Results: HAT-7 cells formed epithelial layers with measureable TER on Transwell permeable supports, and expressed key tight junction proteins claudin-1, -4 and -8. Transport proteins described in maturation amelo- blasts were also present in HAT-7 cells. By microfluorometry we found that the cells were polarized with a high apical membrane CO 2 permeability and vigorous basolateral HCO 3 - uptake which was sensitive to Na þ with- drawal, to the carbonic anhydrase inhibitor acetazolamide and to H 2 DIDS inhibition. Measurements of transepithelial HCO 3 - transport showed a marked increase in response to Ca 2þ - and cAMP-mobilizing stimuli. Taken together, these studies provide evidence for a regulated, vectorial, baso- lateral to apical bicarbonate transport in polarized HAT-7 cells. Conclusion: We propose that the HAT-7 cell line is a useful functional model for studying electrolyte transport of ameloblasts. Supported by NIH-NIDCR (5R01DE013508subaward:7743sc), TAMOP- 4.2.1/B-09/1/KMR-2010-0001, TAMOP-4.2.2/B-10/1-2010-0013. 890. c-Myc downregulation is required for pre-acinar to acinar cell maturation Victor Javier Sanchez-Arevalo 1 , Luis Cesar Fernandez 1 , Laia Richart 1 , Enrique Carrillo 1 , Ulises Moreno 2 , Jaroslav Cendrovski 3 , Francisco X. Real 1 1 CNIO, Madrid, Spain 2 University of Queretaro, Mexico 3 International Institute of Molecular and Cell Biology, Warsaw, Poland Introduction: Multipotent pancreatic progenitors (MPC) can be detected in the embryo and are defined as Ptf1a þ , Myc high , Cpa þ cells. During the transition from MPC to unipotent acinar progenitors, c-Myc is down-regulated whereas Ptf1a is up-regulated, leading to the amplifica- tion of the acinar program. Aims: To determine the role of c-MYC in acinar cell maturation. Patients & methods: Co-immunoprecipitation, lineage tracing, RNA- Seq, and chromatin immunoprecipitation (ChIP). Results: c-MYC and PTF1A interact directly and c-MYC binds to, and represses, the transcriptional activity of the PTF1 complex in vitro. Using Ela1-Myc mice in which c-Myc is overexpressed in acinar cells starting at E14.5, we find incomplete acinar maturation at P1 followed by a massive subsequent repression of the acinar programme. Lineage tracing with Ptf1a CreERT2 ;Rosa26 YFP and Ela-Myc;Ptf1a CreERT2 ;Rosa26 YFP mice receiving TMX at E15.5 and analyzed at E18.5 revealed that c-Myc overexpression results in a blockade of acinar cell maturation without evidence of lineage misspecification. At 8 weeks age, the silencing of the acinar program is associated with increased expression of the PRC2 complex in a c-MYC dependent manner. Genome wide studies show that PTF1A and c-MYC display partially overlapping chromatin occupancy patterns and ChIP- qPCR demostrates DNA binding competition. Conclusion: c-MYC down-regulation during development is crucial for the progression of pre-acinar to acinar cells. c-MYC overexpression may contribute to pancreatic carcinogenesis by maintaining an undifferenti- ated state rendering cells susceptible to transformation. 1151. Schwann cell-associated adhesion molecules beta-1-Integrin, L1CAM, N-Cadherin and PMP22 enhance pancreatic cancer cell adhesion during neural invasion in pancreatic cancer Lea Krauss, Ihsan Ekin Demir, Eva Brunner, Natascha Klose, Helmut Friess, Güralp O. Ceyhan Department of Surgery, Klinikum Rechts der Isar, TU München, Germany Introduction: Neural Invasion (NI) represents a prognostic factor for the overall survival and the rate of local recurrence of pancreatic cancer (PCa). For NI to occur, a direct adhesion of PCa cells (PCC) to nerves is needed. Aims: Here, we investigated whether an adhesion takes place