MicroRNAs contribute to ATP-binding cassette transporter- and autophagy-mediated chemoresistance in hepatocellular carcinoma

Table 1 miRNAs and ABC transporter-mediated drug resistance in hepatocellular carcinoma cells

miRNA	Expression Level in HCC	Role in ABC transporter expression and/or function	Involvement in cell viability and/or drug resistance	Ref.
miR122	Downregulated in tumors (reduced levels correlate with patient poor prognosis and metastasis) and in human HepG2, HuH-7 and Hep3B HCC cell lines	miR122-overexpressing HCC cells treated with DOX and vincristine showed reduced levels of P-gp mRNA expression, and MRP1 mRNA and protein levels	Adenovirus-transduced cells to overexpress miR122 became more sensitive to DOX- and vincristine-induced death	[12,14]
miR27a	Low in drug-resistant Bel-7402 cells	Negatively correlated with P-gp levels. Upregulation of miR27a reduced P-gp mRNA and protein expression	Cells transfected to overexpress miR27a sensitized resistant cells to 5-FU, mitomycin and DOX	[17]
miR503	Downregulated in HCC tissues (reduced levels correlate with malignant tumor progression), in HCC cell lines (SMMC-7721, Hep3B, HepG2, MHCC97H and LM3) and HepG2 resistant to drugs	Cells transfected to overexpress miR503 showed downregulation of both P-gp and MRP1, at mRNA and protein levels, and accumulated more intracellular rhodamine-123 (extruded through P-gp)	miR503 overexpression restored sensitivity to DOX in HepG2 resistant cells	[19,20]
miR375	Downregulated in patient tumor tissues and cells lines (HepG2, HuH-7, Hep3B)	Delivered within nanoparticles decreased P-gp protein expression	Delivered within nanoparticles improved DOX antitumor effect, prevented tumor cell growth in vitro and in vivo	[21,22,24]
miR133a	Downregulated in patient tumor tissues (its low expression correlated with poor differentiated tumors) and in HepG2, SMMC-77231, Hep3B, HuH-7 HCC cells	Through its binding to the 3’UTR of ABCC1 gene specifically downregulated MRP1 expression	miR133a-overexpressing HepG2 cells were more sensitive to DOX-induced death	[27,28]
miR326	Downregulated in human tissues (its low expression correlated with tumor progression and lymph node metastasis) and in HepG2, SMMC-77231, Hep3B, HuH-7 HCC cells	Specifically targeted MRP1 expression through its binding to the 3’UTR of ABCC1 gene	miR326-overexpressing HepG2 cells were more sensitive to DOX than control cells	[28,31]
miR223	Downregulated in HCC patient sera and liver biopsies	Through its binding to the 3’UTR of ABCB1 gene, it specifically downregulated P-gp expression	miR223 overexpression increased sensitivity to DOX and paclitaxel in SMMC-7721 and HepG2 cells	[34,35]
miR491-3p	Downregulated in HCC tissues and in human cell lines (Hep3B, Bel-7402 and SMMC-7721 cells)	Negatively correlated with P-gp expression. Through its binding to the 3’UTR of ABCB1 gene, it specifically downregulated P-gp expression and increased DOX intracellular concentration. Also, miR491-3p downregulated SP3 expression (transcription factor suggested to induce P-gp expression).	Conferred sensitivity to DOX and vinblastine in Hep3B and SMMC-7721 HCC cells	[38]
miR183	Overexpressed in liver tissues and in drug-resistant Bel-7402 cells	Positively correlated with P-gp and MRP2 protein expression	Conferred resistance to 5-FU in Bel-7402 cells	[41,42]

miRNA: MicroRNA; ABC: ATP-binding cassette; HCC: Hepatocellular carcinoma; DOX: Doxorubicin; 5-FU: 5-Fluoroacil; P-gp/ABCB1: P-glycoprotein; MRP1/ABCC1: Multidrug resistance-associated protein 1; 3’-UTR: 3’-untranslated region; MRP2: Multidrug resistance-associated protein 2.

Table 2 miRNAs and autophagy in hepatocellular carcinoma cell drug resistance

miRNA	Expression Level in HCC	Effect on autophagy	Involvement in drug resistance	Ref.
miR26a/b	Downregulated in tissues and cell lines (HepG2, Hep3B, MHCC97-H and SMCC-7721), also by chemotherapeutic drugs and autophagy inhibitors	Inhibited autophagy, by targeting the expression of ULK1, the key initiator of autophagy	Sensitized HepG2 cells and tumors to apoptosis induced by DOX through targeting autophagy	[53,54]
miR199a-5p	Downregulated in HepG2 and HuH-7 cells and tissues, also by chemotherapeutic drugs	Inhibited cisplatin-induced autophagy, by interacting with the 3’UTR region of ATG7 transcript (an autophagy related gene)	Protected HepG2 and HuH-7 cells from cisplatin-induced resistance	[56,58]
miR101	Downregulated in cell lines (SMMC-7721, HepG2, Bel-4404, and 97L) and tissues, associated with distant metastasis and related to poor prognosis	Inhibited autophagy, by reducing STMN1, RAB5A, ATG4D and mTOR expression (involved in the phagosome formation)	Sensitized HepG2 cells to apoptosis induced by cisplatin	[61,62]
miR216b	Downregulated in patient plasma and tissues, related to poor prognosis	Inhibited autophagy, by targeting . MALAT1 (an oncogenic long non-coding RNA generally upregulated in HCC that modulates chemosensitivity)	Sensitized BEL-7402/5-FU resistant cells to 5-FU-, DOX- and mitomycin-induced death	[65,66]
miR142-3p	Downregulated in tissues, also by sorafenib treatment	Inhibited sorafenib-induced autophagy by binding to the 3’-UTR of ATG5 and ATG16L1	Sensitized SMCC-7721 and HepG2 cells to sorafenib-induced death	[69,70]
miR21	Overexpressed in patient tissues and in drug-resistant cells	Inhibited autophagy, and downregulated PTEN pathway	miR21-dependent autophagy inhibition contributed to sorafenib resistance in Huh7 and HepG2 cells and HCC tumors developed in mice	[72-74]
miR423-5p	Overexpressed in tissues, also elevated in serum of sorafenib-treated patients, and secreted in high levels from sorafenib-treated cells	Induced autophagy	Proposed as a helpful tool to predict patient response to sorafenib treatment	[77,78]

miRNA: MicroRNA; HCC: Hepatocellular carcinoma; ULK1: Unc-51 like autophagy activating kinase; DOX: Doxorubicin; 3’-UTR: 3’-untranslated region; ATG: autophagy-related protein; STMN1: Stathmin 1; RAB5A: RAS related protein; ATG4D: autophagy-related 4D cysteine peptidase; mTOR: The mammalian target of rapamycin; MALAT1: Metastasis associated lung adenocarcinoma transcript 1; 5-FU: 5-Fluoroacil; PTEN: Phosphatase and tensin homologue.