REGULATORY MECHANISMS
David M. Gibson, Robert A. Harris in Metabolic Regulation in Mammals, 2001
Of increasing importance is the ubiquitin-protcasomc degradativc system which stereospecificallv targets many rapidlv turning over proteins, llhiquitin, a small molecular weight (8.5kDa), highly conserved protein, is activated first by ATP (similar to the formation of fatty acyl-CoA thiol esters) before it is transferred, stepwise, to a target protein. The first thiol ester transfer is from the protein El to E2 which is the ubiquitin donor. The third component, E3, ubiquitm ligase, fingers a specific cognate proteolytic substrate by the covalent attachment of activated uhiquitins to terminal amino groups of lysine siile chains. There are many kinds of ubiquitin ligases each of which recognize specific sequences of amino acids on the target proteins, for example one ligase class has an SI 12 domain (Table 3.2) that recognizes a tyrosine-phosphorylatcd protein target, llhiquinatcd proteins are processed by p rot caso m es, giant (2,500kl)a) barrel-shaped multiprotcin complexes which hvdrolyze ubiquitin-tagged proteins by an ATP-dependent process in which ubiquitin is released for further employment. The ubiquitin-protcasóme system provides a mechanism for controlling the levels of proteins instrumental in the progression of the cell cycle, in cell differentiation and lor removal of misfolded proteins.
Ascorbate and the Hypoxic Response in Cancer
Qi Chen, Margreet C.M. Vissers in Cancer and Vitamin C, 2020
The proline hydroxylases (PHD1–3) target two prolines in the oxygen-dependent degradation domains of the HIF-α subunit (P402 and P564 of HIF-1α; P405 and P531 of HIF-2α) [57,62]. Hydroxylation of these amino acids enables binding of the VHL-E3 ubiquitin ligase complex and targets it for polyubiquitylation and proteasomal degradation (Figure 4.2). PHD2 is the dominant enzyme for hydroxylation of HIF-1α, and PHD1 and PHD3 have more influence on HIF-2α [63]. Hydroxylation of an asparagine in the CAD (N803 of HIF-1α, N847 of HIF-2α) by factor inhibiting HIF (FIH) disrupts recruitment of the coactivator CBP/p300, which interferes with the transactivation activity of HIF [60]. FIH has a higher affinity for oxygen reflected by a lower Km value (90 μM) than PHDs (230–250 μM) and remains active at mild hypoxia, which means it can reduce the transcriptional activity of HIF even in conditions where HIF protein is stabilized [64–66]. Of the two HIF isoforms, HIF-1α has been shown to be more sensitive than HIF-2α to regulation by FIH [67].
Molecular Biology of Lung Cancer as the Basis for Targeted Therapy
Kishan J. Pandya, Julie R. Brahmer, Manuel Hidalgo in Lung Cancer, 2016
Knowledge of 3-D protein structure was also important for the discovery of the proteasome, its function, and subsequent development of proteasome inhibitors (78). Proteasomes are intracellular, barrel-shaped macromolecules that specifically digest other proteins into short polypeptides and amino acids. Target proteins are recognized by the proteasome based on a ubiquitin tag, which is added by the ubiquitin ligases. The proteasome removes the ubiquitin tag and degrades the target protein in an ATP-dependent process. Many important proteins involved in cell cycling and apoptosis are degraded by the proteasome complex, including the cyclins and IKB. The elucidation of this system led to the development of the proteasome inhibitor bortezomib (Velcade, PS-341), which is clinically active as a single agent and in combination with cytotoxic drugs in many tumor types, including lung cancer (79,80). The proposed mechanism of action of bortezomib in lung cancer cells rests on the induction of G2-M arrest and apoptosis. Large clinical trials are ongoing to define optimal administration schedules of bortezomib and combinations with cytotoxic drugs in patients with NSCLC and SCLC.
