ATP-binding Cassette Sub-family B Member 1 Expression Research Articles

Alkaliptosis induction counteracts paclitaxel-resistant ovarian cancer cells via ATP6V0D1-mediated ABCB1 inhibition.

Paclitaxel serves as the cornerstone chemotherapy for ovarian cancer, yet its prolonged administration frequently culminates in drug resistance, presenting a substantial challenge. Here we reported that inducing alkaliptosis, rather than apoptosis or ferroptosis, effectively overcomes paclitaxel resistance. Mechanistically, ATPase H+ transporting V0 subunit D1 (ATP6V0D1), a key regulator of alkaliptosis, plays a pivotal role by mediating the downregulation of ATP-binding cassette subfamily B member 1 (ABCB1), a multidrug resistance protein. Both ATP6V0D1 overexpression through gene transfection and pharmacological enhancement of ATP6V0D1 protein stability using JTC801 effectively inhibit ABCB1 upregulation, resulting in growth inhibition in drug-resistant cells. Additionally, increasing intracellular pH to alkaline (pH 8.5) via sodium hydroxide application suppresses ABCB1 expression, whereas reducing the pH to acidic conditions (pH 6.5) with hydrochloric acid amplifies ABCB1 expression in drug-resistant cells. Collectively, these results indicate a potentially effective therapeutic strategy for targeting paclitaxel-resistant ovarian cancer by inducing ATP6V0D1-dependent alkaliptosis.

Abstract 1998: ABCB1 promotes uveal melanoma cell resistance to FR900359 and identifies a tumor cell subpopulation with a distinct gene expression signature

Abstract Uveal melanoma (UM) is the leading form of intraocular cancer in adults and the second most common form of melanoma. Although rare, UM has a median survival rate of ~1 year after metastasis occurs. Metastatic UM is largely refractory to treatment and there are no effective pharmacological therapies, resulting in poor overall survival. In >90% UM cases, the oncogenic initiator proteins are constitutively active mutant GNAQ or GNA11 proteins (GNAQ/11). FR900359 (FR) is a natural compound that inhibits GNAQ/11 and has anti-proliferative effects on UM cells. To identify key oncogenic mechanisms downstream of mutant GNAQ/11, we performed a Sleeping Beauty (SB) transposon forward genetic screen to identify drivers of FR resistance. The SB screen identified ATP-binding cassette sub-family B member 1 (ABCB1) as one of the top genes upregulated by SB in FR-resistant UM cell populations. We determined that although ABCB1 does not provide immediate resistance to FR, the overexpression of ABCB1 leads to emergence of resistant colonies at a much higher rate than spontaneous resistance, validating ABCB1 as contributors to FR resistance. Unexpectedly, immunofluorescence revealed that a relatively small fraction of UM cells strongly expresses the transgenes after stable transfection. Immunoblotting confirmed that ABCB1 expression was initially modest in ABCB1-transfected populations but increased in the cells that developed resistance to FR. To examine the kinetics of FR resistance, population doubling versus time (PDVT) assays were performed in UM cells expressing ABCB1 or empty vector control treated with FR or vehicle. FR potently suppressed the proliferation of vector control cells. Drug-naïve ABCB1-transfected cells developed resistance to FR over time but accomplished fewer population doublings than vehicle-treated cells in the same time interval. Once transgenic populations emerged as resistant populations in FR, they grew similarly in drug or vehicle. Ongoing RNA-sequencing analysis from PDVT samples has identified distinct gene expression signatures associated with FR treatment and ABCB1 expression. These findings are expected to illuminate tumor cell heterogeneity amongst UM cell populations that may be related to drug resistance and metastasis. Citation Format: Sarina Dion Murray, Jesse D. Riordan, Eric R. Anderson, Michael D. Onken, Kendall J. Blumer, Adam J. Dupuy, Christopher S. Stipp. ABCB1 promotes uveal melanoma cell resistance to FR900359 and identifies a tumor cell subpopulation with a distinct gene expression signature [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1998.

