Background and aims c-Myc is highly expressed in pancreatic multipotent progenitor cells (MPC) and in pancreatic cancer. The transition from MPC to unipotent acinar progenitors is associated with c-Myc downregulation; a role for c-Myc in this process, and its possible relationship to a role in cancer, has not been established.
Design Using coimmunoprecipitation assays, we demonstrate that c-Myc and Ptf1a interact. Using reverse transcriptase qPCR, western blot and immunofluorescence, we show the erosion of the acinar programme. To analyse the genomic distribution of c-Myc and Ptf1a and the global transcriptomic profile, we used ChIP-seq and RNA-seq, respectively; validation was performed with ChIP-qPCR and RT-qPCR. Lineage-tracing experiments were used to follow the effect of c-Myc overexpression in preacinar cells on acinar differentiation.
Results c-Myc binds and represses the transcriptional activity of Ptf1a. c-Myc overexpression in preacinar cells leads to a massive erosion of differentiation. In adult Ela1-Myc mice: (1) c-Myc binds to Ptf1a, and Tcf3 is downregulated; (2) Ptf1a and c-Myc display partially overlapping chromatin occupancy but do not bind the same E-boxes; (3) at the proximal promoter of genes coding for digestive enzymes, we find reduced PTF1 binding and increased levels of repressive chromatin marks and PRC2 complex components. Lineage tracing of committed acinar precursors reveals that c-Myc overexpression does not restore multipotency but allows the persistence of a preacinar-like cell population. In addition, mutant KRas can lead to c-Myc overexpression and acinar dysregulation.
Conclusions c-Myc repression during development is crucial for the maturation of preacinar cells, and c-Myc overexpression can contribute to pancreatic carcinogenesis through the induction of a dedifferentiated state.
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Contributors VJS-AL designed and performed the majority of the experiments. LCF and DM performed the immunofluorescence experiments and quantification in TMX-treated mice. EC-d-S-P was responsible for bioinformatics analysis. LR performed reporter assays. IC performed endogenous coimmunoprecipitations with pancreatic tissue. JC contributed to the RT-qPCR and immunofluorescence experiments. UM performed ChIP to show the co-occupancy between c-Myc and Ptf1a. NdP contributed to the mouse experiments. BB, CVW and MM provided important reagents for the study. VJS-AL and FXR designed and supervised the overall conduct of the study. FXR obtained financial support.
Funding This work was supported, in part, by grants from Ministerio de Economía y Competitividad, Madrid, Spain (SAF2007-60860, SAF2011-29530 and ONCOBIO Consolider), Instituto de Salud Carlos III, Madrid, Spain (RTICC RD12/0036/0034, partially funded by the European Regional Fund), Comunidad Autónoma de Madrid (grant CEL-DD) and European Union Seventh Framework Programme (grants 256974 and 289737) to FX.R. LCF was supported by a Marie Curie Training Grant (FP7-PEOPLE-2010-IEF, project 274946). IC was recipient of a Beca de Formación del Personal Investigador (MINECO, Madrid, Spain). JC was recipient of a grant from the La Caixa International PhD programme. UM was supported by a Beca Mixta CONACyT México, MZO2015.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement All data generated through the work reported in this manuscript are fully available either through public databases or upon request to the authors.
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