Thrombospondin-4 mediates TGF-?-induced angiogenesis.

ABSTRACT: TGF-? is a multifunctional cytokine affecting many cell types and implicated in tissue remodeling processes. Due to its many functions and cell-specific effects, the consequences of TGF-? signaling are process-and stage-dependent, and it is not uncommon that TGF-? exerts distinct and sometimes opposing effects on a disease progression depending on the stage and on the pathological changes associated with the stage. The mechanisms underlying cell- and process-specific effects of TGF-? are poorly understood. We are describing a novel pathway that mediates induction of angiogenesis in response to TGF-?1. We found that in endothelial cells (EC) thrombospondin-4 (TSP-4), a secreted extracellular matrix (ECM) protein, is upregulated in response to TGF-?1 and mediates the effects of TGF-?1 on angiogenesis. Upregulation of TSP-4 does not require the synthesis of new protein, is not caused by decreased secretion of TSP-4, and is mediated by activation of SMAD3. Using Thbs4-/- mice and TSP-4 shRNA, we found that TSP-4 mediated pro-angiogenic functions in cultured EC and angiogenesis in vivo in response to TGF-?1. We observed~3-fold increases in tumor mass and levels of angiogenesis markers in animals injected with TGF-?1, and these effects did not occur in Thbs4-/- animals. Injections of an inhibitor of TGF-?1 signaling SB-431542 also decreased the weights of tumors and cancer angiogenesis. Our results from in vivo angiogenesis models and cultured EC document that TSP-4 mediates upregulation of angiogenesis by TGF-?1. Upregulation of pro-angiogenic TSP-4 and selective effects of TSP-4 on EC may contribute to stimulation of tumor growth by TGF-? despite the inhibition of cancer cell proliferation.

SUBMITTER: Muppala S 

PROVIDER: S-EPMC5589494 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature