Endoglin is a transforming growth factor b (TGFb) superfamily auxiliary receptor. We had previously shown that it suppressed prostate cancer (PCa) cell motility, and that its expression was lost during PCa progression. The mechanism by which endoglin inhibits PCa cell motility is unknown. Here we demonstrate that endoglin abrogates TGFb-mediated cell motility, but does not alter cell surface binding of TGFb. By measuring Smad-specific phosphorylation and Smad-responsive promoter activity, endoglin was shown to constitutively activate Smad1, with little-to-no effect upon Smad3. Knockdown of Smad1 increased motility and abrogated endoglin's effects. As type I activin receptor-like kinases (ALKs) are necessary for Smad activation, we went on to show that knockdown of ALK2, but not TGFbRI (ALK5), abrogated endoglinmediated decreases in cell motility and constitutively active ALK2 was sufficient to restore a low-motility phenotype in endoglin deficient cells. These findings provide the first evidence that endoglin decreases PCa cell motility through activation of the ALK2-Smad1 pathway.
BMP9 signaling has been implicated in hereditary hemorrhagic telangiectasia (HHT) and vascular remodeling, acting via the HHT target genes, endoglin and ALK1. This study sought to identify endothelial BMP9-regulated proteins that could affect the HHT phenotype. Gene ontology analysis of cDNA microarray data obtained after BMP9 treatment of primary human endothelial cells indicated regulation of chemokine, adhesion, and inflammation pathways. These responses included the up-regulation of the chemokine CXCL12/SDF1 and down-regulation of its receptor CXCR4. Quantitative mass spectrometry identified additional secreted proteins, including the chemokine CXCL10/IP10. RNA knockdown of endoglin and ALK1 impaired SDF1/CXCR4 regulation by BMP9. Because of the association of SDF1 with ischemia, we analyzed its expression under hypoxia in response to BMP9 in vitro, and during the response to hindlimb ischemia, in endoglin-deficient mice. BMP9 and hypoxia were additive inducers of SDF1 expression. Moreover, the data suggest that endoglin deficiency impaired SDF1 expression in endothelial cells in vivo. Our data implicate BMP9 in regulation of the SDF1/CXCR4 chemokine axis in endothelial cells and point to a role for BMP9 signaling via endoglin in a switch from an SDF1-responsive autocrine phenotype to an SDF1 nonresponsive paracrine state that represses endothelial cell migration and may promote vessel maturation. IntroductionEndoglin directly interacts with the TGF- receptors, 1 including ALK1, 2 and modulates TGF- and bone morphogenetic protein (BMP) signaling. 3 Mutations in either endoglin 4 or ALK1 5 increase the risk of hereditary hemorrhagic telangiectasia (HHT1 and HHT2, respectively), whose symptoms include arteriovenous malformation, tissue ischemia, and reperfusion defects. 6 The ALK1-endoglin signaling complex in endothelial cells is activated by BMP9, 7 a circulating cytokine produced in the liver reticuloendothelium 8 and endothelial cells, including those lining the mouse aorta. 9 BMP9 interacts with endoglin and ALK1 to activate signaling pathways 7 that promote endothelial cell quiescence 10 and vessel maturation. 11 Several endothelial cell-derived factors, including BMP9, are known to regulate vessel maturation via paracrine recruitment of other cell types. 12 Moreover, our recent work using nonendothelial cells implicates endoglin in the regulation of tumor neoangiogenesis via the secreted insulin-like growth factor binding protein 4. 13 Therefore, elucidation of the role of BMP9 signaling, specifically in terms of its effects on the expression of endothelial cell-secreted factors, is needed to better understand the mechanisms by which BMP9 affects vessel maturation, integrity, the vascular response to injury, and how deficiency in either endoglin or ALK1 impacts vessel integrity and cause HHT.Stromal-derived factor 1 (SDF1, CXCL12) is a chemokine that signals via the chemokine receptor, CXCR4, to modulate hypoxiainduced angiogenesis. 14 SDF1 regulates both endothelial cellmediated paracrine signaling ...
Endoglin is an integral membrane glycoprotein primarily expressed in the vascular endothelium, but also found on macrophages and stromal cells. It binds several members of the transforming growth factor (TGF)-b family of growth factors and modulates TGF-b 1 -dependent cellular responses. However, it lacks cytoplasmic signaling motifs and is considered as an auxiliary receptor for TGF-b. We show here that endoglin is expressed in mouse and human epidermis and in skin appendages, such as hair follicles and sweat glands, as determined by immunohistochemistry. In normal interfollicular epidermis, endoglin was restricted to basal keratinocytes and absent in differentiating cells of suprabasal layers. Follicular expression of endoglin was high in hair bulb keratinocytes, but decreased in parts distal from the bulb. To address the role of endoglin in skin carcinogenesis in vivo, Endoglin heterozygous mice were subjected to long-term chemical carcinogenesis treatment. Reduction in endoglin had a dual effect during multistage carcinogenesis, by inhibiting the early appearance of benign papillomas, but increasing malignant progression to highly undifferentiated carcinomas. Our results are strikingly similar to those previously reported for transgenic mice overexpressing TGF-b 1 in the epidermis. These data suggest that endoglin might attenuate TGF-b 1 signaling in normal epidermis and interfere with progression of skin carcinogenesis.
