Differential regulation of the alpha 2 beta 1 and alpha IIb beta 3 integrin genes during megakaryocytic differentiation of pluripotential K562 cells.

Expression of the alpha 2 beta 1 and alpha IIb beta 3 integrin genes is differentially regulated during megakaryocytic differentiation of pluripotent K562 cells induced with phorbol 12,13-dibutyrate. Upon megakaryocytic differentiation, steady-state alpha 2 mRNA increased markedly from the undetectable level present in the uninduced cells. The level of beta 1 mRNA did not change. Expression of alpha IIb beta 3 is regulated differently. beta 3 mRNA was undetectable in uninduced cells but increased significantly following induction. alpha IIb mRNA was detectable at a low level prior to induction, but at an increased level following differentiation. Altered mRNA stability did not contribute to changes in mRNA levels. Nuclear run-off experiments revealed a 20-fold increase in alpha 2 gene transcription upon megakaryocytic differentiation, but no change in transcription of the beta 1 gene. Transcription of both the alpha IIb and beta 3 genes increased 10- and 5-fold, respectively. Thus, the increase in alpha 2 beta 1 protein which accompanies the megakaryocytic differentiation of K562 cells is a consequence of the increased steady-state level of alpha 2 mRNA due to transcriptional activation of the alpha 2 gene. The long-lived beta 1 mRNA is not altered during differentiation. In contrast, increased alpha IIb beta 3 protein appears due to increased steady-state levels of both alpha IIb and beta 3 mRNAs that result from transcriptional activation of both integrin genes.