title: The membrane mucin MUC4 is elevated in breast tumor lymph node metastases relative to matched primary tumors and confers aggressive properties to breast cancer cells.
abstract: BACKGROUND
  Previous studies indicate that overexpression of the membrane-associated mucin MUC4 is potently anti-adhesive to cultured tumor cells, and suppresses cellular apoptotic response to a variety of insults. Such observations raise the possibility that MUC4 expression could contribute to tumor progression or metastasis, but the potential involvement of MUC4 in breast cancer has not been rigorously assessed. The present study aimed to investigate the expression of the membrane mucin MUC4 in normal breast tissue, primary breast tumors and lymph node metastases, and to evaluate the role of MUC4 in promoting the malignant properties of breast tumor cells.
  
  
  METHODS
  MUC4 expression levels in patient-matched normal and tumor breast tissue was initially examined by immunoblotting lysates of fresh frozen tissue samples with a highly specific preparation of anti-MUC4 monoclonal antibody 1G8. Immunohistochemical analysis was then carried out using tissue microarrays encompassing patient-matched normal breast tissue and primary tumors, and patient-matched lymph node metastases and primary tumors. Finally, shRNA-mediated knockdown was employed to assess the contribution of MUC4 to the cellular growth and malignancy properties of JIMT-1 breast cancer cells.
  
  
  RESULTS
  Immunoblotting and immunohistochemistry revealed that MUC4 levels are suppressed in the majority (58%, p < 0.001) of primary tumors relative to patient-matched normal tissue. On the other hand, lymph node metastatic lesions from 37% (p < 0.05) of patients expressed higher MUC4 protein levels than patient-matched primary tumors. MUC4-positive tumor emboli were often found in lymphovascular spaces of lymph node metastatic lesions. shRNA-mediated MUC4 knockdown compromised the migration, proliferation and anoikis resistance of JIMT-1 cells, strongly suggesting that MUC4 expression actively contributes to cellular properties associated with breast tumor metastasis.
  
  
  CONCLUSIONS
  Our observations suggest that after an initial loss of MUC4 levels during the transition of normal breast tissue to primary tumor, the re-establishment of elevated MUC4 levels confers an advantage to metastasizing breast tumor cells by promoting the acquisition of cellular properties associated with malignancy.
authors.affiliation: Division of Basic Sciences, UC Davis Cancer Center, 4645 2ndAvenue, Sacramento, California 95817, USA. hcworkman@ucdavis.edu
authors.forename: Heather C
authors.initials: HC
authors.lastname: Workman
authors.forename: Jamie K
authors.initials: JK
authors.lastname: Miller
authors.forename: Ellen Q
authors.initials: EQ
authors.lastname: Ingalla
authors.forename: Rouminder P
authors.initials: RP
authors.lastname: Kaur
authors.forename: Diane I
authors.initials: DI
authors.lastname: Yamamoto
authors.forename: Laurel A
authors.initials: LA
authors.lastname: Beckett
authors.forename: Lawrence Jt
authors.initials: LJ
authors.lastname: Young
authors.forename: Robert D
authors.initials: RD
authors.lastname: Cardiff
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Borowsky
authors.forename: Kermit L
authors.initials: KL
authors.lastname: Carraway
authors.forename: Colleen
authors.initials: C
authors.lastname: Sweeney
authors.forename: Kermit L
authors.initials: KL
authors.lastname: Carraway
mesh_terms: D023102:Anoikis / Q000502:physiology; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008198:Lymph Nodes / Q000378:metabolism* / Q000473:pathology*; D008207:Lymphatic Metastasis; D055264:Mucin-4 / Q000032:analysis / Q000096:biosynthesis* / Q000276:immunology; D010997:Pleural Neoplasms / Q000378:metabolism / Q000556:secondary
chemical_list: D000911:Antibodies, Monoclonal; C524658:MUC4 protein, human; D055264:Mucin-4