1. Previous studies have shown that levels of CHIF mRNA are increased in the distal colon of the rat in response to corticosteroids. We have recently reported that this response occurs within 2 h of a single dose of either dexamethasone or aldosterone and that the response is mediated via both the mineralocorticoid and glucocorticoid receptors.
2. In the present study we sought to further define the nature of the various transcripts detected by a CHIF coding region cRNA probe in northern blot analysis of corticosteroid-stimulated colonic RNA. The identification of an intronic sequence was used to synthesize an intron-specific cDNA probe to characterize the transcripts.
3. The presence of an intronic sequence in the originally published sequence was confirmed using coupled reverse transcriptase-polymerase chain reactions with primers spanning and within the intronic sequence. The intronic cDNA probe hybridized to the higher molecular weight transcripts detected by the cRNA probe. These transcripts are induced in response to both corticosteroids.
4. Taken together with our observations that the increase in CHIF mRNA levels in the distal colon in response to corticosteroids is not blocked by prior cycloheximide treatment, the increase in the levels of the primary transcript and partially spliced forms argues that this is a primary transcriptional response. This is the first clear demonstration of an aldosterone-induced gene in vivo in a mammalian system.