Unconjugated
The crosstalk of intracellular signaling pathways is extremely complex. Previous studies have shown that there is a potential crosstalk between MAPKs and NF-κB signaling pathways. It has been reported that JNK regulates cell survival under some conditions. But the molecular mechanism through which JNK regulates cell survival is still unclear. In the present study, we hypothesized that there was a crosstalk between JNK and NF-κB signaling pathway regulating cell survival and HSP27 phosphorylation mediates such a crosstalk. Our data showed that in HepG2 cells, suppression of JNK activation by a specific inhibitor or overexpression of JNK inactive mutant enhanced TNF-α-induced apoptosis. In addition, reduction of JNK activation attenuated HSP27 phosphorylation envoked by TNF-α, especially the phosphorylation of HSP27 at serine 78 residue. Our results also showed that suppression of JNK activation reduced the degradation of IκB-α, but did not affect IKK phosphorylation upon TNF-α stimulation. Co-immunoprecipitation experiments demonstrated that JNK regulated the degradation of IκB-α through promoting the formation of HSP27/IKK/IκB-α ternary complex in response to TNF-α. Suppression of JNK activation hindered HSP27 phosphorylation at Ser78 residue and subsequently reduced the interaction between IKK and IκB-α. Taken together, our study suggests that through modulation the phosphorylation of HSP27, JNK plays an important roles in cell survival via regulating NF-κB signaling pathway.
In the present study, the effect of the heat shock protein 27 (HSP27) signaling pathway on the proliferation and apoptosis of human umbilical vein endothelial cells (HUVECs) induced by high glucose (HG) was investigated. HUVEC proliferation in the indicated conditions was measured by the alamarBlue® assay. Apoptosis in HUVECs cultured with HG was analyzed by an Annexin V‑fluorescein isothiocyanate/propidium iodide apoptosis detection kit. HSP27 activity was evaluated by western blotting with specific phospho‑HSP27 antibody. HUVEC proliferation induced by HG was observed to be reduced by the HSP27 inhibitor quercetin in a concentration‑dependent manner, with a concomitant increase in apoptosis. The phosphorylation of HSP27 induced by HG was blocked by the specific phosphoinositide 3‑kinase (PI3K) inhibitor LY294002 and the specific extracellular signal‑regulated kinase (ERK) 1/2 inhibitor U0126 in a concentration‑dependent manner, with peak inhibition rates of 62.6 and 56.1%, respectively. LY294002 and U0126 also reduced HUVEC proliferation with a concomitant increase in apoptotic rate. In conclusion, HSP27 phosphorylation is important in mediating the proliferation and apoptosis of HUVECs induced by high glucose, and PI3K/Akt and ERK1/2 are important signaling pathways that contribute to HSP27 phosphorylation.