Activation of the thyroid-stimulating hormone beta-subunit gene by LIM homeodomain transcription factor Lhx2.
Although there is evidence that the LIM homeodomain transcription factor, Lhx2, can stimulate transcription of the glycoprotein hormone alpha-subunit gene, the role of Lhx2 in regulating TSH beta-subunit has not been established. In the present studies, the ability of Lhx2 to regulate transcription of the TSH beta-subunit gene was examined. In the thyrotrope-derived TalphaT1 cell line, Lhx2 expression was found to be induced by treatment with either TRH or cAMP, consistent with the possibility that Lhx2 may play a role in mediating the ability of this signaling pathway to stimulate TSH gene expression. Transient, forced overexpression of Lhx2 stimulated activity of a TSH beta-subunit reporter gene. Deletion studies provided evidence that the -177 to -79 region of the TSH beta-subunit promoter was necessary for stimulation of reporter gene activity by Lhx2. A gel mobility shift assay provided the evidence that Lhx2 can bind to this region of DNA. DNase I footprinting studies demonstrated that two distinct regions of the TSHbeta promoter, -118 to -108 and -86 to -68, are protected by Lhx2 from nuclease digestion. These regions contain repeats of the sequence, 5'-(G/T)CAAT(T/A)-3'. Mutation of this sequence, especially in the -86 to -68 region, substantially decreased Lhx2 responsiveness of the TSH beta-subunit reporter gene. In addition, a DNA fragment containing the -177 to -79 region of the TSHbeta promoter was found to confer Lhx2 responsiveness to a minimal promoter. These results provide multiple lines of evidence consistent with a role for Lhx2 in modulating expression of the TSH beta-subunit gene.
Kim
Kee K
KK
Department of Biochemistry, Institute of Biotechnology, Chungnam National University, Daejeon 305-764, Korea.
Song
Seok B
SB
Kang
Kwang I
KI
Rhee
Myungchull
M
Kim
Kyoon Eon
KE
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D000242:Cyclic AMP / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation / Q000187:drug effects*; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D007028:Hypothalamic Hormones / Q000494:pharmacology*; D060850:LIM-Homeodomain Proteins; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D037322:Thyrotropin, beta Subunit / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
D018398:Homeodomain Proteins; D007028:Hypothalamic Hormones; D060850:LIM-Homeodomain Proteins; C489784:Lhx2 protein, mouse; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D037322:Thyrotropin, beta Subunit; D014157:Transcription Factors; D000242:Cyclic AMP; D008156:Luciferases; D003850:Deoxyribonuclease I