Biological and biochemical characteristics of a murine megakaryoblastic cell line (L8057), derived from an irradiated C3H/He mouse, were studied. The L8057 cells grew in liquid cultures with a doubling time of 24 to 27 hours. By light and electron microscopy, the L8057 cells were small and basophilic with a high nuclear/cytoplasmic ratio, but large cells (approximately 25 to 60 microns) were sometimes seen. Western blot analysis of cell extracts demonstrated that murine megakaryocyte and platelet antigens, glycoprotein (GP) IIb/IIIa, fibronectin, and factor VIII:RAg were expressed in L8057 cells. Acetylcholinesterase (AChE)-positive cells were rare (< 2.0%). Flow cytometric analysis demonstrated that 8.7% of the cells were spontaneously polyploid (> 4N DNA levels). In response to phorbol diester (TPA, 50 nm), L8057 cells showed a decrease in proliferation and a marked increase in cell size and amount of cytoplasm. The morphology of the cells became similar to that of megakaryocytes, with larger and lobulated nuclei and expansion of the demarcation membrane system compartment. The proportion of cells with ploidy levels greater than 4N increased to 40.8% (8N, 21.3 +/- 3.2%; 16N, 13.1 +/- 2.6%; > or = 32N, 6.4 +/- 4.9% [n = 4]). More than 90% of the cells became AChE-positive. TPA also increased the expression of GP IIb/IIIa, fibronectin and factor VIII:RAg. Thus, the L8057 cell line provides a potentially superior model with which to study the characteristics of megakaryocytic biology, differentiation and biochemistry.