Overexpression of caveolin-1 induces alteration of multidrug resistance in Hs578T breast adenocarcinoma cells

Evidence of a synthetic lethality interaction between SETDB1 histone methyltransferase and CHD4 chromatin remodeling protein in a triple negative breast cancer cell line

During the tumorigenic process, cancer cells may become overly dependent on the activity of backup cellular pathways for their survival, representing vulnerabilities that could be exploited as therapeutic targets. Certain molecular vulnerabilities manifest as a synthetic lethality relationship, and the identification and characterization of new synthetic lethal interactions may pave the way for the development of new therapeutic approaches for human cancer. Our goal was to investigate a possible synthetic lethal interaction between a member of the Chromodomain Helicase DNA binding proteins family (CHD4) and a member of the histone methyltransferases family (SETDB1) in the molecular context of a cell line (Hs578T) representing the triple negative breast cancer (TNBC), a subtype of breast cancer lacking validated molecular targets for treatment. Therefore, we employed the CRISPR-Cas9 gene editing tool to individually or simultaneously introduce indels in the genomic loci corresponding to the catalytic domains of SETDB1 and CHD4 in the Hs578T cell line. Our main findings included: a) introduction of indels in exon 22 of SETDB1 sensitized Hs578T to the action of the genotoxic chemotherapy doxorubicin; b) by sequentially introducing indels in exon 22 of SETDB1 and exon 23 of CHD4 and tracking the percentage of the remaining wild-type sequences in the mixed cell populations generated, we obtained evidence of the existence of a synthetic lethality interaction between these genes. Considering the lack of molecular targets in TNBC, our findings provided valuable insights for development of new therapeutic approaches not only for TNBC but also for other cancer types.

Costunolide and parthenolide: Novel blood-brain barrier permeable sesquiterpene lactones to improve barrier tightness

Sesquiterpene lactones - such as those found in chicory - are considered promising bioactive compounds. These small molecules have shown several health benefits for various diseases, including brain disorders. However, it is unknown whether these compounds can cross the blood-brain barrier (BBB), and which could be the effects on brain microvascular endothelial cells. We show that six sesquiterpene lactones evaluated in an in vitro model of the BBB have different capacities to be transported through the barrier. Costunolide presented more than 20 % of transport while lactucin, 11β-13-dihydrolactucin, 11β-13-dihydrolactucopicrin, and parthenolide presented between 10 % and 20 %, whilst almost no transport was detected for lactucopicrin. Furthermore, costunolide and parthenolide reduced P-gp ABC transporter expression alongside an increase in caveolin-1, the main protein of caveolae. Remarkably, these two compounds improved barrier tightness by increasing the expression of both tight and adherens junctions. These findings open a new avenue to explore costunolide and parthenolide as promising compounds for brain therapies.

Caveolin-1 promotes glioma progression and maintains its mitochondrial inhibition resistance

BACKGROUND

Glioma is a lethal brain cancer and lacking effective therapies. Challenges include no effective therapeutic target, intra- and intertumoral heterogeneity, inadequate effective drugs, and an immunosuppressive microenvironment, etc. Deciphering the pathogenesis of gliomas and finding out the working mechanisms are urgent and necessary for glioma treatment. Identification of prognostic biomarkers and targeting the biomarker genes will be a promising therapy.

METHODS

From our RNA-sequencing data of the oxidative phosphorylation (OXPHOS)-inhibition sensitive and OXPHOS-resistant cell lines, we found that the scaffolding protein caveolin 1 (CAV1) is highly expressed in the resistant group but not in the sensitive group. By comprehensive analysis of our RNA sequencing data, Whole Genome Bisulfite Sequencing (WGBS) data and public databases, we found that CAV1 is highly expressed in gliomas and its expression is positively related with pathological processes, higher CAV1 predicts shorter overall survival.

RESULTS

Further analysis indicated that (1) the differentiated genes in CAV1-high groups are enriched in immune infiltration and immune response; (2) CAV1 is positively correlated with tumor metastasis markers; (3) the methylation level of CAV1 promoters in glioma group is lower in higher stage than that in lower stage; (4) CAV1 is positively correlated with glioma stemness; (5) higher expression of CAV1 renders the glioma cells' resistant to oxidative phosphorylation inhibitors.

CONCLUSION

Therefore, we identified a key gene CAV1 and deciphered its function in glioma progression and prognosis, proposing that CAV1 may be a therapeutic target for gliomas.

Caveolin-1-ACE2 axis modulates xenobiotic metabolism-linked chemoresistance in ovarian clear cell carcinoma

Among epithelial ovarian cancers, ovarian clear cell carcinoma (OCCC) remains markedly resistant to platinum-based chemotherapy, leading to poor clinical outcomes. In response to xenobiotic insults, caveolar platforms play crucial roles in modulating stress signaling responses in cancer cells. It has been hypothesized that caveolin-1 (Cav-1), a main component of the lipid raft, may regulate the response to platinum-based treatment in OCCC. The clinical transcriptomic evaluation demonstrated that high Cav-1 expression was positively associated with a favorable prognosis in patients with ovarian cancer. Cav-1 overexpression enhanced sensitivity to cisplatin (CDDP) treatment, whereas Cav-1 deficiency promoted chemoresistance in OCCC cells. Mechanistically, although Cav-1 counteracted angiotensin-converting enzyme 2 (ACE2) expression, ACE2 positively facilitated resistance to CDDP in OCCC cells. Furthermore, ACE2 restricted aryl hydrocarbon receptor expression and subsequent transcription of drug-metabolizing enzymes. Of note, ACE2 positively regulated the expression of the platinum-clearing enzyme CYP3A4. These findings suggest that the Cav-1-ACE2 axis modulates xenobiotic metabolism-linked chemoresistance in OCCC, predicting potential roles for the stress sentinel networks in oncogenic processes.

