PHORBOL ESTER TREATMENT OF 2 MEGAKARYOBLASTIC CELL-LINES, CMK AND UT-7, INDUCES SPECIFIC PROTEIN-COMPOSITION CHANGES WITH NONCOINCIDENT TIME-COURSES

The expressions of platelet-specific glycoprotein(GP)s Ib, IIb and III a were analyzed in 2 megakaryoblastic cell lines: CMK and UT-7. Phorbo l-12 myristate 13-acetate (PMA) treatment of CMK induced expressions o f GPs IIb and IIIa that peaked on the 4th day post-treatment, while tr eated UT-7 cells showed maximal levels of these GPs during the 6-8th d ays. Antibody staining to detect the formation of GPIbalpha after PMA induction showed the presence of the intact GP in UT-7 and the degrade d form in CMK. In UT-7, synthesis of GPIIb mRNA increased on days 4-6 after PMA treatment, in parallel with the increase of GPIIb. PMA incre ased the cytoskeletal protein (actin and myosin) contents in both line s, but in contrast to the two GPs, the increase in these proteins star ted immediately after PMA addition to the cells. Cell surface proteins of CMK and UT-7 cells were rapidly modified after PMA induction. Espe cially notable were the degradations of 93-kDa and 140-kDa proteins th at occurred on days 1-2 after PMA treatment. These studies demonstrate that the expression of platelet-specific proteins shows a different t ime dependency than the increment of cytoskeletal proteins, indicating that the syntheses of these two classes of proteins are most likely i nduced through different mechanisms.