Influence of GPRC5A-Regulated ABCB1 Expression on Lung Adenocarcinoma Proliferation

Objective Aberrant expression of ATP binding cassette subfamily B member 1 (ABCB1) plays a key role in several cancers. However, influence of G protein coupled receptor family C group 5 type A (GPRC5A)-regulated ABCB1 expression on lung adenocarcinoma proliferation remains unclear. Therefore, this study investigated the effect of GPRC5A regulated ABCB1 expression on the proliferation of lung adenocarcinoma. Methods ABCB1 expressions in lung adenocarcinoma cell lines, human lung adenocarcinoma tissues, and tracheal epithelial cells and lung tissues of GPRC5A knockout mice and wild-type mice were analyzed with RT-PCR, Western blot, or immunohistochemical analysis. Cell counting kit-8 assay was performed to analyze the sensitivity of tracheal epithelial cells from GPRC5A knockout mice to chemotherapeutic agents. Subcutaneous tumor formation assay was performed to confirm whether down-regulation of ABCB1 could inhibit the proliferation of lung adenocarcinoma in vivo. To verify the potential regulatory relationship between GPRC5A and ABCB1, immunofluorescence and immunoprecipitation assays were performed. Results ABCB1 expression was up-regulated in lung adenocarcinoma cell lines and human lung adenocarcinoma tissues. ABCB1 expression in the tracheal epithelial cells and lung tissues of GPRC5Adeficient mice was higher than that in the wild type mice. Tracheal epithelial cells of GPRC5A knockout mice were much more sensitive to tariquidar and doxorubicin than those of GPRC5A wild type mice. Accordingly, 28 days after injection of the transplanted cells, the volume and weight of lung tumor in ABCB1knockout cell-transplanted GPRC5A-/-C57BL/6 mice were significantly smaller than those in wild type cell-transplanted mice (P= 0.0043, P= 0.0060). Furthermore, immunofluorescence and immunoprecipitation assays showed that GPRC5A regulated ABCB1 expression by direct binding.Conclusion GPRC5A reduces lung adenocarcinoma proliferation via inhibiting ABCB1 expression. The pathway by which GPRC5A regulates ABCB1 expression needs to be investigated.

Fatty acid binding protein 5 regulates docetaxel sensitivity in taxane-resistant prostate cancer cells.

Prostate cancer is a leading cause of cancer-related deaths in men in the United States. Although treatable when detected early, prostate cancer commonly transitions to an aggressive castration-resistant metastatic state. While taxane chemotherapeutics such as docetaxel are mainstay treatment options for prostate cancer, taxane resistance often develops. Fatty acid binding protein 5 (FABP5) is an intracellular lipid chaperone that is upregulated in advanced prostate cancer and is implicated as a key driver of its progression. The recent demonstration that FABP5 inhibitors produce synergistic inhibition of tumor growth when combined with taxane chemotherapeutics highlights the possibility that FABP5 may regulate other features of taxane function, including resistance. Employing taxane-resistant DU145-TXR cells and a combination of cytotoxicity, apoptosis, and cell cycle assays, our findings demonstrate that FABP5 knockdown sensitizes the cells to docetaxel. In contrast, docetaxel potency was unaffected by FABP5 knockdown in taxane-sensitive DU145 cells. Taxane-resistance in DU145-TXR cells stems from upregulation of the P-glycoprotein ATP binding cassette subfamily B member 1 (ABCB1). Expression analyses and functional assays confirmed that FABP5 knockdown in DU145-TXR cells markedly reduced ABCB1 expression and activity, respectively. Our study demonstrates a potential new function for FABP5 in regulating taxane sensitivity and the expression of a major P-glycoprotein efflux pump in prostate cancer cells.

Bioinformatics-Based Characterization of ATP-Binding Cassette Subfamily B Member 1 (ABCB1) Gene Expression in Non-Small-Cell Lung Cancer (NSCLC)

P-glycoprotein (P-gp) has been implicated in lung cancer development, disease progression, and patient survival. Changes in the ABCB1 expression level may correlate with tumorigenesis and the formation of multidrug resistance (MDR). In addition, epigenetic modifications such as DNA methylation are involved in the regulation of the transcriptional activity of this gene. Therefore, we focused on an analysis of changes in the expression of ABCB1 and its methylation, taking into account their potential associations with the clinicopathological parameters of LUAD and LUSC. The TNMplot, UALCAN, cBioPortal, PrognoScan, and MEXPRESS databases were used to investigate the role of this gene in lung cancer progression. ABCB1 expression in lung tissue was significantly downregulated in cancer cells, but differences also resulted from age, gender, ethnicity, and smoking cessation. Moreover, decreased levels of gene transcript were associated with both a higher stage of cancer and a lower probability of survival. It is worth emphasizing that the presence/direction of ABCB1 expression changes are frequently unique to specific histological tumor subtypes. Finally, it is equally important that the main methylation promoter is one of the causes of decreased gene expression in lung cancer cells. Taken together, these data establish the ABCB1 transporter gene as an important prognostic factor that could alter disease progression and contribute to the survival of cancer patients.

