Dissection of the Transactivation Function of the Transcription Factor Encoded by the Eye Developmental Gene PAX6

Tang, Hank Kejun; Singh, Sanjaya; Saunders, Grady F.

doi:10.1074/jbc.273.13.7210

Cited by 85 publications

(78 citation statements)

References 49 publications

(48 reference statements)

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“…Pax-6 contains an unusually long transactivation domain (TAD) suggesting that it could provide interaction surfaces for several cofactors [48,49]. Synergistic interaction of Pax-6 and Cdx-2/3 with the p300 coactivator has been demonstrated [43] but it is not likely that Pax-4 inhibits Pax-6 mediated transcriptional activation by interfering with p300 binding because Cdx-2/3-induced transcription is not impaired by Pax-4.…”

Section: Discussionmentioning

confidence: 99%

The pancreatic beta-cell-specific transcription factor Pax-4 inhibits glucagon gene expression through Pax-6

et al. 2002

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The endocrine pancreas is organised as islets of Langerhans embedded in the exocrine tissue and is composed of four cell types: beta, a, d, and g cells producing insulin, glucagon, somatostatin and the pancreatic polypeptide (PP), respectively. Gene knockout studies have shown the involvement of a variety of transcription factors in pancreas development. Null mutations of the homeodomain proteins pdx-1 and isl-1 result in pancreatic agenesis and the absence of the islets of Langerhans, respectively [1,2]. The lack of Beta2, Pax-6, Pax-4, Nk 2.2, and Nk 6.1 affects the organisation of the endocrine pancreas and the number of endocrine cells or both [3±9]. The formation of specific islet cell types can be affected by the absence of any of these factors: no or few glucagon-producing a cells are observed in homozygous pax-6 mutants, whereas pax-4 knockout mice lack beta and d cells; nk 2.2 and nk 6.1 mu-The pancreatic beta-cell-specific transcription factor Pax-4 inhibits glucagon gene expression through Pax-6 Abstract Aims/hypothesis. The paired-homeobox genes pax-4 and pax-6 are crucial for islet development; whereas the null mutation of pax-6 results in the nearly absence of glucagon-producing a cells, pax-4 homozygous mutant mice lack insulin and somatostatin-producing beta and d cells but contain an increased number of a cells suggesting that a cells could develop by a default mechanism. Methods. To investigate whether beta-cell specific factors act negatively on glucagon gene transcription, we ectopically expressed pax-4 in glucagon producing InR1G9 cells; Pax-4 inhibited basal transcription of the glucagon gene promoter by 60 %. To assess the mechanism of this inhibition, we cotransfected the non-islet cell line BHK-21 with Pax-4 and various transcription factors present in a cells.Results. In addition to a general repressor activity on basal glucagon gene promoter activity of 30±50 %, a specific 90 % inhibition of Pax-6 mediated transactivation was observed. In contrast, Pax-4 had no effect on Cdx-2/3 or HNF3a mediated transcriptional activation. Pax-4 showed similar affinity to the Pax-6 binding sites on the glucagon gene promoter compared to Pax-6, but varying with KCl concentrations. Conclusion/interpretation. Pax-4 impairs glucagon gene transcription specifically through inhibition of Pax-6 mediated transactivation. Transcriptional inhibition seems to be mediated by direct DNA binding competition with Pax-6 and potentially additional mechanisms such as protein-protein interactions and a general repressor activity of Pax-4. Glucagon gene expression in a cells could thus result from both the presence of islet cell specific transcription factors and the absence of Pax-4. [Diabetologia (2002) 45: 97±107]

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Section: Discussionmentioning

confidence: 99%

The pancreatic beta-cell-specific transcription factor Pax-4 inhibits glucagon gene expression through Pax-6

et al. 2002

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“…The PDs of other genes of the Pax family, the Pax2, Pax3, and the binding sequence of Pax-5 (BSAP), and Pax6 proteins can recognize similar DNA sequences (12, 34 -39). Our earlier studies showed that the transactivation function is distributed throughout the PST region (40). Although the involvement of PAX6 in ocular development is well known (41,42), identification of target genes of PAX6 has been hindered by two factors.…”

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confidence: 99%

“…Functional studies using PAX6 missense mutations with observed developmental defects are useful in understanding the mechanism of PAX6 function. Missense mutations in the DNA-binding domains of PAX6 may cause failure to properly recognize binding sites in the target genes, resulting in partial or complete loss of protein function (40,(47)(48)(49).…”