The history of small extracellular vesicles and their implication in cancer drug resistance

Small extracellular vesicles (EVs) in the last 20 years are demonstrated to possess promising properties as potential new drug delivery systems, biomarkers, and therapeutic targets. Moreover, EVs are described to be involved in the most important steps of tumor development and progression including drug resistance. The acquired or intrinsic capacity of cancer cells to resist chemotherapies is one of the greatest obstacles to overcome to improve the prognosis of many patients. EVs are involved in this mechanism by exporting the drugs outside the cells and transferring the drug efflux pumps and miRNAs in recipient cells, in turn inducing drug resistance. In this mini-review, the main mechanisms by which EVs are involved in drug resistance are described, giving a rapid and clear overview of the field to the readers.

Caveolae-Associated Molecules, Tumor Stroma, and Cancer Drug Resistance: Current Findings and Future Perspectives

Simple Summary

Cell membranes contain small invaginations called caveolae. They are a specialized lipid domain and orchestrate cellular signaling events, mechanoprotection, and lipid homeostasis. Formation of the caveolae depends on two classes of proteins, the caveolins and cavins, which form large complexes that allow their self-assembly into caveolae. Loss of either of these two proteins leads to distortion of the caveolae structure and disruption of many physiological processes that affect diseases of the muscle, metabolic states governing lipids, and the glucose balance as well as cancers. In cancers, the expression of caveolins and cavins is heterogenous, and they undergo alterations both in the tumors and the surrounding tumor microenvironment stromal cells. Remarkably, their expression and function has been associated with resistance to many cancer drugs. Here, we summarize the current knowledge of the resistance mechanisms and how this knowledge could be applied into the clinic in future.

Abstract

The discovery of small, “cave-like” invaginations at the plasma membrane, called caveola, has opened up a new and exciting research area in health and diseases revolving around this cellular ultrastructure. Caveolae are rich in cholesterol and orchestrate cellular signaling events. Within caveola, the caveola-associated proteins, caveolins and cavins, are critical components for the formation of these lipid rafts, their dynamics, and cellular pathophysiology. Their alterations underlie human diseases such as lipodystrophy, muscular dystrophy, cardiovascular disease, and diabetes. The expression of caveolins and cavins is modulated in tumors and in tumor stroma, and their alterations are connected with cancer progression and treatment resistance. To date, although substantial breakthroughs in cancer drug development have been made, drug resistance remains a problem leading to treatment failures and challenging translation and bench-to-bedside research. Here, we summarize the current progress in understanding cancer drug resistance in the context of caveola-associated molecules and tumor stroma and discuss how we can potentially design therapeutic avenues to target these molecules in order to overcome treatment resistance.

Membrane tension buffering by caveolae: a role in cancer?

Caveolae are bulb-like invaginations made up of two essential structural proteins, caveolin-1 and cavins, which are abundantly present at the plasma membrane of vertebrate cells. Since their discovery more than 60 years ago, the function of caveolae has been mired in controversy. The last decade has seen the characterization of new caveolae components and regulators together with the discovery of additional cellular functions that have shed new light on these enigmatic structures. Early on, caveolae and/or caveolin-1 have been involved in the regulation of several parameters associated with cancer progression such as cell migration, metastasis, angiogenesis, or cell growth. These studies have revealed that caveolin-1 and more recently cavin-1 have a dual role with either a negative or a positive effect on most of these parameters. The recent discovery that caveolae can act as mechanosensors has sparked an array of new studies that have addressed the mechanobiology of caveolae in various cellular functions. This review summarizes the current knowledge on caveolae and their role in cancer development through their activity in membrane tension buffering. We propose that the role of caveolae in cancer has to be revisited through their response to the mechanical forces encountered by cancer cells during tumor mass development.

Caveolae and lipid sorting: Shaping the cellular response to stress

Caveolae are an abundant and characteristic surface feature of many vertebrate cells. The uniform shape of caveolae is characterized by a bulb with consistent curvature connected to the plasma membrane (PM) by a neck region with opposing curvature. Caveolae act in mechanoprotection by flattening in response to increased membrane tension, and their disassembly influences the lipid organization of the PM. Here, we review evidence for caveolae as a specialized lipid domain and speculate on mechanisms that link changes in caveolar shape and/or protein composition to alterations in specific lipid species. We propose that high membrane curvature in specific regions of caveolae can enrich specific lipid species, with consequent changes in their localization upon caveolar flattening. In addition, we suggest how changes in the association of lipid-binding caveolar proteins upon flattening of caveolae could allow release of specific lipids into the bulk PM. We speculate that the caveolae-lipid system has evolved to function as a general stress-sensing and stress-protective membrane domain.

