This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Huang, H. Articles by Geradts, J. Search for Related Content PubMed PubMed Citation Articles by Huang, H. Articles by Geradts, J.

Aberrant Expression of Novel and Previously Described Cell Membrane Markers in Human Breast Cancer Cell Lines and Tumors

Authors' Affiliations: Departments of ¹ Pathology and ² Cancer Genetics, Roswell Park Cancer Institute, Buffalo, New York; and ³ Department of Pathology, Brown University School of Medicine, Providence, Rhode Island

Requests for reprints: Joseph Geradts, Department of Pathology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263. Phone: 716-845-3506; Fax: 716-845-3427; E-mail: joseph.geradts{at}roswellpark.org.

Purpose: In a previous gene expression array study, we identified some 300 genes that were differentially expressed in human epidermal growth factor receptor tyrosine kinase 2 (HER2)–positive versus HER2-negative breast cancer cells. We have now done validation experiments on a group of three cell membrane components that had previously not been implicated in breast cancer. We also studied the expression of three other cell membrane proteins known to play a role in mammary neoplasia.

Experimental Design: By immunohistochemistry, we examined up to 130 archival breast carcinomas for Celsr2, E-cadherin, Kai1, and CD9 expression. The expression levels of NET-6 and TROP-2 were determined by quantitative reverse transcription-PCR in a subset of frozen tumors. We also studied fresh pellets and paraffin-embedded cell buttons of nine human breast cell lines. The relationship between the expression of all six membrane proteins and a variety of pathologic and biological variables, including estrogen receptor, HER2, and epidermal growth factor receptor status, was also examined. The NET-6 gene was transfected into a low-expressing cell line, and the effect on cellular morphology, growth, and invasion in vitro was recorded.

Results: Celsr2 was down-regulated in one cell line and in 7% of breast cancers. E-cadherin, Kai1, and CD9 were down-regulated in 35%, 76%, and 79% of tumors, respectively, confirming the important role of these markers in human mammary neoplasia. In breast cancer cell lines and tissues, TROP-2 was generally expressed at low levels, although a few specimens showed relative overexpression. NET-6 levels were lower in HER2-negative breast carcinoma cells. In addition, NET-6 was markedly down-regulated in estrogen receptor–negative breast cancers, and expression was lowest in "basal-like" tumors. Ectopic expression of NET-6 in low-expressing MDA-MB-231 cells altered cellular morphology, inhibited growth in vitro, and decreased invasion in a Boyden chamber assay.

Conclusions: We have confirmed the expression of three new membrane markers that had previously not been implicated in human breast cancer, and one of them (NET-6) was correlated with HER2 and estrogen receptor status. NET-6 levels were decreased in estrogen receptor–negative and high-grade tumors, and ectopic expression of this gene had an inhibitory effect on proliferation and invasion. Thus, NET-6 may represent a novel breast cancer suppressor gene.

Key Words: tetraspanins • cadherins • tumor suppressor genes