Hsf4 counteracts Hsf1 transcription activities and increases lens epithelial cell survival in vitro

Abstract

The interplay between Hsf4 and Hsf1 plays an important role in the regulation of lens homeostasis. However, the mechanism of the intermolecular association involved is still unclear. In this paper, we find that reconstitution of Hsf4b into Hsf4-/- lens epithelial (mLEC/Hsf4-/-) cells can simultaneously downregulate Hsp70 expression and upregulate the expression of small heat shock proteins Hsp25 and αB-crystallin at both RNA and protein levels. ChIP assay results indicate Hsf4b, which binds to the promoters of Hsp90α, Hsp70.3, Hsp25 and αB-crystallin but not Hsp70.1, can inhibit Hsf1 binding to Hsp70.3 promoter and the heat shock mediated Hsp70 promoter activity by reducing Hsf1 protein expression. Hsf4b N-terminal hydrophobic region can interact with Hsf1 N-terminal hydrophobic region. Their interaction impairs Hsf1's intramolecular interaction between the N- and C-terminal hydrophobic regions, leading to Hsf1's cytosolic retention and protein degradation. Both lysosome inhibitors (chloroquine, pepstatin A plus E64d) and proteasome inhibitor MG132 can inhibit Hsf4-mediated Hsf1 protein degradation, but MG132 can induce Hsf1 activation as well. Upregulation of Hsf4b can significantly inhibit cisplatin and staurosporine induced lens epithelial cell apoptosis through direct upregulation of Hsp25 and αB-crystallin expression. Taken together, our results imply that upregulation of Hsf4b modulates the expression pattern of heat shock proteins in lens tissue by either directly binding to their promoters or promoting Hsf1 protein degradation. Moreover, upregulation of Hsf4b protects lens cell survival by upregulating anti-apoptotic pathways. These studies reveal a novel regulatory mechanism between Hsf1 and Hsf4b in modulating lens epithelial cell homeostasis.

Gypenosides improve diabetic cardiomyopathy by inhibiting ROS‐mediated NLRP3 inflammasome activation

“…Co‐immunoprecipitation (CoIP) was carried out as previously described . 1 mg of cell lysate was treated with protein A/G agarose beads for 1 hour.…”

Decorin inhibits glucose-induced lens epithelial cell apoptosis via suppressing p22phox-p38 MAPK signaling pathway

“…High glucose-induced oxidative stress is an important cause of diabetic cataract [2]. The human lens epithelial cell line (HLEB3) was widely used to do research [13][14][15]. Here, using the lens epithelial cell line, we found that high glucose can directly induce the oxidative stress and cell apoptosis.…”

BCAS2 interacts with HSF4 and negatively regulates its protein stability via ubiquitination

“…Further investigation revealed that residue K206 was a key site for HSF4 ubiquitination. It was showed that the HRA/B domain could mediate the interaction between HSF1 and other factors (Cui et al, 2015;Hu and Mivechi, 2011). Herein, we have shown that the HRA/B domain (130-203) of HSF4 is indispensable for the interaction of HSF4 with BCAS2.…”