title: The secretome of colon cancer stem cells contains drug-metabolizing enzymes.
abstract: Drug-resistant cancer stem cells (CSCs) have been implicated in tumor recurrence following chemotherapy. However, the contribution of CSCs to drug-resistance in colorectal cancer is unclear and CSC-intrinsic drug-resistance mechanisms are ill-defined. Here, we address these issues by proteomic analysis of the secretomes of CSCs and isogenic differentiated tumor cells (DTCs) isolated from three distinct metastasized colon tumors. Mass spectrometry-based proteomics identified 1254 unique proteins in the conditioned media of the paired CSC and DTC cultures. Ingenuity Pathway Analysis revealed that proteins governing 'Cell Death' were most significantly enriched in the CSC secretome. The vast majority of these (37/43) promote cell survival. The CSC secretome is also characterized by a pro-survival Nrf2 antioxidant signature. Interestingly, proteome-maintenance networks are highly enriched in the CSC secretome. CSCs also secrete high levels of drug-metabolizing enzymes, including aldehyde dehydrogenase 1 (ALDH1A1) and bleomycin hydrolase (BLMH). We show that these enzymes cause extracellular detoxification of maphosphamide and bleomycin respectively. We conclude that colorectal CSCs are characterized by extensive survival and anti-oxidant networks, which are likely to contribute to CSC-intrinsic drug-resistance. In addition, CSCs may modulate drug responses in nearby tumor cells by detoxifying chemotherapeutic drugs in the extracellular space.
  
  
  CONCLUSIONS
  Cancer stem cells are thought to play an important role in mediating drug resistance and tumor recurrence following chemotherapy. Therefore, it is important to identify the factors that are secreted by them. Our results provide novel insights into the pathways that govern the intrinsic resistance of CSCs to chemotherapy and, furthermore, demonstrate that they can also inactivate chemotherapeutic drugs in the extracellular space. A better understanding of the pathways that govern drug resistance in CSCs may help in developing effective CSC-targeting drugs.
authors.affiliation: Department of Surgery, University Medical Center Utrecht, G04-228, PO Box 85500, 3508GA Utrecht, The Netherlands.
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Emmink
authors.forename: André
authors.initials: A
authors.lastname: Verheem
authors.forename: Winan J
authors.initials: WJ
authors.lastname: Van Houdt
authors.forename: Ernst J A
authors.initials: EJ
authors.lastname: Steller
authors.forename: Klaas M
authors.initials: KM
authors.lastname: Govaert
authors.forename: Thang V
authors.initials: TV
authors.lastname: Pham
authors.forename: Sander R
authors.initials: SR
authors.lastname: Piersma
authors.forename: Inne H M
authors.initials: IH
authors.lastname: Borel Rinkes
authors.forename: Connie R
authors.initials: CR
authors.lastname: Jimenez
authors.forename: Onno
authors.initials: O
authors.lastname: Kranenburg
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D000975:Antioxidants / Q000737:chemistry / Q000378:metabolism; D001761:Bleomycin / Q000494:pharmacology; D045744:Cell Line, Tumor; D002469:Cell Separation; D002470:Cell Survival; D003110:Colonic Neoplasms / Q000378:metabolism*; D019295:Computational Biology; D017077:Culture Media, Conditioned / Q000737:chemistry; D003520:Cyclophosphamide / Q000031:analogs & derivatives / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D014411:Neoplastic Stem Cells / Q000378:metabolism; D018384:Oxidative Stress; D017510:Protein Folding; D020543:Proteome / Q000378:metabolism*; D040901:Proteomics; D012008:Recurrence
chemical_list: D000970:Antineoplastic Agents; D000975:Antioxidants; D017077:Culture Media, Conditioned; D020543:Proteome; C087936:maphosphamide; D001761:Bleomycin; D003520:Cyclophosphamide
keywords: Cancer stem cells; Colorectal cancer; Drug resistance; Mass-spectrometry; Secretome