence. In this study, naturally serum-free basement membranes were used as invasion substrates. Immunoassays were used to compare the roles of

Although CD36 is generally recognized to be an inhibitory signaling receptor for thrombospondin-1 (TSP1), the molecular mechanism for transduction of this signal remains unclear. Based on evidence that myristic acid and TSP1 each modulate endothelial cell nitric oxide signaling in a CD36-dependent manner, we examined the ability of TSP1 to modulate the fatty acid translocase activity of CD36. TSP1 and a CD36 antibody that mimics the activity of TSP1 inhibited myristate uptake. Recombinant TSP1 type 1 repeats were weakly inhibitory, but an anti-angiogenic peptide derived from this domain potently inhibited myristate uptake. This peptide also inhibited membrane translocation of the myristoylated CD36 signaling target Fyn and activation of Src family kinases. Myristate uptake stimulated cGMP synthesis via endothelial nitric-oxide synthase and soluble guanylyl cyclase. CD36 ligands blocked myristate-stimulated cGMP accumulation in proportion to their ability to inhibit myristate uptake. TSP1 also inhibited myristate-stimulated cGMP synthesis by engaging its receptor CD47. Myristate stimulated endothelial and vascular smooth muscle cell adhesion on type I collagen via the NO/cGMP pathway, and CD36 ligands that inhibit myristate uptake blocked this response. Therefore, the fatty acid translocase activity of CD36 elicits proangiogenic signaling in vascular cells, and TSP1 inhibits this response by simultaneously inhibiting fatty acid uptake via CD36 and downstream cGMP signaling via CD47. Pathological angiogenesis or the lack thereof underlies a number of major diseases (1). Proangiogenic signals from vascular endothelial growth factors (VEGF)2 and fibroblast growth factors (FGF1 and FGF2) to induce blood vessel formation are opposed by signals from endogenous angiogenesis inhibitors, including two thrombospondins (TSP1 and TSP2) and proteolytic fragments of several extracellular matrix components (2, 3). Defining the mechanism of action of these inhibitors has been complicated by the finding that vascular cells express multiple receptors for several of these molecules. In the case of TSP1, endothelial cells express at least eight receptors, and some of these elicit pro-rather than anti-angiogenic responses (4, 5). The activities of some TSP1 receptors differ between large vessel and microvascular endothelial cells, and some are regulated by specific contextual signals (4 -6). CD36, a member of the scavenger receptor B family, is a TSP1 receptor that is selectively expressed in microvascular endothelium (7,8). CD36 was initially reported to recognize CSVTCG sequences in the type 1 repeats of TSP1 (9), but further studies identified higher affinity binding to the adjacent GVQXR sequences in the second and third type 1 repeats (10, 11). CD36 binding was markedly enhanced by epimerization of the first Ile in a peptide from the second type 1 repeat 434 GDGVITRIR 442 , where I (Ile) is the D isomer (11). TSP1, recombinant type 1 repeats of TSP1, and peptide mimetics of its CD36 binding sequences inhibit FGF2-stimulated endo...

A 5 B 1 Integrin interacts with the PHSRN sequence of plasma fibronectin, causing constitutive invasion by human prostate cancer cells. Inhibition of this process reduces tumorigenesis and prevents metastasis and recurrence. In this study, naturally serum-free basement membranes were used as in vitro invasion substrates. Immunoassays were employed to dissect the roles of focal adhesion kinase (FAK), phosphatidylinositol 3 ¶-kinase (PI3K), and protein kinase CD (PKCD) in A 5 B 1 -mediated, matrix metalloproteinase-1 (MMP-1)-dependent invasion by metastatic human DU 145 prostate cancer cells. We found that a peptide composed of the PHSRN sequence induced rapid FAK phosphorylation at Tyr 397 (Y397), a site whose phosphorylation is associated with kinase activation. The technique of RNA silencing [small interfering RNA (siRNA)] confirmed the role of FAK in PHSRN-induced invasion. PHSRN also induced the association of the p85-regulatory subunit of PI3K with FAK at a time corresponding to FAK phosphorylation and activation, and maximal PI3K activity occurred at this same time. The necessity of PI3K activity in both PHSRN-induced invasion and MMP-1 expression was confirmed by using specific PI3K inhibitors. By employing a specific inhibitor, Rottlerin, and by using siRNA, we also found that PKCD, a PI3K substrate found in focal adhesions, functions in PHSRN-induced invasion. In addition, the induction of MMP-1 in PHSRN-treated DU 145 cells was shown by immunoblotting, and the role of MMP-1 in PHSRNinduced invasion was confirmed by the use of blocking anti-MMP-1 monoclonal antibody. Finally, a close temporal correspondence was observed between PHSRN-induced invasion and PHSRN-induced MMP-1 activity in DU 145 cells.

