OUT, a novel basic helix-loop-helix transcription factor with an Id-like inhibitory activity.
Transcription factors belonging to the basic helix-loop-helix (bHLH) family are involved in various cell differentiation processes. We report the isolation and functional characterization of a novel bHLH factor, termed OUT. OUT, structurally related to capsulin/epicardin/Pod-1 and ABF-1/musculin/MyoR, is expressed mainly in the adult mouse reproductive organs, such as the ovary, uterus, and testis, and is barely detectable in tissues of developing embryos. Physical association of OUT with the E protein was predicted from the primary structure of OUT and confirmed by co-immunoprecipitation. However, unlike other bHLH factors, this novel protein failed to bind E-box or N-box DNA sequences and inhibited DNA binding of homo- and heterodimers consisting of E12 and MyoD in gel mobility shift assays. In luciferase assays, OUT inhibited the induction of E-box-dependent transactivation by MyoD-E12 heterodimers. Deletion studies identified the domain responsible for the inhibitory action of OUT in its bHLH and C-terminal regions. Moreover, terminal differentiation of C2C12 myoblasts was inhibited by exogenous introduction of OUT. These inhibitory functions of OUT closely resemble those of the helix-loop-helix inhibitor Id proteins. Based on these findings, we propose that this novel protein functions as a negative regulator of bHLH factors through the formation of a functionally inactive heterodimeric complex.
Narumi
O
O
Department of Molecular Genetics, Graduate School of Medicine, Kyoto University, Shogoin Kawahara-cho 53, Sakyo-ku, 606-8507 Kyoto, Japan.
Mori
S
S
Boku
S
S
Tsuji
Y
Y
Hashimoto
N
N
Nishikawa
S
S
Yokota
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D018257:Helix-Loop-Helix Motifs / Q000235:genetics; D051379:Mice; D008813:Mice, Inbred ICR; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D014157:Transcription Factors / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism
D051792:Basic Helix-Loop-Helix Proteins; D018076:DNA, Complementary; D014157:Transcription Factors; C404514:Tcf23 protein, mouse