Abstract
Death Associated Protein Kinase 1 (DAPK1) is an important signaling kinase mediating the biological effect of multiple natural biomolecules such as IFN-γ, TNF-α, curcumin, etc. DAPK1 is degraded through both ubiquitin-proteasomal and lysosomal degradation pathways. To investigate the crosstalk between these two DAPK1 degradation pathways, we carried out a screen using a set of ubiquitin E2 siRNAs at the presence of Tuberous Sclerous 2 (TSC2) and identified that the small ubiquitin-like molecule (SUMO) pathway is able to regulate the protein levels of DAPK1. Inhibition of the SUMO pathway enhanced DAPK1 protein levels and the minimum domain of DAPK1 protein required for this regulation is the kinase domain, suggesting that the SUMO pathway regulates DAPK1 protein levels independent of TSC2. Suppression of the SUMO pathway did not enhance DAPK1 protein stability. In addition, mutation of the potential SUMO conjugation sites on DAPK1 kinase domain did not alter its protein stability or response to SUMO pathway inhibition. These data suggested that the SUMO pathway does not regulate DAPK1 protein degradation. The exact molecular mechanism underlying this regulation is yet to be discovered.
Highlights
Death-Associated Protein Kinase 1 (DAPK1) is an important serine/threonine kinase that is involved in multiple cellular processes such as apoptosis, autophagy, inflammation [1]
We discovered that Tuberous Sclerous 2 (TSC2) and a splice variant of Death Associated Protein Kinase 1 (DAPK1) (s-DAPK1) induced the lysosomal degradation of DAPK1 [20,21]
Co-transfection of SENPs enhanced the level of HA-DAPK1 protein (Figure 1B,C), but not to the level without TSC2 co-transfection, suggesting inhibition of small ubiquitin-like molecule (SUMO) pathway is not able to abrogate the effect of TSC2 towards DAPK1 protein levels
Summary
Death-Associated Protein Kinase 1 (DAPK1) is an important serine/threonine kinase that is involved in multiple cellular processes such as apoptosis, autophagy, inflammation [1]. The degradation of DAPK1 protein is controlled by both proteasomal and lysosomal degradation pathways [15]. Proteins known to be involved in the DAPK1 protein of lysosomal degradation include s-DAPK, Tuberin (TSC2) and cathepsin B. The SENP family can be divided into three subfamilies based on the degree of amino acid sequence homology, cell localization, and substrate preference. The first subfamily comprises SENP-1 and SENP-2, which are located on the nuclear membrane and have the widest selection of substrates, which participate in the deubiquitination of proteins modified by SUMO-1 and SUMO-2/3 [30,31]. The degradation of DAPK protein is regulated by both proteasome and lysosome. The research of E2 on degradation of DAPK1 protein will help to better understand the regulation of DAPK protein degradation by ubiquitin and ubiquitin-like small molecule signaling pathways and to discover the link between ubiquitin-related small molecule and lysosomal degradation signaling pathways
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