The pancreatic and duodenal homeobox protein PDX-1 regulates the ductal specific keratin 19 through the degradation of MEIS1 and DNA binding.
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.
von Burstin
Johannes
J
Division of Gastroenterology, Department of Medicine and Genetics, Abramson Cancer Center, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
Reichert
Maximilian
M
Wescott
Melanie P
MP
Rustgi
Anil K
AK
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
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
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