GENE-EXPRESSION DURING PHORBOL ESTER-INDUCED DIFFERENTIATION OF CULTURED HUMAN MEGAKARYOBLASTIC CELLS

Platelet protein makeup is determined during transformation of megakar yoblasts to mature megakaryocytes, the immediate precursor of circulat ing platelets. To better understand the molecular mechanisms of megaka ryocyte formation, gene expression was characterized by Northern analy sis and RNA fingerprinting of cultured human CHRF-288 megakaryoblastic cells undergoing phorbol ester-stimulated megakaryocytic differentiat ion or serum-stimulated megakaryoblast proliferation. Protooncogenes c -fos and c-jun were coordinately upregulated in both proliferating and differentiating cells, whereas c-myc transcripts were upregulated dur ing proliferation only. In contrast, mRNAs for transforming growth fac tor-beta 1 (TGF-beta 1) and thromboxane receptors were coordinately up regulated during differentiation but differentially regulated during p roliferation. RNA fingerprinting revealed multiple transcripts specifi c to either proliferating or differentiated cells. Three of these were identified by homology to known DNA sequence: CDw44 adhesion molecule (upregulated during differentiation), glutathione sulfhydryl peroxida se (downregulated during differentiation), and plectin cytoskeletal pr otein (upregulated during differentiation). Thus, although megakaryobl ast proliferation and megakaryocyte differentiation both involve DNA a nd protein synthesis, each growth response is characterized by a disti nct pattern of gene expression.