Increased retinoblastoma gene expression is associated with late stages of differentiation in many different cell types.

The retinoblastoma (Rb) gene is a recessive oncogene or tumor-suppressor gene whose inactivation leads to the development of tumors. Recently, evidence pointing to a role for the Rb gene in the differentiation of certain human cell types has been presented. We have studied three mouse cell lineages to determine whether there is a correlation between Rb gene expression and differentiation. We find that induction of mouse erythroleukemia cell differentiation with either dimethylsulfoxide (DMSO) or hexamethylene bisacetamide (HMBA) leads to increased expression of Rb mRNA. Increased expression of Rb mRNA was also found in S2 myoblasts induced by mitogen depletion to become differentiated myotubes. In the B-cell lineage, Rb expression is low in pre-B and B cell lines but high in plasmacytomas, which represent late stages of B cell differentiation. Thus, in all three lineages (erythroid, muscle, and B-cell) late stages of differentiation are associated with increased amounts of Rb mRNA.