Leptin Drives Breast Cancer Aggressiveness Acting Through the Activation of the NCOA1/STAT3 Pathway

<b>Background/Objectives</b>: Obesity-associated hyperleptinemia has been linked to breast cancer (BC) progression via mechanisms that remain incompletely understood. This study explores the role of leptin and its receptor (LEPR) in facilitating BC cell proliferation, migration, epithelial-mesenchymal transition (EMT), and STAT3 signaling pathway activation. <b>Methods</b>: We analyzed gene expression and survival data from TCGA BRCA dataset. MCF-7 and MDA-MB-231 BC cells were exposed to leptin at 10 ng/mL (lean-associated levels) and 100 ng/mL (elevated levels linked to obesity). MTT assays, colony formation tests, wound-healing and tumor spheroid dissemination experiments evaluated cell proliferation and migration. Immunofluorescence and Western blot analysis assessed changes in EMT markers and cytoskeletal alterations, while Western blotting and qPCR assessed STAT3 and <i>NCOA1</i> expression and activation levels. <b>Results</b>: Elevated <i>LEPR</i> expression was linked with unfavorable prognosis in BC patients. Higher doses of leptin (100 ng/mL) significantly enhanced cellular proliferation rates and migratory capabilities, in both cell lines, and promoted EMT characteristics marked by downregulated E-cadherin and cytoskeleton structural changes. Whereas heightened JAK2/STAT3 signaling correlated with elevated leptin dosages, STAT3 inhibition using AG490 reversed leptin-induced migration while reinstating E-cadherin levels to baseline. Furthermore, leptin upregulated <i>NCOA1</i>, an essential STAT3 coactivator, facilitating increased expression of <i>Cyclin D1</i> and <i>VEGF</i> target genes. Clinical positive relationships were seen between <i>LEP</i>/<i>LEPR</i> expressions and <i>NCOA1</i> levels and between <i>NCOA1</i> and various gene signatures related to STAT3/P-STAT3 within BC specimens. <b>Conclusions</b>: Obesity-associated hyperleptinemia enhances aggressiveness in BC through a mechanism involving LEPR-mediated activation pathways encompassing NCOA1/STAT3, which drive proliferation, migration, and EMT. This assigns a potential therapeutic utility for obesity-related advancements found within BC pathology.