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Proteasomal ubiquitin receptor ADRM1 (ADRM1) functions as a proteasomal ubiquitin receptor. ADRM1 is an integral plasma membrane protein which promotes cell adhesion. ADRM1 is assumed to undergo O-linked glycosylation. ADRM1 gene expression is induced by gamma interferon in some cancer cells. ADRM1 employs the deubiquitinating enzyme UCHL5 at the 26S proteasome and promotes its activity.

UCHL1 (PGP9.5) belongs to a gene family whose products hydrolyze small C-terminal adducts of ubiquitin to produce the ubiquitin monomer. Protein Gene Product (PGP9.5) is a neuron specific protein, structurally and immunologically distinct from neuron specific enolase. Human UCHL1 and UCHL3 have an extremely complicated knot structure for a protein, with five knot crossings. It is considered that the knot structure may increase a protein''s resistance to degradation in the proteasome. The protein, which has a molecular weight of 27 kDa was first defined by high resolution two dimetional PAGE. Standard immunohistochemical techniques have demonstrated the presence of PGP9.5 in neurons and nerve fibers at all levels of the central and peripheral nervous system, in many neurodcrine cells, in segments of the renal tubules, in spermatogonia and leydig cells of the testis, in ova and in some cells of both the pregnant and non pregnant corpus luteum. A point mutation (I93M) in UCHL1 is implicat

HERPUD1 is a multi-pass membrane protein which is a part of the endoplasmic reticulum quality control system. HERPUD1 owns 1 N-terminal ubiquitin-like domain and is expressed highly in the brain. HERPUD1 is also known as ER-associated degradation (ERAD) which takes part in ubiquitin-dependent degradation of misfolded endoplasmic reticulum proteins.

BRCC3 is a subunit of the BRCA1-BRCA2-containing complex (BRCC), which is an E3 ubiquitin ligase. BRCC3 is also thought to be involved in the cellular response to ionizing radiation and progression through the G2/M checkpoint.

IFIH1 is a DEAD box protein which is upregulated in response to treatment with beta-interferon and a protein kinase C-activating compound, mezerein. Irreversible reprogramming of melanomas can be attained by therapy with both these agents; treatment with either agent alone only achieves reversible differentiation. DEAD box proteins are implicated in several cellular processes involving alteration of RNA secondary structure such as translation initiation, nuclear and mitochondrial splicing, and ribosome and spliceosome assembly.

Otubain 1 (OTUB1) belongs to the ovarian tumor (OUT) superfamily of predicted cysteine proteases and inhibits cytokine gene transcription in the immune system through its interaction with a ubiquitin protease and E3 ubiquitin ligase. OTUB1 is a highly specific ubiquitin iso-peptidase, it cleaves ubiquitin from branched poly-ubiquitin chains but not from ubiquitinated substrates. OTUB1 is believed to work in specific ubiquitin-dependent pathways, possibly by providing an editing function of polyubiquitin chain growth. OTUB1 is a hydrolase that removes conjugated ubiquitin from proteins in vitro and may therefore have a significant regulatory role in the level of protein turnover by preventing degradation. Additionally, OTUB1 is a regulator of T-cell anergy, a phenomenon that occurs when T-cells are rendered impassive to antigen re-challenge and no longer respond to their cognate antigen. OTUB1 acts via its interaction with RNF128/GRAIL, which is an essential inductor of CD4 T-cell anergy.

UCK2 is a member of the uridinekinase family. UCK2 catalyzes the phosphorylation of uridine monophosphate to uridine diphosphate and cytidine monophosphate. UCK2 has a part in the production of pyrimidine nucleoside triphosphates essential for RNA and DNA synthesis. Furthermore, an allele of this gene is an important player in mediating nonhumoral immunity to Hemophilus influenzae type B.

Uroplakin 2 (UPK2) is one of the proteins of the highly urothelium-specific integral membrane proteins of the asymmetric unit membrane which forms urothelium apical plaques in mammals. The asymmetric unit membrane is thought to strengthen the urothelium by preventing cell rupture during bladder distention. The UPK2 protein is expressed in the peripheral blood of bladder cancer patients with transitional cell carcinomas.

