Fig. 5

PDIA3 inhibits mitochondrial function by suppressing pS727 STAT3. a STAT3 S727 phosphorylation was increased in PDIA3-/- CMECs, as confirmed by densitometry (b), * p < 0.05, Student’s t-test). Phosphorylation of STAT3 Y705 was not obviously different in PDIA3-/- CMECs, considering the total amounts of STAT3 and the β-actin loading control. We previously found that FAK drives mitochondrial bioenergetics via STAT3 S727 phosphorylation [34] but pFAK was not different in PDIA3-/- (KO) CMECs, as confirmed by densitometry (c). d Overexpression of WT human PDIA3 in PDIA3-/- CMECs reduced pSTAT3 S727, as seen by western blotting and densitometry (e). f) The inhibitory effect of PDIA3 on STAT3 S727 phosphorylation was confirmed by siRNA mediated knockdown of PDIA3 (siPDIA3) in WT CMECs relative to a non-targeting control siRNA (siCtrl). Knockdown increased STAT3 S727 phosphorylation (g). h Finally, we tested whether increased STAT3 S727 phosphorylation was necessary for PDIA3-/- increased respiratory function. Inhibition of STAT3 with stattic in PDIA3-/- CMECs, reduced respiratory function compared within 1 h, as measured by Seahorse assay (n = 6, p < 0.01, one-way ANOVA). i Quantification showed decreased basal and ATP-linked respiration (n = 6, p < 0.01, two-way ANOVA), which indicates PDIA3 suppresses mitochondrial function through inhibition of STAT3