5-Azacytidine-induced uncoupling of differentiation and tumorigenicity in a murine cell line

Highly tumorigenic, myogenically defective T984-15 murine cells were treated with the hypomethylating agent 5-azacytidine (5-azaC). In response to drug treatment, T984-15 cells formed colonies that were myosin-positive and contained fused myotubes. When cloned, these differentiated colonies gave rise to cells that maintained their myogenic potential even after prolonged growth in tissue culture. The myogenic differentiation observed in response to 5-azaC treatment was not the result of selection of a preexisting myogenic subpopulation, inasmuch as treatment of a subcloned population of nondifferentiating cells with 5-azaC also resulted in the induction of myogenesis. In addition to inducing myogenic potential, 5-azaC generally suppressed the tumorigenic potential of the treated cells. Whereas 19 of 19 untreated T984-15 clones when injected into BALB/c nude mice produced tumors, 8 of 9 of the 5-azaC-treated clones injected displayed suppressed tumorigenicity under identical conditions. Tumorigenic suppression, however, was independent of the induction of differentiation: 1 myogenic clone remained tumorigenic and 5 clones whose tumorigenic potential was suppressed were nonmyogenic. Thus treatment with the hypomethylating agent 5-azaC not only affected the expression of differentiated and tumorigenic phenotypes but also dissociated their usually coordinate regulation.