Small Ubiquitin-like Modifiers (SUMOs) are a family of small, related proteins that can be enzymatically attached to a target protein by a post-translational modification process termed sumoylation. Unlike ubiquitination, which targets proteins for degradation, sumoylation participates in a number of cellular processes, such as nuclear transport, transcriptional regulation, apoptosis, and protein stability. All SUMO proteins share the conserved ubiquitin domain and the C-terminal diglycine cleavage/attachment site. Human SUMO2, also known as Sentrin2 and SMT3B is synthesized as a 95 amino acid (aa), 11 kDa propeptide that contains a two aa C-terminal prosegment, and an 18 aa N-terminal protein interacting region (aa 33 -50). Following prosegment cleavage, the C-terminal glycine is enzymatically attached to a lysine on a target protein. Human SUMO2 shares 100% sequence identity to SUMO-2 from mouse. SUMO2 also has very high sequence homology to SUMO3 and SUMO4, 86 % and 85%, respectivel

ULBP2 is a member of the MHC class I family. ULBP2 is ligand for the NKG2D receptor, composed with at least ULBP1 and ULBP3. ULBPs promote multiple signaling pathways in primary NK cells, triggering the production of cytokines and chemokines. Binding of ULBPs ligands to NKG2D encourages calcium mobilization and activation of the JAK2, STAT5, ERK and PI3K kinase/Akt signal transduction pathway. In CMV infected cells, ULBP2 cooperates with soluble CMV glycoprotein UL16. This cooperation is blocked with the NKG2D receptor, providing a mechanism in which CMV infected cells can escape the immune system. Additionally, UL16 causes ULBP2 to be held in the ER and cis-Golgi apparatus so that it does not reach the cell surface.

UL16 Binding Protein 3 (ULBP3) is a ligand for the NKG2D receptor in NK cells. ULBPs activate different signaling pathways resulting in the production of cytokines and chemokines. ULBP3 is a ligand for the KLRK1/NKG2D receptor, along with at least ULBP1 and ULBP2. Binding of ULBPs ligands to KLRK1/NKG2D stimulates calcium mobilization and activation of the JAK2, STAT5, ERK and PI3K kinase/Akt signal transduction pathway. ULBP3 has lower affinity for KLRK1/NKG2D compared to ULBP1 and ULBP2 and stimulates weaker signaling responses than does ULBP2 or ULBP1.

Ubiquinol-Cytochrome C Reductase (UQCRQ) is a small core-associated protein and a subunit of ubiquinol-cytochrome c reductase complex III that belongs to the mitochondrial respiratory chain. UQCRQ is also a ubiquinone-binding protein of low molecular mass.

UPK3A is a member of the uroplakin-3 family. Uroplakins (UP) which are transmembrane proteins are important components of the urothelium that pass the lipid bilayer once (UPII, UPIIIa, and UPIIIb) or four times (UPIa and UPIb; both members of the "tetraspanin" family). All hold great luminal/extracellular domains, but only UPIIIa and UPIIIb have significant cytoplasmic shares in their C-termini. UPK3A is an extremely specific and moderately sensitive immunohistochemical marker for primary and metastatic urothelial carcinomas. Alterations in this gene are related to renal adysplasia.

Cytochrome b-c1 complex subunit 2, mitochondrial (UQCRC2) is a member of the peptidase M16 family. UQCRC2 is a component of the ubiquinol-cytochrome c reductase complex (complex III), which is a part of the mitochondrial respiratory chain. UQCRC2 is essential for the compilation of the complex.

Ubiquinol-Cytochrome C Reductase Hinge Protein (UQCRH) is a member of the UQCRH/QCR6 family. UQCRH is a component of the ubiquinol-cytochrome c reductase complex (complex III or cytochrome b-c1 complex), which is part of the mitochondrial respiratory chain. The UQCRH protein mediates formation of the complex between cytochromes c and c1.

ISG15 ubiquitin-like Modifier is conjugated to the intracellular target proteins after IFN-alpha or IFN-beta stimulation. ISG15 enzymatic pathway is partially distinct from that of ubiquitin, differing in substrate specificity and interaction with ligating enzymes. ISG15 conjugation pathway uses a dedicated E1 enzyme, but seems to converge with the ub conjugation pathway at the level of a specific E2 enzyme. ISG15 protein targets include STAT1, SERPINA 3G/SPI2A, JAK1, MAPK3/ERK1, PLCG1, EIF2AK2/PKR, MX1/MXA, and RIG-1. Deconjugated by USP18/UBP43 shows specific chemotactic activity towards neutrophils and activates them to induce release of eosinophil chemotactic factors. ISG15 serves as a trans-acting binding factor directing the association of ligated target proteins to intermediate filaments. ISG15 plays a role in autocrine, paracrine and endocrine mechanisms, as in cell-to-cell signaling, possibly partly by inducing ifn-gamma secretion by monocytes and macrophages. ISG15 displays a

