c-Myb function in fibroblasts

The protooncogene c-myb is a nuclear transcription factor that shares significant sequence homology with two other myb family members, A-myb and B-myb. Recent studies have suggested that c-myb is involved in regulation of the cell cycle via control of intracellular calcium [Ca2+]i concentration. Given the limited cell type expression of the c-myb gene, we set out to investigate whether myb-dependent cell cycle regulation occurs in cells not known to express the c-myb protein. NIH 3T3 fibroblasts were stably transfected with an inducible c-myb dominant negative construct composed of a myb DNA binding domain linked to the Drosophila engrailed transcription suppresser (pGREMEn) and a full-length murine c-myb cDNA sequence. Induced expression of the dominant negative construct was associated with a G1 cell cycle arrest and a failure to increase late G1 intracellular calcium levels. Similar expression studies in mouse embryonic fibroblasts derived from the c-myb knockout mouse have demonstrated lower baseline [Ca2+]i levels than in normal mice fibroblasts that were not further lowered by MEn expression. We conclude that regulation of calcium homeostasis and cell cycle progression via myb-dependent transcription may play an important role in cells not possessing detectable levels of c-myb protein.