ICAT is a novel Ptf1a interactor that regulates pancreatic acinar differentiation and displays altered expression in tumours.

The PTF1 (pancreas transcription factor 1) complex is a master regulator of differentiation of acinar cells, responsible for the production of digestive enzymes. In the adult pancreas, PTF1 contains two pancreas-restricted transcription factors: Ptf1a and Rbpjl. PTF1 recruits P/CAF [p300/CREB (cAMP-response-element-binding protein)-binding protein-associated factor] which acetylates Ptf1a and enhances its transcriptional activity. Using yeast two-hybrid screening, we identified ICAT (inhibitor of ß-catenin and Tcf4) as a novel Ptf1a interactor. ICAT regulates the Wnt pathway and cell proliferation. We validated and mapped the ICAT-Ptf1a interaction in vitro and in vivo. We demonstrated that, following its overexpression in acinar tumour cells, ICAT regulates negatively PTF1 activity in vitro and in vivo. This effect was independent of ß-catenin and was mediated by direct binding to Ptf1a and displacement of P/CAF. ICAT also modulated the expression of Pdx1 and Sox9 in acinar tumour cells. ICAT overexpression reduced the interaction of Ptf1a with Rbpjl and P/CAF and impaired Ptf1a acetylation by P/CAF. ICAT did not affect the subcellular localization of Ptf1a. In human pancreas, ICAT displayed a cell-type-specific distribution; in acinar and endocrine cells, it was nuclear, whereas in ductal cells, it was cytoplasmic. In ductal adenocarcinomas, ICAT displayed mainly a nuclear or mixed distribution and the former was an independent marker of survival. ICAT regulates acinar differentiation and it does so through a novel Wnt pathway-independent mechanism that may contribute to pancreatic disease.

Valor del ensayo de las cadenas ligeras libres en suero para los pacientes de gammapatías monoclonales e insuficiencia renal / The value of serum free light chain assay in patients with monoclonal gammopathies and renal failure

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Unique mechanisms of growth regulation and tumor suppression upon Apc inactivation in the pancreas.

beta-catenin signaling is heavily involved in organogenesis. Here, we investigated how pancreas differentiation, growth and homeostasis are affected following inactivation of an endogenous inhibitor of beta-catenin, adenomatous polyposis coli (Apc). In adult mice, Apc-deficient pancreata were enlarged, solely as a result of hyperplasia of acinar cells, which accumulated beta-catenin, with the sparing of islets. Expression of a target of beta-catenin, the proto-oncogene c-myc (Myc), was increased in acinar cells lacking Apc, suggesting that c-myc expression is essential for hyperplasia. In support of this hypothesis, we found that conditional inactivation of c-myc in pancreata lacking Apc completely reversed the acinar hyperplasia. Apc loss in organs such as the liver, colon and kidney, as well as experimental misexpression of c-myc in pancreatic acinar cells, led to tumor formation with high penetrance. Surprisingly, pancreas tumors failed to develop following conditional pancreas Apc inactivation. In Apc-deficient acini of aged mice, our studies revealed a cessation of their exaggerated proliferation and a reduced expression of c-myc, in spite of the persistent accumulation of beta-catenin. In conclusion, our work shows that beta-catenin modulation of c-myc is an essential regulator of acinar growth control, and unveils an unprecedented example of Apc requirement in the pancreas that is both temporally restricted and cell-specific. This provides new insights into the mechanisms of tumor pathogenesis and tumor suppression in the pancreas.