Regulation of leukaemic cells by interleukin 6 and leukaemia inhibitory factor.

Abstract

Interleukin 6 (IL-6) and leukaemia inhibitory factor (LIF) can have pleiotropic effects on different cell types. M1 myeloid leukaemic cells respond to IL-6 with activation of a terminal differentiation programme which includes activation of genes for certain haemopoietic regulatory proteins (IL-6, IL-1 alpha, IL-1 beta, granulocyte-macrophage colony-stimulating factor [GM-CSF], M-CSF, tumour necrosis factor and transforming growth factor [TGF] beta 1) and for receptors for some of these proteins, thus establishing a network of positive and negative regulatory cytokines. IL-6 and some other cytokines also induce during differentiation sustained levels of transcription factors that can regulate and maintain gene expression in the differentiation programme. M1 leukaemic cells induced to differentiate with IL-6 undergo programmed cell death (apoptosis) on withdrawal of IL-6, and can be rescued from apoptosis by IL-6, IL-3, M-CSF, G-CSF or IL-1, but not by GM-CSF. These differentiating leukaemic cells can also be rescued from apoptosis by the tumour promoter TPA (12-O-tetradecanoylphorbol-13-acetate) but not by the non-tumour-promoting isomer 4-alpha-TPA, and rescue from apoptosis can be achieved by different pathways. Apoptosis can also be induced in undifferentiated M1 leukaemic cells by expression of the wild-type form of the tumour suppressor p53 protein and IL-6 can rescue the cells from this wild-type p53-mediated apoptosis. There are clones of M1 cells that differentiate with IL-6 but not with LIF and another M1 clone that differentiates with either IL-6 or LIF. Differentiation induced by IL-6 or LIF is inhibited by TGF-beta 1. The pleiotropic effects of LIF, like those of IL-6, are presumably also in a network of interacting regulatory proteins.