CD44/PI3K/NF-κB/AHR is a Novel Signaling Pathway Mediating Breast Tumor Progression

Abstract Cell adhesion molecules (CAMs), present on cell surfaces, are involved in cell-to-cell and cell-extracellular adhesion. The hyaluronic acid (HA) receptor, CD44, is a CAM protein that is highly generally highly expressed in metastatic solid tumors, including breast cancer (BC), and correlates with poor prognosis. To increase our understanding of the underlying CD44-downstream signaling pathways involved in BC metastasis, we developed a tetracycline (tet)-off regulated expression of CD44s gene in BC cell line MCF-7 (B5 clone) and identified aryl hydrocarbon receptor (AHR) as a potential CD44-downstream transcriptional target by microarray analysis. To validate this observation in vitro, RNA and protein lysates collected from human metastatic BC cell lines MDA-MB-231 (expressing high levels of CD44), were examined for both CD44 and its target AHR, in the presence of HA. Our results confirmed that CD44 activation by HA significantly increased the expression of AHR at HA activation of CD44 increased significantly the expression of AHR at both mRNA and protein levels. More interestingly, inhibition of CD44 gene by its siRNA decreased significantly AHR expression, and further inhibited BC cell migration/invasion. Interestingly, pharmacological approach using inhibitors of major known transduction signaling pathways revealed that CD44 activates the transcription of AHR at least via PI3K/ Nuclear factor-kappa B (NF-κB) signaling pathway. These data support our hypothesis revealing AHR as a novel transcriptional target that underpin CD44-promoted BC cell invasion, via CD44/PI3K/AKT/ NF-κB/AHR novel signaling pathways.