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 trans cription 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 r egard to grading, staging, histology, steroid-receptor-expression status an d c-erbB2/neu expression. For comparison, normal breast-tissue samples, hum an 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-f os and fra2, a relatively uniform expression pattern without significant di fferences among tumors was observed. junD-protein amounts varied strongly i n the tumor specimens. fosB-expression levels also varied strongly in the t umors, weak/absent expression being found in 47%, while 45% exhibited stron g/very strong levels of expression. While none of the other AP-1 family mem bers showed significant correlations with clinico-pathological tumor parame ters or receptor status, expression of fosB was found to correlate signific antly 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 differe ntiation. We conclude that strong differences in the expression pattern of AP-I 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 pathogenes is of these tumors. Int. J. Cancer (Pred. Oncol.) 84:533-538, 1999. (C) 199 9 Wiley-Liss, Inc.