CYCLIC-AMP INHIBITS CELL-GROWTH AND NEGATIVELY INTERACTS WITH PLATELET MEMBRANE GLYCOPROTEIN EXPRESSION ON THE DAMI HUMAN MEGAKARYOBLASTIC CELL-LINE

Intracellular signaling processes by which hematopoietic growth factor s regulate megakaryocytopoiesis remain uncompletely understood. Cyclic AMP (cAMP) has been shown to be implicated in the regulation of growt h and differentiation in various normal and malignant cell types. Sinc e a few studies have suggested the possible involvement of the cAMP pa thway as one of the intracellular mechanisms whereby megakaryocytopoie sis may be regulated, we investigated the functional effects of cAMP o n the human megakaryoblastic Dami cell line. We observed that exposure of Dami cells to cAMP analogs or to agents elevating intracellular cA MP levels yielded dose-dependent cell growth inhibition. Cell cycle pr ogression analysis of cells predominantly synchronized at the G1/S bou ndary by prior treatment with hydroxyurea revealed that cAMP transient ly accumulated cells in the G2/M phase, then slowing down cell cycle. On the other hand, immunofluorescence and Northern blot analysis of me gakaryocytic differentiation marker expression showed that probes we h ave used significantly inhibited GPIb expression. Moreover, although t hese agents used alone did not affect GPIIb/IIIa expression, they mark edly reversed phorbol ester-induced GPIIb/IIIa expression increase. Th ese inhibitory cAMP actions on glycoprotein expression were not the re sult of cell cycle perturbation since we observed that GPIb and GPIIb/ IIIa expression were not cell cycle dependent. All these data may then be consistent with a potential negative regulatory role of the cAMP i ntracellular signaling pathway during megakaryocytopoiesis. (C) 1995 W iley-Liss, Inc.