| The covalent binding of ubiquitin(ubiquitination)to cellular proteins is one of the main post-translational modifications(PTM),which plays an important role in regulating various cell physiological processes.Studies have shown that disorder of the ubiquitination system leads to development of a variety of human diseases,including malignant tumors,neurodegenerative diseases,and many diseases of immune and inflammatory reactions.Therefore,understanding the mechanism of ubiquitination is beneficial to targeted therapy and drug development..THEMIS is an important factor that controls the positive selection of thymocytes.It is only expressed in T cell lineage and regulates TCR signal transduction.Recent studies have shown that the interaction between HBZ,a human T-cell leukemia virus type-1(HTLV-1)encoded protein,and THEMIS will weaken the interaction between THEMIS and Grb2,and impede the T cell growth inhibitory signal.However,the specific mechanism of HBZ and THEMIS is still unclear.In this paper,we found that HBZ can interact with THEMIS,and that HBZ can promote the protein degradation of THEMIS in a dose-dependent manner.The down-regulation effect of HBZ on the protein level of THEMIS may be achieved through the proteasome pathway to a large extent.At the same time,through ubiquitination experiments,we also proved that the ubiquitination sites of THEMIS are K362 and K635.We found that HBZ can interact with DDB1 and Cullin4,which also suggests that HBZ may promote the degradation of THEMIS through the Cullin4-DDB1 E3 ubiquitin ligase complex.However,the specific mechanisms need to be further clarified.In addition,we found that,in the basal state,the regulation of the protein level of THEMIS may not be through the Cullin4-DDB1 E3 ubiquitin ligase complex,indicating that the recruitment of Cullin4-DDB1 complex for THEMIS degradation is a specific event for HTLV-1 infected T cells.Hence,this study provides a theoretical basis for the further function and mechanism study on the ubiquitination of Themis. |
