Extensive alternative splicing and dual promoter usage generate Tcf-1 protein isoforms with differential transcription control properties.
Previously, we reported the isolation of cDNA clones representing four alternative splice forms of TCF-1, a T-cell-specific transcription factor. In the present study, Western blotting (immunoblotting) yielded a multitude of TCF-1 proteins ranging from 25-55 kDa, a pattern not simply explained from the known splice alternatives. Subsequent cDNA cloning, PCR amplification, and analysis by rapid amplification of 5' cDNA ends revealed (i) the presence of an alternative upstream promoter, which extended the known N terminus by 116 amino acids, (ii) the presence of four alternative exons, and (iii) the existence of a second reading frame in the last exon encoding an extended C terminus. Inclusion of the extended N terminus into the originally reported protein resulted in a striking similarity to the lymphoid factor Lef-1. Several of the TCF-1 isoforms, although less potent, mimicked Lef-1 in transactivating transcription through the T-cell receptor alpha-chain (TCR-alpha) enhancer. These data provide a molecular basis for the complexity of the expressed TCF-1 proteins and establish the existence of functional differences between these isoforms. Furthermore, the functional redundancy between Tcf-1 and Lef-1 explains the apparently normal TCR-alpha expression in single Tcf-1 or Lef-1 knockout mice despite the firm in vitro evidence for the importance of the Tcf/Lef site in the TCR-alpha enhancer.
Van de Wetering
M
M
Department of Immunology, University Hospital Utrecht, The Netherlands.
Castrop
J
J
Korinek
V
V
Clevers
H
H
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D018014:Gene Transfer Techniques; D051538:Hepatocyte Nuclear Factor 1-alpha; D051821:Lymphoid Enhancer-Binding Factor 1; D051379:Mice; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D016415:Sequence Alignment; D051822:T Cell Transcription Factor 1; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D051538:Hepatocyte Nuclear Factor 1-alpha; C496488:Hnf1a protein, mouse; C497574:Lef1 protein, mouse; D051821:Lymphoid Enhancer-Binding Factor 1; D051822:T Cell Transcription Factor 1; C497576:TCF7 protein, human; D014157:Transcription Factors