Studies of the Induction of Tumour Cell Terminal differentiation

Abstract

A wide variety of agents, at marginally sub-toxic concentrations, induce terminal differentiation of HL-60human promyelocytic leukaemia cells to granulocyte- or monocyte-like cells.170mM N-methylformamide induced >70% of HL-60 cells to differentiate to granulocytes while viability remained at >70%. Commitment to differentiationGia 106" occur until” after a minimum of 24 hours of incubation with NMF. Manipulation of growth conditions in the presence of NMF showed that inhibition of proliferative potential of the cells was required for the induction of differentiation, but at least one cell division was required for development of the mature phenotype. The hypothesis that the induction of a stress response was important in the induction of differentiation by pharmacologic agents was tested. There was no evidence for the induction of gene amplification during commitment to differentiation with NMF, but there was evidence to support the involvement of the heat shock response inHL-60 cell differentiation. Six known inducers of heat shock protein (hsp) synthesis induced HL-60 cell differentiation: ethanol (213mM), sodium arsenite (6uM), lidocaine (3mM), procaine (5mM), cadmium (60uM), and hyperthermia (43.5°C for 1 hour). The extent of maximal differentiation induced by these agents was inversely correlated with the inhibition of normal protein synthesis; the "weak" inducers cadmium and hyperthermia (which induced <30% of cells to differentiate) inhibited protein synthesis more than the "strong" inducers such as NMF, ethanol, arsenite and local anaesthetics (which induced >50% differentiation). Synthesis of hsps was unexpectedly repressed rather than induced during differentiation, but cellular levels of hsp70 increased concomitant with commitment to differentiation induced by NMF. The data support the hypothesis that a stress response, possibly involving heat shock proteins, is important in the induction of HL-60cell differentiation by disparate pharmacologic agents.