title: Loss of LKB1 disrupts breast epithelial cell polarity and promotes breast cancer metastasis and invasion.
abstract: BACKGROUND
  LKB1, also known as STK11, is a master kinase that serves as an energy metabolic sensor and is involved in cell polarity regulation. Recent studies have indicated that LKB1 is related to breast tumorigenesis and breast cancer progression. However, little work has been done on the roles of LKB1 in cell polarity and epithelial-mesenchymal transition in breast cancer. In this study, we tried to prove that loss of LKB1 disrupts breast epithelial cell polarity and causes tumor metastasis and invasion.
  
  
  METHODS
  The relationships of LKB1 expression to clinic-pathological parameters and epithelial markers E-cadherin and high-molecular-weight -cytokeratin (HMW-CK) were investigated in 80 clinical breast cancer tissue samples and their paired normal control breast tissue samples by using immunohistochemistry. Then, the LKB1 expressions in metastatic and non-metastatic breast cancer cell lines were compared. The roles of LKB1 in cell polarity and epithelial-mesenchymal transition in breast cancer were determined by using immunofluorescence, western blot assay, and cell migration and invasive assays. Finally, the non-transformed human breast cell line MCF-10A was cultured in three dimensions to further reveal the role of LKB1 in breast epithelial cell polarity maintenance.
  
  
  RESULTS
  Histopathological analysis showed that LKB1 expression level was significantly negatively correlated with breast cancer TNM stage, and positively correlated with ER/PR status and expression levels of E-cadherin and HMW-CK. Immunofluorescence staining showed that LKB1 was co-localized with E-cadherin at adheren junctions. In vitro analysis revealed that loss of LKB1 expression enhanced migration, invasion and the acquisition of mesenchymal phenotype, while LKB1 overexpression in MDA-MB-435 s cells, which have a low basal level of LKB1 expression, promoted the acquisition of epithelial phenotype. Finally, it was found for the first time that endogenous LKB1 knockdown resulted in abnormal cell polarity in acini formed by non-transformed breast epithelial cells grown in 3D culture.
  
  
  CONCLUSIONS
  Our data indicated that low expression of LKB1 was significantly associated with established markers of unfavorable breast cancer prognosis, such as loss of ER/PR, E-cadherin and HMW-CK. Knockdown of endogenous LKB1 gave rise to dysregulation of cell polarity and invasive phenotype of breast cancer cells.
authors.affiliation: Center for Translational Medicine, The First Affiliated Hospital, Xian Jiaotong University College of Medicine, 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China. gougoubeibei@126.com.
authors.forename: Juan
authors.initials: J
authors.lastname: Li
authors.affiliation: Center for Translational Medicine, The First Affiliated Hospital, Xian Jiaotong University College of Medicine, 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China. 0118liujie@163.com.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.affiliation: Center for Translational Medicine, The First Affiliated Hospital, Xian Jiaotong University College of Medicine, 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China. lipingping715@139.com.
authors.forename: Pingping
authors.initials: P
authors.lastname: Li
authors.affiliation: Center for Translational Medicine, The First Affiliated Hospital, Xian Jiaotong University College of Medicine, 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China. maoxiaona882005@126.com.
authors.forename: Xiaona
authors.initials: X
authors.lastname: Mao
authors.affiliation: Center for Translational Medicine, The First Affiliated Hospital, Xian Jiaotong University College of Medicine, 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China. lwjclever@163.com.
authors.forename: Wenjie
authors.initials: W
authors.lastname: Li
authors.affiliation: Department of Oncology, The First Affiliated Hospital, Xian Jiaotong University College of Medicine, 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China. yangjin@mail.xjtu.edu.cn.
authors.forename: Jin
authors.initials: J
authors.lastname: Yang
authors.affiliation: Center for Translational Medicine, The First Affiliated Hospital, Xian Jiaotong University College of Medicine, 277 West Yanta Road, Xi'an, Shaanxi, 710061, People's Republic of China. liupeijun@mail.xjtu.edu.cn.
authors.forename: Peijun
authors.initials: P
authors.lastname: Liu
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D016022:Case-Control Studies; D002465:Cell Movement; D016764:Cell Polarity; D015536:Down-Regulation; D004847:Epithelial Cells / Q000201:enzymology* / Q000473:pathology; D058750:Epithelial-Mesenchymal Transition; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D061986:MCF-7 Cells; D042361:Mammary Glands, Human / Q000201:enzymology* / Q000473:pathology; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction; D014162:Transfection
chemical_list: D014408:Biomarkers, Tumor; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases