Fig. 6.

Differential gene expression pattern is correlated with EMT pathways and WNT signaling. The DEGs determined by RNA sequencing demonstrated (a) upregulation of EMT pathways and Wnt signaling. Individual genes, fold changes and p-values are listed. Right panel shows representative western blots of several EMT markers and different integrin proteins validate the RNA sequencing findings. (b) Western blots showing upregulation of STAT3 phosphorylation (Y705 and S727) and FYN activation. (c) ABI1 interacts with STAT3 and FYN in RWPE-1 cells. Western blotting results indicating that FYN (top panel) and STAT3 (middle panel) co-immunoprecipitated with Abi1. Input, RWPE-1 cell lysate; Flow-Through, unbound fraction of the lysate; IgG, control immunoprecipitation lacking anti-Abi1 antibody; IP, immunoprecipitation including the anti-Abi1 antibody. Asterisk in top panel indicates the corresponding bands in fractions. (d-f) ABI1 loss promotes nuclear localization of activated STAT3 as determined by pY705 antibody. (d) Western blotting analysis of p-STAT3 Y705 expression in cytoplasmic (left panel) or, nuclear fraction (right panel) of RWPE ABI1 KO, control and ABI1-rescued clones. (e) Immunofluorescence analysis of p-STAT3 Y705 levels in RWPE ABI1 KO clones. (f) Quantification of nuclear p-STAT3 Y705 levels, n = 3, p < 0.001. (g) An example of inverse correlation of ABI1 and pSTAT3 Y705 expression levels in a prostate tumor. Serial tumor sections were immunostained with antibodies to either ABI1 (left panel), or pSTAT3 Y705 (right panel). Arrows depict two example areas of correlation of low ABI1 and high pSTAT. (h) Schematic depicting the proposed mechanism of how Abi1 loss promotes the invasive potential of prostate epithelial cells. Center, ABI1 (ABI1) is critical for cell junction maintenance through WAVE complex-mediated actin polymerization; disruption of ABI1 leads to loss of WAVE complex (WAVE complex) stability, resulting in lower levels of E-cadherin (CDH1) at cell-cell contacts and downregulation of cell-cell adhesion. Right, ABI1 pY421 binds with high affinity to FYN-SH2 domain. Disruption of ABI1 leads to constitutive activation of the SRC family kinase FYN (FYN) to stimulate STAT3 activation and promote its nuclear localization. Nuclear STAT3 promotes transcription of the epithelial-to-mesenchymal transition (EMT) gene program, including extracellular matrix metalloproteinases that promote migration through matrix degradation in the absence of proper cell-cell adhesion. Left, In the absence of ABI1, activated FYN acts on FAK kinase (FAK) to promote integrin signaling, which also supports cell migratory activity. Activated FAK may also directly bind and activate pSTAT3, thus providing another possibility for EMT pathway activation