title: Autophagy inhibition suppresses the tumorigenic potential of cancer stem cell enriched side population in bladder cancer.
abstract: The mechanisms that underlie tumor formation and progression have not been elucidated in detail in cancer biology. Recently, the identification of a tumor cell subset defined as cancer stem cells (CSCs), which is enriched for tumor initiating capacity, has engendered new perspectives towards selective targeting of tumors. In this study, we isolated the side population (SP) cells which share characteristics of CSCs from bladder cancer cell lines, T24 and UM-UC-3 by fluorescence activated cell sorting. The cells were cultured in serum free medium and expression profile of stem cell like markers (SOX-2, NANOG, KLF-4 and OCT-4), drug resistant genes (ABCG2 and MDR1) and spheroid forming capability were examined in SP, non-side population (NSP) and bulk T24 and UM-UC-3 cells. We observed that SP cells possessed a higher mRNA expression of SOX-2, NANOG, KLF-4, OCT-4, ABCG2, and MDR1 as well as a higher spheroid forming ability as compared to other bulk cells or NSP cells. The SP cells had low ROS levels and high GSH/GSSG ratio which may contribute to radio-resistance. The SP cells also showed substantial resistance to gemcitabine, mitomycin and cisplatin compared with the NSP counterpart. A high autophagic flux was observed in the SP cells. Both pharmacological and siRNA mediated inhibition of autophagy potentiated the chemotherapeutic effects of gemcitabine, mitomycin and cisplatin in these cells. We concluded that the ABCG2 expressing SP cells show autophagy associated cell survival and may be a potent target for developing more effective treatment in bladder carcinoma to enhance patient survival.
authors.affiliation: Department of Urology, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India.
authors.forename: Rani
authors.initials: R
authors.lastname: Ojha
authors.affiliation: Department of Nephrology, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India.
authors.forename: Vivekanand
authors.initials: V
authors.lastname: Jha
authors.affiliation: Department of Urology, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India.
authors.forename: Shrawan Kumar
authors.initials: SK
authors.lastname: Singh
authors.affiliation: Department of Biophysics, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India. Electronic address: shalmoli2007@yahoo.co.in.
authors.forename: Shalmoli
authors.initials: S
authors.lastname: Bhattacharyya
keywords: Autophagy; Bladder cancer; Cancer stem cell; Side population; T24; UM-UC-3