Characterizing A Novel Variant in ABCB1 in a Family with Activated PI3K Delta Syndrome-like Presentation

IntroductionActivated PI3K delta syndrome (APDS) is a rare inborn error of immunity (IEI) due to a heterozygous gain-of-function mutation in the PIK3CD or PIK3R1 genes. APDS patients have high variability in clinical manifestations including recurrent sinopulmonary infections, lymphoproliferation, and susceptibility to CMV and/or EBV viremia. APDS is characterized by a block in B-cell development to follicular stage. Therefore, increase in transitional compartment is almost exclusively seen in untreated APDS patients. We describe a family that present with APDS-like clinical and laboratory findings, while harboring a novel variant in ATP binding cassette subfamily B member 1 (ABCB1), which is involved in adenosine salvage and mTORC1 pathways. MethodsRetrospective chart review was performed for clinical and laboratory data. Extensive immune phenotyping was obtained. Genetic evaluation included targeted immune panel and whole exome sequencing. Mitotracker-green detection by flow cytometry was used to determine progression to follicular B cell stage. Case PresentationIndex case is a 14-year-old female with a complex presentation of infectious and non-infectious complications notable for lifelong hypogammaglobulinemia with poor vaccine response, multiple intubations for upper respiratory illnesses, bronchiectasis, and short stature. Patient had 3 other siblings who also had similar presentation with varied severity, including features of short stature, recurrent infections, alopecia universalis and immune dysregulation. Three siblings required immunoglobulin replacement therapy. Extensive immune-phenotyping revealed significant expansion of CD24hiCD38hi transitional and CD19hiCD21lo B-cells, with decrease in follicular and memory B-cell compartment in all. Although clinical and lab findings prompted APDS diagnosis, repeated targeted genetic panel testing did not show variants in PIK3CD or PIK3R1. Consequent whole exome sequencing revealed a candidate variant in ABCB1 p.Ala1187Thr that was shared among all. Interestingly, surface expression of ABCB1 was significantly elevated in patients compared to healthy controls. Initial functional testing showed disruption in mitochondrial efflux, further supporting the block from transitional to follicular stage. Discussion/ConclusionsDetermining diagnostic approaches in APDS-like disorders liked to ABCB1 variant is challenging, especially when pathogenesis is yet to be determined. Although further functional testing of ABCB1 and its potential role in PI3K signaling is needed, ABCB1 gene may play an important role in APDS pathology.

Overcoming ABCB1-mediated multidrug resistance by transcription factor BHLHE40

Multidrug resistance (MDR) hinders treatment efficacy in cancer therapy. One typical mechanism contributing to MDR is the overexpression of permeability-glycoprotein (P-gp) encoded by ATP-binding cassette subfamily B member 1 (ABCB1). Basic helix-loop-helix family member e40 (BHLHE40) is a well-known transcription factor that has pleiotropic effects including the regulation of cancer-related processes. However, whether BHLHE40 regulates MDR is still unknown. Chromatin immunoprecipitation-seq study revealed BHLHE40 occupancy in the promoter of ABCB1 gene. Adriamycin (ADM)-resistant human chronic myeloid leukemia cells (K562/A) and human breast cancer cells (MCF-7/A) were established. BHLHE40 expression was downregulated in the ADM-resistant cell lines. Overexpression of BHLHE40 resensitized resistant cells to ADM, promoted cell apoptosis in vitro and suppressed tumor growth in vivo, whereas BHLHE40 knockdown induced resistance to ADM in parental cells. Moreover, we found that BHLHE40 regulated drug resistance by directly binding to the ABCB1 promoter (-1605 to -1597) and inactivating its transcription. In consistence, the expression of BHLHE40 was negatively correlated with ABCB1 in various cancer cells, while positively with cancer cell chemosensitivity and better prognosis of patients with breast cancer. The study reveals the role of BHLHE40 as a transcriptional suppressor on the expression of ABCB1, major ABC transporter in chemoresistance. The findings extend the function of BHLHE40 in tumor progression and provides a novel mechanism for the reversal of multidrug resistance.

