Translational control of specific genes during differentiation of HL-60 cells.

Eukaryotic gene expression can be regulated through selective translation of specific mRNA species. Nevertheless, the limited number of known examples hampers the identification of common mechanisms that regulate translation of specific groups of genes in mammalian cells. We developed a method to identify translationally regulated genes. This method was used to examine the regulation of protein synthesis in HL-60 cells undergoing monocytic differentiation. A partial screening of cellular mRNAs identified five mRNAs whose translation was specifically inhibited and five others that were activated as was indicated by their mobilization onto polysomes. The specifically inhibited mRNAs encoded ribosomal proteins, identified as members of the 5'-terminal oligopyrimidine tract mRNA family. Most of the activated transcripts represented uncharacterized genes. The most actively mobilized transcript (termed TA-40) was an untranslated 1.3-kilobase polyadenylated RNA with unusual structural features, including two Alu-like elements. Following differentiation, a significant change in the cytoplasmic distribution of Alu-containing mRNAs was observed, namely, the enhancement of Alu-containing mRNAs in the polysomes. Our findings support the notion that protein synthesis is regulated during differentiation of HL-60 cells by both global and gene-specific mechanisms and that Alu-like sequences within cytoplasmic mRNAs are involved in such specific regulation.