Differential potency and trans‐activation of normal and mutant T24 human H‐ras1 gene promoters

Abstract

We have employed a short-term transfection assay system in which we monitored the transient expression of the chloramphenicol acetyltransferase (CAT) gene linked to the promoter region of the normal and mutant T24 H-rasl gene or the human s-globin gene in Chinese hamster lung (CHL) cells or cells derived from them which carry and express one or the other of the polyoma virus early genes. Our findings can be summarized as follows: (i) The mutant T24 H-rusl promoter region behaves as a stronger promoter than the H-rasl gene in all these types of cells as well as in rat 208F fibroblast cells. (ii) In CHL cells expressing the polyoma large T antigen the normal and mutant T24 Ha-rsl promoters are not trans-activated in these cells and only a 2.5fold activation of the s-globin promoter is observed. (iii) In cells expressing the polyoma middle T antigen both the normal and mutant H-rasl are tram-activated whereas transcription from the s-globin promoter is not affected when compared to the normal CHL cells. (iv) In cells expressing the polyoma small T antigen the normal and mutant H-ru.sl as well as the s-globin promoters are trans-activated. We suggest from these data that a tissue-specific element exists in the promoter region of the H-rarl gene and that the polyoma middle and small T antigens trigger the expression of proteins that trans-activate these promoters.

Phorbol ester‐responsive H‐ras1 gene promoter contains multiple TPA‐inducible/AP‐1‐binding consensus sequence elements

“…Regulatory sequences have also been found in the first [21] and fourth [22] intron of the H-rasl gene. In the first case a six base pair deletion in the first intron of the T24 H-rasl gene increases transcriptional activity from the H-rasl promoter [21] whereas in the latter case a point mutation in the fourth intron is responsible for increased expression and transforming activity of the oncogene [22]. Moreover, it has been suggested that the regulation of H-rasl transcription may involve the Spl transcriptional factor since a number of Spl-binding sites have been found in the promoter region [23].…”