title: The pancreatic and duodenal homeobox protein PDX-1 regulates the ductal specific keratin 19 through the degradation of MEIS1 and DNA binding.
abstract: BACKGROUND
  Pancreas organogenesis is the result of well-orchestrated and balanced activities of transcription factors. The homeobox transcription factor PDX-1 plays a crucial role in the development and function of the pancreas, both in the maintenance of progenitor cells and in determination and maintenance of differentiated endocrine cells. However, the activity of homeobox transcription factors requires coordination with co-factors, such as PBX and MEIS proteins. PBX and MEIS proteins belong to the family of three amino acid loop extension (TALE) homeodomain proteins. In a previous study we found that PDX-1 negatively regulates the transcriptional activity of the ductal specific keratin 19 (Krt19). In this study, we investigate the role of different domains of PDX-1 and elucidate the functional interplay of PDX-1 and MEIS1 necessary for Krt19 regulation.
  
  
  RESULTS
  Here, we demonstrate that PDX-1 exerts a dual manner of regulation of Krt19 transcriptional activity. Deletion studies highlight that the NH(2)-terminus of PDX-1 is functionally relevant for the down-regulation of Krt19, as it is required for DNA binding of PDX-1 to the Krt19 promoter. Moreover, this effect occurs independently of PBX. Second, we provide insight on how PDX-1 regulates the Hox co-factor MEIS1 post-transcriptionally. We find specific binding of MEIS1 and MEIS2 to the Krt19 promoter using IP-EMSA, and siRNA mediated silencing of Meis1, but not Meis2, reduces transcriptional activation of Krt19 in primary pancreatic ductal cells. Over-expression of PDX-1 leads to a decreased level of MEIS1 protein, and this decrease is prevented by inhibition of the proteasome.
  
  
  CONCLUSIONS
  Taken together, our data provide evidence for a dual mechanism of how PDX-1 negatively regulates Krt19 ductal specific gene expression. These findings imply that transcription factors may efficiently regulate target gene expression through diverse, non-redundant mechanisms.
authors.affiliation: Division of Gastroenterology, Department of Medicine and Genetics, Abramson Cancer Center, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Johannes
authors.initials: J
authors.lastname: von Burstin
authors.forename: Maximilian
authors.initials: M
authors.lastname: Reichert
authors.forename: Melanie P
authors.initials: MP
authors.lastname: Wescott
authors.forename: Anil K
authors.initials: AK
authors.lastname: Rustgi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D015536:Down-Regulation; D017930:Genes, Reporter / Q000235:genetics; D018398:Homeodomain Proteins / Q000737:chemistry / Q000378:metabolism*; D053539:Keratin-19 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism*; D009928:Organ Specificity; D010183:Pancreatic Ducts / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D020033:Protein Isoforms / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D018398:Homeodomain Proteins; D053539:Keratin-19; C000616392:Meis1 protein, mouse; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D004247:DNA
references.citation: J Biol Chem. 2000 Sep 8;275(36):28230-9
references.pmid: 10859317
references.citation: Dev Biol. 2009 Feb 1;326(1):4-35
references.pmid: 19013144
references.citation: Dev Biol. 2006 Dec 15;300(2):748-57
references.pmid: 17049510
references.citation: J Cell Biol. 2006 Jul 17;174(2):169-74
references.pmid: 16831889
references.citation: Mol Cell Biol. 1995 Oct;15(10):5434-43
