Lactate Is a Major Promotor of Breast Cancer Cell Aggressiveness

<b>Background</b>: Lactate dehydrogenase (LDH) activity, producing high levels of lactate from pyruvate in cancer cells, is often associated with poor patient prognosis. We previously showed enhanced LDH/lactate levels in estrogen receptor (ER) compared to ER + breast cancer cells; lactate or pyruvate supplementation to ER + cells significantly enhanced their motile ability, while LDHB gene knockout (KO) or treatment with LDH inhibitors reduced the motility of the highly aggressive ER breast cancer cells. <b>Aims</b>: To investigate the molecular mechanisms by which lactate, LDHB KO, or treatment with LDH inhibitors can modulate the motile capabilities of breast cancer cell lines. <b>Methods</b>: KO experiments were performed using siRNA, and global expression was determined by proteomic profiling with Proteome Profiler Human XL Oncology arrays, Western blot, and immunofluorescence. <b>Results</b>: Lactate supplementation to ER + breast cancer cells enhanced expression of vimentin, N-cadherin, and snail, while reducing the expression of JAM-A, E-cadherin, and nectin-4. This expression profile was reversed with LDHB KO in ER cells. LDHB KO, or treatment with LDH inhibitors in ER cells, also reduced the expression of IL-6, IL-8, and MMP-2. The expressions of other markers such as PECAM-1, CCL20, and ENPP-2 were differentially modulated with LDH B KO in de novo ER cells (MDA-MB-231) vs. those that had ER knockout (pII). <b>Conclusions</b>: Our data show a novel role for lactate in modulating the EMT status in breast cancer cells and highlight the important role of lactate in breast cancer motility in part through modulating EMT status and the expression profile of cytokines, adhesion molecules, MMP-2, and nectin-4.