Bufalin reverses ABCB1-mediated resistance to docetaxel in breast cancer

BackgroundDocetaxel (DCT) is widely used in clinical practice, but the drug resistance of breast cancer patients has become an important reason to limit its clinical efficacy. Chan’su is a commonly used traditional Chinese medicine for the treatment of breast cancer. Bufalin (BUF) is a bioactive polyhydroxy steroid extracted from chan’su and has strong antitumor activity, but there are few studies on reversing drug resistance in breast cancer. The aim of this study is to determine whether BUF can reverse the drug resistance to DCT and restore efficacy in breast cancer. MethodologyThe reversal index of BUF was detected by Cell Counting Kit-8 (CCK-8) assays. The effects of BUF on enhancing the apoptosis of DCT were detected by flow cytometry and Western Blot (WB), and the main differential expression levels of sensitive and resistant strains were detected by high-throughput sequencing. Rhodamine 123 assay, WB and ATP Binding Cassette Subfamily B Member 1 (ABCB1) ATPase activity experiments were used to detect the effect of BUF on ABCB1. The nude mouse orthotopic model was constructed to investigate the reversal effect of BUF on DCT resistance in vivo. ResultsWith BUF intervention, the sensitivity of drug-resistant cell lines to DCT was increased. BUF can inhibit the expression of ABCB1 protein, increase the drug accumulation of DCT in drug-resistant strains, and reduce the ATPase activity of ABCB1. Animal experiments show that BUF can inhibit the growth of drug-resistant tumors in an orthotopic model of breast cancer and decrease the expression of ABCB1. ConclusionBUF can reverse ABCB1-mediated docetaxel resistance in breast cancer.

Terfenadine resensitizes doxorubicin activity in drug-resistant ovarian cancer cells via an inhibition of CaMKII/CREB1 mediated ABCB1 expression.

Ovarian cancer is one of the most lethal gynecological malignancies. Recurrence or acquired chemoresistance is the leading cause of ovarian cancer therapy failure. Overexpression of ATP-binding cassette subfamily B member 1 (ABCB1), commonly known as P-glycoprotein, correlates closely with multidrug resistance (MDR). However, the mechanism underlying aberrant ABCB1 expression remains unknown. Using a quantitative high-throughput combinational screen, we identified that terfenadine restored doxorubicin sensitivity in an MDR ovarian cancer cell line. In addition, RNA-seq data revealed that the Ca2+-mediated signaling pathway in the MDR cells was abnormally regulated. Moreover, our research demonstrated that terfenadine directly bound to CAMKIID to prevent its autophosphorylation and inhibit the activation of the cAMP-responsive element-binding protein 1 (CREB1)-mediated pathway. Direct inhibition of CAMKII or CREB1 had the same phenotypic effects as terfenadine in the combined treatment, including lower expression of ABCB1 and baculoviral IAP repeat-containing 5 (BIRC5, also known as survivin) and increased doxorubicin-induced apoptosis. In this study, we demonstrate that aberrant regulation of the Ca2+-mediated CAMKIID/CREB1 pathway contributes to ABCB1 over-expression and MDR creation and that CAMKIID and CREB1 are attractive targets for restoring doxorubicin efficacy in ABCB1-mediated MDR ovarian cancer.

Nrf2/p‑Fyn/ABCB1 axis accompanied by p‑Fyn nuclear accumulation plays pivotal roles in vinorelbine resistance in non‑small cell lung cancer.

Adjuvant cisplatin‑vinorelbine is a standard therapy for stageII/III lung cancer. However, a poor survival rate of patients with lung cancer is attributed to vinorelbine resistance arising from ATP‑binding cassette (ABC) sub‑family B member 1 (ABCB1) and phosphorylated Fyn (p‑Fyn) overexpression. However, the underlying mechanisms remain unclear. NF‑E2‑related factor2 (Nrf2) regulates the ABC family and activates the nuclear transport of Fyn. The present study evaluated the roles of the Nrf2/p‑Fyn/ABCB1 axis in vinorelbine‑resistant (VR) cells and clinical samples. To establish VRcells, H1299 cells were exposed to vinorelbine, and the intracellular reactive oxygen species (ROS) level in the H1299 cells was determined using a DCFH‑DA assay. The total and subcellular expression of Nrf2, ABCB1 and p‑Fyn in VRcells was evaluated. Immunofluorescence was used to detect the subcellular localization of p‑Fyn in VRcells. A cell viability assay was used to examine whether the sensitivity of VRcells to vinorelbine is dependent on Nrf2 activity. Immunohistochemistry was performed on 104tissue samples from patients with lung cancer who underwent surgery followed by cisplatin‑vinorelbine treatment. The results revealed that persistent exposure to vinorelbine induced intracellular ROS formation in H1299 cells. p‑Fyn was localized in the nucleus, and ABCB1 and Nrf2 were overexpressed in VRcells. ABCB1 expression was dependent on Nrf2 downstream activation. The decreased expression of Nrf2 restored the sensitivity of VRcells to vinorelbine. In the surgical samples, Nrf2 and ABCB1 were associated with disease‑free survival, and p‑Fyn was associated with overall survival (P<0.05). On the whole, the present study demonstrates that Nrf2 upregulates ABCB1 and, accompanied by the nuclear accumulation of p‑Fyn, induces vinorelbine resistance. These findings may facilitate the development of drug resistance prevention strategies or new drug targets against non‑small cell lung cancer.