between Schwann cells (SC) and PCC during NI in PCa. Materials & methods: Expression of SC- and PCC-associated adhesion molecules Beta-1-Integrin, L1CAM, N-Cadherin and Peripheral-Myelin- Protein-22 (PMP22) was examined via immunohistochemistry, immuno- cytofluorescence, immunoblotting and quantitative-RT-PCR in PCa tissues, SC and human PCC. In vitro-adhesion assays and 3D-migration-assays were performed to study the heterotypic adhesion between SC and PCC. MCherry-transduced murine PCC were tracked via digital-time-lapse-mi- croscopy after their injection into the murine sciatic nerve either before or after demyelination with lysolecithin. Results: Beta-1-Integrin, L1CAM and N-Cadherin were detected on SC and PCC on mRNA and protein level. Intrapancreatic nerves were strongly immunoreactive for SC adhesion molecules. Nerves with increasing NI- severity exhibited stronger N-Cadherin and PMP22 immunoreactivity. In comparison, the expression of Beta-1-Integrin and N-Cadherin in SC was around 10,000-fold higher than that of L1CAM and PMP22. In vitro blockade of Beta-1-Integrin, L1CAM and N-Cadherin on SC and PCC led to reduced adhesion between SC and PCC and diminished the migration of SC toward PCC. Demyelination of the sciatic nerve modulated the perineural migration pattern of injected PCC. Conclusion: Adhesion between SC and PCC in the NI of PCa seems to be mediated by Beta-1-Integrin, L1CAM and N-Cadherin. Therapeutic blockade of these molecules may result in a prognostic improvement in PCa. 919. Nr5a2 restrains an inflammatory program in the pancreas through the regulation of AP-1 activity Isidoro Cobo 1 , Paola Martinelli 2 , Enrique Carrillo 1 , Latifa Bakiri 1 , Erwin Wagner 1 , Francisco X. Real 1 1 CNIO, Spain 2 Medical University of Viena, Austria Introduction: The orphan nuclear receptor Nr5a2 participates in ste- roid metabolism, replaces Oct4 during reprogramming, and regulates the pancreatic exocrine program. SNPs in the vicinity of NR5A2 are associated with pancreas cancer risk. Adult Nr5a2þ/- mice have a histologically normal pancreas but recover poorly from damage and Nr5a2 hap- loinsufficiency cooperates with mutant KRas and pancreatitis in driving tumor progression. Aims: To identify the mechanisms underlying the coopearation be- tween Nr5a2, inflammation and mutanta KRas in pancreatic cancer progression. Materials & methods: RNA-Seq and Chromatin Immunoprecipitation was utilised. Western Blot and Immunohistochemistry was performed for protein detection. Co-immunoprecipitation was also used Results: RNA-Seq of wild type and Nr5a2þ/- pancreata uncovered a pre-proinflammatory phenotype in the latter. Bioinformatics analyses showed an enrichment of AP-1 binding motifs around the TSS of genes upregulated in Nr5a2þ/- pancreata. c-Jun, Junb, Jund, and c-Fos mRNA and protein levels were significantly higher in Nr5a2þ/- pancreata. In wt mice, chromatin immunoprecipitation showed that Nr5a2 and its co-repressor partner Nr0b2 bind to the promoter of c-Jun, Junb, and Jund. Moreover, Nr0b2 modulated the effects of Nr5a2 on a c-Jun reporter promoter construct in vitro. In Nr5a2þ/- mice, we observed increased Nr5a2 and AP- 1 binding to the promoter of inflammatory genes. Endogenous co-immu- noprecipitation demonstrated that Nr5a2 and AP-1 members are present in the same complex. Conclusion: In the pancreas, Nr5a2 not only regulates exocrine dif- ferentiation but also an anti-inflammatory program, the latter through the direct repression of AP-1 components. This mechanism is lost in Nr5a2þ/- mice and may contribute to explain the reported tumor suppressive role of Nr5a2. Abstracts / Pancreatology 15 (2015) S1eS141 S47