LAF-4 is aberrantly expressed in human breast cancer

LAF-4, which encodes a nuclear protein with transactivation potential, is fused to the MLL gene in acute lymphoblastic leukemia (ALL). We identified LAF-4 as a gene that is transcriptionally deregulated in breast tumors and thus may have a pathological role in mammary tumorigenesis. In line with the previous finding that LAF-4 expression is tissue specific, we did not detect any LAF-4 mRNA in normal mammary epithelial cell lines. However, 2 of 5 breast cancer cell lines were found to express LAF-4 at both the RNA and protein levels. In 2 of 9 primary tumor-normal pairs, the expression of LAF-4 was clearly elevated in the tumor tissue. Using RNA in situ hybridization, we demonstrated that LAF-4 is expressed in mammary tumor cells but not in normal acini. In a group of 64 primary human breast tumors, we found that LAF-4 was overexpressed in approximately 20% of the cases. Although epigenetic changes may be involved in altered expression of some genes, differences in LAF-4 expression were not associated with DNA methylation of the predicted promoter region. Our results suggest that LAF-4 may be a proto-oncogene that is transcriptionally activated in some cases of breast cancer.