Collagen mediates changes in intracellular calcium in primary mouse megakaryocytes through syk-dependent and -independent pathways.
We have characterized changes in [Ca2+]i in primary mouse megakaryocytes in response to fibrillar collagen and in response to cross-linking of the collagen receptor, the integrin alpha2beta1. The response to collagen was markedly different from that seen to a triple helical collagen-related peptide (CRP), which signals via the tyrosine kinases p59(fyn) and p72(syk). This peptide binds to the collagen receptor glycoprotein VI (GPVI), but not to the integrin alpha2beta1. Collagen elicited a sustained increase in [Ca2+]i composed primarily of influx of extracellular Ca2+ with some Ca2+ release from internal stores. In contrast to CRP, this response was only partially (approximately 30%) inhibited by the src-family kinase inhibitor PP1 (10 micromol/L) or by microinjection of the tandem SH2 domains of p72(syk). Collagen also caused an increase in [Ca2+]i in megakaryocytes deficient in either p59(fyn) or p72(syk), although the response was reduced by approximately 40% in both cases: Cross-linking of the alpha2 integrin increased [Ca2+]i in these cells exclusively via Ca2+ influx. This response was reduced by approximately 50% after PP1 pretreatment, but was significantly increased in fyn-deficient megakaryocytes. Collagen therefore increases [Ca2+]i in mouse megakaryocytes via multiple receptors, including GPVI, which causes Ca2+ mobilization, and alpha2beta1, which stimulates a substantial influx of extracellular Ca2+.
Briddon
S J
SJ
Department of Pharmacology, University of Oxford, Oxford, UK; and the National Institute for Medical Research, London, UK.
Melford
S K
SK
Turner
M
M
Tybulewicz
V
V
Watson
S P
SP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003094:Collagen / Q000494:pharmacology*; D004792:Enzyme Precursors / Q000378:metabolism*; D016023:Integrins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D017136:Ion Transport / Q000187:drug effects; D008533:Megakaryocytes / Q000378:metabolism*; D051379:Mice; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D038981:Receptors, Collagen; D015398:Signal Transduction / Q000187:drug effects*; D000072377:Syk Kinase
D004792:Enzyme Precursors; D016023:Integrins; D047908:Intracellular Signaling Peptides and Proteins; D038981:Receptors, Collagen; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D002118:Calcium