Characterization of the chicken L-Maf, MafB and c-Maf in crystallin gene regulation and lens differentiation.
BACKGROUND
Members of the Maf family, including L-Maf, MafB and c-Maf, are "basic region/leucine zipper" (bZIP) transcription factors. Maf proteins contain a highly conserved acidic transactivation domain (AD), and a bZIP region that mediates DNA-binding activity. The hinge region between AD and bZIP varies considerably in length between different proteins. Recent studies reveal that L-Maf, c-Maf and MafB play key roles in vertebrate lens development.


RESULTS
We investigated the transactivation activity of individual factors in culture cells to analyse their specific functions. In transient transfection assays with a reporter gene containing Maf responsive elements, MafB and c-Maf activated higher levels of the reporter gene than L-Maf. However, L-Maf transactivated the alphaA-crystallin promoter as effectively as MafB and c-Maf, and induced the expression of the endogenous delta-crystallin gene more efficiently than the other two proteins. Domain-swapping experiments reveal that the bZIP region of MafB takes part in strong transcriptional activity, while the acidic and hinge regions (AH) of c-Maf collectively serve as a strong transactivation domain. The AH region of L-Maf (but not c-Maf) conferred transactivation activity to induce delta-crystallin gene expression.


CONCLUSIONS
These results suggest that despite their similar DNA binding properties, L-Maf, MafB and c-Maf regulate different sets of target genes by complex interactions with multiple factors that recognize cis-elements in promoters. The AH region of L-Maf has a distinct role in inducing endogenous delta-crystallin gene.
Yoshida
Tomonori
T
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Takayama 8916-5, Ikoma 630-0101, Japan.
Yasuda
Kunio
K
D016475:3T3 Cells; D000818:Animals; D030161:Avian Proteins; D001665:Binding Sites; D002645:Chickens; D003459:Crystallins / Q000235:genetics* / Q000502:physiology; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D007908:Lens, Crystalline / Q000196:embryology* / Q000502:physiology; D051258:MafB Transcription Factor; D051379:Mice; D015513:Oncogene Proteins / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051257:Proto-Oncogene Proteins c-maf; D011994:Recombinant Proteins / Q000235:genetics; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors; D014158:Transcription, Genetic
D030161:Avian Proteins; D003459:Crystallins; D004268:DNA-Binding Proteins; C495608:Maf protein, mouse; D051258:MafB Transcription Factor; C490406:Mafb protein, mouse; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D051257:Proto-Oncogene Proteins c-maf; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D004247:DNA