Suppression by heat shock protein 20 of hepatocellular carcinoma cell proliferation via inhibition of the mitogen‐activated protein kinases and AKT pathways

Abstract

Heat shock protein (HSP) 20, one of the low-molecular weight HSPs, is known to have versatile functions, such as vasorelaxation. However, its precise role in cancer proliferation remains to be elucidated. While HSP20 is constitutively expressed in various tissues including the liver, we have previously reported that HSP20 protein levels in human hepatocellular carcinoma (HCC) cells inversely correlate with the progression of HCC. In this study, we investigated the role of HSP20 in HCC proliferation. The activities of extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), and AKT were negatively correlated with the HSP20 protein levels in human HCC tissues. Since HSP20 proteins were hardly detected in HCC-derived cell lines, the effects of HSP20 expression were evaluated using human HCC-derived HuH7 cells that were stably transfected with wild-type human HSP20 (HSP20 overexpressing cells). In HSP20 overexpressing cells, cell proliferation was retarded, and the activation of the mitogen-activated protein kinases (MAPKs) signaling pathways, including the ERK and JNK, and AKT pathways, as well as cyclin D1 accumulation induced by either transforming growth factor-α (TGFα) or hepatocyte growth factor, were significantly suppressed compared with the empty vector-transfected cells (control cells). Taken together, our findings strongly suggest that HSP20 suppresses the growth of HCC cells via the MAPKs and AKT signaling pathways, thus suggesting that the HSP20 could be a new therapeutic target for HCC.

Study of HSPB6: Insights into the Properties of the Multifunctional Protective Agent

“…For example, the expression of HSPB6 in human HCC cells inversely correlated with the TNM stage. HSPB6 reportedly inhibited the proliferation of HCC cells via suppression of the MAPK family, including JNK and the PI3K/Akt pathway [84,85]. Furthermore, in consistent with the previous result that HSPB6 inhibited LPS-induced NF-κB activation in cardiomyocytes, HSPB6 acts as a negative regulator of HCC via down-regulation of TNF-α-stimulated IKK/IκB/NF-κB pathway [86].…”

Heat shock protein 20 (HSPB6) regulates apoptosis in human hepatocellular carcinoma cells: Direct association with Bax

“…We have previously shown that HSP20 suppresses HCC cell growth by downregulation of proliferation signals via the AKT and mitogen-activated protein kinase pathways (11,12). Cell growth is affected by both the survival and apoptosis signals.…”

“…These cells were established as described previously, by means of Tet-Off™ gene expression systems (Clontech Laboratories Inc., Palo Alto, CA, USA) according to the manufacturer's instructions (11). Induction of HSP20 protein expression in the HSP20-overexpressing cells can be controlled by the presence of doxycycline (Sigma-Aldrich).…”

“…The lysates were then centrifuged at 10,000 x g at 4˚C for 30 min, and the supernatant was collected as TNE-soluble proteins, as previously described (12). For the western blot analysis, the serum-starved cells were lysed, homogenized and sonicated in lysis buffer, as previously described (11).…”

“…We previously reported that HSP20 protein levels in HCC inversely correlate with the TNM stage (10). In our previous studies on HCC (11,12), we demonstrated that the HSP20 protein directly interacts with phosphoinositide 3-kinase (PI3K) which activates AKT, a major mediator of cell survival, and suppresses its activity resulting in reducing the cell proliferation (11,12).…”