A fatty acid-binding protein 7/RXRβ pathway enhances survival and proliferation in triple-negative breast cancer

FABP7 has been implicated in tumour cell proliferation, cell migration, and poor prognosis in patients with high-grade astrocytoma and melanoma. In this study, we examine FABP7 expression in a cohort of 176 primary breast cancers by gene profiling and tissue microarray immunostaining. We show that FABP7 is significantly up-regulated in triple-negative breast cancer. Elevated FABP7 levels are associated with poor prognosis, absence of oestrogen and progesterone hormone receptors (ER, PR) and HER2, increased cell proliferation, and high tumour grade. Depletion of FABP7 in the ER/PR-negative cell line, MDA-MB-435S, significantly reduced cell growth rate and sensitized the cells to growth inhibition by omega-3 docosahexaenoic acid (DHA). A target of DHA-bound FABP7 in the nucleus is RXR beta, a retinoid-activated nuclear receptor that functions as a transcription factor by either homodimerizing or heterodimerizing with other nuclear receptors such as PPARs. Based on our microarray data, RXR beta, like FABP7, is an adverse prognostic factor for breast cancer. We propose that the DHA-FABP7-RXR beta pathway promotes cell survival/proliferation in triple-negative breast cancer. Targeting this pathway may thus provide an alternate route for the treatment of triple-negative breast cancer. Copyright (c) 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.