Activation of the smooth muscle-specific telokin gene by thyrotroph embryonic factor (TEF).
Transcription of the telokin gene is restricted to smooth muscle cells throughout development, making this gene an excellent model for unraveling the mechanisms that regulate gene expression in smooth muscle tissues. To identify proteins that bind to the telokin promoter, the AT-rich/CArG core of the promoter was used as a probe to perform a Southwestern screen of a mouse bladder cDNA library. Four clones corresponding to two distinct isoforms of mouse thyrotroph embryonic factor (TEFalpha and TEFbeta) were identified from this screen. The two TEF isoforms differ from each other at their amino termini and result from alternative promoter usage. An RNase protection assay showed that both TEF isoforms are expressed at high levels in mouse lung, bladder, kidney, gut, and brain. Gel mobility shift assays demonstrated that purified TEF protein can specifically bind to an AT-rich region within the core of the telokin promoter. Furthermore, when overexpressed in 10T1/2 cells, TEF significantly increased the activity of a telokin promoter-reporter gene; this activation was further augmented by elevated intracellular calcium levels. In contrast, overexpression of TEF had no effect on reporter genes driven by SM22alpha, smooth muscle alpha-actin, or smooth muscle myosin heavy chain promoters. Consistent with these results, overexpression of TEFalpha and TEFbeta in A10 cells, using adenoviral vectors, increased expression of endogenous telokin without altering expression of myosin light chain 20, SM22alpha, smooth muscle alpha-actin, or calponin. These findings suggest that TEF factors contribute to the activation of the telokin promoter in smooth muscle cells in a calcium-dependent manner. These data also suggest that distinct transcription factors are required to control the expression of different smooth muscle genes in a single tissue.
Zhou
Jiliang
J
Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120, USA.
Hoggatt
April M
AM
Herring
B Paul
BP
D000199:Actins / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors; D002118:Calcium / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics*; D009130:Muscle, Smooth / Q000502:physiology; D009219:Myosin-Light-Chain Kinase / Q000235:genetics; D010446:Peptide Fragments; D010455:Peptides; D011401:Promoter Regions, Genetic / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D000199:Actins; D050976:Basic-Leucine Zipper Transcription Factors; D009124:Muscle Proteins; D010446:Peptide Fragments; D010455:Peptides; C489490:TEF protein, human; C489491:Tef protein, mouse; D014157:Transcription Factors; C060640:telokin; D009219:Myosin-Light-Chain Kinase; D002118:Calcium