Research article
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
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* Corresponding author: Kermit L Carraway klcarraway@ucdavis.edu
1 Division of Basic Sciences, UC Davis Cancer Center, 4645 2ndAvenue, Sacramento, California 95817, USA
2 Department of Dermatology, UC Davis School of Medicine, 4645 2nd Avenue, Sacramento, California 95817, USA
3 Division of Biostatistics, UC Davis School of Medicine, Medical Sciences Building 1-C, Davis, California 95616, USA
4 Center for Comparative Medicine, Department of Pathology and Laboratory Medicine, UC Davis, County Road 98 and Hutchison Drive, Davis, California 95616, USA
5 Department of Cell Biology and Anatomy, University of Miami School of Medicine, 1550 NW 10th Avenue, Miami, Florida 33101, USA
Breast Cancer Research 2009, 11:R70 doi:10.1186/bcr2364
Published: 18 September 2009Abstract
Introduction
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.