Uncleaved TFIIA Is a Substrate for Taspase 1 and Active in Transcription

NCMLS, Department of Molecular Biology, 191, Radboud University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
Molecular and Cellular Biology (Impact Factor: 4.78). 05/2006; 26(7):2728-35. DOI: 10.1128/MCB.26.7.2728-2735.2006
Source: PubMed


In higher eukaryotes, the large subunit of the general transcription factor TFIIA is encoded by the single TFIIAαβ gene and
posttranslationally cleaved into α and β subunits. The molecular mechanisms and biological significance of this proteolytic
process have remained obscure. Here, we show that TFIIA is a substrate of taspase 1 as reported for the trithorax group mixed-lineage
leukemia protein. We demonstrate that recombinant taspase 1 cleaves TFIIA in vitro. Transfected taspase 1 enhances cleavage
of TFIIA, and RNA interference knockdown of endogenous taspase 1 diminishes cleavage of TFIIA in vivo. In taspase 1−/− MEF cells, only uncleaved TFIIA is detected. In Xenopus laevis embryos, knockdown of TFIIA results in phenotype and expression defects. Both defects can be rescued by expression of an
uncleavable TFIIA mutant. Our study shows that uncleaved TFIIA is transcriptionally active and that cleavage of TFIIA does
not serve to render TFIIA competent for transcription. We propose that cleavage fine tunes the transcription regulation of
a subset of genes during differentiation and development.

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Available from: Dimitra J Mitsiou
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    • "Our study suggests that Taspase1-mediated proteolytic cleavage of TFIIAa-b could serve to interconnect and fine-tune the general and tissuespecific transcription. In somatic cells, precursor TFIIAa-b binds TBP and is functionally active in transcription (Zhou et al., 2006). Therefore, in this context the cleavage of TFIIAa-b may serve to fine-tune the rate of transcription through regulating its stability, as processed TFIIAa/b is known to be more susceptible to degradation (Høiby et al., 2004). "
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    ABSTRACT: The evolution of tissue-specific general transcription factors (GTFs), such as testis-specific TBP-related factor 2 (TRF2), enables the spatiotemporal expression of highly specialized genetic programs. Taspase1 is a protease that cleaves nuclear factors MLL1, MLL2, TFIIAα-β, and ALFα-β (TFIIAτ). Here, we demonstrate that Taspase1-mediated processing of TFIIAα-β drives mammalian spermatogenesis. Both Taspase1(-/-) and noncleavable TFIIAα-βnc/nc testes release immature germ cells with impaired transcription of Transition proteins (Tnp) and Protamines (Prm), exhibiting chromatin compaction defects and recapitulating those observed with TRF2(-/-) testes. Although the unprocessed TFIIA still complexes with TRF2, this complex is impaired in targeting and thus activating Tnp1 and Prm1 promoters. The current study presents a paradigm in which a protease (Taspase1) cleaves a ubiquitously expressed GTF (TFIIA) to enable tissue-specific (testis) transcription, meeting the demand for sophisticated regulation of distinct subsets of genes in higher organisms.
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    • "The basis for these differences between the two independently generated mouse lines is unclear since detailed description of the mice generated by Takeda et al. was not reported [25], but may be due to differences in genetic backgrounds of the ES cells or the targeting vector. Nevertheless, our results indicate that MLL processing does not serve rate-limiting roles for proliferation and suggest that the growth defects caused by Taspase 1-deficiency may be attributed to other substrates such as MLL2 [25] or TFIIA [34]. "
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    ABSTRACT: The mixed lineage leukemia (MLL) protein is an epigenetic transcriptional regulator that controls proliferative expansion of immature hematopoietic progenitors, whose aberrant activation triggers leukemogenesis. A mature MLL protein is produced by formation of an intra-molecular complex and proteolytic cleavage. However the biological significance of these two post-transcriptional events remains unclear. To address their in vivo roles, mouse mutant alleles were created that exclusively express either a variant protein incapable of intra-molecular interaction (designated de) or an uncleavable mutant protein (designated uc). The de homozygous mice died during midgestation and manifested devastating failure in embryonic development and reduced numbers of hematopoietic progenitors, whereas uc homozygous mice displayed no apparent defects. Expression of MLL target genes was severely impaired in de homozygous fibroblasts but unaffected in uc homozygous fibroblasts. These results unequivocally demonstrate that intra-molecular complex formation is a crucial maturation step whereas proteolytic cleavage is dispensable for MLL-dependent gene activation and proliferation in vivo.
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    • "Taspase 1 was first identified as the enzyme responsible for the cleavage of the mixed lineage leukemia (MLL) protein, a proteolytic event which is crucial for MLL stabilization and, in consequence, for proper HOX gene expression and MLL-mediated tumorigenesis (Hsieh et al., 2003; Takeda et al., 2006). Taspase 1 is also over-expressed in solid tumors and acts on other regulatory proteins such as transcription factor IIA (TFIIA) or DNA polymerase zeta (DPOLZ), among other substrates (Zhou et al., 2006; Knauer et al., 2011). Interestingly, taspase 1 has been reported to be required for in vitro transformation of mouse embryonic fibroblasts by diverse combinations of oncogene pairs (Takeda et al., 2006), but also to maintain the transformed phenotype of these cells (Chen et al., 2010). "
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