references.pmid: 7565694
references.citation: Leukemia. 2008 Mar;22(3):665-7
references.pmid: 17805329
references.citation: Science. 2008 Dec 5;322(5907):1490-4
references.pmid: 19056973
references.citation: Proc Natl Acad Sci U S A. 2004 Feb 10;101(6):1662-7
references.pmid: 14757827
references.citation: Gastroenterology. 2004 Jul;127(1):250-60
references.pmid: 15236190
references.citation: Development. 1996 Mar;122(3):983-95
references.pmid: 8631275
references.citation: J Biol Chem. 2000 Jun 16;275(24):18000-10
references.pmid: 10748030
references.citation: Mol Cell Biol. 2000 Nov;20(22):8623-33
references.pmid: 11046157
references.citation: Proc Natl Acad Sci U S A. 2001 Jan 30;98(3):1065-70
references.pmid: 11158595
references.citation: Mol Cell Biol. 1997 Jul;17(7):3987-96
references.pmid: 9199333
references.citation: Gastroenterology. 2009 Jul;137(1):361-71, 371.e1-5
references.pmid: 19362090
references.citation: Development. 1996 May;122(5):1409-16
references.pmid: 8625829
references.citation: J Biol Chem. 2006 Dec 15;281(50):38385-95
references.pmid: 17056599
references.citation: Dev Biol. 2006 Mar 15;291(2):193-206
references.pmid: 16515781
references.citation: Nature. 1994 Oct 13;371(6498):606-9
references.pmid: 7935793
references.citation: Mol Cell Biol. 2003 Oct;23(20):7425-36
references.pmid: 14517309
references.citation: Genes Dev. 1997 Apr 15;11(8):957-72
references.pmid: 9136925
references.citation: Mol Cell Biol. 1999 Apr;19(4):3051-61
references.pmid: 10082572
references.citation: Proc Natl Acad Sci U S A. 2002 Oct 1;99(20):13125-30
references.pmid: 12232053
references.citation: Biochim Biophys Acta. 2008 Dec;1786(2):153-77
references.pmid: 18558098
references.citation: Proc Natl Acad Sci U S A. 2009 Nov 10;106(45):19090-5
references.pmid: 19855005
references.citation: FEBS Lett. 1998 Jul 24;431(3):362-6
references.pmid: 9714543
references.citation: J Biol Chem. 2004 Dec 24;279(52):54241-7
references.pmid: 15496408
references.citation: Dev Biol. 2010 Apr 15;340(2):306-17
references.pmid: 20123093
references.citation: Genes Dev. 2005 Feb 1;19(3):316-21
references.pmid: 15687255
references.citation: Dev Biol. 2005 Oct 1;286(1):225-37
references.pmid: 16126192
references.citation: Development. 2008 Mar;135(5):805-11
references.pmid: 18216174
references.citation: Mol Biol Cell. 2009 Nov;20(22):4838-44
references.pmid: 19793922
references.citation: Trends Cell Biol. 2005 Nov;15(11):608-17
references.pmid: 16202602
references.citation: Trends Endocrinol Metab. 1997 May-Jun;8(4):145-51
references.pmid: 18406800
references.citation: J Virol. 2005 Dec;79(24):15302-13
references.pmid: 16306601
references.citation: Mol Cell Biol. 2002 Jan;22(2):412-20
references.pmid: 11756538
references.citation: J Biol Chem. 2002 Jul 12;277(28):25798-814
references.pmid: 11960979
references.citation: Proc Natl Acad Sci U S A. 1994 May 10;91(10):4509-13
references.pmid: 8183939
references.citation: Mol Cell Biol. 1999 Nov;19(11):7577-88
references.pmid: 10523646
references.citation: Dev Cell. 2009 Oct;17(4):561-7
references.pmid: 19853569
references.citation: Biochem J. 2009 Dec 14;425(1):107-16
references.pmid: 19799567
references.citation: Genome Res. 1997 Feb;7(2):142-56
references.pmid: 9049632
references.citation: Cell. 1982 Nov;31(1):11-24
references.pmid: 6186379
references.citation: EMBO J. 2004 Jan 28;23(2):450-9
references.pmid: 14713950
references.citation: Nat Genet. 2002 Apr;30(4):430-5
references.pmid: 11912494
references.citation: Mol Endocrinol. 1991 Jul;5(7):897-904
references.pmid: 1944296