Toreveal the mechanism by which the programmed death-ligand 1 （PD-L1）- protein tyrosine phosphatase 1B （PTP1B）-focal adhesion kinase （FAK） signaling axis promotes the progression of hepatocellular carcinoma （HCC） and elucidate its effector functions in HCC.

GEPIA database was used to plot a 10-year survival curve for PD-L1 and FAK expression levels in HCC patients. Immunohistochemical （IHC） staining was utilized to analyze the relative expression levels of PD-L1 and FAK phosphorylated at the Y397 site ［p-FAK（Y397）］ in HCC tissues，and the results were compared to those in the adjacent non-tumor tissues. Subsequently，endogenous PD-L1 expression was detected with Western blotting in HCC cell lines with low （SNU-387） and high （Hep3B） PD-L1 expression levels. After lentivirus-transduced SNU-387^PDL1+ and Hep3B^PDL1-cells were constructed，the effect of high and low expression of PD-L1 on the expression of p-FAK（Y397） with Western blotting. To elucidate the functional mechanism of FAK in HCC，functional rescue experiments were performed by administering a FAK inhibitor to SNU-387^PDL1+ cells and a FAK activator to Hep3B^PDL1- cells，combined with wound healing scratch assay，Transwell invasion assay，EdU proliferation assay，and colony formation assay to evaluate tumor malignant effects. The GENEMANIA database predicted functional interactions between protein tyrosine phosphatase 1B （PTP1B），PD-L1，and FAK. IHC staining was performed to analyze the correlation among PD-L1，PTP1B，and p-FAK（Y397） expression. Co-immunoprecipitation （Co-IP） and indirect immunofluorescence （IF） were applied to validate the interaction between PD-L1 and PTP1B. Western blotting was utilized to confirm the regulatory relationship between PD-L1 and PTP1B. In vitro PTP1B phosphatase activity assay measured the changes in PTP1B activity. Subsequently，Western blotting was used to screen cell lines with high endogenous PTP1B expression （SNU-387） and low endogenous PTP1B expression （Hep3B）. Furthermore，Hep3B^PTP1B+ and SNU-387^PTP1B- cell lines were generated，and then p-FAK（Y397） levels were then detected in these modified cell lines，and the aforementioned functional effect assays （migration，invasion，proliferation and colony formation） and rescue experiments were repeated. Furthermore，Western blotting was employed to detect changes in downstream signaling pathways following enhancement or attenuation of p-FAK（Y397） in SNU-387 and Hep3B cells.

IHC staining revealed a positive correlation between PD-L1 and p-FAK（Y397） expression in HCC tissues （95%CI：1.065~3.801，P<0.01）. In SNU-387^PDL1+ cells，PD-L1 overexpression significantly enhanced phosphorylation at the FAK Y397 site （P<0.01） and increased cell migration，invasion，proliferation，and colony formation capabilities （P<0.01），and these effects could be reversed by FAK inhibitor treatment （P<0.05）. Conversely，in Hep3B^PDL1- cells，PD-L1 knockdown significantly reduced FAK Y397 phosphorylation （P<0.01） and decreased cell migration，invasion，proliferation，and colony formation abilities （P<0.01），and these effects were restored by FAK activator treatment （P<0.05）. IHC staining further showed a negative correlation between PTP1B expression and both PD-L1 and p-FAK（Y397） in HCC tissues （95%CI：1.886~3.514，P<0.05）. Co-IP and IF assays confirmed a direct interaction between PD-L1 and PTP1B，with PD-L1 suppressing PTP1B expression level and reducing its activity （P<0.01）. In SNU-387^PTP1B- cells，PTP1B knockdown significantly increased FAK Y397 phosphorylation （P<0.01） and enhanced cell migration，invasion，proliferation，and colony formation （P<0.01），and these effects were reversed by FAK inhibitor （P<0.05）. While in Hep3B^PTP1B+ cells，PTP1B overexpression significantly decreased FAK Y397 phosphorylation （P<0.01） and reduced cell migration，invasion，proliferation，and colony formation （P<0.01），and those effects were restored by FAK activator treatment （P<0.05）. Furthermore，enhanced phosphorylation at the FAK Y397 site in SNU-387 cells activated downstream PI3K/AKT and MEK/ERK signaling pathways （P<0.01），whereas inhibition of FAK（Y397） phosphorylation in Hep3B cells attenuated the activation of these signaling pathways （P<0.01）.

PD-L1 activates FAK by suppressing PTP1B，thereby promoting migration，invasion，and proliferation in HCC.