ABSTRACT

Background and purpose: Angiogenesis involves multiple signaling pathways that must be considered when developing agents to modulate pathological angiogenesis. Because both cyclooxygenase inhibitors and dithioles have demonstrated antiangiogenic properties, we investigated the activities of a new class of anti-inflammatory drugs containing dithiolethione moieties (S-NSAIDs) and S-valproate. Experimental approach: Anti-angiogenic activities of S-NSAIDS, S-valproate, and the respective parent compounds were assessed using umbilical vein endothelial cells, muscle and tumor tissue explant angiogenesis assays, and developmental angiogenesis in Fli:EGFP transgenic zebrafish embryos. Key results: Dithiolethione derivatives of diclofenac, valproate, and sulindac inhibited endothelial cell proliferation and induced Ser 78 phosphorylation of hsp27, a known molecular target of anti-angiogenic signaling. The parent drugs lacked this activity, but dithiolethiones were active at comparable concentrations. Although dithiolethiones can potentially release hydrogen sulphide, NaSH did not reproduce some activities of the S-NSAIDs, indicating that the dithioles regulate angiogenesis through mechanisms other than release of H 2 S. In contrast to the parent drugs, S-NSAIDs, S-valproate, NaSH, and dithiolethiones were potent inhibitors of angiogenic responses in muscle and HT29 tumor explants assessed by 3-dimensional collagen matrix assays. Dithiolethiones and valproic acid were also potent inhibitors of developmental angiogenesis in zebrafish embryos, but the S-NSAIDs, remarkably, lacked this activity. Conclusions and implication: S-NSAIDs and S-valproate have potent anti-angiogenic activities mediated by their dithiole moieties. The novel properties of S-NSAIDs and S-valproate to inhibit pathological versus developmental angiogenesis suggest that these agents may have a role in cancer treatment.

hsp27 has been reported to participate in a wide variety of activities, including resistance to thermal and metabolic stress, regulation of growth and differentiation, and acting as a molecular chaperone or a regulator of actin polymerization. We hypothesized that these diverse functions are regulated in a cell-or tissue-specific manner via interaction with various binding proteins. To investigate this hypothesis, we used hsp27 as a "bait" to screen a yeast two-hybrid cDNA library from rat kidney glomeruli and identified a novel hsp27 binding protein, hic-5 (also known as ARA55), a focal adhesion protein and steroid receptor co-activator. Biochemical interaction between hsp27 and hic-5 was confirmed by co-immunoprecipitation, and critical protein⅐protein interaction regions were mapped to the hic-5 LIM domains and the hsp27 C-terminal domain. Initial analysis of the functional role of hsp27⅐hic-5 interaction revealed that hic-5 significantly inhibited the protection against heatinduced cell death conferred by hsp27 overexpression in co-transfected 293T cells. In contrast, when a non-hsp27-interacting hic-5 truncation mutant (hic-5/⌬LIM4) was co-expressed with hsp27, the hic-5 inhibition of hsp27 protection was absent. We conclude that hic-5 is a true hsp27 binding protein and inhibits the ability of hsp27 to provide protection against heat shock in an interaction-dependent manner.

Thiolutin is a dithiole synthesized by Streptomyces sp. that inhibits endothelial cell adhesion and tumor growth. We show here that thiolutin potently inhibits developmental angiogenesis in zebrafish and vascular outgrowth from tissue explants in 3D cultures.

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