Advanced oxidation protein products upregulate ABCB1 expression and activity via HDAC2-Foxo3α-mediated signaling in vitro and in vivo

The unpredictable pharmacokinetics of non-renal cleared drugs in chronic kidney disease (CKD) patients is associated with the activity of drug transporters. However, the mechanisms underlying regulation of drug transporters are yet to be established. In this study, we demonstrated the involvement of a HDAC2-Foxo3α pathway in advanced oxidation protein products (AOPPs)-induced ATP-binding cassette subfamily B member 1 (ABCB1) expression and activity. The correlation of AOPPs accumulation with concentration of cyclosporine in plasma was evaluated in 194 patients with transplantation. Molecular changes in acetylation of various histones and related regulatory molecules were examined in HepG2 cell cultures treated with AOPPs. Accumulation of AOPPs in serum in relation to molecular changes in HDAC2-Foxo3α in vivo were evaluated in 5/6 nephrectomy (5/6 nx) and oral adenine (Adenine) CKD rat models. Interestingly, the cyclosporine level was negatively correlated with AOPPs in plasma. In addition, AOPPs markedly suppressed the expression of histone deacetylase 2 (HDAC2), inducing ABCB1 expression and activity in vitro and in vivo. Importantly, AOPPs modulated phosphorylation of Foxo3α and the upstream Akt protein. Our findings indicate that AOPPs regulate the expression and activity of ABCB1 via reducing HDAC2 expression and activating Foxo3α-dependent signaling. The collective results support the utility of AOPPs as a potential target for drug and/or dosage adjustment in CKD patients. Targeting of AOPPs presents a novel approach to regulate non-renal clearance.

The Effect of Nano Albumin Combined with Paclitaxel on Drug Resistance of Breast Cancer Through Regulating ATP Binding Cassette Subfamily B Member 1 (ABCB1)

The paclitaxel is a common-used chemotherapy drug and its combination with nano albumin reduces drug side effect. However, whether nab-paclitaxel affects drug resistance of breast cancer remains unclear. This study intends to discuss the mechanism of drug resistance induced by nab-paclitaxel. The drug resistance of MCF-7/nab-paclitaxel in MCF-7 cell and cell proliferation was detected by MTT along with analysis of ABCB1 expression, cell cycle, and apoptosis. There was stronger drug resistance of nab-paclitaxel in the MCF-7/nab-paclitaxel cell group through be adopted with different concentration of nab-paclitaxel at the 0th hour, 24th hour and 48th hour. There was remarkable abnormal expression of the ABCB1 in the MCF-7/nab-paclitaxel cell group. The si-ABCB1 could release the quantity of the MCF-7/nab-paclitaxel cell blocked at S period. And the si-ABCB1 could reduce the expression of cyclin D1 and CDK2 in the MCF-7/nab-paclitaxel cell notably. But the expression level of p21 was increased when there was high concentration of si-ABCB1. The si-ABCB1 could increase the quantity of the MCF-7/nab-paclitaxel cell at the later period of cell apoptosis notably. The rat’s tumor growth was delayed obviously at the MCF-7/nabpaclitaxel cell group treated by si-ABCB1. But the inhibiting effect of the MCF-7/nab-paclitaxel cell on tumor growth was less. There was stronger drug resistance of cell for the nano albumin combined with paclitaxel. The function of cell proliferation in breast cancer was restrained by the nano albumin combined with paclitaxel mainly through inducing the expression of ABCB1, adjusting the growth of cell cycle and the expression of P21/BCL-2 protein.

