Transcriptional and posttranscriptional mechanisms modulate creatine kinase expression during differentiation of osteoblastic cells.

Enhancement of energy metabolism is fundamental to the developmental programs of many cell types. This work examines the molecular mechanisms that mediate changes in energy metabolism during differentiation of osteoblastic cells. When the rat osteoblastic cell line, ROS 17/2.8, is induced to differentiate with 1,25-dihydroxyvitamin D3, expression of creatine kinase-b (ck-b), a pivotal enzyme in energy metabolism, is enhanced. Maximum enhancement occurs at 48 h of induction with 10 nM 1,25-dihydroxyvitamin D3 when creatine kinase activity is 2.1-fold over uninduced cells. This is associated with a 2-fold increase in transcription rate and the formation of a second protein-DNA complex on the ck-b gene promoter that is supplementary to the one present in undifferentiated cells. In addition, the contribution of posttranscriptional regulatory mechanisms is suggested by (1) the increase in ck-b mRNA abundance exceeds that of transcription rate, indicating an increase in message stability, (2) the increase in ck-b mRNA precedes and exceeds that of protein activity, indicating translational modulation, and (3) RNA mobility-shift assays indicate that a cytosolic factor in ROS 17/2.8 cells interacts specifically with the highly conserved 3'-untranslated region of the ck-b mRNA. We have previously reported that such an interaction mediates translational control (Ch'ng, J. L. C., Shoemaker, D. L., Schimmel, P., and Holmes, E.W. (1990) Science 248, 1003-1006). The physiological roles of these regulatory mechanisms during osteoblast differentiation are discussed.