Human epidermal growth factor receptor 2 (HER2)-amplified breast
cancers are treated using targeted
antibodies and
kinase inhibitors, but resistance to these
therapies leads to systemic
tumor recurrence of metastatic disease. Herein, we conducted gene expression analyses of HER2
kinase inhibitor-resistant cell lines as compared to their
drug-sensitive counterparts. These data demonstrate the induction of epithelial-mesenchymal transition (EMT), which included enhanced expression of
fibroblast growth factor receptor 1 (FGFR1) and axonal guidance molecules known as
neuropilins (NRPs). Immunoprecipitation of FGFR1 coupled with mass spectroscopy indicated that FGFR1 forms a physical complex with NRPs, which is enhanced upon induction of EMT. Confocal imaging revealed that FGFR1 and NRP1 predominantly interact throughout the cytoplasm. Along these lines,
short hairpin RNA-mediated depletion of NRP1, but not the use of NRP1-blocking
antibodies, inhibited FGFR signaling and reduced
tumor cell growth in vitro and in vivo. Our results further indicate that NRP1 upregulation during EMT is mediated via binding of the
chromatin reader
protein, bromodomain containing 4 (BRD4) in the NRP1 proximal promoter region. Pharmacological inhibition of BRD4 decreased NRP1 expression and ablated FGF-mediated
tumor cell growth. Overall, our studies indicate that NRPs facilitate aberrant
growth factor signaling during EMT-associated drug resistance and
metastasis. Pharmacological combination of epigenetic modulators with FGFR-targeted
kinase inhibitors may provide improved outcomes for
breast cancer patients with
drug-resistant metastatic disease.