We previously developed a highly aggressive cell line from heart
metastases of 4T1
breast carcinoma (designated 4THM), which produced liver
metastases (designated 4TLM). In this study, gene array analysis (GAEA) compared gene expression profiles in 4TLM with profiles in 4T1 and 4THM primary
tumors. GAEA demonstrated that 4T1 and 4THM
tumors differed in about 250 genes. Over 1,000 genes, however, were expressed differently in 4TLM compared with primary
tumors. A cohort of 16 genes showed significantly decreased expression in 4THM
tumors, which decreased even further in 4TLM. Many of these genes have been implicated in
breast cancer, and many are involved in cell adhesion and junctional complexes. Expression of multiple tight and adherence junction
proteins was either downregulated or disappeared in 4TLM; downregulation of
claudin 4,
claudin 7 and
gamma-catenin was confirmed by quantitative polymerase chain reaction, immunoblot, and immunocytochemical (ICC) analyses. At the
protein level, intact ZO-1 was also observed in 4T1
tumors, but was not expressed in 4THM or 4TLM
tumors. ICC demonstrated expression of
gamma-catenin at the plasma membrane with 4T1
tumors, whereas staining appeared to be nuclear/perinuclear in 4THM
tumors.
Claudin 7 staining was also seen in monocyte/pmacrophage-like cells in liver around metastatic lesions by ICC, and it appeared that larger 4TLM
tumors apparently reexpressed
claudin 7
RNA and
protein. Our results demonstrate that decreased or abnormal expression of a number of cell adhesion/junctional
proteins, including
claudin 4, 7, ZO-1 and
gamma-catenin, correlates with liver
metastases, and that
cell adhesion molecules in the microenvironment are also altered.