Activation and Suppression of a Cryptic Promoter in the Intron of the Human Melanoma‐associated ME491 Antigen Gene

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Abstract
A deletion mutant of the human melanoma‐associated ME491 antigen gene starting at the first intron (λR31) differentially mediates the antigen expression depending on the cell type. Cryptic promoter activity residing in a 270‐base‐pair (bp) fragment of the first intron was examined by primer extension analysis and recombinant chloramphenicol acetyltransferase (CAT) assay. The cryptic promoter, further localized within a 153‐bp fragment (fr153BN), exerted its effect in Ltk‐ and H‐ras‐transformed NIH3T3 (3T3‐Hras) but not in parental NIH3T3 cells. The results suggested that the cryptic promoter was associated with a novel ras‐responsive positive regulatory element, since fr153BN did not contain an AP‐1‐binding sequence motif, known as the rew‐responsive enhancer element. The cryptic promoter activity of fr153BN was suppressed by an upstream 121‐bp fragment (fr121SB) which contained a consensus sequence motif for binding of a repressor protein, GC factor, and regions showing sequence similarity with putative cis‐acting repressor elements found in the vimentin gene. The degree of the suppression was greater in 3T3‐Hras than in Ltk‐ cells. These positive and negative regulatory elements may be differentially involved in the regulation of ME491 antigen expression depending on the cell type.