Immunofluorescence images of 5hmC in zebrafish larva (Credit: IHB)
 

The research team led by Prof. XIAO Wuhan from Institute of Hydrobiology (IHB) of Chinese Academy of Sciences reported the von-Hippel Linau tumor suppressor ( pVHL), as a key component of the E3 ligase complex of hypoxia signaling complex, has an impact on the ten-eleven translocation enzyme (TET) protein stability and function in mediating DNA demethylation. The results were published online in Journal of Biological Chemistry.  

The TET proteins (TET1, TET2, TET3), which are key factors identified in DNA demethylation, play important roles in various biological processes, including the regulation of gene expression, meiotic mitosis, embryogenesis, stem cell function and cancer.   

Previous studies have reported that vhl-null (vhl ^-/-) zebrafish exhibits the general hyperproliferation of the hematopoietic stem cells (HSCs), alongside white hematopoietic lineages and upregulation of Cytokine gene expression in immune response. In contrast, as the major 5-methylcytosine dioxygenases in the zebrafish embryo, tet2 and tet3 exhibit a combined requirement in HSCs emergence. In brief, these existing studies suggest that pVHL and TET might be closely related.    

Researchers used TALEN to knock out vhl in zebrafish, and found that the global 5hmC levels were enhanced significantly in vhl-null zebrafish larvae compared with wildtype control larvae.   

By performing a series of biochemical experiments, IHB researchers demonstrated that pVHL interacts with TET and induces degradation of TET by ubiquitin-proteasome pathway, leading to reduction of globe 5hmC levels.  

In this process, it is essential that the prolyl hydroxylase enzyme (PHD) bind to TET and exert its prolyl-hydroxylase activity, revealing a mechanism of PHD-pVHL in regulating TET proteins.   

These observations not only extend the knowledge about regulation of DNA methylation through post-translational modification of TET proteins, but shed new light on the physiological functions of pVHL during diverse biological processes as well. 

 
Zebrafish vhl mediate reducton of global 5hmC levels in vivo (Credit: IHB)