Endoglin is an accessory receptor for transforming growth factor-β (TGF-β) that has been implicated in prostate cancer cell detachment, migration and invasiveness. However, the pathophysiological significance of endoglin to prostate tumorigenesis has yet to be fully established. In this study we addressed this question by investigation of endoglin-dependent prostate cancer progression in a TRAMP mouse model where endoglin was genetically deleted. In this model, endoglin was haploinsufficient such that its allelic deletion slightly increased the frequency of tumorigenesis, yet produced smaller, less vascularized, and less metastatic tumors than TRAMP control tumors. Most strikingly, TRAMP:eng+/− tumors lacked the pronounced infiltration of carcinoma-associated fibroblasts (CAFs) that characterize TRAMP prostate tumors. Studies in human primary prostate-derived stromal fibroblasts (PrSC) confirmed that suppressing endoglin expression decreased cell proliferation, the ability to recruit endothelial cells, and the ability to migrate in response to tumor cell-conditioned medium. We found increased levels of secreted insulin-like growth factor binding proteins (IGFBPs) in the conditioned media from endoglin-deficient PrSCs, and that endoglin-dependent regulation of IGFBP-4 secretion was crucial for stromal cell-conditioned media to stimulate prostate tumor cell growth. Together, our results firmly establish the pathophysiological involvement of endoglin in prostate cancer progression, and they show how endoglin acts to support the viability of tumor infiltrating CAFs in the tumor microenvironment to promote neovascularization and growth.
BACKGROUND Slug is a transcription factor of the Snail/Slug zinc-finger family and is implicated in metastasis of tumors, but its role in cell proliferation of prostate cancers is unclear. METHODS Expression level of Slug and other genes was examined by Western blot, RT-PCR, and QPCR analyses. The forced expression of Slug was mediated by retroviruses and adenoviruses. Slug was down-regulated by shRNA. Cell growth was measured by the MTT assay and the quick cell proliferation assay. RESULTS Here, we demonstrated that Slug expression is elevated in mouse prostate tumors, and human prostate cancer cell lines LNCaP, PC-3, and 22RV1. Forced expression of Slug inhibited proliferation of prostate cancer cells PC-3 and DU-145. Conversely, reduced expression of Slug by shRNA promoted growth of PC-3 cancer cells. Consistent with these data, we found that forced expression of Slug in prostate cancer cells led to G1 cell cycle arrest. Furthermore, ectopic expression of Slug decreased cyclin D1 expression in both PC-3 and DU-145 cells, and knockdown of Slug by shRNA upregulated cyclin D1 expression in these cancer cells. In addition, we demonstrated that ectopic expression of cyclin D1 relieved Slug-mediated inhibition of proliferation of prostate cancer cells. CONCLUSIONS We provide the first compelling evidence that Slug is a negative regulator of proliferation of prostate cancer cells. Our findings in this study are distinct from the previously reported role of Slug as a promoter for tumor metastasis, and suggest that Slug is a prognostic marker and potential therapeutic target.
SummaryLoss of tissue organization is a hallmark of the early stages of cancer, and there is considerable interest in proteins that maintain normal tissue architecture. Prostate epithelial cells cultured in Matrigel form three-dimensional acini that mimic aspects of prostate gland development. The organization of these structures requires the tumor suppressor Dickkopf-3 (Dkk-3), a divergent member of the Dkk family of secreted Wnt signalling antagonists that is frequently downregulated in prostate cancer. To gain further insight into the function of Dkk-3 in the prostate, we compared the prostates of Dkk3-null mice with those of control littermates. We found increased proliferation of prostate epithelial cells in the mutant mice and changes in prostate tissue organization. Consistent with these observations, cell proliferation was elevated in acini formed by human prostate epithelial cells stably silenced for Dkk-3. Silencing of Dkk-3 increased TGF-b/Smad signalling, and inhibitors of TGF-b/Smad signalling rescued the defective acinar phenotype caused by loss of Dkk-3. These findings suggest that Dkk-3 maintains the structural integrity of the prostate gland by limiting TGF-b/Smad signalling.
Endoglin is a transmembrane receptor that suppresses human prostate cancer (PCa) cell invasion. Small molecule therapeutics now being tested in humans can activate endoglin signaling. It is not known whether endoglin can regulate metastatic behavior, PCa tumor growth, nor what signaling pathways are linked to these processes. This study sought to investigate the effect of endoglin on these parameters. We used a murine orthotopic model of human PCa metastasis, designed by us to measure effects at early steps in the metastatic cascade, and implanted PCa cells stably engineered
Although condom use among all women declined markedly once they initiated long-term hormonal contraception, frequency of condom use varied by subgroup and was associated with several factors. Most importantly, women with more than one sexual partner and those who received a message during counseling on the need to continue using condoms were more likely than others to use condoms in conjunction with the implant or injectable.
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