[Enhancement of cellular transforming activities of truncated EJ c-H-ras-1 with viral enhancers or with c-myc].
The 2.9kb Sac I fragment (EJ2.9), which lacks the previously reported promoter/enhancers of the activated human c-H-ras-1, was used to study the interaction with the tumor virus promoter/enhancers or with the activated c-myc. When EJ2.9 constructs linked to the viral promoter/enhancers or to a viral enhancer even in the antisense orientation was transfected to the mouse cells, 16-39% of the foci induced with those linked in the sense orientation were formed. Further, the transforming activity decreased dramatically when the deletion was introduced from the upstream Sac I site to the 61 bases (-61) upstream of translational initiation codon, but the deletions to -144 did not significantly change the activity. Cotransfections with the activated c-myc were found also to enhance the transforming activity of EJ2.9 constructs either with or without the LTR linked in the antisense orientation. The transfected ras and myc were expressed as 1.2 and 2.5kb mRNAs, respectively, in each transformant. The in vitro mutagenesis suggested that the c-myc protein was involved in the enhancement. These results raise the possibility that the viral enhancers activate a cryptic promoter (s) within the region between -1 and -144 of p21 initiation codon by interacting with the region between -61 and -144 and that the c-myc protein also activates the same or different cryptic promoter(s) within the intron 0 or noncoding region of exon I, thus leading to the enhancement of the EJ2.9 transforming activity.
Koyama
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First Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Tokyo Medical and Dental University.
D000818:Animals; D001483:Base Sequence; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000473:pathology; D004742:Enhancer Elements, Genetic; D016259:Genes, myc / Q000502:physiology*; D011905:Genes, ras / Q000502:physiology*; D005822:Genetic Vectors; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000502:physiology*; D011401:Promoter Regions, Genetic; D051381:Rats; D012190:Retroviridae / Q000235:genetics; D014407:Tumor Cells, Cultured