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

Abstract

Abstract.A small heat shock protein (HSP), HSP20 (HSPB6) is ubiquitously expressed in various tissues and has several functions. We previously reported that the expression of HSP20 protein in human hepatocellular carcinoma (HCC) cells is inversely proportional to the progression of HCC. In addition, we showed that HSP20 is associated with phosphoinositide 3-kinase (PI3K) and inhibits the proliferation of HCC cells via suppression of the AKT signaling pathway. However, the relationship between HSP20 and apoptosis in HCC has not yet been elucidated. To clarify whether HSP20 is implicated in the apoptosis of HCC cells, in the present study, we examined the effect of HSP20 on caspases, the central regulators of apoptosis, using human HCC-derived HuH7 cells that are transfected with wild-type human HSP20 (HSP20-overexpressing cells). The cleavage of caspase-3 and caspase-7 in HSP20-overexpressing cells was enhanced compared with the empty vector-transfected cells (control cells). In addition, the cleavage of nuclear poly (ADP-ribose) polymerase (PARP) in HSP20-overexpressing cells was also strengthened. We further investigated the direct targets of HSP20 focusing on Bcl-2 family proteins in the HSP20-overexpressing cells. HSP20 proteins in the cells were coimmunoprecipitated with Bax. On the contrary, Bad, Bcl-2 and Bcl-xL were not coimmunoprecipitated with HSP20. These findings strongly suggest that HSP20 directly associates with Bax and stimulates caspase cascade in human HCC cells.

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

“…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]. Additionally, HSPB6 directly associated with Bax, whereby it stimulated caspase cascade and induced apoptosis in HCC [11]. Collectively, HSPB6 might suppress HCC cell growth via both the downregulation of cell proliferation signals and the activation of apoptosis pathway.…”

Heat shock protein 20 (HSPB6) regulates TNF-α-induced intracellular signaling pathway in human hepatocellular carcinoma cells

“…We previously demonstrated that HSP20 decreases the proliferation and increases the apoptosis of HCC cells in the absence of TNF-a [12,14]. It is firmly established that the inflammatory signaling of TNF-a contributes to HCC development [3].…”

“…HSP20 directly interacts with PI3K and inhibits the PI3K activity in HCCs [13]. Moreover, we recently showed that HSP20 directly interacts with Bax and regulates apoptosis in HCC cells [14].…”

Gene and protein delivery using four cell penetrating peptides for HIV‐1 vaccine development

“…Among them, small Hsps (sHsps) are conserved and critical in stress tolerance among species. The sHsps (MW: ∼12–43 kDa) are identified by a highly conserved sequence (length: 80–100 amino acids) in the C‐terminal domain known as “α‐crystallin domain.” These types of Hsps possess major roles in differentiation, development, proteasomal degradation, autophagy, and apoptosis …”