Programmed Death Ligand-1 (PD-L1) Regulated by NRF-2/MicroRNA-1 Regulatory Axis Enhances Drug Resistance and Promotes Tumorigenic Properties in Sorafenib-Resistant Hepatoma Cells

Abstract

Sorafenib, a multi-tyrosine kinase inhibitor, is a standard treatment for advancedhepatocellular carcinoma (HCC), but the clinical response to sorafenib is seriouslylimited by drug-resistance. Programmed death ligand-1 (PD-L1) is one of the mostimportant inhibitory molecules involved in tumor immune evasion. Recently, it has beenreported that PD-L1 could play crucial roles in drug-resistance of many kinds ofcancers. However, the expression, function and regulation of PD-L1 in sorafenibresistanthepatoma cells remain unclear. In this study, we reported that PD-L1 wasoverexpressed in sorafenib-resistant hepatoma cells and shRNA-mediated PD-L1depletion attenuated drug-resistance and suppressed the migration, invasion, colonyformation and tumorigenesis in sorafenib-resistant hepatoma cells in vitro and in vivo.Mechanistic investigations indicated that loss of microRNA-1 (miR-1), a tumorsuppressivemicroRNA, contributed to the PD-L1 up-regulation in sorafenib-resistanthepatoma cells and PD-L1 was a direct regulatory target of miR-1. Further studyrevealed that an oncogenic transcriptional factor: Nuclear factor E2-related factor 2(NRF-2) was induced in sorafenib-resistant hepatoma cell and inhibited expression ofmiR-1 in vitro. From molecular mechanism insight back to the functional verification,we eventually demonstrated that miR-1 executed its tumor suppressive effects on drugresistanceand other malignant properties in sorafenib-resistant hepatoma cells partiallyby PD-L1 inhibition in vitro and in vivo. In conclusion, our data suggested a NRF-2/miR-1/PD-L1 regulatory axis contributed to development and maintenance of drugCopyright© 2020 Cognizant Communication Corporation4ORM-A-3264 Oncology Research E-pubresistance and other tumorigenic properties in sorafenib-resistant hepatoma cells andprovided a potential therapeutic target for overcoming sorafenib resistance in HCC.

Inhibition of the VEGF signaling pathway attenuates tumor‑associated macrophage activity in liver cancer

“…Yao et al (42) reported that PD-L1 expression by macrophages was positively regulated by the PI3K/Akt signaling pathway, in support of the current results. Another study previously reported that PD-L1 expression by liver cancer cells was regulated by the Nrf2 pathway (43), and a previous report by the authors previously revealed that VEGF secreted by TAMs may activate the Nrf2 pathway in liver cancer cells (18). Therefore, VEGF inhibition can suppress the VEGF autocrine loop in macrophages and reduce PD-L1 expression in cancer cells through the inactivation of the AKT/mTOR pathway in TAMs, possibly due to the suppression of the Nrf2 pathway in cancer cells.…”

Overexpression of PD-L1 is an Independent Predictor for Recurrence in HCC Patients Who Receive Sorafenib Treatment After Surgical Resection

“…Overexpression of PD-L1 has been proven to promote immune evasion and tumor growth in HCC by suppressing tumor-infiltrating lymphocytes, and the mechanism mainly involves reduction of cytotoxic CD8 + T cells and expression of cytokines ( 20 , 30 ). Aberrant upregulation of PD-L1 was observed in sorafenib-resistant HCC cells and overexpression of PD-L1 played an essential role in developing and maintaining resistance to sorafenib which contributed to persistent aggressiveness of HCC cells ( 31 ). PD-L1 facilitated EMT and aggressive properties of sorafenib-resistant cells by activating PI3K/Akt pathway which was modulated by expression of Sterol regulatory element-binding protein 1 (SREBP-1) ( 21 ).…”

“…PD-L1 facilitated EMT and aggressive properties of sorafenib-resistant cells by activating PI3K/Akt pathway which was modulated by expression of Sterol regulatory element-binding protein 1 (SREBP-1) ( 21 ). Reversal of EMT was observed after knockdown of PD-L1 and sensitivity of HCC cells to sorafenib was significantly improved ( 31 , 32 ). More importantly, unlike TNF-α ( 26 ), the aforementioned predictor for RFS which was not influenced by sorafenib treatment, PD-L1 expression was significantly upregulated upon exposure to sorafenib and in sorafenib-resistant HCC ( 20 , 31 , 33 ), and also in relapsed HCC ( 19 ).…”

“…Reversal of EMT was observed after knockdown of PD-L1 and sensitivity of HCC cells to sorafenib was significantly improved ( 31 , 32 ). More importantly, unlike TNF-α ( 26 ), the aforementioned predictor for RFS which was not influenced by sorafenib treatment, PD-L1 expression was significantly upregulated upon exposure to sorafenib and in sorafenib-resistant HCC ( 20 , 31 , 33 ), and also in relapsed HCC ( 19 ). In sorafenib-resistant HCC, nuclear factor E2-related factor 2 (NRF-2) promoted expression of PD-L1 by suppressing microRNA-1 (miR-1) which was a tumor-inhibitory microRNA ( 31 ).…”

“…More importantly, unlike TNF-α ( 26 ), the aforementioned predictor for RFS which was not influenced by sorafenib treatment, PD-L1 expression was significantly upregulated upon exposure to sorafenib and in sorafenib-resistant HCC ( 20 , 31 , 33 ), and also in relapsed HCC ( 19 ). In sorafenib-resistant HCC, nuclear factor E2-related factor 2 (NRF-2) promoted expression of PD-L1 by suppressing microRNA-1 (miR-1) which was a tumor-inhibitory microRNA ( 31 ). In terms of untreated cells, upregulation of PD-L1 in HCC cells was driven by enhanced expression of TGF-β1 ( 32 ) upon exposure to sorafenib, In the present study, 43 (35.2%) out of 122 HCC cases were defined as PD-L1 overexpressed according to x-tile, higher than 25% based on the 75th percentile in the previous study ( 17 ) where sorafenib was not applied.…”