The Molecular Mechanism Of Phosphorylated Hsp27Involved Trail Resistance In Tumor Cells

Heat shock protein27is a member of the small Hsp family expressed in different adult cell types. In addition to its protective function in heat shock and other conditions of stress, HSP27has been linked to different signaling pathways regulating critical cellular functions such as development, apoptosis, differentiation, cell growth and actin polymerization. Most of the previous studies focused on the regulatory role of HSP27protein itself in apoptosis signaling pathways. However, the protective effect of its phosphorylation state during apoptosis is unclear. In the present study, we report that phosphorylated HSP27regulates the TRAIL-triggered pro-survival signaling pathways.TRAIL belongs to the TNF (Tumor Necrosis Factor) superfamily of ligands and receptors, as TRAIL is the only member that exhibits a relative selectivity for tumor cells and its lack of evident toxicity in animal models, it has a very broad application prospects in cancer treatment. However, the clinical application of TRAIL indicates a considerable number of cancer patients are resistant to TRAIL. Thus further clarify the molecular mechanism of TRAIL resistance is critical for the tumor clinical treatment. Here, we report a novel function of phosphorylated HSP27in regulating TRAIL-induced signaling. Either using specific inhibitor KRIBB3and silencing of MAPKAPK2(MK2) expression level through RNA interference (RNAi) suppresses the activity of upstream kinases to inhibit the HSP27phosphorylation indirectly or overexpressing HSP27-3A and HSP27-3D mutants directly regulates the activity of HSP27demonstrated that decreasing the level of HSP27phosphorylation augments the TRAIL-induced apoptosis (morphological changes characteristic of apoptosis, enhanced multicaspase activity, increased rate of apoptosis, increased cleaved apoptotic proteins). HSP27facilitates Akt and ERK phosphorylation by promoting their common upstream kinase Src activation and influences the transduction of intracellular pro-survival signaling. Overexpression of HSP27-15A and HSP27-78/82A non-phosphorylated mutants verified the key role of HSP27serine78and82residues. On the one hand, the phosphorylated form of HSP27during TRAIL treatment indirectly interacts with Src and guides Src locating inside of cell membrane together. On the other hand, phosphorylated HSP27promotes TRAIL death receptors endocytosis through an unknown mechanism. Thereby, these effects of HSP27resulted in augmentation of the interaction between TRAIL receptors and Src. And TRAIL signaling is prone to transduce along the pro-survival signaling pathway.In conclusion, our study reveals a novel role of phosphorylated HSP27as an cell protection factor involved in TRAIL-induced apoptosis and elucidates a new function of HSP27to regulate Src-Akt-ERK pro-survival signaling cascades, which will provide a new insight for analyzing the molecular mechanism of TRAIL resistance in clinical tumor treatment and a scientific basis for expanding the scope of TRAIL application as well as reducing the dose of TRAIL.