It was shown previously [(1984) EMBO J. 3, 453-459] that after treatment of the human erythroleukemia cell line HEL with phorbol ester and dimethyl sulfoxide there was a marked increase in the amounts of megakaryotic markers, especially of platelet α-granule proteins and platelet glycoproteins. In order to investigate this differentiation process further we have studied the expression of the mRNA encoding PDGF-A and PDGF-B (c-sis). Upon addition of the phorbol ester to the culture medium the expression of the c-sis transcript was enhanced about 7-fold over a period of 4 days. With dimethyl sulfoxide there was no significant stimulation of the expression. Addition of cycloheximide to HEL cells treated for a short period with phorbol ester superinduced the expression of the c-sis gene. The HEL cells did not express the A-chain mRNA even in the presence of phorbol ester or dimethyl sulfoxide. This leads us to propose that synthesis of the PDGF-A chain and PDGF-B chain is differentially regulated in the megakaryocytic-like HEL cell line.
