Kiyokawa H, Ngo L, Kurosaki T, Rifkind R A, Marks P A
DeWitt Wallace Research Laboratory, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
Cell Growth Differ. 1992 Jun;3(6):377-83.
Hexamethylene bisacetamide (HMBA)-induced murine erythroleukemia (MELC) differentiation is characterized by a prolongation of the initial G1 which follows passage through S phase in the presence of inducer. Commitment to terminal cell division is first detected in a portion of the cell population during this prolonged G1. HMBA-induced commitment is stochastic. This study has examined changes in two known cell cycle regulators, p34cdc2 and cyclin A, in cycle-synchronized MELC in the absence and presence of HMBA. Histone H1 kinase activity of p34cdc2, and the levels of CDC2Mm mRNA, 1.8-kilobase mRNA of cyclin A, and cyclin A protein changed during cell cycle progression in MELC, and all of them were suppressed during G1. The suppression of the H1 kinase activity and cyclin A expression continued through the prolonged G1 in MELC cultured with HMBA, whereas p34cdc2 protein level did not vary through the cell cycle in MELC cultured without or with inducer. Phosphorylation of p34cdc2 in uninduced MELC gradually increased as cells progressed from G1 to S. In induced MELC, an increase in phosphorylation of p34cdc2 occurred during the prolonged G1, and prior to the exit of the bulk of the cells from G1 to S. These results suggest that in HMBA-induced MELC, p34cdc2 phosphorylation per se is not a limiting factor in determining G1 to S progression. The persistent suppression of cyclin A expression and histone H1 kinase activity may play a role in HMBA-induced commitment to terminal differentiation.
六亚甲基双乙酰胺（HMBA）诱导的小鼠红白血病（MELC）分化的特征是，在诱导剂存在的情况下，经过S期后初始G1期延长。在这个延长的G1期，一部分细胞群体中首次检测到对终末细胞分裂的决定。HMBA诱导的决定是随机的。本研究检测了在有无HMBA的情况下，周期同步化的MELC中两种已知细胞周期调节因子p34cdc2和细胞周期蛋白A的变化。在MELC的细胞周期进程中，p34cdc2的组蛋白H1激酶活性、CDC2Mm mRNA水平、细胞周期蛋白A的1.8千碱基mRNA水平和细胞周期蛋白A蛋白均发生变化，并且在G1期均受到抑制。在用HMBA培养的MELC中，H1激酶活性和细胞周期蛋白A表达的抑制在延长的G1期持续存在，而在未加或加诱导剂培养的MELC中，p34cdc2蛋白水平在整个细胞周期中没有变化。在未诱导的MELC中，随着细胞从G1期进入S期，p34cdc2的磷酸化逐渐增加。在诱导的MELC中，p34cdc2的磷酸化增加发生在延长的G1期，且在大部分细胞从G1期进入S期之前。这些结果表明，在HMBA诱导的MELC中，p34cdc2磷酸化本身不是决定G1期到S期进程的限制因素。细胞周期蛋白A表达和组蛋白H1激酶活性的持续抑制可能在HMBA诱导的终末分化决定中起作用。