Expression of ATP-binding cassette subfamily B member 1 gene in peripheral blood of patients with acute myocardial infarction

ABSTRACT This study aimed to determine the amount of expression of the ATP-binding cassette subfamily B member 1 (ABCB1) gene chip as a prospective diagnostic marker for acute myocardial infarction (AMI) in a wide population . In the AMI and control groups, 113 patients with AMI and 83 persons with non-coronary artery disease were selected for peripheral venous leukocyte collection. Western blot and real-time polymerase chain reaction (RT-PCR) were employed to detect relative ABCB1 expression in both groups. The results showed that the ABCB1 transcription and protein levels in the AMI group were higher than in the control. The relative mRNA expression of ABCB1 was 0.26 (0.03–0.79) in the AMI group and 0.13 (0.01–0.52) in the control group (P < 0.05). The expression of the ABCB1 gene at the protein level in the AMI group was 1.65 times that in the control (P < 0.05). Further, the subjects in the AMI group were older (P < 0.001), had lower levels of high-density lipoprotein cholesterol (P = 0.038), and had higher incidence of type II diabetes mellitus (P = 0.003) compared with the control. Logistic regression analysis showed that the expression of ABCB1 in peripheral blood was correlated with the occurrence of AMI (P = 0.003). High ABCB1 expression, type II diabetes, and advanced age were found to serve as potential independent risk factors for AMI, with a 4.88-fold, 2.99-fold, and 2.63-fold increased risk of AMI. Overall, the high expression of ABCB1 in peripheral blood might be related to the occurrence of AMI.

A novel epigenetic marker, Ten-eleven translocation family member 2 (TET2), is identified in the intractable epileptic brain and regulates ATP binding cassette subfamily B member 1 (ABCB1) in the blood–brain barrier

ABSTRACT Drug-resistant epilepsy (DRE) is a chronic condition derived from spontaneous changes and regulatory effects in the epileptic brain. As demethylation factors, ten-eleven translocation (TET) family members have become a focus in recent studies of neurological disorders. Here, we quantified and localized TET1, TET2 and 5-hydroxymethylcytosine (5-hmC) in the temporal lobe cortex of DRE patients (n = 27) and traumatic brain hemorrhage controls (n = 10) by immunochemical staining. TET2 and ATP binding cassette subfamily B member 1 (ABCB1) expression patterns were determined in the isolated brain capillaries of DRE patients. TET2 expression was significantly increased in the temporal cortical tissue of DRE patients with or without hippocampal sclerosis (HS) compared to control patients, while TET1 and 5-hmC showed no differences in expression. We also found that a particularly strong expression of TET2 in the vascular tissue of DRE patients. ABCB1 and TET2 have evidently higher expression in the vascular endothelium from the neocortex of DRE patients. In blood–brain barrier (BBB) model, TET2 depletion can cause attenuated expression and function of ABCB1. Data from a cohort study and experiments in a BBB model suggest that TET2 has a specific regulatory effect on ABCB1, which may serve as a potential mechanism and target in DRE.

CircRNA_103615 contributes to tumor progression and cisplatin resistance in NSCLC by regulating ABCB1.

Lung cancer is one of the main causes of tumor lethality worldwide. Circular RNAs (circRNAs) have essential roles in tumor progression. However, in non-small cell lung carcinoma (NSCLC), the role of circRNAs remains unknown. In the present study, the expression, function and molecular mechanisms of a new circRNA, circRNA_103615, were investigated in NSCLC. Reverse transcription-quantitative PCR (RT-qPCR) was used to detect circRNA_103615 expression levels in NSCLC and normal tissues, as well as in NSCLC cell lines. MTT assay, flow cytometric assay, colony formation assay, and cell migration and invasion assays were used to examine the function of circRNA_103615 in NSCLC cells. MTT assay, colony formation assay, RT-qPCR, and western blotting were used to detect the effect of circRNA_103615 on cisplatin resistance. The results demonstrated that NSCLC cell lines and tissues had increased levels of circRNA_103615 compared with normal cells and normal tissues, respectively. Functionally, silencing of circRNA_103615 by small interfering RNA resulted in suppression of cell growth, migration, and invasion, but promotion of cell apoptosis. In addition, the cisplatin resistance of NSCLC was reversed by the silencing of circRNA_103615. Notably, ATP binding cassette subfamily Bmember 1 (ABCB1) expression was significantly decreased following circRNA_103615 knockdown, and ABCB1 overexpression reversed the effects of circRNA_103615 silencing on NSCLC cisplatin resistance. Thus, the present study indicated that circRNA_103615 may serve as a critical oncogene and potential novel biomarker in NSCLC, as well as a potential cisplatin resistance promoter, by regulating ABCB1 expression.

A Long Noncoding RNA, GAS5 Can Be a Biomarker for Docetaxel Response in Castration Resistant Prostate Cancer.