RAET1L plays a role as a stress-induced ligand for NKG2D receptor. Retinoic Acid Early Transcript 1L (RAET1L) is linked to the cell membrane by the GPI anchor. HCMV infection triggers RAET1L’sexpression but HCMV alters its function. HCMV-encoded UL16 glycoprotein retains RAET1L/ULBP6 inside the cells, preventing it from reaching the cell surface and being exposed to cells of the immune system. RAET1L has a more restricted expression profile in cell lines and primary human tissues than other NKG2D ligands.

UBX Domain Protein 2B (UBXN2B) is a 331 amino acid protein which comprises one UBX domain and one SEP domain. UBXN2B is essential for ER and Golgi biogenesis and also takes a place in their maintenance during interphase, as well as their reassembly at the end of mitosis. Through interaction with VCP, UBXN2B forms a complex that has membrane fusion activity.

UL16 Binding Protein 4 (ULBP4) is a member of the RAET1 family, which is comprised of major histocompatibility complex (MHC) class I-related genes located in a cluster on chromosome 6q24.2-q25.3. ULBP4 functions as a ligand for the NKG2D receptor on the surface of NK cells. ULBP4 binding to the receptor induces expansion of anti-tumor cytotoxic lymphocytes. ULBP4 is expressed mainly in the skin, but also in the testis or trachea. ULBP4 is upregulated in different tumors. ULBP4 doesn’t interact with the CMV glycoprotein UL16. ULBP4 is also a ligand for the KLRK1 receptor. ULBP4 distributes activating signals to NK cells and stimulates tumor immune surveillance by inducing the expansion of anti-tumor cytotoxic lymphocytes.

Ubiquinol-Cytochrome C Reductase Core Protein I (UQCRC1) is a member of the peptidase M16 family,UQCRC1/QCR1 subfamily. UQCRC1 is a part of the ubiquinol-cytochrome c reductase complex (complex III or cytochrome b-c1 complex), which is component of the mitochondrial respiratory chain. UQCRC1 can mediate formation of the complex between cytochromes c and c1.

USH1C gene product Harmonin, is a scaffold protein which functions in the assembly of Usher protein complexes. Harmonin is able to attach to various proteins in cell membranes and coordinate their activities. Harmonin contains PDZ domains, a coiled-coil region with a bipartite nuclear localization signal and a PEST degradation sequence. USH1C is expressed in the small intestine, colon, kidney, eye, vestibule of the inner ear and weakly in the pancreas.
Mutations in the USH1C gene cause the Usher syndrome type I which is an autosomal recessive sensory defect involving congenital profound sensorineural deafness, vestibular dysfunction, and blindness due to progressive retinitis pigmentosa. Sensorineural deafness is caused by damage to the neural receptors of the inner ear, the nerve pathways to the brain, or the area of the brain that receives sound information. The 3 types of the Usher syndrome (1- 3) are distinguished by age at onset and differences in auditory and vestibular function. USH1C gene defects cause of non-syndromic sensorineural deafness autosomal recessive type 18 (DFNB18), is a form of sensorineural hearing loss.

rRNA-processing protein UTP23 homolog (UTP23) is a small subunit (SSU) processome component. The SSU processome is a complex involved in ribosome biogenesis and essential for pre-18S rRNA maturation. UTP23 is vital for the first 3 cleavage steps in 18S rRNA maturation. Furthermore, single-point mutations in the conserved putative active site of Utp24 but not Utp23 annul its function in ribosome biogenesis.

SQSTM1 is an adapter protein which binds ubiquitin and mediates the activation of NFKB1 by TNF-a, NGF and IL-1. SQSTM1 is involved in titin/TTN downstream signaling in muscle cells. SQSTM1 controls signaling cascades through ubiquitination. SQSTM1 participates in cell differentiation, apoptosis, immune response and regulation of K(+) channels. Mutations in UBA domain of the SQSTM1 protein cause Paget’s disease because the UBA is essential for aggregate sequestration and cell survival.