title: Thrombospondin 2 inhibits microvascular endothelial cell proliferation by a caspase-independent mechanism.
abstract: The matricellular protein thrombospondin 2 (TSP2) regulates a variety of cell-matrix interactions. A prominent feature of TSP2-null mice is increased microvascular density, particularly in connective tissues synthesized after injury. We investigated the cellular basis for the regulation of angiogenesis by TSP2 in cultures of murine and human fibroblasts and endothelial cells. Fibroblasts isolated from murine and human dermis synthesize TSP2 mRNA and secrete significant amounts of immunoreactive TSP2, whereas endothelial cells from mouse lung and human dermis did not synthesize TSP2 mRNA or protein. Recombinant mouse TSP2 inhibited growth of human microvascular endothelial cells (HMVECs) mediated by basic fibroblast growth factor, insulin-like growth factor-1, epidermal growth factor, and vascular endothelial growth factor (VEGF). HMVECs exposed to TSP2 in the presence of these growth factors had a decreased proportion of cells in S and G2/M phases. HMVECs cultured with a combination of basic fibroblast growth factor, insulin-like growth factor-1, and epidermal growth factor displayed an increased proportion of nonviable cells in the presence of TSP2, but the addition of VEGF blocked this TSP2-mediated impairment of cell viability. TSP2-mediated inhibition of DNA synthesis by HMVECs in the presence of VEGF was not affected by the broad-spectrum caspase inhibitor zVAD-fmk. Similar findings were obtained with TSP1. Taken together, these observations indicate that either TSP2 or TSP1 can inhibit HMVEC proliferation by inhibition of cell cycle progression and induction of cell death, but the mechanisms responsible for TSP2-mediated inhibition of cell cycle progression are independent from those leading to cell death.
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Lucas C
authors.initials: LC
authors.lastname: Armstrong
authors.forename: Benny
authors.initials: B
authors.lastname: Björkblom
authors.forename: Kurt D
authors.initials: KD
authors.lastname: Hankenson
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Siadak
authors.forename: Charlotte E
authors.initials: CE
authors.lastname: Stiles
authors.forename: Paul
authors.initials: P
authors.lastname: Bornstein
mesh_terms: D000818:Animals; D020169:Caspases / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D016228:Endothelial Growth Factors / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000166:cytology* / Q000187:drug effects; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology; D008168:Lung / Q000098:blood supply; D008222:Lymphokines / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D008833:Microcirculation; D010446:Peptide Fragments / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038601:Ribosomal Protein S6 / Q000235:genetics; D012867:Skin / Q000098:blood supply; D019699:Thrombospondins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D014471:Umbilical Veins; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D000099262:Thrombospondin 2
chemical_list: D020169:Caspases; D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D010446:Peptide Fragments; D012333:RNA, Messenger; D011994:Recombinant Proteins; D038601:Ribosomal Protein S6; D019699:Thrombospondins; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D000099262:Thrombospondin 2