Heat shock protein 70 (HSP70) and HSP70-peptide complexes (HSP70-PCs) have been implicated in the pathogenesis of multiple tumors in humans and have been experimentally shown to increase the proliferation of cell lines derived from hepatocellular carcinoma. The goal of this study was to elucidate the molecular mechanisms through which extracellular HSP70/HSP70-PCs stimulate the proliferation of hepatocellular carcinoma (HCC). The molecular mechanisms of HSP70/HSP70-PC action were studied in the human hepatocellular carcinoma cell lines HepG2 and Huh-7, as well as tumor tissue collected from patients with HCC (n = 95). We found that HSP70/HSP70-PCs can stimulate the proliferation of HepG2 cells and that this effect is blocked by knocking down TLR2 and TLR4 expression by RNA interference. A physical interaction between HSP70/HSP70-PCs and TLR2/4 was established using co-immunoprecipitation and pull-down assays. Pharmacological inhibition of different branches of the MAPK intracellular signaling pathway indicated that the extracellular HSP70/HSP70-PC effect was mediated by the JNK1/2 signaling pathway within the cell. We also studied TLR2 and TLR expression at the protein and messenger RNA (mRNA) level in tumor and non-tumor tissue in patients with HCC (n = 95), finding that TLR2 and 4 are increased in HCC tumor tissue and that the expression of TLR2 correlates with clinicopathologic features of HCC. Our data conclusively demonstrates that extracellular HSP70/HSP70-PCs can promote the proliferation of HCC cells through activation of TLR2 and TLR4 and subsequent activation of the intracellular JNK1/2/MAPK signaling pathway.
Keywords: Extracellular HSP70-PCs; Hepatocellular carcinoma; JNK1/2MAPK; Proliferation; TLR2; TLR4.