Expression of the collagen receptor glycoprotein VI during megakaryocyte differentiation

This study examined the expression of the platelet collagen receptor glycoprotein VI (GPVI) in megakaryocyte cell lines and primary megakaryocytes by reverse transcriptase-polymerase chain reaction and by fiow cytometry and ligand blotting using the snake venom toxin convulxin. Expression of GPVI is increased in the megakaryoblastic cell lines HEL and CMK on differentiation with the phorbol ester phorbol 12-myristate 13-acetate (PMA), along with the Fc receptor γ-chain (FcR γ-chain). The increase in GPVI expression is associated with marked potentiation of tyrosine phosphorylation and Ca⁺⁺ elevation in response to convulxin. Syk, linker for activated T cells, and phospholipase Cγ2 (PLCγ2) are among the proteins tyrosine phosphorylated on convulxin stimulation in PMA-differentiated HEL cells. Studies on primary murine megakaryocytes grown in vitro confirmed that GPVI is up-regulated in parallel with functional activation, assessed by measurement of [Ca⁺⁺](l), during differentiafion. The results demonstrate that expression of GPVI is up-regulated along with the FcR γ-chain during differenfiation of megakaryocytes. (C) 2000 by The American Society of Hematology.