Z Gastroenterol 2015; 53 - KG225
DOI: 10.1055/s-0035-1559251

The inner plasma membrane protein Plac8 regulates cell cycle progression in pancreatic ductal adenocarcinoma (PDAC)

M Buchholz 1, B Kaistha 1, H Lorenz 2, H Schmidt 1, N Weber-Lassalle 1, T Gress 1
  • 1Philipps-Universität Marburg, Klinik für Gastroenterologie, Zentrum für Tumor- und Immunbiologie (ZTI), Marburg, Deutschland
  • 2Universität Heidelberg, ZMBH Imaging Facility, Heidelberg, Deutschland

Introduction: Pancreatic ductal adenocarcinoma (PDA) is the most aggressive pancreatic cancer with an overall 5-year survival rate of < 5%. Despite significant advances in treatment of the disease, the median survival rate (˜6 months) remains unchanged, warranting the need to identify new targets for therapeutic approaches. Our previous transcriptomic analyses as well as parallelized cell-based assays indicated a previously unknown role for Plac8 in pancreatic cancer. Plac8 is a small protein whose physiological functions remain largely unclear. The main aim of this project is to characterize the cellular localization as well as the molecular function of Plac8 PDAC cells.

Methods: Tissue microarrays, RNAi, FLIP-, FRAP-, and TIRF microscopy, cell proliferation and viability assays, FACS analysis, Western blot, transgenic mouse models.

Results: qRT-PCR as well as tissue microarray data confirmed strong ectopic expression of Plac8 in pancreatic cancer tissues. High Plac8 expression is also retained in the majority of pancreatic tumor cell lines in vitro, with negligible expression in non-transformed cell lines. Using TIRF microscopy and FLIP/FRAP experiments we show for the first time that Plac8 locates to the inner face of the plasma membrane and stably interacts with distinct membrane structures. Functionally, proliferation and viability were strongly impaired by Plac8 down-regulation, achieved by transient RNAi mediated-knockdown. Western blot and flow cytometry did not show any involvement of classical apoptosis pathway (Caspase-3 and PARP cleavage). Flow cytometry analyses and time course experiments with cell cycle inhibitors demonstrated strong attenuation of cell cycle progression after loss of Plac8 expression. In vivo, genetic Plac8 deficiency selectively prolonged survival in Kras-driven, but not Kras/p53-driven PDAC mouse models.

Conclusion: Our experimental data show that ectopic expression of Plac8 is indispensable for proliferation, viability and cell cycle progression in pancreatic cancer cells and suggests Plac8 as a potential new therapeutic target in pancreatic ductal adenocarcinoma.