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confidence: 99%

PAX6, Paired Domain Influences Sequence Recognition by the Homeodomain

Shukla

Gorlov

Chao

et al. 2002

Journal of Biological Chemistry

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PAX6 functions as a transcription factor and has two DNA-binding domains, a paired domain (PD) and a homeodomain (HD), joined by a glycine-rich linker and followed by a proline-serine-threonine-rich (PST) transactivation region at the C terminus. The mechanism of PAX6 function is not clearly understood, and few target genes in vertebrates have been identified. In this report we described the functional analyses of patient missense mutations from the paired domain region of PAX6 and a paireddomain-less isoform (PD-less) of Pax6 that lacks the paired domain and part of the glycine-rich linker. The PD-less was expressed in the brain, eyes, and pancreas of mouse. The level of expression of this isoform was relatively higher in brain. The mutation sites PAX6-L46R and -C52R were located in the PD of PAX6 on either end of the 5a-polypeptide insert of the alternatively spliced form of PAX6, PAX6-5a. Another PAX6 mutant V53L described in this report was adjacent to C52R. We created corresponding mutations in PAX6 and PAX6-5a, and evaluated their transcriptional activation and DNA binding properties. The PD mutants of PAX6 (L46R, C52R, and V53L) exhibited lower transactivation activities and variable DNA binding ability than wildtype PAX6 with PD DNA-binding consensus sequences. The mutated amino acids containing PAX6-5a isoforms showed unexpected transactivation properties with a reporter containing HD DNA-binding sequences. PAX6-5a-C52R, and -V53L showed lower transactivation activities, but PAX6-5a-L46R had greater transactivation ability than PAX6-5a. The PD-less isoform of Pax6 lost its transactivational ability but could bind to the HD DNAbinding sequences. Functional analysis of the PD-less isoform of Pax6 as well as findings related to missense mutations in the PD suggest that the PD of PAX6 is required for HD function.

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“…21 Furthermore, in the C-terminal part of the protein there is a proline, serine and threonine rich (PST) domain of 152 amino acids 3 which resembles the activation domain of transcription factors CTF-1 (CAAT-box binding transcription factor) 22 and Oct2, 23 and has been shown to possess transcriptional activity in vitro. 12,24,25 Quail Pax-6 has been shown to transactivate its own promoter, 26 and Pax-6 from mouse, chicken and guinea pig was shown to be involved in transcriptional regulation of crystallin genes. 27 Pax-6 belongs to the Pax family of developmental control factors 28 all possessing the paired domain originally identified in the Drosophila melanogaster segmentation gene paired.…”

Section: Introductionmentioning

confidence: 99%

Mutational analysis of PAX6: 16 novel mutations including 5 missense mutations with a mild aniridia phenotype

Grønskov

Rosenberg²,

Sand

et al. 1999

Eur J Hum Genet

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Mutations in the developmental control gene PAX6 have been shown to be the genetic cause of aniridia, which is a severe panocular eye disease characterised by iris hypoplasia. The inheritance is autosomal dominant with high penetrance but variable expressivity. Here we describe a mutational analysis of 27 Danish patients using a dideoxy fingerprinting method, which identified PAX6 mutations in 18 individuals with aniridia. A thorough phenotype description was made for the 18 patients. A total of 19 mutations, of which 16 were novel, are described. Among these were five missense mutations which tended to be associated with a milder aniridia phenotype, and in fact one of them seemed to be non-penetrant. Four of the five missense mutations were located in the paired domain. We also describe a third alternative spliced PAX6 isoform in which two of the four missense mutations would be spliced out. Our observations support the concept of dosage effects of PAX6 mutations as well as presenting evidence for variable expressivity and gonadal mosaicism.

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Dissection of the Transactivation Function of the Transcription Factor Encoded by the Eye Developmental Gene PAX6

Cited by 85 publications

References 49 publications

The pancreatic beta-cell-specific transcription factor Pax-4 inhibits glucagon gene expression through Pax-6

The pancreatic beta-cell-specific transcription factor Pax-4 inhibits glucagon gene expression through Pax-6

PAX6, Paired Domain Influences Sequence Recognition by the Homeodomain

Mutational analysis of PAX6: 16 novel mutations including 5 missense mutations with a mild aniridia phenotype

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