ABCG2 confers promotion in gastric cancer through modulating downstream CRKL in vitro combining with biostatistics mining

Linking ABC transporters to the hallmarks of cancer

Human ATP-binding cassette (ABC) transporters are ubiquitously expressed and transport a broad range of endogenous and xenobiotic substrates across extra- and intracellular membranes. Mutations in ABC genes cause 21 monogenic diseases, and polymorphisms in these genes are associated with susceptibility to complex diseases. ABC transporters also play a major role in drug bioavailability, and they mediate multidrug resistance in cancer. At least 13 ABC transporters were shown to be involved in drug resistance in vitro. In the past decade, efforts have been made to elucidate their roles in tumor biology. Herein, we explore their involvement in tumorigenesis, focusing on the hallmarks of cells as they make their way from normalcy to neoplastic growth states.

Tamoxifen resistance induction results in the upregulation of ABCG2 expression and mitoxantrone resistance in MCF-7 breast cancer cells

Cancer endocrine therapy can promote evolutionary dynamics and lead to changes in the gene expression profile of tumor cells. We aimed to assess the effect of tamoxifen (TAM)-resistance induction on ABCG2 pump mRNA, protein, and activity in ER + MCF-7 breast cancer cells. We also evaluated if the resistance to TAM leads to the cross-resistance toward mitoxantrone (MX), a well-known substrate of the ABCG2 pump. The ABCG2 mRNA and protein expression were compared in MCF-7 and its TAM-resistant derivative MCF-7/TAMR cells using RT-qPCR and western blot methods, respectively. Cross-resistance of MCF-7/TAMR cells toward MX was evaluated by the MTT method. Flow cytometry was applied to compare ABCG2 function between cell lines using MX accumulation assay. ABCG2 mRNA expression was also analyzed in tamoxifen-sensitive (TAM-S) and tamoxifen-resistant (TAM-R) breast tumor tissues. The levels of ABCG2 mRNA, protein, and activity were significantly higher in MCF-7/TAMR cells compared to TAM-sensitive MCF-7 cells. MX was also less toxic in MCF-7/TAMR compared to MCF-7 cells. ABCG2 was also upregulated in tissue samples obtained from TAM-R cancer patients compared to TAM-S patients. Prolonged exposure of ER + breast cancer cells to the active form of TAM and clonal evolution imposed by the selective pressure of the drug can lead to higher expression of the ABCG2 pump in the emerged TAM-resistant cells. Therefore, in choosing a sequential therapy for a patient who develops resistance to TAM, the possibility of the cross-resistance of the evolved tumor to chemotherapy drugs that are ABCG2 substrates should be considered. Prolonged exposure of MCF-7 breast cancer cells to tamoxifen can cause resistance to it and an increase in the expression of the ABCG2 mRNA and protein levels in the cells. Tamoxifen resistance can lead to cross-resistance to mitoxantrone.

Tumor microenvironment-induced tumor cell plasticity: relationship with hypoxic stress and impact on tumor resistance

The role of tumor interaction with stromal components during carcinogenesis is crucial for the design of efficient cancer treatment approaches. It is widely admitted that tumor hypoxic stress is associated with tumor aggressiveness and thus impacts susceptibility and resistance to different types of treatments. Notable biological processes that hypoxia functions in include its regulation of tumor heterogeneity and plasticity. While hypoxia has been reported as a major player in tumor survival and dissemination regulation, the significance of hypoxia inducible factors in cancer stem cell development remains poorly understood. Several reports indicate that the emergence of cancer stem cells in addition to their phenotype and function within a hypoxic tumor microenvironment impacts cancer progression. In this respect, evidence showed that cancer stem cells are key elements of intratumoral heterogeneity and more importantly are responsible for tumor relapse and escape to treatments. This paper briefly reviews our current knowledge of the interaction between tumor hypoxic stress and its role in stemness acquisition and maintenance. Our review extensively covers the influence of hypoxia on the formation and maintenance of cancer stem cells and discusses the potential of targeting hypoxia-induced alterations in the expression and function of the so far known stem cell markers in cancer therapy approaches. We believe that a better and integrated understanding of the effect of hypoxia on stemness during carcinogenesis might lead to new strategies for exploiting hypoxia-associated pathways and their targeting in the clinical setting in order to overcome resistance mechanisms. More importantly, at the present time, efforts are oriented towards the design of innovative therapeutical approaches that specifically target cancer stem cells.

