To investigate the modulation of HDAC6 activity by the extracellular matrix in triple negative breast cancer cells

Histone deacetylase 6 (HDAC6) is a cytoplasmic enzyme which deacetylates  -tubulin, cortactin and heat shock protein Hsp90 to mediate a wide range of cellular responses. Cellular responses of HDAC6 contribute to tumorigenic transformation by cell proliferation and migration in which the overexpression of HDAC6 has been identified in a wide variety of tumors. The specific mode of action of how HDAC6 activity is regulated in cancer is poorly described and could explain the limited efficacy of HDAC6 inhibitory therapy in solid tumors. Extracellular matrix (ECM) proteins such as collagen, fibronectin and laminins provide biochemical and biomechanical regulation of cancer proliferation, survival, and invasion by modifying tubulin dynamics in cells. Therefore, the objective of this study was to elucidate the modulation of HDAC6 activity in triple negative breast cancer (TNBC) cells. In this study, TNBC cell lines, MDA-MB-231 and Cal51, were cultured on ECM protein coated plates as 2D cultures and HDAC6 activity was analyzed. The rate of cell proliferation of Cal51 cells was not significantly affected by ECM coatings, however, they grew fastest on fibronectin. In contrast, laminin inhibited MDA-MB-231 cell proliferation. The overexpression of HDAC6 produced a growth inhibitory effect in MDA-MB-231 cells and potentiated laminin inhibition, which was not observed in CAL51 cells. Fibronectin downregulated HDAC6 activity in MDA-MB-231 cells. Fibronectin increased the phosphorylation levels of focal adhesion kinase activated protein kinase AKT and paxillin. Gene expression of the focal adhesion protein, paxillin, was four-fold higher in MDA-MB-231 cells compared to Cal51 cells. Further research will examine the role of differential paxillin levels and its activation by the ECM-driven signaling pathway to modulate HDAC6 activity in TNBC cells. In conclusion, this research will provide a greater understanding of the interaction between ECM signaling pathways and the enzymatic functions of HDAC6 in TNBC.