J. Lazarus1, M. Perusina Lanfranca1, W. Wang1, T. Maj1, W. Zou1, T. Frankel1 1University Of Michigan,Ann Arbor, MI, USA
Introduction:
Pancreatic cancer (PDAC) is the 3rd leading cause of cancer death in the United States. Patients diagnosed with PDAC have a poor 5-year survival which has not significantly improved in decades. Chemotherapy, including platinum based agents, is often ineffective and the development of chemo-resistance is common. Recent data has shown that interleukin-22 (IL-22), a cytokine produced by immune cells which acts primarily on epithelial cells, is associated with a worse prognosis in PDAC. We hypothesize that IL-22 enhances chemoresistance leading to the observed impairment in survival.
Methods:
PDAC cells were incubated with and without IL-22 for 3 days followed by cisplatin treatment for 24 hours. Cell death was determined by propidium iodide (PI) staining. Apoptosis was assessed by annexin V staining by flow cytometry and immunoblotting for cleaved caspase 3 (cCASP3). Cisplatin mediated DNA damage was evaluated by western blot for the DNA damage marker γH2AX. Genes and proteins involved in apoptosis, DNA damage recognition and repair were assessed by rtPCR and western blotting, respectively.
Results:
Cells pretreated with IL-22 exhibited less platinum chemotherapy-mediated cell death compared to controls as determined by PI staining. In particular, IL-22 decreased the number of cisplatin-induced apoptotic cells and inhibited cCASP3. To investigate the mechanism of IL-22 protection, we first examined differences in apoptotic related gene expression and determined no appreciable differences in Bcl-2, Bcl-xL, caspase 3, and BAX. However, we found cisplatin-induced γH2AX was decreased significantly following IL-22 pre-treatment, suggesting IL-22 controls cisplatin resistance at the DNA damage response level. The role of IL-22 in DNA damage response was investigated by examining expression of genes involved in homologous recombination, non-homologous end-joining, base excision repair and nucleotide excision repair. Data revealed that IL-22 increased gene expression of BRCA2 and PARP in cells also treated with cisplatin.
Conclusion:
Elevated IL-22 is associated with a poor prognosis in pancreas cancer. We determined that IL-22 protected PDAC cells from platinum induced cell death by enhancing DNA damage repair by homologous recombination and base excision repair as evidenced by decreased γH2AX and up-regulation of BRCA2 and PARP. Strategies to derail DNA damage repair in tumors with a high level of IL-22 may improve sensitivity to chemotherapy and subsequently survival.