Multifaceted Roles of Caveolin-1 in Lung Cancer: A New Investigation Focused on Tumor Occurrence, Development and Therapy

Lung cancer is one of the most common and malignant cancers with extremely high morbidity and mortality in both males and females. Although traditional lung cancer treatments are fast progressing, there are still limitations. Caveolin-1 (Cav-1), a main component of caveolae, participates in multiple cellular events such as immune responses, endocytosis, membrane trafficking, cellular signaling and cancer progression. It has been found tightly associated with lung cancer cell proliferation, migration, apoptosis resistance and drug resistance. In addition to this, multiple bioactive molecules have been confirmed to target Cav-1 to carry on their anti-tumor functions in lung cancers. Cav-1 can also be a predictor for lung cancer patients’ prognosis. In this review, we have summarized the valuable research on Cav-1 and lung cancer in recent years and discussed the multifaceted roles of Cav-1 on lung cancer occurrence, development and therapy, hoping to provide new insights into lung cancer treatment.

Caveolin as a Universal Target in Dermatology

Caveolin-1 is strongly expressed in different dermal and subdermal cells and physically interacts with signaling molecules and receptors, among them with transforming growth factor beta (TGF-β), matrix metalloproteinases, heat shock proteins, toll-like and glucocorticoid receptors. It should therefore be heavily involved in the regulation of cellular signaling in various hyperproliferative and inflammatory skin conditions. We provide an overview of the role of the caveolin-1 expression in different hyperproliferative and inflammatory skin diseases and discuss its possible active involvement in the therapeutic effects of different well-known drugs widely applied in dermatology. We also discuss the possible role of caveolin expression in development of the drug resistance in dermatology. Caveolin-1 is not only an important pathophysiological factor in different hyperproliferative and inflammatory dermatological conditions, but can also serve as a target for their treatment. Targeted regulation of caveolin is likely to serve as a new treatment strategy in dermatology.

Targeted enhancement of flotillin-dependent endocytosis augments cellular uptake and impact of cytotoxic drugs

Cellular uptake is limiting for the efficacy of many cytotoxic drugs used to treat cancer. Identifying endocytic mechanisms that can be modulated with targeted, clinically-relevant interventions is important to enhance the efficacy of various cancer drugs. We identify that flotillin-dependent endocytosis can be targeted and upregulated by ultrasound and microbubble (USMB) treatments to enhance uptake and efficacy of cancer drugs such as cisplatin. USMB involves targeted ultrasound following administration of encapsulated microbubbles, used clinically for enhanced ultrasound image contrast. USMB treatments robustly enhanced internalization of the molecular scaffold protein flotillin, as well as flotillin-dependent fluid-phase internalization, a phenomenon dependent on the protein palmitoyltransferase DHHC5 and the Src-family kinase Fyn. USMB treatment enhanced DNA damage and cell killing elicited by the cytotoxic agent cisplatin in a flotillin-dependent manner. Thus, flotillin-dependent endocytosis can be modulated by clinically-relevant USMB treatments to enhance drug uptake and efficacy, revealing an important new strategy for targeted drug delivery for cancer treatment.

Exosomal miRNA confers chemo resistance via targeting Cav1/p-gp/M2-type macrophage axis in ovarian cancer

Background

Circulating miRNAs are known to play important roles in intercellular communication. However, the effects of exosomal miRNAs on cells are not fully understood.

Methods

To investigate the role of exosomal miR-1246 in ovarian cancer (OC) microenvironment, we performed RPPA as well as many other in vitro functional assays in ovarian cancer cells (sensitive; HeyA8, Skov3ip1, A2780 and chemoresistant; HeyA8-MDR, Skov3-TR, A2780-CP20). Therapeutic effect of miR-1246 inhibitor treatment was tested in OC animal model. We showed the effect of OC exosomal miR-1246 uptake on macrophages by co-culture experiments.

Findings

Substantial expression of oncogenic miR-1246 OC exosomes was found. We showed that Cav1 gene, which is the direct target of miR-1246, is involved in the process of exosomal transfer. A significantly worse overall prognosis were found for OC patients with high miR-1246 and low Cav1 expression based on TCGA data. miR-1246 expression were significantly higher in paclitaxel-resistant OC exosomes than in their sensitive counterparts. Overexpression of Cav1 and anti-miR-1246 treatment significantly sensitized OC cells to paclitaxel. We showed that Cav1 and multi drug resistance (MDR) gene is involved in the process of exosomal transfer. Our proteomic approach also revealed that miR-1246 inhibits Cav1 and acts through PDGFβ receptor at the recipient cells to inhibit cell proliferation. miR-1246 inhibitor treatment in combination with chemotherapy led to reduced tumor burden in vivo. Finally, we demonstrated that when OC cells are co-cultured with macrophages, they are capable of transferring their oncogenic miR-1246 to M2-type macrophages, but not M0-type macrophages.

Interpretation

Our results suggest that cancer exosomes may contribute to oncogenesis by manipulating neighboring infiltrating immune cells. This study provide a new mechanistic therapeutic approach to overcome chemoresistance and tumor progression through exosomal miR-1246 in OC patients.

