Induction of cell cycle proteins. (I) Regulation of expression of G1-S cell cycle regulatory proteins in human CD34⁺ cells. Equal number of cells were treated without or with 1K3, or IL-1, KL, and IL-3 for 72 hours. Cell extracts were immunoblotted with the indicated antibodies. In panel I, (A and B) are two different exposures of the same autoradiogram. (II) Immunoblotting for p34CDC2 and cyclin B1 was performed from the same blot, and of cyclin D and A from another blot. (III) G-CSF can replace IL-3 to induce the expression of cell cycle proteins in human CD34⁺ cells. Cells were treated with either 1K3 or combination of IL-3 and KL (K3), G-CSF, and combination of IL-1, KL, and G-CSF (1KG) for 72 hours. Cell extracts were immunoblotted with the indicated antibodies. Immunoblotting for p34CDC2 and cyclin E was performed from the same blot. Results shown are representative of three separate experiments.