Establishment and characterization of a murine megakaryoblastic cell line growing in protein-free culture (L8057Y5)

A murine megakaryoblastic cell line growing in protein-free culture (L8057Y5) was established from an experimentally induced murine leukemia (MK8057). Most of the Y5 cells were small and blast-like, with 2-4N in DNA content. Also, large cells possessing a lobulated nucleus characteristic of megakaryocytes, which showed polyploidization to more than 4N up to 16N, were occasionally seen. Nearly 5% of the total number of Y5 cells were positive for acetylcholinesterase reaction. The survival time of C3H/He mice after injection with Y5 cells was longer than that of mice injected with the original MK8057 cells. The colony-forming ability of Y5 cells in the spleen of the lethally irradiated mouse was much lower, whereas the number of in vitro colonies derived from Y5 was greater than that of MK8057. The plating efficiency of colony formation in serum-free methylcellulose culture was higher at a low O2 tension. Conditioned medium of Y5 cells enhanced colony formation as well as 3H-TdR uptake by Y5 cells, which implies that Y5 cells may produce autocrine growth factor(s). mRNAs for IL-6, LIF, and INF-gamma were expressed in Y5 cells; these cytokines may have roles in the growth mechanisms of the cell line.