p85α is a microRNA target and affects chemosensitivity in pancreatic cancer

Background: We previously identified a correlation between increased expression of the phosphoinositide 3-kinase (PI3K) regulatory subunit p85 alpha and improved survival in human pancreatic ductal adenocarcinoma (PDAC). The purpose of this study was to investigate the impact of changes in p85 alpha expression on response to chemotherapy and the regulation of p85 alpha by microRNA-21 (miR-21). Materials and methods: PDAC tumor cells overexpressing p85 alpha were generated by viral transduction, and the effect of p85 alpha overexpression on sensitivity to gemcitabine was tested by MTT assay. Primary human PDAC tumors were stained for p85 alpha and miR-21 via immunohistochemistry and in situ hybridization, respectively. Additionally, PDAC cells were treated with miR-21 mimic, and changes in p85 alpha and phospho-AKT were assessed by Western blot. Finally, a luciferase reporter assay system was used to test direct regulation of p85 alpha by miR-21. Results: Higher p85 alpha expression resulted in increased sensitivity to gemcitabine (P < 0.01), which correlated with decreased PI3K-AKT activation. Human tumors demonstrated an inverse correlation between miR-21 and p85 alpha expression levels (r = -0.353, P < 0.001). In vitro, overexpression of miR-21 resulted in decreased levels of p85 alpha and increased phosphorylation of AKT. Luciferase reporter assays confirmed the direct regulation of p85a by miR-21 (P < 0.01). Conclusions: Our results demonstrate that p85 alpha expression is a determinant of chemosensitivity in PDAC. Additionally, we provide novel evidence that miR-21 can influence PI3K-AKT signaling via its direct regulation of p85 alpha. These data provide insight into potential mechanisms for the known relationship between increased p85 alpha expression and improved survival in PDAC. (C) 2015 Elsevier Inc. All rights reserved.