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The promoter activities of rat cardiac myosin heavy chain (MHC) genes respond to diabetes
Author(s) -
Giger Julia M,
Haddad Fadia,
Baldwin Kenneth M
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1187-d
Subject(s) - transcription (linguistics) , promoter , microbiology and biotechnology , biology , gene , reporter gene , genetics , gene expression , philosophy , linguistics
The rat heart expresses two MHC isoforms: alpha (a) and beta (b). The b and a genes are arranged in tandem on the chromosome. Using strand‐specific RT‐PCR, we recently reported that both the a and b MHC pre‐mRNAs and corresponding mRNAs are transcribed, and the opposite strand is also transcribed. The transcription of this other strand generates an antisense (AS) RNA which starts in the intergenic (IG) region between b and a genes and extends to overlap the b MHC gene, and thus is called AS b RNA. We propose that in control rat hearts, both b sense promoter and IG bi‐directional promoter are activated, but the transcription of AS bRNA interferes with the accumulation of sense b, resulting in a low levels of mature b mRNA. In streptozotocin‐treated (STZ) diabetic hearts, the bi‐directional promoter is inhibited, thus downregulating AS bRNA and sense a, so more sense b accumulates. A dual reporter plasmid containing the −2.6 bi‐directional promoter, injected into control rat hearts, shows that bi‐directional transcriptional activity of IG is coordinated. Fragments of the 4.5kb IG region were inserted into a luciferase plasmid in the 3′ to 5′ AS direction. The reporter activity of −2.3kb promoter was higher than that of the 4.5kb promoter. A −1.7kb fragment abolished activity. A 1340bp promoter corresponding to the −2285/−945 region of the IG sequence was activated in control heart comparable to the 2.3kb promoter. The activity of this 1340bp promoter decreased >50% in response to STZ. Further deletions caused decreases in activity, and the short 424bp promoter activity was only ~25% of that of the 1340 promoter in control hearts, yet all fragments were responsive to STZ.