TPPII, MYBBP1A and CDK2 form a protein–protein interaction network

Linking TPPII to the protein interaction and signalling networks

Tripeptidyl peptidase II (TPPII) is primarily considered a house-keeping exopeptidase, which contributes to the functions of the ubiquitin-proteasome system by the maintenance of the cellular amino acid homeostasis. Although functionally well-characterised in vitro and using the mammalian cell models, less is known about the molecular mechanisms of its involvement in the signalling and metabolic pathways, which mediate its cellular functions. The present protein-protein interaction network analysis identified these mechanisms involved in the adaptive and innate immunity, the metabolism of the glucose, cancer cell growth, apoptosis, cell cycle and DNA damage responses. The interaction network constructed based on the publicly available protein-protein interaction data was extended by the application GeneMania, which was further used for the pathway enrichment, the protein function prediction and the protein node prioritisation analysis. The analysis suggested that the molecular mechanisms linked to the adaptive and innate immunity (ID, Kit receptor, BCR, IL-2 and G-CSF signalling; the regulation of NFκB), the aerobic glycolysis (ID and IL-2 signalling), tumorigenesis (TGF-β and p53 signalling; the top priority nodes MAPKs, mTOR regulation), diabetes (Kit receptor signalling; the top priority node GSK3β) and neurodegeneration (the control of mTOR and Aβ peptide degradation) are controlling the resulting TPPII interaction network. The uncharacterized interactions with two lung cancer suppressors (DOK3, DENND2D), a protein involved in the increased risk of the lung cancer in smokers (CYP1A1) and a protein implicated in asthmatic reactions (CHIA) suggest potential roles of TPPII in the lung cancer pathology. The interactions with methyltransferase CARNMT1, which modifies di- and tripeptides and the xenobiotic processing enzyme CYP1A1, are additional candidates for the breakthrough in new functions discovery of TPPII.

The Tumor Suppressor Roles of MYBBP1A, a Major Contributor to Metabolism Plasticity and Stemness

The MYB binding protein 1A (MYBBP1A, also known as p160) acts as a co-repressor of multiple transcription factors involved in many physiological processes. Therefore, MYBBP1A acts as a tumor suppressor in multiple aspects related to cell physiology, most of them very relevant for tumorigenesis. We explored the different roles of MYBBP1A in different aspects of cancer, such as mitosis, cellular senescence, epigenetic regulation, cell cycle, metabolism plasticity and stemness. We especially reviewed the relationships between MYBBP1A, the inhibitory role it plays by binding and inactivating c-MYB and its regulation of PGC-1α, leading to an increase in the stemness and the tumor stem cell population. In addition, MYBBP1A causes the activation of PGC-1α directly and indirectly through c-MYB, inducing the metabolic change from glycolysis to oxidative phosphorylation (OXPHOS). Therefore, the combination of these two effects caused by the decreased expression of MYBBP1A provides a selective advantage to tumor cells. Interestingly, this only occurs in cells lacking pVHL. Finally, the loss of MYBBP1A occurs in 8%–9% of renal tumors. tumors, and this subpopulation could be studied as a possible target of therapies using inhibitors of mitochondrial respiration.

Role of tripeptidyl peptidase II in MHC class I antigen presentation: Biological characteristics, cellular crosstalk and signaling

Tripeptidyl peptidase II (TPPII) is a multifunctional cytoplasmic serine protease. The main function of TPPII is to cleave proteasome-generated peptides into tripeptides, which can then be further degraded into free amino acids. Recent evidence suggests that TPPII plays an important role in epitope generation, but the mechanisms of TPPII in MHC class I antigen presentation remain unclear. Recent research has shed new light on the mechanisms and functions of TPPII in MHC class I antigen presentation. We therefore provide an updated review of the biological characteristics of TPPII and explore its role in MHC class I antigen presentation.

Novel protein-protein interactions of TPPII, p53, and SIRT7

Novel protein-protein interactions of TPPII, SIRT7, and p53 were detected by co-immunoprecipitation using both HeLa cell lysates and the cytoplasmic fraction prepared by fractionation of mouse liver tissue. The interactions were further verified in vivo by in situ proximity ligation assay (PLA) within control HEK293 cells transformed with empty vector, highactTPPII HEK293 cells over-expressing murine TPPII displaying high specific enzymatic activity and in lowactTPPII HEK293 cells over-expressing human TPPII having low specific activity of the enzyme. Besides an abundant cytoplasmic localization of TPPII-p53 interaction signal, the nuclear interactions were also demonstrated. The cytoplasmic interactions were likewise detected between TPPII and SIRT7 in control HEK293 and lowactTPPII HEK293 cells. The interactions of SIRT7 with p53 were confirmed in three HEK293 cell transformants as well. The cytoplasmic occurrence of SIRT7 protein was demonstrated by immunofluorescence, when both nucleolar and cytoplasmic signals were identified within HEK293 cells and primary human fibroblasts. The unique cytoplasmic localization of SIRT7 protein was discussed based on an epitope specificity of N-terminus specific SIRT7 antibodies utilized in the present study compared with C-terminus specific antibodies previously used for nuclear detection of SIRT7 by other authors. The epitope sequence of N-terminal antibodies is occurring in all three splicing variants of SIRT7 compared to the epitope of C-terminal antibody, which is specific exclusively to the splicing variant 1. The cytoplasmic localization of p53 detected by immunofluorescence supported the results from its interactions with TPPII and SIRT7 observed by in situ PLA within model cells. Novel interactions of TPPII, p53, and SIRT7 presented in this study might contribute to the knowledge of the regulatory effects of these proteins on apoptotic pathways and to the understanding mechanisms of aging and lifespan regulation.