Downregulation of caveolin-1 increased EGFR-TKIs sensitivity in lung adenocarcinoma cell line with EGFR mutation

Although epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), including gefitinib and erlotinib, have shown notable effects in lung adenocarcinoma patients harboring EGFR mutations, there are significant differences between individual patients in the degree of benefits provided by EGFR-TKIs. Some evidence supports a role for caveolin-1 (Cav-1) in modulating drug sensitivity. This study aimed to investigate whether Cav-1 plays an important role in sensitivity to EGFR-TKIs in lung adenocarcinoma cells. Downregulation of Cav-1 in PC-9 cells were performed to investigate changes in sensitivity to EGFR-TKIs in vitro and in vivo. Knockdown of Cav-1 dramatically enhanced sensitivity to EGFR-TKIs by down-regulating phosphorylation of EGFR. These results suggest that Cav-1 may be a predictor of the poor efficacy of EGFR-TKIs treatment in lung adenocarcinoma with EGFR mutations.

Caveolin-1: An Oxidative Stress-Related Target for Cancer Prevention

Aberrant oxidative metabolism is one of the hallmarks of cancer. Reactive species overproduction could promote carcinogenesis via inducing genetic mutations and activating oncogenic pathways, and thus, antioxidant therapy was considered as an important strategy for cancer prevention and treatment. Caveolin-1 (Cav-1), a constituent protein of caveolae, has been shown to mediate tumorigenesis and progression through oxidative stress modulation recently. Reactive species could modulate the expression, degradation, posttranslational modifications, and membrane trafficking of Cav-1, while Cav-1-targeted treatments could scavenge the reactive species. More importantly, emerging evidences have indicated that multiple antioxidants could exert antitumor activities in cancer cells and protective activities in normal cells by modulating the Cav-1 pathway. Altogether, these findings indicate that Cav-1 may be a promising oxidative stress-related target for cancer antioxidant prevention. Elucidating the underlying interaction mechanisms between oxidative stress and Cav-1 is helpful for enhancing the preventive effects of antioxidants on cancer, for improving clinical outcomes of antioxidant-related therapeutics in cancer patients, and for developing Cav-1 targeted drugs. Herein, we summarize the available evidence of the roles of Cav-1 and oxidative stress in tumorigenesis and development and shed novel light on designing strategies for cancer prevention or treatment by utilizing the interaction mode between Cav-1 and oxidative stress.

Caveolin-1, a stress-related oncotarget, in drug resistance

Caveolin-1 (Cav-1) is both a tumor suppressor and an oncoprotein. Cav-1 overexpression was frequently confirmed in advanced cancer stages and positively associated with ABC transporters, cancer stem cell populations, aerobic glycolysis activity and autophagy. Cav-1 was tied to various stresses including radiotherapy, fluid shear and oxidative stresses and ultraviolet exposure, and interacted with stress signals such as AMP-activated protein kinase. Finally, a Cav-1 fluctuation model during cancer development is provided and Cav-1 is suggested to be a stress signal and cytoprotective. Loss of Cav-1 may increase susceptibility to oncogenic events. However, research to explore the underlying molecular network between Cav-1 and stress signals is warranted.

Caveolin-1 in Breast Cancer: Single Molecule Regulation of Multiple Key Signaling Pathways

Caveolin-1 is a 22-kD trans-membrane protein enriched in particular plasma membrane invaginations known as caveolae. Cav-1 expression is often dysregulated in human breast cancers, being commonly upregulated in cancer cells and downregulated in stromal cells. As an intracellular scaffolding protein, Cav-1, is involved in several vital biological regulations including endocytosis, transcytosis, vesicular transport, and signaling pathways. Several pathways are modulated by Cav-1 including estrogen receptor, EGFR, Her2/neu, TGFβ, and mTOR and represent as major drivers in mammary carcinogenesis. Expression and role of Cav-1 in breast carcinogenesis is highly variable depending on the stage of tumor development as well as context of the cell. However, recent data have shown that downregulation of Cav-1 expression in stromal breast tumors is associated with frequent relapse, resistance to therapy, and poor outcome. Modification of Cav-1 expression for translational cancer therapy is particularly challenging since numerous signaling pathways might be affected. This review focuses on present understanding of Cav-1 in breast carcinogenesis and its potential role as a new biomarker for predicting therapeutic response and prognosis as well as new target for therapeutic manipulation.

Caveolin-1 mediates chemoresistance in cisplatin-resistant ovarian cancer cells by targeting apoptosis through the Notch-1/Akt/NF-κB pathway

