Expression pattern of the AP‐1 family in breast cancer: Association of fosB expression with a well‐differentiated, receptor‐positive tumor phenotype

In the present study, the expression of members of the AP‐1 family of transcription factors in breast tumors (n = 53) was investigated by Western blot with antibodies specific for each of the AP‐1 family members (c‐jun, junB, junD and c‐fos, fosB, fra1 and fra2). The tumors were characterized with regard to grading, staging, histology, steroid‐receptor‐expression status and c‐erbB2/neu expression. For comparison, normal breast‐tissue samples, human breast‐cancer cell lines (T47D and MDA‐MB231) and the transformed human breast epithelial cell line HBL100 were also analyzed. For c‐jun, junB, c‐fos and fra2, a relatively uniform expression pattern without significant differences among tumors was observed. junD‐protein amounts varied strongly in the tumor specimens. fosB‐expression levels also varied strongly in the tumors, weak/absent expression being found in 47%, while 45% exhibited strong/very strong levels of expression. While none of the other AP‐1 family members showed significant correlations with clinico‐pathological tumor parameters or receptor status, expression of fosB was found to correlate significantly with positive steroid‐hormone‐receptor status (in the tumors and the cell lines) and a more differentiated tumor phenotype. Expression of 2 fra‐1‐specific bands of 33 and 36.5 kDa showed significant negative correlation with fosB expression, as well as with estrogen‐receptor status and differentiation. We conclude that strong differences in the expression pattern of AP‐1 family members are present in breast tumors, and that certain members of this family, such as fosB and fra‐1, might be involved in the pathogenesis of these tumors. Int. J. Cancer (Pred. Oncol.) 84:533–538, 1999. © 1999 Wiley‐Liss, Inc.