Differentiation-dependent repression of c-myc, B22, COX II and COX IV genes in murine erythroleukemia (MEL) cells

Abstract

Murine erythroleukemia (MEL) cells provide a valuable model system for uncovering the cellular and molecular mechanisms of differentiation of proerythroid cells in culture. In order to characterize genes and gene expression patterns unique for erythropoiesis, we: (i) cloned and sequenced a 226bp cDNA encoding portion of the 3'-end B22 subunit of mitochondrial NADH-ubiquinone oxidoreductase (complex I); (ii) assessed the steady state level of RNA transcripts encoded by B22, cytochrome c oxidase (COX II, COX IV) and c-myc genes in MEL cells undergoing terminal differentiation induced by dimethylsulfoxide (DMSO) and/or 2-(3-ethylureido)-6-methylpyridine; and (iii) investigated whether the gene expression patterns of B22, COX IV and c-myc genes seen in differentiating cells are affected by N(6)-methyladenosine, an inhibitor of commitment and RNA methylation. These studies have indicated: (a) c-myc, COX II and COX IV genes exhibited biphasic expression pattern; a transient accumulation of c-myc, COX II and COX IV mRNAs was followed by a decline after 36hr incubation with DMSO and/or 2-(3-ethylureido)-6-methylpyridine, (b) B22 gene expression declined progressively in differentiated cells, (c) blockade of differentiation of MEL cells with N(6)-methyladenosine failed to prevent the transient accumulation of c-myc, COX II and COX IV mRNAs, but abrogated the irreversible expression of all four genes. These findings indicated that B22, c-myc, COX II and COX IV genes are gradually repressed in terminally differentiating MEL cells presumably via different patterns of expression (gradual vs. biphasic). Overall, these results showed that erythroid maturation of MEL cells is accompanied by transcriptional inactivation (or repression) of at least three genes encoding mitochondrial enzyme subunits involved in cell respiration.