Epithelial-Mesenchymal Transition (EMT) is a biological process enabling epithelial cells to acquire mesenchymal characteristics, including reduced cell-cell adhesion and enhanced motility, thereby facilitating processes such as cancer metastasis and tissue repair. Platelet-derived growth factor-BB (PDGF-BB) is a key regulator of cell proliferation, migration, and angiogenesis, playing a crucial role in wound healing, vascular remodeling, and pathological conditions. PAK4 (p21-activated kinase 4), a serine/threonine kinase, governs essential cellular functions, including cytoskeletal dynamics, proliferation, survival, migration, and invasion.

This study aimed to investigate the potential role of PDGF-BB-mediated PAK4 function in EMT process and metastatic properties of MDA-MB-231 triple negative breast cancer (TNBC) cells. For this purpose, cells were stimulated with PDGF-BB and also treated with PAK4 inhibitor PF-3758309, separately and in combination. PAK4 activation and expression levels of EMT markers; E-cadherin, N-cadherin and vimentin were determined by Western blotting. Additionally, an in vitro wound healing assay was conducted to assess migration potential.

According to obtained results, PDGF-BB stimulation did not result in a substantial alteration of the endogenous PAK4 levels, however it induced a 3.63-fold increase in p-PAK4 levels. As expected, PAK4 activation was suppressed in PF-3758309-treated cells despite PDGF-BB stimulation. PAK4 inhibition significantly upregulated E-cadherin (2.91-fold) while downregulating vimentin (2-fold), with no notable change in N-cadherin levels. Even though PDGF-BB stimulation, PAK4 suppression caused a 2.96-fold increase in E-cadherin, a 2.5-fold decrease in N-cadherin, and a 4-fold decrease in vimentin levels. Migration analysis showed that PDGF-BB stimulation promoted cell motility by 32% for 24 hours and 40% for 48 hours compared to control. PF-3758309 reversed this effect and suppressed the PDGF-BB-dependent cell motility. These findings suggest that PAK4 plays a key role in the PDGF-BB-mediated EMT and metastasis processes in TNBC cells.

Consequently, the PDGF-BB/PDGFR/PAK4 axis can be considered a significant therapeutic target in the management of cancer progression.