Side population in human non-muscle invasive bladder cancer enriches for cancer stem cells that are maintained by MAPK signalling

• Published in: PloS one 2012-11, Vol.7 (11), p.e50690
• Main Authors: Hepburn, Anastasia C, Veeratterapillay, Rajan, Williamson, Stuart C, El-Sherif, Amira, Sahay, Neha, Thomas, Huw D, Mantilla, Alejandra, Pickard, Robert S, Robson, Craig N, Heer, Rakesh
• Format: Article
• Language: English
• Subjects: ABC transporter; Analysis; Animals; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters - genetics; Biology; Bladder; Bladder cancer; Cancer; Cell cycle; Cell Line, Tumor; Correlation; Disease-Free Survival; Enrichment; Female; Flow cytometry; Gene Expression Regulation, Neoplastic; Genotype & phenotype; Health aspects; Hospitals; Humans; Invasiveness; Kinases; MAP kinase; MAP Kinase Signaling System; Medical prognosis; Medical research; Medicine; Metabolic pathways; Mice; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Muscles; Mutation; Neoplasm Grading; Neoplasm Invasiveness; Neoplasm Proteins - genetics; Neoplasm Staging; Neoplastic Stem Cells - pathology; Notch1 protein; Pathology; Phenotype; Phosphoproteins - metabolism; Population; Prostate; Recurrence; Regulatory mechanisms (biology); Side-Population Cells - pathology; Signal transduction; Signaling; Stem cells; Survival; Tissues; Tumor cell lines; Tumorigenesis; Tumors; Urinary bladder; Urinary Bladder Neoplasms - genetics; Urinary Bladder Neoplasms - pathology; Urology
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0050690

Side population (SP) and ABC transporter expression enrich for stem cells in numerous tissues. We explored if this phenotype characterised human bladder cancer stem cells (CSCs) and attempted to identify regulatory mechanisms. Focusing on non-muscle invasive bladder cancer (NMIBC), multiple human cell lines were used to characterise SP and ABC transporter expression. In vitro and in vivo phenotypic and functional assessments of CSC behaviour were undertaken. Expression of putative CSC marker ABCG2 was assessed in clinical NMIBC samples (n = 148), and a role for MAPK signalling, a central mechanism of bladder tumourigenesis, was investigated. Results showed that the ABCG2 transporter was predominantly expressed and was up-regulated in the SP fraction by 3-fold (ABCG2(hi)) relative to the non-SP (NSP) fraction (ABCG2(low)). ABCG2(hi) SP cells displayed enrichment of stem cell markers (Nanog, Notch1 and SOX2) and a three-fold increase in colony forming efficiency (CFE) in comparison to ABCG2(low) NSP cells. In vivo, ABCG2(hi) SP cells enriched for tumour growth compared with ABCG2(low) NSP cells, consistent with CSCs. pERK was constitutively active in ABCG2(hi) SP cells and MEK inhibition also inhibited the ABCG2(hi) SP phenotype and significantly suppressed CFE. Furthermore, on examining clinical NMIBC samples, ABCG2 expression correlated with increased recurrence and decreased progression free survival. Additionally, pERK expression also correlated with decreased progression free survival, whilst a positive correlation was further demonstrated between ABCG2 and pERK expression. In conclusion, we confirm ABCG2(hi) SP enriches for CSCs in human NMIBC and MAPK/ERK pathway is a suitable therapeutic target.