Differential interactions of thrombospondin-1, -2, and -4 with CD47 and effects on cGMP signaling and ischemic injury responses.
Thrombospondin-1 regulates nitric oxide (NO) signaling in vascular cells via CD47. Because CD47 binding motifs are conserved in the C-terminal signature domains of all five thrombospondins and indirect evidence has implied CD47 interactions with other family members, we compared activities of recombinant signature domains of thrombospondin-1, -2, and -4 to interact with CD47 and modulate cGMP signaling. Signature domains of thrombospondin-2 and -4 were less active than that of thrombospondin-1 for inhibiting binding of radiolabeled signature domain of thrombospondin-1 or SIRPalpha (signal-regulatory protein) to cells expressing CD47. Consistent with this binding selectivity, the signature domain of thrombospondin-1 was more potent than those of thrombospondin-2 or -4 for inhibiting NO-stimulated cGMP synthesis in vascular smooth muscle cells and downstream effects on cell adhesion. In contrast to thrombospondin-1- and CD47-null cells, primary vascular cells from thrombospondin-2-null mice lack enhanced basal and NO-stimulated cGMP signaling. Effects of endogenous thrombospondin-2 on NO/cGMP signaling could be detected only in thrombospondin-1-null cells. Furthermore, tissue survival of ischemic injury and acute recovery of blood flow in thrombospondin-2-nulls resembles that of wild type mice. Therefore, thrombospondin-1 is the dominant regulator of NO/cGMP signaling via CD47, and its limiting role in acute ischemic injury responses is not shared by thrombospondin-2.
Isenberg
Jeff S
JS
Laboratory of Pathology, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
Annis
Douglas S
DS
Pendrak
Michael L
ML
Ptaszynska
Malgorzata
M
Frazier
William A
WA
Mosher
Deane F
DF
Roberts
David D
DD
D000818:Animals; D051928:CD47 Antigen / Q000378:metabolism*; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism*; D006801:Humans; D007511:Ischemia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000378:metabolism; D011485:Protein Binding; D011971:Receptors, Immunologic / Q000378:metabolism; D015398:Signal Transduction; D019699:Thrombospondins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
D051928:CD47 Antigen; C501922:Sirpa protein, mouse; D011971:Receptors, Immunologic; D019699:Thrombospondins; D009569:Nitric Oxide; D006152:Cyclic GMP