Abstract
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.
Highlights
One of the main features of chemoresistant cancer cells is the high cell surface expression of ATP binding cassette (ABC) transporters, such as P-glycoprotein (Pgp/ ABCB1), multidrug resistance (MDR) related proteins (MRPs/ABCCs) and breast cancer resistance protein (BCRP/ABCG2)
Among the ABC transporters detected on the surface of chemoresistant cells, ABCC1/MRP1 was more abundant on HT29/dx cells, and ABCC3/MRP3, ABCA1, ABCA2 showed lower expression levels
In this work we analyzed the surfaceome of chemosensitive Pgp-negative and chemoresistant Pgppositive human colon cancer cells and identified carbonic anhydrase type XII (CAXII) more highly expressed in the latter
Summary
One of the main features of chemoresistant cancer cells is the high cell surface expression of ATP binding cassette (ABC) transporters, such as P-glycoprotein (Pgp/ ABCB1), multidrug resistance (MDR) related proteins (MRPs/ABCCs) and breast cancer resistance protein (BCRP/ABCG2). These studies have identified proteins that were overexpressed in MDR cells, such as CD44 [8], dihydropyridine receptor alpha 2 and laminin subunit alpha 5 [9] These cell surface proteins could be of clinical utility as potential biomarkers predictive of chemoresistance and/or potential therapeutic targets. We applied the Cell Surface Capturing (CSC) technology to investigate the surfaceome of a Pgp-negative (chemosensitive) and Pgp-positive (chemoresistant) human colon cancer model system, with the goal to identify quantitative surfaceome changes indicative of chemoresistance This analysis identified carbonic anhydrase type XII (CAXII; accession number O43570, UniProtKB; http://www.uniprot.org) as a protein with significantly higher expression on the surface of chemoresistant cells. We investigated whether changes in CAXII cell surface abundance were able to induce and/or maintain the MDR phenotype and whether CAXII could potentially be exploited as therapeutic target to chemosensitize MDR cells
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