Cytoplasmic TRAIL-R1 is a positive prognostic marker in PDAC

Background: The death receptors TRAIL-R1 and TRAIL-R2 are frequently overexpressed in cancer and there is an emerging evidence for their important role in malignant progression, also in the case of pancreatic ductal adenocarcinoma (PDAC). In their canonical localization at the plasma membrane, TRAIL-R1/-R2 may induce cell death and/or pro-inflammatory signaling leading to cell migration, invasion and metastasis. Although, they have repeatedly been found intracellular, in the cytoplasm and in the nucleus, their functions in intracellular locations are still not well understood. Likewise, studies dealing with the prognostic relevance of TRAIL-Rs located in particular cellular compartments are very rare. For PDAC, the correlation of nuclear TRAIL-R2 with worse patients' prognosis has been shown recently. Corresponding data on TRAIL-R1 are not available so far. Methods: In the present study we analyzed the expression of TRAIL-R1 in 106 PDACs and 28 adjacent, peritumoral non-malignant pancreatic ducts with special emphasis on its cytoplasmic and nuclear localization and correlated the immunohistochemical findings with clinico-pathological patient characteristics. Results: TRAIL-R1 was found in 93.4% of all PDAC samples. Cytoplasmic staining was present with very similar intensity in tumor and normal tissue. In contrast, nuclear TRAIL-R1 staining was significantly stronger in tumor compared to normal tissue (p=0.006). Interestingly, we found that the number of cells with cytoplasmic TRAIL-R1 staining negatively correlates with tumor grading (p=0.043). No such correlation could be detected for nuclear TRAIL-R1. Neither, cytoplasmic nor nuclear TRAIL-R1 staining showed a correlation with other clinico-pathological parameter such as pTNM categories. However, Kaplan-Meier analyses revealed significantly prolonged median survival of patients with positive cytoplasmic TRAIL-R1 expression in more than 80% of tumor cells compared to patients with tumors containing a smaller quantity of cells positively stained for cytoplasmic TRAIL-R1 (20 vs. 8months; p=0.004). Conclusion: Cytoplasmic TRAIL-R1 is a positive prognostic marker for patients with PDAC. Our findings indicate that loss of cytoplasmic TRAIL-R1 results in recurrent disease with more malignant phenotype thus suggesting anti-tumor activities of cytoplasmic TRAIL-R1 in PDAC.