Abstract
The induction of murine erythroleukemia cells (MELC; DS19/Sc9) to terminal differentiation by hexamethylenebisacetamide (HMBA) is characterized by a latent period of 10-12 hr before onset of commitment to terminal-cell division and increased transcription of globin genes. MELC variants, derived from this parental cell line, selected for resistance to vincristine (VC), can be induced to differentiate with little or no latent period. This study shows that accelerated HMBA-induced commitment is characteristic of MELC with a low level (2- to 5-fold) of VC resistance in four independently derived cell lines. Both resistance to VC and accelerated differentiation are stable phenotypes for at least 50 passages (approximately 5 months) in the absence of VC. Low-level VC-resistant MELC do not display increased levels of P-glycoprotein or mdr1, mdr2, and mdr3 mRNAs, nor do they exhibit cross-resistance to colchicine or doxorubicin. These cells do show (i) increased level of protein kinase C activity, (ii) reduced accumulation of [3H]VC, and (iii) restoration of VC sensitivity in the presence of verapamil. MELC selected for higher levels of VC resistance (approximately 500-fold) do express high levels of P-glycoprotein and the mdr3 gene. During HMBA-induced differentiation, DS19/Sc9 decrease [3H]VC accumulation, but P-glycoprotein content does not change. A VC-transport-associated protein, also critical for the process of induced differentiation, may be constitutively present in VC-resistant MELC, accounting for their enhanced sensitivity to inducer. This protein accumulates by exposure of VC-sensitive cells to HMBA, contributing to their differentiation and decreased level of VC accumulation.