Unconjugated
Triple-negative breast cancer (TNBC) is an aggressive breast cancer with a generally poor prognosis. Due to lack of specific targets for its treatment, an efficient therapy is needed. G protein-coupled estrogen receptor (GPER), a novel estrogen receptor, has been reported to be expressed in TNBC tissues. In this study, we investigated the effects of blocking non-genomic signaling mediated by the estrogen/GPER pathway on cell viability and motility in the TNBC cells. GPER was strongly expressed in the TNBC cell lines MDA-MB-468 and MDA-MB-436, and the estrogen-mediated non-genomic ERK signaling activated by GPER was involved in cell viability and motility of TNBC cells. Treatment with 17β-estradiol (E2), the GPER-specific agonist G-1 and tamoxifen (TAM) led to rapid activation of p-ERK1/2, but not p-Akt. Moreover, estrogen/GPER/ERK signaling was involved in increasing cell growth, survival, and migration/invasion by upregulating expression of cyclinA, cyclinD1, Bcl-2, and c-fos associated with the cell cycle, proliferation, and apoptosis. Immunohistochemical analysis of TNBC specimens showed a significantly different staining of p-ERK1/2 between GPER-positive tissues (58/66, 87.9%) and GPER-negative tissues (13/30, 43.3%). The positivity of GPER and p-ERK1/2 displayed a strong association with large tumor size and poor clinical stage, indicating that GPER/ERK signaling might also contribute to tumor progression in TNBC patients which corresponded with in vitro experimental data. Our findings suggest that inhibition of estrogen/GPER/ERK signaling represents a novel targeted therapy in TNBC.
Acetate is the major short-chain fatty acid produced by commensal bacteria in the gut and is known as a nutrient source for epithelial cells of the mucosa. Acetate also suppresses interleukin (IL)-2 production in T cells by inhibiting nuclear factor of activated T cells (NFAT) nuclear translocation via tubulin-α acetylation. Using acetylation of tubulin-α as a biomarker, we have examined the influence of acetate in the large intestine. Because of high concentrations of acetate in fecal material, tubulin-α acetylation is dominant in the proximal large intestine relative to other sections of the large intestine and is induced in epithelial cells of the colonic mucosa. Flagellin stimulation induces IL-8 production in epithelial cells and acetate suppresses this IL-8 production via tubulin-α acetylation. Flagellin stimulation activates nuclear factor-κB, CREB and AP-1, but not NFAT. Of these transcription factors, acetate specifically inhibits AP-1 activation. Acetate impairs flagellin-induced activation of the Rap1-MEK-ERK-Elk-1 pathway with acetylation of tubulin-α that is bound to Rap1, resulting in reduced expression of c-Fos, a subunit of AP-1. These findings reveal a novel action of acetate via tubulin-α acetylation in epithelial cells of the colonic mucosa.