Caveolin-1 (Cav-1), a family of ubiquitously expressed oligomeric structural proteins in many mammalian cells, has been shown to be an effective regulator of tumorigenesis. Recent studies have indicated that Cav-1 can promote resistance to chemotherapy in a variety of tumors. However, the regulation of Cav-1 on chemoresistance in ovarian cancer is still unknown. In the present study, the mRNA and protein expression level was investigated by RT-PCR and western blot analysis, respectively, and the 50% inhibitory concentration (IC50) value was measured by MTT assay. The protein expression level of P-glycoprotein (P-gp), Notch-1, p-Akt and p-NF-κB p65 were detected using western blot analysis and the apoptotic ratio was determined using the Annexin V-FITC/PI detection kit. The results showed that the mRNA and protein expression levels of Cav-1 were significantly higher in SKOV3/DDP and A2780/DDP than in SKOV3 and A2780, respectively. Knockdown of Cav-1 significantly decreased the IC50 value in cisplatin-resistant cells. The protein expression level of P-gp in SKOV3/DDP and A2780/DDP was significant higher than SKOV3 and A2780, respectively, and had no correlation with the Cav-1 siRNA transfection. The apoptotic ratio induced by cisplatin in normal ovarian cancer cells was higher than cisplatin-resistant ovarian cancer cells, and knockdown of Cav-1 could significantly enhance cisplatin induced cell apoptosis. Furthermore, knockdown of Cav-1 was also able to significantly downregulate the protein expression level of Notch-1, p-Akt and p-NF-κB p65 in cisplatin-resistant ovarian cancer cells. Overexpression of Cav-1 upregulated the IC50 value, but under the effect of Notch-1 siRNA or LY294002 or PDTC, the IC50 value was markedly decreased. Our results suggested that Cav-1 can promote the chemoresistance of ovarian cancer by targeting apoptosis through the Notch-1/Akt/NF-κB pathway.

The influence of a caveolin-1 mutant on the function of P-glycoprotein

The genetic heterogeneity in cancer cells has an increased chance in the acquisition of new mutant such as drug-resistant phenotype in cancer cells. The phenotype of drug resistance in cancer cells could be evaluated by the number or function of drug transporters on cell membranes, which would lead to decreased intracellular anti-cancer drugs concentration. Caveolae are flask-shaped invaginations on cell membrane that function in membrane trafficking, endocytosis, and as a compartment where receptors and signaling proteins are concentrated. Caveolin-1 (CAV1) is the principal structural protein of caveolae and closely correlates with multidrug resistance in cancer cells. In a systematic study of the ubiquitin-modified proteome, lysine 176 of CAV1 was identified as a potential post-translational modification site for ubiquitination. In this article, we identified a mutation at lysine 176 to arginine (K176R) on CAV1 would interfere with the biogenesis of caveolae and broke the interaction of CAV1 with P-glycoprotein. Functional assays further revealed that K176R mutant of CAV1 in cancer cells increased the transport activity of P-glycoprotein and decreased the killing ability of anti-cancer drugs in non-small-cell lung cancer cell lines.

Carbonic anhydrase XII is a new therapeutic target to overcome chemoresistance in cancer cells

Multidrug resistance (MDR) in cancer cells is a challenging phenomenon often associated with P-glycoprotein (Pgp) surface expression. Finding new ways to bypass Pgp-mediated MDR still remains a daunting challenge towards the successful treatment of malignant neoplasms such as colorectal cancer.

We applied the Cell Surface Capture technology to chemosensitive and chemoresistant human colon cancer to explore the cell surface proteome of Pgp-expressing cells in a discovery-driven fashion. Comparative quantitative analysis of identified cell surface glycoproteins revealed carbonic anhydrase type XII (CAXII) to be up-regulated on the surface of chemoresistant cells, similarly to Pgp. In cellular models showing an acquired MDR phenotype due to the selective pressure of chemotherapy, the progressive increase of the transcription factor hypoxia-inducible factor-1 alpha was paralleled by the simultaneous up-regulation of Pgp and CAXII. CAXII and Pgp physically interacted at the cell surface. CAXII silencing or pharmacological inhibition with acetazolamide decreased the ATPase activity of Pgp by altering the optimal pH at which Pgp operated and promoted chemosensitization to Pgp substrates in MDR cells.

We propose CAXII as a new secondary marker of the MDR phenotype that influences Pgp activity directly and can be used as a pharmacological target for MDR research and potential treatment.

HER2 as therapeutic target for overcoming ATP-binding cassette transporter-mediated chemoresistance in small cell lung cancer

Small cell lung cancer (SCLC) easily acquires multidrug resistance after successful initial therapy. Overexpression of ATP-binding cassette (ABC) transporters is important for the multidrug resistance. Among them, ABCB1 and ABCG2 are known to be upregulated in chemoresistant SCLC cells. We found that human epidermal growth factor receptor 2 (HER2) expressions are also upregulated in chemoresistant SBC-3/ETP, SBC-3/SN-38, and SBC-3/CDDP cells, compared with chemosensitive SBC-3 cells. Lapatinib, a tyrosine kinase inhibitor of HER2, could not suppress proliferation of these HER2-positive SCLC cells alone but successfully restored chemosensitivity to etoposide and SN-38 with a clinically applicable concentration. The reversal effect of lapatinib was thought to be caused by inhibition of drug efflux pump functions of ABC transporters, although lapatinib itself has been reported to be a substrate for them. Moreover, knocking down of HER2 by an short interfering RNA weakened the effect of lapatinib on ABCB1, indicating the involvement of HER2 in the inhibitory mechanisms. Notably, we showed that caveolin-1 and Src play key roles in modulating ABCB1 function via HER2 inactivation. In SBC-3/ETP cells, dephosphorylation of HER2 by lapatinib activates Src and successively leads to increased caveolin-1 phosphorylation. Through this process, caveolin-1 dissociates from HER2 and strengthens association with ABCB1, and finally impairs the pump functions. Furthermore, we showed that treatment by lapatinib in combination with etoposide or irinotecan significantly suppresses the growth of subcutaneous SBC-3/ETP and SBC-3/SN-38 tumors in mice, respectively. Collectively, these results indicate that combination therapy with lapatinib and cytotoxic agents could conquer ABC transporter-mediated chemoresistance especially in HER2-positive SCLC.