Polymorphisms of xenobiotic-metabolizing and transporter genes, and the risk of gastric and colorectal cancer in an admixed population from the Brazilian Amazon

Colorectal (CRC) and gastric (GC) cancers are associated with increased morbidity and mortality. Single nucleotide polymorphisms (SNPs) of xenobiotic metabolism and transporter genes may play a role in the individual responses to exposure to substances implicated in susceptibility to cancer. The investigation of the genetic variation related to the activation and detoxification of xenobiotics may thus help to clarify the prevalence of neoplasms. We analyzed the role of 30 SNPs in xenobiotic-metabolizing and transporter genes in susceptibility to CRC and GC. The study included individuals diagnosed with CRC (n = 121) and GC (n = 95), and 141 controls (non-cancer patients) from the population of Belém, in the Brazilian Amazon. The results indicated an association between the polymorphisms rs2231142 (P = 0.013; OR = 3.01; 95% CI = 1.26-7.13), in the ABCG2 gene, and rs1801159 (P = 0.03; OR = 2.35; 95% CI = 1.14-5.05), in DPYD gene, with the risk of developing GC. The polymorphism rs17116806 of the DPYD gene was found to be associated with a lower risk of developing gastric (P≤0.0001; OR = 0.043; 95% CI = 0.015-0.12) or colorectal (P≤0.0001; OR = 0.076; 95% CI = 0.33-0.18) cancers, indicating that the same variant may play a similar role in different types of cancer tissue. Additionally, the carriers of the TT genotype of the polymorphism in the ABCB1 gene (rs1128503) presented a reduced probability of developing CRC (P = 0.0001; OR = 0.16; 95% CI = 0.06-0.41) as well as GC (P = 0.007; OR = 0.27; 95% CI = 0.1-0.7). Our findings indicate that polymorphisms in xenobiotic-metabolizing and transporter genes may modulate susceptibility to colorectal and gastric cancers.

Pseudogene AKR1B10P1 enhances tumorigenicity and regulates epithelial-mesenchymal transition in hepatocellular carcinoma via stabilizing SOX4

Pseudogenes exert potential functions in tumorigenicity and tumour process in human beings. In our previous research on oncogene AKR1B10 in hepatocellular carcinoma (HCC), its pseudogene, AKR1B10P1, was preliminarily noticed being anomalistic transcribed, whereas whether AKR1B10P1 plays any specific function in HCC is poorly understood. By using shRNA transfection and lentiviral infection, we regulated the expression of ARK1B10P1 transcript and the relative targets in two ways. As we discovered, pathological transcription of AKR1B10P1 in HCC cells significantly promotes cell growth and motility either in vitro or in vivo. AKR1B10P1 was correlated with relatively dismal features of HCC. The epithelial‐mesenchymal transition (EMT) was enhanced by up‐regulating AKR1B10P1. And, a potential sequence of AKR1B10P1 transcript was discovered directly interacting with miR‐138. SOX4, a pivotal promotor of EMT, was validated as the down‐streaming target of miR‐138. Mechanistically, degradation of SOX4 mRNA induced by miR‐138 was effectively abrogated by AKR1B10P1. In conclusion, pseudogene AKR1B10P1 exerts stabilizing effect on SOX4 in HCC, associated EMT process, by directly sponging miR‐138, which post‐transcriptionally modulates SOX4’s regulating gene.

Effect of sodium butyrate on ABC transporters in lung cancer A549 and colorectal cancer HCT116 cells

Histone deacetylase (HDAC) inhibitors and DNA alkylators are effective components of combination chemotherapy. The aim of the present study was to investigate the possible mechanism of their synergism by detecting the effect of HDAC inhibitors on the expression levels of drug transporters that export DNA alkylators. It was demonstrated that the HDAC inhibitor sodium butyrate (NaB) induced the differential expression of multidrug resistant ATP-binding cassette (ABC) transporters in lung cancer and colorectal cancer cells. Specifically, NaB increased the mRNA expression levels of ABC subfamily B member 1 (ABCB1), ABCC10 and ABCC12, and protein expression levels of multidrug resistance-1 (MDR1), multidrug resistance-associated protein 7 (MRP7) and MRP9. Moreover, NaB decreased the expression levels of ABCC1, ABCC2 and ABCC3 mRNAs, as well as those of MRP1, MRP2 and MRP3 proteins. The molecular mechanism underlying this process was subsequently investigated. NaB decreased the expression of HDAC4, but not HDAC1, HDAC2 or HDAC3. In addition, NaB promoted histone H3 acetylation and methylation at lysine 9, as well as MDR1 acetylation, suggesting that acetylation and methylation may be involved in NaB-mediated ABC transporter expression. Thus, the present results indicated that the synergism of the HDAC inhibitors with the DNA alkylating agents may due to the inhibitory effect of MRPs by HDAC inhibitors. The findings also suggested the possibility of antagonistic effects following the combined treatment of HDAC inhibitors with MDR1 ligands.

