PROSTAGLANDIN-D SYNTHASE IN HUMAN MEGAKARYOBLASTIC CELLS

The cytosol fraction of human platelets did not convert prostaglandin (PG) H-2 to PGD(2). However, a homogenate of human megakaryoblastic CM K cells (precursor cells of platelets) produced PGD(2) from PGH(2). Th e PGD synthase activity was localized in the cytosol of CMK cells, and absolutely required glutathione. The catalytic properties and Western and Northern blottings indicated that the enzyme was PGD synthase of the hematopoietic type rather than the lipocalin type, When CMK cells were differentiated to megakaryocytes with phorbol ester along with in duction of cyclooxygenase-l, the PGD synthase activity increased about 2-fold for 2 days and then decreased. In another human megakaryoblast ic cell line, Dami, the PGD synthase increased about 10-fold by the ad dition of phorbol ester. Thus, the PGD synthase, which was undetectabl e in platelets, appeared during differentiation of megakaryoblasts to megakaryocytes.