The role of caveolin-1 in human breast cancer

Caveolin-1 is the essential constituent protein of specialised plasma membrane invaginations called caveolae. The unique topology of caveolin-1 facilitates the role of caveolae as molecular hubs, integrating the activity of a multitude of signalling molecules. Despite improvements in our understanding of caveolin-1 interactions and the function of caveolae, the relationship between dysfunctional caveolin-1 and tumourigenesis remains contentious. Perhaps most intriguing has been the demonstration of both oncogenic and tumour suppressor function within particular tumour types, including breast cancer. In this review, the biological and clinical relevance of caveolin-1 in human breast cancer are considered. Evidence is systematically presented for the potential tumour suppressor and oncogenic functions of caveolin-1. Specific reference is made to interactions between caveolin-1 and signalling pathways in the clinical and biological subtypes of breast cancer. Areas of controversy are discussed and technical considerations are highlighted. Translational implications and potential for specific therapeutic manipulation of caveolin-1 are evaluated in the context of evidence from in vitro and in vivo studies.

Rab4 interacts with the human P-glycoprotein and modulates its surface expression in multidrug resistant K562 cells

P-glycoprotein (P-gp) is a plasma membrane glycoprotein that has been signaled as a primary cause of multidrug resistance (MDR) in tumors. We performed a yeast 2-hybrid screen using the C-terminal domain of P-gp and identified 2 small GTPases involved in vesicular trafficking, Rab4 and Rab14, which complex with P-gp. The overexpression of GFP-Rab4, either transiently or stably, but not of Rab14, in K562ADR cells decreased the presence of P-gp in the cell surface. As a result, expression of this GTPase reduced the MDR phenotype of K562ADR cells, by augmenting the intracellular accumulation of daunomycin (DNM). This effect was mimicked by the constitutively active Rab4Q72L mutant, but not by the dominant negative Rab4S27N mutant. Rab4 regulated excocytotic P-gp trafficking to the plasma membrane from intracellular compartments, and this modulation required the interaction of both proteins and the GTPase activity. Noteworthy, K562ADR cells exhibited a significant reduction of Rab4 levels, but not of other Rab GTPases, as compared with the sensitive parental cell line, suggesting that the development of the MDR phenotype in these cells involves upregulation of P-gp and a concomitant downregulation of proteins that regulate its surface expression. Attenuation of endogenous Rab4 levels in K562ADR by RNA interference enhanced the expression of P-gp in the cell surface, and reduced the uptake of DNM. Accordingly, these findings substantiate the notion that modulation of the temporal and spatial distribution of P-gp in cancer cells may be a valid therapeutic strategy to alleviate the MDR phenotype, and signal to Rab4 as a potential target.

Knockdown of caveolin-1 decreases activity of breast cancer resistance protein (BCRP/ABCG2) and increases chemotherapeutic sensitivity

The ATP-binding cassette transporter breast cancer resistance protein (BCRP/ABCG2) is supposed to be a major determinant of the multidrug resistance phenotype of tumors by extruding chemically diverse cytostatic drugs out of tumor cells. BCRP physically and possibly also functionally interacts with caveolin-1 (CAV1, encoded by Cav1), an integral membrane protein of lipid rafts important for signal transduction and membrane trafficking. Moreover, Cav1 is linked to an aggressive phenotype of cancer cells in various tumors. We therefore investigated whether Cav1 plays a functional role in the regulation of BCRP transport activity and in the resistance against chemotherapeutics that are BCRP substrates. As a cell model, we used the BCRP overexpressing cell line MDCKII-BCRP and the corresponding parental cell line MDCKII as a control. Cav1 expression was down-regulated using retrovirus-mediated RNA interference technology. BCRP activity was assessed by pheophorbide A efflux assay and the resistance towards cytostatic drugs was measured by proliferation assays. Efficient knockdown of Cav1 reduced Cav1 expression by 85-95% and BCRP activity by 35%. Concurrently, it reduced resistance towards the BCRP substrate mitoxantrone but not towards vincristine, a chemotherapeutic that is not extruded by BCRP. Western blot analysis of gradient ultracentrifugation fractions and immunofluorescence demonstrates that BCRP localization within the plasma membrane was largely unaltered in Cav1-deficient cells compared to controls. The diminished BCRP function after Cav1 knockdown is, thus, likely mediated by alterations in protein-protein interactions and suggests a positive regulation of BCRP function by CAV1.

Modulation of endocrine and transport functions in human trophoblasts by saquinavir and nelfinavir

OBJECTIVES

The distribution of drugs to the maternal-fetal interface is influenced by the expression of various efflux transporters. Among these transporters, P-glycoprotein (P-gp) is responsible for the efflux of a great number of drugs such as protease inhibitors of the human immunodeficiency virus, thus reducing the chemical exposure of the fetus.

