BCR-ABL and interleukin 3 promote haematopoietic cell proliferation and survival through modulation of cyclin D2 and p27(Kip1) expression

Although it is evident that BGR-ABL can rescue cytokine-deprived hematopoie tic progenitor cells from cell cycle arrest and apoptosis, the exact mechan ism of action of BCR/ABL and interleukin (IL)-3 to promote proliferation an d survival has not been established. Using the pro-B cell line BaF3 and a B aF3 cell line stably overexpressing BCR-ABL (BaF3-p210), we investigated th e proliferative signals derived from BCR-ABL and IL-3, The results indicate that both IL-3 and BCR-ABE target the expression of cyclin Ds and down-reg ulation of p27(Kip1) mediate pRB-related pocket protein phosphorylation, E2 F activation, and thus S phase progression. These findings were further con firmed in a BaF3 cell line (TonB.210) where the BCR-ABL expression is induc ible by doxycyclin and by using the drug STI571 to inactivate BCR-ABL activ ity in BaF3-p210. To establish the functional significance of cyclin D2 and p27(Kip1) expression in response to IL-3 and BCR-ABL expression, me studie d the effects of ectopic expression of cyclin D2 and p27(Kip1) On cell prol iferation and survival. Our results demonstrate that both cyclin D2 and p27 (Kip1) have a role in BaF3 cell proliferation and survival, as ectopic expr ession of cyclin D2 is sufficient to abolish the cell cycle arrest and apop tosis induced by IL-3 withdrawal or by BCR-ABL inactivation, while overexpr ession of p27(Kip1) can cause cell cycle arrest and apoptosis in the BaF3 c ells. Furthermore, our data also suggest that cyclin D2 functions upstream of p27(Kip1), cyclin E, and cyclin D3, and therefore, plays an essential pa rt in integrating the signals from IL-3 and BCR-ABL with the pRB/ESF pathwa y.