Effects of histone deacetylase inhibitors on ATP-binding cassette transporters in lung cancer A549 and colorectal cancer HCT116 cells

Histone deacetylase (HDAC) inhibitors and DNA alkylators are effective components used in combination chemotherapy. In the present study, the effects of HDAC inhibitors on the expression of ATP-binding cassette (ABC) transporters were investigated. It was observed that HDAC inhibitors induced the expression of multidrug-resistant ABC transporters differently in lung cancer A549 cells than in colorectal cancer HCT116 cells. In these two cell lines, the HDAC inhibitors suberoylanilide hydroxamic acid (SAHA) and trichostatin A (TSA) significantly increased ABCB1 expression at the mRNA and protein levels, whereas they had no evident effect on ABCG2 protein expression. SAHA and TSA decreased ABCG2 mRNA expression in A549 cells and had no evident effect on ABCG2 mRNA expression in HCT116 cells. Notably, SAHA and TSA increased the mRNA expression levels of ABCC5, ABCC6, ABCC10, ABCC11 and ABCC12, as well as the protein expression levels of ABCC2, ABCC10 and ABCC12. By contrast, these inhibitors decreased the mRNA expression levels of ABCC1, ABCC2, ABCC3 and ABCC4, as well as the expression of ABCC1 and ABCC3 proteins. Furthermore, SAHA and TSA were found to downregulate HDAC3 and HDAC4, but not HDAC1 and HDAC2. Taken together, the results suggested that HDAC inhibitors work synergistically with DNA alkylators, in part, due to the inhibitory effect of these inhibitors on ABCC1 expression, which translocates these alkylators from inside to outside of cancer cells. These results further suggested the possibility of antagonism when HDAC inhibitors are combined with anthracyclines and other ABCB1 drug ligands in chemotherapy.

Role of breast cancer resistance protein in gastrointestinal tumors

The breast cancer resistance protein, also known as ABCG2, is a member of the drug efflux membrane transporters. As a drug discharge pump, ABCG2 can reduce the concentration of intracellular drugs and protect cells from toxic substances. ABCG2 is not only able to protect normal cells, but also to influence the chemotherapy effect by making tumor cells resistant to various anti-cancer drugs. In order to provide a reference for the basic and clinical research of gastrointestinal tumors, we review the physiological function of ABCG2, factors affecting ABCG2 expression, and its relationship with gastrointestinal tumors.

Ribophorin II potentiates P-glycoprotein- and ABCG2-mediated multidrug resistance via activating ERK pathway in gastric cancer

Multidrug resistance (MDR) is a critical reason of cancer chemotherapy failure. Ribophorin II (RPN2) has emerged as a vital regulator of MDR in multiple cancers including gastric cancer (GC). However, the roles and molecular mechanisms of RPN2 in MDR have not been well featured till now. The present study aimed to explore the roles and molecular mechanisms of RPN2 in MDR of drug-resistant GC cells. Results showed that the expressions of RPN2, multidrug resistance 1 (MDR1), and ATP binding cassette subfamily G member 2 (ABCG2) were upregulated in SGC7901/DDP and SGC7901/VCR cells. Knockdown of RPN2 alleviated MDR through downregulating MDR1 and ABCG2 expressions in SGC7901/DDP and SGC7901/VCR cells. RPN2 depletion inhibited the activation of MEK/ERK pathway. RPN2 overexpression enhanced MDR by upregulating P-glycoprotein (P-gp) and ABCG2 protein expressions in SGC7901/DDP or SGC7901/VCR cells, while this effect of RPN2 was abrogated by ERK knockdown or treatment with ERK inhibitor PD98059. Our findings suggested that RPN2 potentiated P-gp- and ABCG2-mediated MDR via activating MEK/ERK pathway in GC, hinting the critical values of RPN2 in ameliorating MDR and providing a promising target for GC therapy.

Effect of targeted regulation of ABCG2 signaling pathway by miR-144-3p on invasion and migration of gastric cancer cells

AIM

To investigate the effect of targeted regulation of ATP-binding transporter G family member 2 (ABCG2) signaling pathway by miR-144-3p on the invasion and migration of gastric cancer (GC) cells HGC-27, and to explore the underlying mechanism.

