title: Cathepsin S-mediated autophagic flux in tumor-associated macrophages accelerate tumor development by promoting M2 polarization.
abstract: BACKGROUND
  Tumor-associated macrophages (TAMs) are the major component of tumor-infiltrating leukocytes. TAMs are heterogeneous, with distinct phenotypes influenced by the microenvironment surrounding tumor tissues, but relatively little is known about the key molecular in these cells that contribute to malignant phenotypes. Autophagic activity is a critical factor in tumor development that contributes to enhancing cellular fitness and survival in the hostile tumor microenvironment. However, the molecular basis and relations between autophagy and TAMs polarization remain unclear.
  
  
  METHODS
  Cathepsin S (Cat S) expression was analyzed in human colon carcinoma and normal colon tissues. In vivo effects were evaluated using PancO2 subcutaneous tumor model and SL4 hepatic metastasis model. Immunofluorescence staining, flow cytometry and real-time PCR were done to examine TAMs polarization. Western blotting assay, transmission electron microscopy, mCherry-GFP-LC3 transfection and DQ-BSA degradation assays were carried out to determine its role in regulating autophagy.
  
  
  RESULTS
  In the present study, we showed that the enhanced expression of Cat S correlated with the severity of histologic grade as well as clinical stage, metastasis, and recurrence, which are known indicators of a relatively poor prognosis of human colon carcinoma. Cat S knockout led to decreased tumor growth and metastasis. Moreover, Cat S knockout inhibited M2 macrophage polarization during tumor development. We further demonstrated that Cat S was required for not only autophagic flux but also the fusion processes of autophagosomes and lysosomes in TAMs. Importantly, we found that Cat S contributed to tumor development by regulating the M2 phenotype of TAMs through the activation of autophagy.
  
  
  CONCLUSIONS
  These results indicated that Cat S-mediated autophagic flux is an important mechanism for inducing M2-type polarization of TAMs, which leads to tumor development. These data provide strong evidence for a tumor-promoting role of autophagy in TAMs and suggest Cat S could be a potential target for cancer therapy.
authors.forename: Min
authors.initials: M
authors.lastname: Yang
authors.forename: Jingwei
authors.initials: J
authors.lastname: Liu
authors.forename: Jianghua
authors.initials: J
authors.lastname: Shao
authors.forename: Yanwen
authors.initials: Y
authors.lastname: Qin
authors.forename: Qunsheng
authors.initials: Q
authors.lastname: Ji
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Beijing Anzhen Hospital, Capital Medical University, Beijing, China. jdu@bcm.edu.
authors.forename: Jie
authors.initials: J
authors.lastname: Du
mesh_terms: D000230:Adenocarcinoma / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D000818:Animals; D001343:Autophagy; D015153:Blotting, Western; D002403:Cathepsins / Q000378:metabolism*; D016764:Cell Polarity; D003110:Colonic Neoplasms / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology*; D004195:Disease Models, Animal; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D064593:Heterografts; D006801:Humans; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D060888:Real-Time Polymerase Chain Reaction; D059016:Tumor Microenvironment / Q000276:immunology
chemical_list: D002403:Cathepsins; C028217:cathepsin S