STUDY DESIGN

The effects of saquinavir and nelfinavir were evaluated on human trophoblast functions and integrity by investigating their effect on human chorionic gonadotropin (hCG) secretion and on P-gp expression and functionality.

RESULTS

Nelfinavir significantly reduced hCG secretion by 30% after a 48-h treatment but it had no effect on syncytia formation. Saquinavir had no effect on hCG secretion but significantly increased both expression (to a 2-fold extent) and functionality (by 17.9%) of P-gp, whereas nelfinavir only increased functionality (by 23.1%) with a dissociation of P-gp from caveolin-1.

CONCLUSION

These results suggest that the effects of saquinavir and nelfinavir differ on trophoblast functions.

MDR1 3435T and 1236T alleles delay disease progression to pediatric AIDS but have no effect on HIV-1 vertical transmission

BACKGROUND

Single nucleotide polymorphisms (SNPs) in the MDR1 gene, coding for the drug transporter P-glycoprotein, may modulate the response to antiretroviral therapy and susceptibility to HIV-1 infection. We investigated whether the MDR1 SNPs C1236T (exon 12) and C3435T (exon 26) affect HIV-1 vertical transmission and progression to pediatric AIDS.

METHODS

The MDR1 genotypes were identified by PCR-restriction fragment length polymorphism (RFLP) assays in 219 HIV-infected, 128 exposed uninfected children and 231 HIV-seronegative blood donors. Genotype and haplotype frequencies were estimated in the different groups. The median follow-up time of the infected cohort was 108 months and AIDS-free time was evaluated for the different MDR1 genotypes in 171 HIV-infected children.

RESULTS

We found that both C1236T and C3435T polymorphisms were highly frequent in the studied groups (approximately 0.44) and showed strong linkage disequilibrium. There was no association between MDR1 genotypes and HIV-1 vertical transmission. However, a protective effect against progression to AIDS was associated with MDR1 3435CT, 1236CT and 1236TT genotypes (P = 0.005, P = 0.024 and P = 0.026, respectively). Moreover, haplotype pairs' analysis showed that the 3435CT/1236CT and 3435CT/1236TT exerted a significant protection against progression to pediatric AIDS (P = 0.0025 and P = 0.006, respectively).

CONCLUSION

We conclude that in Argentinean children, MDR1 genotypes are associated with progression to AIDS, but they do not affect HIV-1 susceptibility by vertical transmission. These results support the notion that P-glycoprotein plays a role in HIV-1 infection independently from its role in drug transport.

Caveats of caveolin-1 in cancer progression

Caveolin-1, an essential scaffold protein of caveolae and cellular transport processes, lately gained recognition as a stage- and tissue-specific tumor modulator in vivo. Patient studies and rodent models corroborated its janus-faced role as a tumor suppressor in non-neoplastic tissue, its down-regulation (loss of function) upon transformation and its re-expression (regain of function) in advanced-stage metastatic and multidrug resistant tumors. This review is focussed on the role of caveolin-1 in metastasis and angiogenesis and its clinical implications as a prognostic marker in cancer progression.

Suppression of staurosporine-mediated apoptosis in Hs578T breast cells through inhibition of neutral-sphingomyelinase by caveolin-1

Caveolin-1, a 21-24kDa integral membrane protein, is a principal structural component of caveolae in vivo. To investigate the roles of caveolin-1, we established stable transfectants in Hs578T breast adenocarcinoma cells that had up- and down-regulated caveolin-1 expression. In the paper, we demonstrated that caveolin-1 overexpression in Hs578T cells significantly reduced staurosporine-induced apoptosis and the levels of caveolin-1 expression positively correlated with the number of colonies and colony size in soft agar. Our findings indicate for the first time in Hs578T cells that caveolin-1 might play a pivotal role in regulating apoptosis as a suppressor rather than a facilitator through inhibition of neutral-sphingomyelinase, decrease of ceramide, furthermore, activation of Akt signaling pathway.

Modulation of p-glycoprotein function by caveolin-1 phosphorylation

p-glycoprotein (p-gp) is an ATP-binding cassette transporter and its overexpression is responsible for the acquisition of the multidrug resistance phenotype in human tumors. p-gp is localized at the blood-brain barrier and is involved in brain cytoprotection. Our previous work used immunoprecipitation to show that caveolin-1 can interact with p-gp. In this study, we provide evidence that caveolin-1 regulates p-gp transport activity in a rat brain endothelial cell line (RBE4). Down-regulation of caveolin-1 by siRNA reduced the interaction between p-gp and caveolin-1, followed by a decrease in [3H]-Taxol and [3H]-Vinblastine accumulation in RBE4 cells. The latter result showed that down-regulation of caveolin-1 enhanced p-gp transport activity. RBE4 cells were also transfected with Sarcoma in order to modulate caveolin-1 phosphorylation. Overexpression of Sarcoma, a protein tyrosine kinase, stimulated caveolin-1 phosphorylation and increased both [3H]-Taxol and [3H]-Vinblastine accumulation as well as Hoechst 33342 accumulation. Transfection of caveolin-1 inhibits p-gp transport activity. Conversely, transfection of the mutant cavY14F decreased the p-gp/caveolin-1 interaction and reduced accumulation of the two p-gp substrates. Thus, our data show that caveolin-1 regulates p-gp function through the phosphorylation state of caveolin-1 in endothelial cells from the blood-brain barrier.