METHODS

The expression of miR-144-3p and ABCG2 in human GC cell line HGC-27 and human gastric mucosal epithelial cell line GES-1 was detected by qRT-PCR. The target gene prediction software was used to predict whether miR-144-3p binds to ABCG2, and the binding site was used to detect whether miR-144-3p targets ABCG2 by dual luciferase reporter gene assay. The expression of miR-144-3p and ABCG2 was detected by qRT-PCR after transfection of miR-144-3p mimic or miR-144-3p inhibitor into GC cells. The expression of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) in GC cells transfected with ABCG2 siRNA was detected by gelatin zymography assay. Transwell invasion and migration assays were employed to detect the effect of miR-144-3p mimic, miR-144-3p inhibitor, and ABCG2 siRNA on the invasion and migration of GC cells.

RESULTS

Compared with GES-1 cells, the expression of miR-144-3p in HGC-27 cells was significantly decreased and the expression of ABCG2 was significantly increased (P < 0.05). The target gene prediction software predicted the binding site of miR-144-3p in the ABCG2 3'UTR, and the dual luciferase reporter gene experiment confirmed the targeted binding relationship of miR-144-3p and ABCG2. Compared with the control group, the expression of miR-144-3p was significantly increased, the expression of ABCG2 was significantly decreased, and the cell invasion and migration ability were significantly decreased in the miR-144-3p mimic transfected group (P < 0.05), while transfection with miR-144-3p inhibitor showed the opposite effect. Gelatin zymography assay showed that ABCG2 siRNA transfection significantly inhibited the activity of MMP-2 and MMP-9 proteins in GC cells and suppressed the invasion and migration of GC cells (P < 0.05).

CONCLUSION

MiR-144-3p can inhibit the invasion and migration of GC cells possibly via mechanisms related to targeted regulation of the ABCG2-MMP-2/9 signaling pathway.

Rab23 promotes the cisplatin resistance of ovarian cancer via the Shh-Gli-ABCG2 signaling pathway

As a novel member of the Rab GTPase family, the role of Rab23 has been reported in multiple types of tumor. However, to the best of our knowledge, the role of Rab23 in ovarian cancer (OC) has not yet been reported. In the present study, immunohistochemistry analysis demonstrated that Rab23 was upregulated in OC tissue; survival analysis indicated that Rab23 expression was associated with a reduced overall survival (OS) rate and disease-free survival (DFS) time. In vitro experiments also demonstrated the increased expression of Rab23 in the OC cells lines, A2780 and SKOV-3, compared with in the normal ovarian cell line, IOSE80. Following the silencing of ABCG2 in SKOV-3 cells, ATP-binding cassette sub-family G member 2 (ABCG2) expression was significantly downregulated both at the RNA and protein levels. The cisplatin (DDP) IC₅₀ declined from 43.09±7.12 µmol/l in control cells to 26.46±5.38 µmol/l in SKOV-3 cells with silenced Rab23. In contrast, in A2780 cells overexpressing Rab23 (A2780-Rab23), ABCG2 expression was significantly upregulated and the DDP IC₅₀ increased from 27.42±6.54 µmol/l in control cells to 45.92±5.23 µmol/l in A2780-Rab23. Investigation into the potential molecular mechanisms for this revealed that the expression of sonic hedgehog (Shh) and Gli family zinc finger 1 (Gli1) was increased in A2780-Rab23 cells, whereas silencing Rab23 in SKOV-3 cells significantly inhibited the expression of Shh and Gli1. The Gli1 inhibitor GANT-61 significantly abrogated the increased ABCG2 expression in A2780-Rab23 cells. Furthermore, the DDP IC₅₀ in A2780-Rab23 cells decreased significantly following the silencing of ABCG2 expression; the IC₅₀ declined from 51.66±8.32 µmol/l in A2780-Rab23 cells to 25.61±6.17 µmol/l in A2780-Rab23 cells with silenced ABCG2. Collectively, the results indicate that Rab23 promotes the DDP resistance of OC cells via the Shh-Gli1-ABCG2 pathway, providing the proof of principle for the further investigation of drug resistance therapy targeting Rab23.

Role of ATP-binding cassette transporters, apoptosis, and long non-coding RNAs in gastric cancer multidrug resistance

Cancer multidrug resistance refers to the cross resistance of cancer cells to a variety of anticancer drugs, which can be primary or secondary. Several mechanisms attribute to cancer multidrug resistance. In this paper, the recent progress in the understanding of the mechanisms of multi-drug resistance of gastric cancer cells with regard to the role of adenosine triphosphate binding cassette transporters, apoptosis, and long non-coding RNAs is reviewed.