Overexpression of the proto‐oncogene/translation factor 4E in breast‐carcinoma cell lines

The expression of the proto‐oncogene, translation factor elF‐4E, was examined in breast‐cell lines: 5 carcinomas and 2 normal. At the protein level, elF‐4E was 10 times higher in the carcinoma lines than in normal cells, which is comparable to the level found in breast‐cancer biopsies. The elevation appears to be due to increased transcription, since the elF‐4E mRNA was correspondingly increased. These results demonstrate that cells isolated from naturally occurring breast carcinomas maintain an elevated expression of the factor. Turnover rates for elF‐4E (mRNA and protein) were determined for normal and cancer cells. We found that elF‐4E mRNA is relatively stable during an 8‐hr incubation with Actinomycin D, but the half‐life of the protein is fairly short (≈4.5 hr). This suggests that, in proliferating cells, elF‐4E may be turning over rapidly, possibly to fine‐tune the changes in translation rates which occur during the cell cycle. © 1996 Wiley‐Liss, Inc.