Opposing effects of tumour promoters on erythroid differentiation

Abstract

TUMOUR promoters are compounds which are not carcinogens but which can induce tumours in mice treated with a subcarcinogenic dose of a chemical carcinogen^1,2. The mechanism of action of tumour promoters in vivo is unknown, although recent reports suggest that they may inhibit terminal differentiation of certain cells in vitro. Myogenesis of chick embryo myoblasts³, spontaneous and induced erythroid differentiation of Friend virus-transformed proerythroid cells^4,5 and lipogenesis in a clone of BALB/c 3T3 preadipocyte cells are examples of in vitro differentiation processes inhibited by tumour promoters. Unfortunately, inhibition of differentiation by tumour promoters has not yet been shown to occur in vivo. It is also uncertain whether the cells used in the above studies are representative of the actual target cells for tumour promoters in vivo. We report here that tumour promoters can induce as well as inhibit differentiation of virus-transformed proerythroid cells in vitro. Detection of the opposing effects depends on measuring tumour promoter action in more than one virus-transformed proerythroid cell line.