Novel Regulatory Factors Interacting with the Promoter of the Gene Encoding the mRNA Cap Binding Protein (eIF4E) and Their Function in Growth Regulation

ABSTRACT

Regulation of the mRNA cap binding protein (eIF4E) is critical to the control of cellular proliferation since this protein is the rate-limiting factor in translation initiation and transforms fibroblasts and since eIF4E mutants arrest budding yeast in the G₁ phase of the cell cycle (cdc33). We previously demonstrated regulation of eIF4E by altered transcription of its mRNA in serum-stimulated fibroblasts and in response to c-myc. To identify additional factors regulating eIF4E transcription, we used linker-scanning constructs to characterize sites in the promoter of the eIF4E gene required for its expression. Promoter activity was dependent on sites at −5, −25, −45, and −75; the site at −75 included a previously described myc box. Electrophoretic mobility shift assays identified DNA-protein interactions at −25 and revealed a binding site (TTACCCCCCCTT) that is unique to the eIF4E promoter. Proteins of 68 and 97 kDa bound this site in UV cross-linking and Southwestern experiments. Levels of 4E regulatory factor activities correlated with c-Myc levels, eIF4E expression levels, and protein synthesis in differentiating U937 and HL60 cells, suggesting that these activities may function to regulate protein synthesis rates during differentiation. Since the eIF4E promoter lacked typical TATA and initiator elements, further studies of this novel initiator-homologous element should provide insights into mechanisms of transcription initiation and growth regulation.

ACKNOWLEDGMENTS

This work, Kelly Johnston, Michael Polymenis, John Branda, and Emmett Schmidt were supported by PHS grant RO1-CA63117. Shanping Wang was supported by departmental funds of The Pediatric Service, Massachusetts General Hospital.

We thank R. Weinberg, A. Ezekowitz, and B. Kreskel for providing cell lines.