Downregulation of protein disulfide-isomerase A3 expression inhibits cell proliferation and induces apoptosis through STAT3 signaling in hepatocellular carcinoma

Protein disulfide-isomerase A3 (PDIA3) is a chaperone protein that modulates folding of newly synthesized glycoproteins and responds to endoplasmic reticulum (ER) stress. Previous studies reported that increased expression of PDIA3 in hepatocellular carcinoma (HCC) is a marker for poor prognosis. However, the mechanism remains poorly understood. The aim of the present study, therefore, was to understand the role of PDIA3 in HCC development. First, immunohistochemical staining of tissues from 53 HCC cases revealed that HCC tissues with high PDIA3 expression exhibited a higher proliferation index and contained fewer apoptotic cells than those with low expression. In addition, the knockdown of PDIA3 significantly inhibited cell proliferation and induced apoptosis in HCC cell lines. These results suggest that PDIA3 regulates cell proliferation and apoptosis in HCC. An examination of whether PDIA3 knockdown induced apoptosis through ER stress revealed that PDIA3 knockdown did not increase ER stress marker, 78 kDa glucose-regulated protein, in HCC cell lines. Furthermore, the association between PDIA3 and the signal transducer and activator of transcription 3 (STAT3) signaling pathway were investigated in vitro and in vivo. Immunofluorescence staining and co-immunoprecipitation experiments revealed colocalization and binding, respectively, of PDIA3 and STAT3 in HCC cell lines. The knockdown of PDIA3 decreased the levels of phosphorylated STAT3 (P-STAT3; Tyr705) and downstream proteins of the STAT3 signaling pathway: The anti-apoptotic proteins (Bcl-2-like protein 1, induced myeloid leukemia cell differentiation protein Mcl-1, survivin and X-linked inhibitor of apoptosis protein). In addition, PDIA3 knockdown provided little inhibitory effect on cell proliferation in HCC cell lines treated with AG490, a tyrosine-protein kinase JAK/STAT3 signaling inhibitor. Finally, an association was demonstrated between PDIA3 and P-STAT3 expression following immunostaining of 35 HCC samples. Together, the present data suggest that PDIA3 promotes HCC progression through the STAT3 signaling pathway.