While functional studies of long noncoding RNAs (lncRNAs) have mostly focused on how they influence disease diagnosis and prognosis, the pharmacogenomic relevance of lncRNAs remains largely unknown. Here, we test the hypothesis that the expression of a lncRNA, grow arrest-specific 5 (GAS5) can be a biomarker for docetaxel response in castration resistant prostate cancer (CRPC) using both prostate cancer (PCa) cell lines and CRPC patient datasets. Our results suggest that lower GAS5 expression is associated with docetaxel resistance in both PCa cell lines and CRPC patients. Further experiments also suggest that GAS5 is downregulated in docetaxel resistant CRPC cell lines, which reinforces its potential as a biomarker for docetaxel response. To examine the underlying biological mechanisms, we transiently knockdown GAS5 expression in PCa cell lines and then subject the cells to docetaxel treatment overtime. We did not observe a decrease in docetaxel induced growth inhibition or apoptosis in the siRNA treated cells. The findings suggest that there is no direct causal relationship between change in GAS5 expression and docetaxel response. Subsequently, we explored the indirect regulation among GAS5, ATP binding cassette subfamily B member 1 (ABCB1), and docetaxel sensitivity. We showed that transient knockdown GAS5 did not lead to significant changes in ABCB1 expression. Therefore, we rule out the hypothesis that GAS5 directly down regulate ABCB1 that lead to docetaxel sensitivity. In conclusion, our work suggests that GAS5 can serve as a predictive biomarker for docetaxel response in CRPC; however, the exact mechanism behind the observed correlation remain to be elucidated.

Upregulation of Chemoresistance by Mg2+ Deficiency through Elevation of ATP Binding Cassette Subfamily B Member 1 Expression in Human Lung Adenocarcinoma A549 Cells.

Several anticancer drugs including cisplatin (CDDP) induce hypomagnesemia. However, it remains fully uncertain whether Mg2+ deficiency affects chemosensitivity of cancer cells. Here, we investigated the effect of low Mg2+ concentration (LM) on proliferation and chemosensitivity using human lung adenocarcinoma A549 cells. Cell proliferation was reduced by continuous culture with LM accompanied with the elevation of G1 phase proportion. The amounts of reactive oxygen species (ROS) and stress makers such as phosphorylated-ataxia telangiectasia mutated and phosphorylated-p53 were increased by LM. Cell injury was dose-dependently increased by anticancer drugs such as CDDP and doxorubicin (DXR), which were suppressed by LM. Similar results were obtained by roscovitine, a cell cycle inhibitor. These results suggest that LM induces chemoresistance mediated by ROS production and G1 arrest. The mRNA and protein levels of ATP binding cassette subfamily B member 1 (ABCB1) were increased by LM and roscovitine. The LM-induced elevation of ABCB1 and nuclear p38 expression was suppressed by SB203580, a p38 MAPK inhibitor. PSC833, an ABCB1 inhibitor, and SB203580 rescued the sensitivity to anticancer drugs. In addition, cancer stemness properties were suppressed by SB203580. We suggest that Mg2+ deficiency reduces the chemotherapy sensitivity of A549 cells, although it suppresses cell proliferation.

Decrease of ABCB1 protein expression and increase of G1 phase arrest induced by oleanolic acid in human multidrug-resistant cancer cells.

Oleanolic acid (OA) is a natural compound that can be found in a number of edible and medicinal plants and confers diverse biological actions. However, the direct target of OA in human tumor cells remains poorly understood, preventing its application in clinical and health settings. A previous study revealed that overexpression of caveolin-1 in human leukemia HL-60 cells can increase its sensitivity to OA. The present study aimed to investigate the effects of OA on the doxorubicin-resistant human breast cancer MCF-7 cell line (MCF-7/DOX), harringtonine-resistant human leukemia HL-60 cells (HL-60/HAR) and their corresponding parental cell lines. Western blotting was performed to measure protein expression levels, whilst Cell Counting Kit-8 (CCK-8) assays, cell cycle analysis (by flow cytometry) and apoptosis assays (with Annexin V/PI staining) were used to assess drug sensitivity. CCK-8 assay results suggested that MCF-7/DOX cells, which overexpress the caveolin-1 protein, have similar OA susceptibility to their parent line. In addition, sensitivity of MCF-7/DOX cells to OA was not augmented by knocking down caveolin-1 using RNA interference. HL-60/HAR cells exhibited a four-fold increased sensitivity to OA compared with that in their parental HL-60 cells according to CCK-8 assay. Both of the resistant cell lines exhibited higher numbers of cells at G1 phase arrest compared with those in their parent lines, as measured via flow cytometry. Treatment of both MCF-7 cell lines with 100 µM OA for 48 h induced apoptosis, with increased effects observed in resistant cells. However, no PARP-1 or caspase-3 cleavage was observed, with some positive Annexin V staining found after HL-60/HAR cells were treated with OA, suggesting that cell death occurred via non-classical apoptosis or through other cell death pathways. It was found that OA was not a substrate of ATP-binding cassette subfamily B member 1 (ABCB1) in drug-resistant cells, as indicated by the accumulation of rhodamine 123 assessed using flow cytometry. However, protein expression of ABCB1 in both of the resistant cell lines was significantly decreased after treatment with OA in a concentration-dependent manner. Collectively, these results suggest that OA could reduce ABCB1 protein expression and induce G1 phase arrest in multidrug-resistant cancer cells. These findings highlight the potential of OA for cancer therapy.