Enhanced antitumor activity induced by a DNA vaccine encoding E7 antigen fused to an ERAD-targeting sequence
Published in Journal of Drug Targeting, 2023
David Hernán Martínez-Puente, Rodolfo Garza-Morales, José Juan Pérez-Trujillo, Federico Bernabé-Acosta, Arnulfo Villanueva-Olivo, Aracely García-García, Laura Mireya Zavala-Flores, Humberto Rodríguez-Rocha, Jesús Valdés, Odila Saucedo-Cárdenas, Roberto Montes de Oca-Luna, María de Jesús Loera-Arias
In the present study, the expression of proteins that contained the membrane-binding domain (COX2-E7 and SP-MBD-E7-ERAD-K) was not affected by the presence of the MG132 proteasome inhibitor. At the same time, the expression of proteins that did not contain the MBD (SP-E7-ERAD-K and SP-E7-ERAD-S) was enhanced, indicating that the degradation of COX-2 is proteasome-dependent (Figure 3). This finding suggests the use of different degradation pathways that depend on the presence of the membrane-binding domain. In yeasts, it has been reported that there are three types of degradation by the ERAD pathway depending on the nature of the proteins as follows: ERAD-L for ER lumen proteins, ERAD-M for transmembrane proteins, and ERAD-C for cytosolic proteins. These pathways are differentiated by the ubiquitin ligases that directly degrade these proteins. However, there are fewer studies on the types of degradation by the ERAD pathway in mammalian cells [55].
A patent review of discoidin domain receptor 1 (DDR1) modulators (2014-present)
Published in Expert Opinion on Therapeutic Patents, 2020
Particularly, allosteric inhibitors targeting the extracellular domain could be considered as a new approach to specifically modulate DDR1-mediated downstream signaling. Since extracellular regions of DDR1 and DDR2 bind different collagens and share a relatively low degree of sequence identity, highly specific DDR1 or DDR2 inhibition might be achieved by utilizing this strategy. Encouragingly, a small-molecule allosteric regulator targeting the extracellular domain of DDR2 was recently discovered to exhibit good target specificity which paved a solid foundation for the discovery of new generation DDR1 inhibitors with improved target specificity [69]. PROTACs or heterobifunctional degrader molecules typically comprise an E3 ligase binding scaffold (hereafter E3-moiety), attached through a linker to another small molecule (hereafter target-moiety) that binds a target protein of interest. Recruitment of this target protein to the E3 ubiquitin ligase facilitates ubiquitination and subsequent degradation of the target protein. PROTACs represent a promising new pharmacologic modality now widely explored in chemical biology and drug discovery. The PROTAC technique can be applied in the development of DDR1 modulators, which would open a new window for targeted DDR1 therapies. The monoclonal antibody binds to a specific antigen on the cancer cell. The main advantage of antibody over kinase inhibitors is higher selectivity and safety.
Parkin, PINK1 and DJ1 as possible modulators of mTOR pathway in ganglioglioma
Published in International Journal of Neuroscience, 2018
Katarzyna Drapalo, Jaroslaw Jozwiak
Parkin (PARK2), PINK1 (PTEN-induced putative kinase 1) and DJ1 belong to the group of proteins responsible for normal cell cycle. Parkin is a cytoplasmic protein belonging to the family of ubiquitin ligases. In the cell, it plays the role of E3 ubiquitin ligase, which stimulates binding proteins to ubiquitin through a two-step mechanism. In the first step, ubiquitin bound to enzyme E2 is cleaved and binds with thioester bond to cysteine 431 of parkin. Then, ubiquitin is transferred to a protein substrate, most frequently to a side-chain lysine, forming an isopeptide bond. This process causes accumulation of α-synuclein (also in many cases of GG, as evidenced by immunostaining [23]), which is recognized by proteasomes and undergoes degradation (Figure 5). In the result of these changes, inhibition of neurodegenerative process in neuronal structures takes place, such as those found in the pathogenesis of Parkinson's disease [24,25]. PINK1, on the other hand, is a mitochondrial serine/threonine kinase, which displays neuroprotective properties by phosphorylating HTRA2 (high temperature requirement) protein. Activation of HTR2, with its proteolytic properties, protects cells against stress response during mitochondrial dysfunction. PINK1 and parkin affect proteins involved in the process of mitochondrial fission and division (Figure 6).
Related Knowledge Centers
- Cyclin
- Isopeptide Bond
- Lysine
- Proteasome
- Protein
- Ubiquitin
- Ubiquitin-Conjugating Enzyme
- Cyclin-Dependent Kinase Inhibitor Protein
- Ubiquitin-Activating Enzyme
- Adenosine Triphosphate