Human homologues of PIWI proteins identified are PIWIL1, PIWIL2, PIWIL3 and PIWIL4 (Sasaki et al. 2003). Aberrant expression of these proteins has been associated with hallmarks of cancer, and have also a potential prognostic and diagnostic markers for different cancers (Suzuki et al. 2012). However, their functional and clinical significance in pancreatic ductal adenocarcinoma (PDAC) remains unknown. The purpose of this study was to dissect the role of PIWI proteins and their prognostic relevance.
PIWI proteins expression were analyzed by western blot in human PDAC derived cell lines and one non-transformed pancreatic cell line. Functional experiments were performed with PIWIL3 and/or PIWIL4 downregulated PDAC derived cell lines and one non-transformed cell line. Immunohistochemistry was performed to evaluate expression of PIWI proteins in 124 PDAC samples from Fundacion Jimenez Diaz Hospital, and with 124 validation cohort from TGCA. Then, association between PIWI proteins expression and survival was assessed.
Only PIWIL3 and PIWIL4 showed differential expression in PDAC cell lines. Both wound-healing and transwell assay showed a decrease in migration ratio after PIWIL3 and/or PIWIL4 downregulation (P < 0.05). Furthermore, both PIWIL3 and/or PIWIL4 are necessary for the maintenance of undifferentiated phenotype highlighted by a reduction in size and number of pancreatic spheres after PIWIL3 and/or PIWIL4 downregulation (P < 0.05). On the other hand, PIWIL1 associated with shorter survival (P = 0.056), and this finding was validated in the TGCA cohort (P = 0.021). PIWIL2 associated significantly to shorter survival (P = 0.046) in our training set, and validation set exhibited a high trend toward significance (P = 0.051). Although PIWIL3 and PIWIL4 did not show association with survival in our training set, validation set revealed a statistically significant association of PIWIL4 with shorter overall survival (P = 0.027).
The present study demonstrate that PIWIL3 and PIWIL4 regulates PDAC aggressiveness by inhibiting cell migration and regulate undifferentiated phenotype of cancer cells. Furthermore, PIWIL1, PIWIL2 and PIWIL4 are potential prognostic biomarkers in PDAC.
Fundación Instituto de Investigación Sanitaria - Fundación Jiménez Díaz (G-85874949).
Spanish Ministry of Economy and Competitiveness.
All authors have declared no conflicts of interest.