Circ_0002060 Enhances Doxorubicin Resistance in Osteosarcoma by Regulating the miR-198/ABCB1 Axis

Background: Osteosarcoma (OS) is a common, aggressive primary sarcoma of bone. Drug resistance is a huge obstacle to chemotherapy for cancer. This study aimed to investigate the role and mechanism of circ_0002060 in OS resistance to doxorubicin (DOX). Methods: The levels of circ_0002060, miR-198, and ATP-binding cassette subfamily B member 1 (ABCB1) in OS tissues and DOX-resistant OS cells were measured by quantitative real-time polymerase chain reaction or western blot assay. Kaplan-Meier analysis was performed to determine the relationship between circ_0002060 expression in OS tissues and overall survival of OS patients. The half-inhibitory concentration (IC50) of DOX was calculated using the Cell Counting Kit-8 (CCK-8) assay. Proliferation and apoptosis of DOX-resistant OS cells were assessed by colony formation assay and flow cytometry. The levels of apoptosis-related proteins in DOX-resistant OS cells were measured by western blot assay. Xenograft assay was utilized to analyze the effect of circ_0002060 on DOX resistance in vivo. The interactions among circ_0002060, miR-198, and ABCB1 in DOX-resistant OS cells were confirmed by dual-luciferase reporter assay, RNA immunoprecipitation assay, or RNA pull-down assay. Results: circ_0002060 and ABCB1 were upregulated, while miR-198 was downregulated in OS tissues and DOX-resistant OS cells. circ_0002060 silencing reduced DOX resistance in vitro and in vivo. Moreover, circ_0002060 enhanced DOX resistance by sponging miR-198. Besides, miR-198 decreased DOX resistance by binding to ABCB1. In addition, circ_0002060 sponged miR-198 to upregulate ABCB1 expression. Conclusions: circ_0002060 promoted DOX resistance and OS progression by regulating the miR-198/ABCB1 axis, suggesting that circ_0002060 might be a promising biomarker for OS therapy.

MEK reduces cancer-specific PpIX accumulation through the RSK-ABCB1 and HIF-1\u03b1-FECH axes

The efficacy of aminolevulinic acid (5-ALA)-based photodynamic diagnosis (5-ALA-PDD) and photodynamic therapy (5-ALA-PDT) is dependent on 5-ALA-induced cancer-specific accumulation of protoporphyrin IX (PpIX). We previously reported that inhibition of oncogenic Ras/MEK increases PpIX accumulation in cancer cells by reducing PpIX efflux through ATP-binding cassette sub-family B member 1 (ABCB1) and ferrochelatase (FECH)-catalysed PpIX conversion to haem. Here, we sought to identify the downstream pathways of Ras/MEK involved in the regulation of PpIX accumulation via ABCB1 and FECH. First, we demonstrated that Ras/MEK activation reduced PpIX accumulation in RasV12-transformed NIH3T3 cells and HRAS transgenic mice. Knockdown of p90 ribosomal S6 kinases (RSK) 2, 3, or 4 increased PpIX accumulation in RasV12-transformed NIH3T3 cells. Further, treatment with an RSK inhibitor reduced ABCB1 expression and increased PpIX accumulation. Moreover, HIF-1α expression was reduced when RasV12-transformed NIH3T3 cells were treated with a MEK inhibitor, demonstrating that HIF-1α is a downstream element of MEK. HIF-1α inhibition decreased FECH activity and increased PpIX accumulation. Finally, we demonstrated the involvement of RSKs and HIF-1α in the regulation of PpIX accumulation in human cancer cell lines. These results demonstrate that the RSK-ABCB1 and HIF-1α-FECH axes are the downstream pathways of Ras/MEK involved in the regulation of PpIX accumulation.