cDNA microarray analysis of isogenic paclitaxel- and doxorubicin-resistant breast tumor cell lines reveals distinct drug-specific genetic signatures of resistance

cDNA microarray analysis is a highly useful tool for the classification of tumors and for prediction of patient prognosis to specific cancers based on this classification. However, to date, there is little evidence that microarray approaches can be used to reliably predict patient response to specific chemotherapy drugs or regimens. This is likely due to an inability to differentiate between genes affecting patient prognosis and genes that play a role in response to specific drugs. Thus, it would be highly useful to identify genes whose expression correlates with tumor cell sensitivity to specific chemotherapy agents in a drug-specific manner. Using cDNA microarray analysis of wildtype MCF-7 breast tumor cells and isogenic paclitaxel-resistant (MCF-7(TAX)) or doxorubicin-resistant (MCF-7(DOX)) derivative cell lines, we have uncovered drug-specific changes in gene expression that accompany the establishment of paclitaxel or doxorubicin resistance. These changes in gene expression were confirmed by quantitative reverse transcription polymerase chain reaction and immunoblotting experiments, with a confirmation rate of approximately 91-95%. The genes identified may prove highly useful for prediction of response to paclitaxel or doxorubicin in patients with breast cancer. To our knowledge this is the first report of drug-specific genetic signatures of resistance to paclitaxel or doxorubicin, based on a comparison of gene expression between isogenic wildtype and drug-resistant tumor cell lines. Moreover, this study provides significant insight into the wide variety of mechanisms through which resistance to these agents may be acquired in breast cancer.

The implications of P-glycoprotein in HIV: friend or foe?

P-glycoprotein (P-gp), coded by the ABCB1 gene, has a wide tissue distribution. The drug transporter is known to limit the bioavailability of a plethora of drugs and xenobiotics including the human immunodeficiency virus (HIV) protease inhibitors. There remains a considerable degree of debate in the literature with respect to the role of ABCB1 polymorphisms in HIV-treatment outcome and some studies have also implicated antiretroviral drugs as inducers of P-gp. Recent evidence indicates a role for P-gp in the inhibition of viral infectivity and/or release and cellular relationships with other infection-related proteins (and cholesterol). It is becoming increasingly clear that future studies on P-gp in HIV should consider both pharmacological and virological issues.

Suppression of P-glycoprotein gene expression in Hs578T/Dox by the overexpression of caveolin-1

Caveolin-1, the principal component of caveolae, is a 21-24 kDa integral membrane protein. The interaction of the caveolin-1 scaffolding domain with signaling molecules can functionally inhibit the activity of these signaling proteins. Little is known about how caveolin-1 influences the expression of P-glycoprotein (P-gp), an ABC transporter encoded by multi-drug resistance (MDR1) gene. To elucidate the possible mechanism between caveolin-1 and P-gp expression, in the present study, we overexpressed caveolin-1 in the Hs578T/Dox breast adenocarcinoma cells, a multidrug resistant line, and then selected single clone cells highly expressing caveolin-1 level. Both Western blot and confocal microscopy analyses showed that caveolin-1 was markedly overexpressed in the transfectants, while P-gp protein was almost abolished. Reverse transcription polymerase chain reaction also showed that the expression of P-gp mRNA was significantly suppressed in the transfectants. It was confirmed further by Northern blot analysis. Moreover, through measuring the changes of drug resistance and P-gp transport activity in the transfectants, we found that overexpression of caveolin-1 reversed drug resistance of transfectants and lowered their P-gp transport activity to the level of Hs578T/S. Taken together, our results indicate that such suppression of P-gp in the transfectants overexpressing caveolin-1 may occur at the transcriptional level.

Overexpression of caveolin-1 increases plasma membrane fluidity and reduces P-glycoprotein function in Hs578T/Dox

Cholesterol is a key lipid in mediating the enzyme activity or signaling pathway of many proteins on the plasma membrane in mammalian cells. In this report, we demonstrate for the first time that after overexpressing caveolin-1, the plasma membrane cholesterol level was decreased by about 12% and 30% for doxorubicin-sensitive and doxorubicin-resistant Hs578T breast cancer cells, respectively. However, the total cholesterol level in both cell lines was increased by about 10%. By measuring fluorescence and flow cytometry using the fluorescence dyes 1,6-diphenyl-1,3,5-hexatriene and Merocyanine 540, we found that overexpressing caveolin-1 resulted in a similar increase in membrane fluidity and loosening of lipid packing density as cholesterol depletion by 1 mM methyl-beta-cyclodextrin (MbetaCD) or 2-hydroxypropyl-beta-cyclodextrin (HbetaCD). Moreover, we found that the transport activity of P-gp was significantly inhibited by 1 mM MbetaCD or HbetaCD, which is also similar to the inhibitory effect of caveolin-1 overexpression. Our data demonstrate for the first time that the reduction of the plasma membrane cholesterol level induced by overexpressing caveolin-1 may indirectly inhibit P-gp transport activity by increasing plasma membrane fluidity.