GGC promoted the expression of PTPε protein.
To study the mechanism of GGC-mediated inhibition of STAT3 phosphorylation, we elucidated the impact of GGC by modulating of protein tyrosine phosphatase. Pretraetment with sodium pervanadate abrogated reduction in p-STAT3 levels caused by GGC (Fig. 2E). Moreover, we noted that GGC led to a dramatic increase in PTPε protein levels (Fig. F) however at mRNA level an augmentation was noted only in PTPε M, but not PTPε C. Moreover, in A549 cells with PTPε siRNA, PTPε expression was substantially reduced ((Fig. 2H) and GGC was unable to affect STAT3 phosphorylation in PTPε knockdown cells (Fig. 2I). In addition, PTPε knockdown attenuated GGC-induced PARP cleavage suggesting that this phosphatase may have a vital role in regulating anti-cancer properties of GCC.