ERα/LKB1 complex upregulates E-cadherin expression and stimulates breast cancer growth and progression upon adiponectin exposure

Adiponectin is the major adipocytes-secreted protein involved in obesity-related breast cancer growth and progression. We proved that adiponectin promotes proliferation in ERa-positive breast cancer cells, through ERa transactivation and the recruitment of LKB1 as ERa-coactivator. Here, we showed that adiponectin-mediated ERa transactivation enhances E-cadherin expression. Thus, we investigated the molecular mechanism through which ERa/LKB1 complex may modulate the expression of E-cadherin, influencing tumor growth, progression and distant metastasis. We demonstrated that adiponectin increases E-cadherin expression in ERa-positive 2D and higher extent in 3D cultures. This occurs through a direct activation of E-cadherin gene promoter by ERa/LKB1-complex. The impact of E-cadherin on ERa-positive breast cancer cell proliferation comes from the evidence that in the presence of E-cadherin siRNA the proliferative effects of adiponectin is no longer noticeable. Since E-cadherin connects cell polarity and growth, we investigated if the adiponectin-enhanced E-cadherin expression could influence the localization of proteins cooperating in cell polarity, such as LKB1 and Cdc42. Surprisingly, immunofluorescence showed that, in adiponectin-treated MCF-7 cells, LKB1 and Cdc42 mostly colocalize in the nucleus, impairing their cytosolic cooperation in maintaining cell polarity. The orthotopic implantation of MCF-7 cells revealed an enhanced E-cadherin-mediated breast cancer growth induced by adiponectin. Moreover, tail vein injection of MCF-7 cells showed a higher metastatic burden in the lungs of mice receiving adiponectin-treated cells compared to control. From these findings it emerges that adiponectin treatment enhances E-cadherin expression, alters cell polarity and stimulates ERa-positive breast cancer cell growth in vitro and in vivo, sustaining higher distant metastatic burden.