PURPOSE
Inflammatory breast cancer (IBC) is the most aggressive form of locally advanced breast cancer with high metastatic potential. In a previous study, we showed that IBC is a different form of breast cancer compared with non-IBC by cDNA microarray analysis. A list of 756 genes with significant expression differences between IBC and non-IBC was identified. In-depth functional analysis revealed the presence of a high number of nuclear factor-kappaB (NF-kappaB) target genes with elevated expression in IBC versus non-IBC. This led to the hypothesis that NF-kappaB contributes to the phenotype of IBC. The aim of the present study was to further investigate the role of NF-kappaB in IBC.
EXPERIMENTAL DESIGN
Immunohistochemistry and NF-kappaB DNA-binding experiments were done for all NF-kappaB subunits (RelA, RelB, cRel, NFkB1, and NFkB2) using IBC and non-IBC specimens. Transcriptionally active NF-kappaB dimers were identified by means of coexpression analysis. In addition, quantitative real-time reverse transcription-PCR for eight NF-kappaB target genes, selected upon a significant, 3-fold gene expression difference between IBC and non-IBC by cDNA microarray analysis, was done.
RESULTS
We found a significant overexpression for all of eight selected NF-kappaB target genes in IBC compared with non-IBC by quantitative real-time reverse transcription-PCR. In addition, we found a statistically elevated number of immunostained nuclei in IBC compared with non-IBC for RelB (P = 0.038) and NFkB1 (P < 0.001). Immunohistochemical data were further validated by NF-kappaB DNA-binding experiments. Significant correlations between immunohistochemical data and NF-kappaB DNA binding for RelA, RelB, NFkB1, and NFkB2 were found. Transcriptionally active NF-kappaB dimers, composed of specific combinations of NF-kappaB family members, were found in 19 of 44 IBC specimens compared with 2 of 45 non-IBC specimens (P < 0.001). In addition, we found evidence for an estrogen receptor (ER)-mediated inhibition of the NF-kappaB signaling pathway. NF-kappaB target genes were significantly elevated in ER- versus ER+ breast tumors. Also, the amount of immunostained nuclei for RelB (P = 0.025) and NFkB1 (P = 0.031) was higher in ER- breast tumors versus ER+ breast tumors.
CONCLUSIONS
The NF-kappaB transcription factor pathway probably contributes to the phenotype of IBC and possibly offers new options for treatment of patients diagnosed with this aggressive form of breast cancer.