Lineage-specific regulation of cell cycle gene expression in differentiating myeloid cells

We have analysed the expression of 7 cyclin and cyclinassociated kinase (cdk) genes in the human myeloid cell line HL-60 at different stages of the cell cycle in non-synchro nised cells and during terminal differentiation. A clear cell cycle-dependent expression was found with cyclins A (S+G2), B (G2) and E (late G1 and S), while other cell cycle genes showed only very weak (cdk2) or no periodic expression (cyclin D1, cyclin D2 and cdk4). Induction of macrophage-like differentiation by TPA or granulocytic differentiation by retinoic acid or DMSO was accompanied by a block in G1 and resulted in distinct patterns of gene expression that were lineage- and inducer-specific. These included: (i) a dramatic decrease in the expression of cyclin A, cyclin B and cdk2, and surprisingly an up-regulation of cyclin D1 in TPA-induced macrophage-like cells; (ii) a down-regulation of cyclin E in retinoic acid-induced gran ulocytic cells; and (iii) a decreased abundance of cyclin D1 and D2, but high levels of cyclin A, B and E RNA in DMSOinduced granulocytic cells. These observations suggest that the mechanisms leading to a differentiation-associated cell cycle arrest are lineage-specific, and that the sustained expression of cyclin and cdk genes does not interfere with the induction of terminal differentiation. SUMMARY