Abstract 3539: The noncoding PTEN pseudogene influences PI3K signaling and inhibits breast cancer progression

Abstract

Abstract The PTEN pseudogene is a non-coding RNA, reported to function as a decoy for microRNAs (miRNAs) degrading PTEN mRNA. The purpose of this study was to examine PTENP1 expression and its influence on PTEN expression and PI3K-Akt-mTOR signaling in human breast cancer. Tumor samples from 30 patients with locally advanced breast cancer were examined for PTEN and PTENP1 expression before and after treatment, and the results were correlated to tumor response rates. Furthermore, the human PTENP1 positive MDA-MB231 and the murine PTENP1 negative C3HBA breast cancer cell lines were lentivirally transfected with PTENP1 to assess the effects of PTENP1 overexpression on cell proliferation in vitro, tumor growth in mice, as well as its influence on PTEN and PI3K-Akt-mTOR signaling. Knockdown of PTENP1 by siRNA in MDA-MB231 cells was performed to examine how down regulated gene expression of the pseudogene would affect PTEN. To evaluate PTENP1-associated miRNAs, RNA sequencing from MDA-MB231 transfected with PTENP1 was performed. PTENP1 was present genomically in all human breast cancer samples. PTEN and PTENP1 mRNA expression was concordant in the breast cancer samples before and after 16 weeks of doxorubicin treatment. When comparing the response group, tumor samples from patients with progressive disease (PD) had the lowest PTEN mRNA levels, whereas tumors with stable disease (SD) or partial response (PR) had a higher PTEN expression. PD tumors had a minor change in PTEN and PTENP1 levels after treatment, whereas PTEN and PTENP1 increased in SD and PR tumors. PTENP1 overexpression significantly reduced C3HBA tumor growth in C3H mice. MDA-MB231 primary tumor growth was not affected, but a reduced occurrence of lung metastases was observed in NOD/SCID mice. Cell proliferation was not affected in neither cell line in vitro. This disparate response in vitro vs. in vivo suggests that PTENP1 influences tumor-host interactions in vivo. Lentiviral PTENP1 transfection increased PTEN mRNA and protein expression in murine C3HBA, but with increased pAkt and S6K protein levels indicative of non-PI3K dependent activation. In MDA-MB231 tumors, PTENP1 did not affect PTEN mRNA, but PTEN protein expression increased slightly. The MDA-MB231 tumors were found negative for pAKT and with a low S6K protein expression. PTENP1 knockdown decreased PIK3CA, PTEN, S6K and mTOR gene expression in MDA-MB231, suggesting that PTENP1 facilitates PI3K pathway signaling. While PTENP1 had an effect on PTEN gene and protein expression, it had no obvious effect on PTEN targeting miRNAs in MDA-MB231. Thus, the mechanism behind PTEN regulation mediated by PTENP1 in breast cancer needs to be elaborated on further. In conclusion, PTENP1 is present in human breast cancers and reacts concordantly with PTEN when tumors are exposed to doxorubicin. Up- and down regulation of PTENP1 influences PI3K signaling, and PTENP1 transfection inhibits tumor progression in mice. Citation Format: Synnøve Yndestad, Eilin Austreid, Hans Petter Eikesdal. The noncoding PTEN pseudogene influences PI3K signaling and inhibits breast cancer progression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3539. doi:10.1158/1538-7445.AM2014-3539