Influence of the tumour promoter TPA upon erythroid burst formation in vitro

A dose dependent effect of the tumour promoter TPA on burst formation by rabbit erythroid progenitors (BFU-e) was demonstrated in cultures deficient in the early erythroid regulator burst-promoting activity (BPA). In these culture conditions the burst number was highest (193% of controls) at 10(-9)M TPA and concentrations higher than 3 x 10(-9)M TPA were inhibitory. The degree of burst enhancement by TPA and bone marrow conditioned medium as a source of BPA was similar. The addition of optimal concentrations of both TPA and BPA simultaneously to cultures resulted in no further increase in burst number. Short-term incubation of bone marrow cells with TPA failed to enhance the percentage of S-phase BFU-e under conditions in which BPA significantly increases the number of BFU-e in the cell cycle. These results indicate that the same population of BFU-e responds to TPA and BPA, but TPA does not mimic the mitogenic effect of BPA upon BFU-e.