UCK2 Human
Description
Introduction to UCK2 Human
UCK2 (uridine-cytidine kinase 2) is a homotetrameric enzyme encoded by the UCK2 gene on chromosome 1q22-23.2 . It catalyzes the phosphorylation of uridine and cytidine to uridine monophosphate (UMP) and cytidine monophosphate (CMP), serving as the rate-limiting enzyme in the pyrimidine salvage pathway . While it shares 70% sequence identity with UCK1, UCK2 exhibits 15–20-fold higher catalytic efficiency for uridine/cytidine substrates . Unlike UCK1, which is ubiquitously expressed, UCK2 is primarily detected in placental tissue under normal conditions but is overexpressed in various cancers, making it a therapeutic target .
Enzyme Structure
UCK2 forms a tetramer (112 kDa) with each monomer containing a core five-stranded β-sheet flanked by α-helices and a β-hairpin loop . Key active-site residues include:
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His-117 and Tyr-112: Determine substrate specificity via hydrogen bonding with cytidine’s 4-amino group or uridine’s 6-oxo group .
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Asp-62: Catalyzes nucleophilic attack on ATP’s γ-phosphate by deprotonating the substrate’s 5′-hydroxyl .
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Glu-135, Ser-34, and Asp-62: Coordinate a magnesium ion critical for catalysis .
Crystallographic studies reveal conformational changes in Asp-62 during substrate binding and product release . A novel allosteric site at the tetramer’s intersubunit interface has been identified, offering a potential target for non-competitive inhibitors .
Catalytic Efficiency
| Parameter | UCK2 (Uridine) | UCK1 (Uridine) | Fold Difference |
|---|---|---|---|
| (μM) | 15–20 | 60–80 | 4–6x lower |
| (min⁻¹) | 20–30 | 1–2 | 15–20x higher |
| 1–2 (μM⁻¹ min⁻¹) | 0.02–0.03 | 30–60x higher |
Data compiled from kinetic studies .
Role in Pyrimidine Salvage Pathway
UCK2 facilitates the recycling of extracellular uridine/cytidine into nucleotides for RNA/DNA synthesis. This pathway is critical in rapidly proliferating cells, including cancer . Key differences between de novo and salvage pathways:
| Pathway | Substrates | Rate-Limiting Enzyme | Key Function |
|---|---|---|---|
| Salvage | Uridine/Cytidine | UCK2 | Recycling nucleosides |
| De Novo | Glutamine | CAD | Synthesis from non-nucleoside precursors |
UCK2 also activates nucleoside analogs (e.g., cyclopentenyl cytidine) used in chemotherapy .
Cancer-Associated Overexpression
UCK2 is overexpressed in multiple malignancies, including hepatocellular carcinoma (HCC), lung, pancreatic, and colorectal cancers . Its expression correlates with poor prognosis and metastasis .
| Cancer Type | UCK2 Fold Change vs Normal | Prognostic Impact | Source |
|---|---|---|---|
| Lung Adenocarcinoma | 5.24 | Poor OS | Oncomine |
| Hepatocellular | 4.29 | Early recurrence | TCGA |
| Pancreatic | 3.61 | Reduced survival | Oncomine |
Non-Metabolic Roles
UCK2 modulates non-canonical pathways:
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EGFR-AKT Signaling: Stabilizes EGFR by inhibiting degradation, promoting proliferation and metastasis .
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Immune Modulation: Negatively correlates with HLA/MHC genes, suggesting immune evasion .
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DNA Repair: Associates with mismatch repair (MMR) and homologous recombination (HR) genes, linking to genetic instability .
Targeted Approaches
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Allosteric Inhibition: Small molecules targeting the intersubunit allosteric site reduce without affecting , minimizing host toxicity .
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Combination Therapy: Dual inhibition of UCK2 and EGFR shows synergistic antitumor effects in HCC models .
Diagnostic Biomarker
UCK2 expression levels in lung cancer tissues distinguish adenocarcinoma (ADC), squamous cell carcinoma (SCC), and small cell lung cancer (SCLC) .
Table 1: UCK2 vs UCK1 Functional Comparison
| Parameter | UCK2 | UCK1 |
|---|---|---|
| Tissue Expression | Placenta, tumors | Ubiquitous (heart, liver) |
| Substrate Preference | Uridine/Cytidine | Uridine |
| Feedback Inhibition | UTP/CTP | Absent |
Table 2: UCK2 Expression Across Cancers (Oncomine Data)
| Dataset | Cancer Type | Fold Change | P-value |
|---|---|---|---|
| Hou et al. (2010) | Lung (LCC) | 5.24 | 4.52E-12 |
| Garber et al. (2003) | Lung (ADC) | 3.49 | 3.27E-4 |
| Bhattacharjee et al. | Lung (SCC) | 7.72 | 1.82E-5 |
Product Specs
Q&A
What is UCK2 and what is its primary function in human cells?
UCK2 (uridine-cytidine kinase 2) is a pyrimidine ribonucleoside kinase that plays a critical role in the salvage pathway of nucleotide synthesis. The enzyme (EC 2.7.1.48) catalyzes the phosphorylation of uridine and cytidine to uridine monophosphate (UMP) and cytidine monophosphate (CMP), respectively . Unlike other nucleoside monophosphate (NMP) kinase family members, UCK2 functions as a homotetramer, specifically recognizes ribonucleosides but not 2'-deoxyribonucleosides, and is subjected to UTP- and CTP-mediated feedback inhibition . This enzyme is predominantly expressed in placental tissue under normal conditions but becomes aberrantly overexpressed in various cancer types .
How is UCK2 structurally organized and how does it differ from UCK1?
UCK2 belongs to the nucleoside kinases of nucleoside monophosphate (NMP) kinase fold family based on sequence homology . According to protein structural analysis, UCK2 has been subgrouped into the UCK family along with two non-nucleic acid kinases: pantothenate kinase and phosphoribulokinase .
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Quaternary structure: While UCK1 functions as a monomer like other NMP family members, UCK2 operates as a homotetramer
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Substrate specificity: UCK2 has higher specificity for ribonucleosides
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Tissue distribution: UCK2 expression is more restricted and is notably elevated in cancerous tissues
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Regulatory mechanisms: UCK2 is subject to feedback inhibition by UTP and CTP
What is the chromosomal location and genetic structure of human UCK2?
Human UCK2 was mapped to chromosome 1q22-23.2 in 2001, confirming earlier assignments from the 1970s that provisionally placed it on chromosome 1 . The gene spans more than 19 kb of genomic DNA and contains seven exons . It encodes a 261-amino acid protein with a predicted molecular mass of 29 kDa . The resulting protein functions primarily in the phosphorylation of pyrimidine ribonucleosides, which is essential for nucleotide salvage metabolism.
How is UCK2 expression regulated in normal and disease states?
UCK2 expression is tightly regulated in normal tissues but becomes dysregulated in various pathological conditions, particularly in cancer. Several regulatory mechanisms have been identified:
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Gene amplification: Some cancers show UCK2 gene amplification, contributing to overexpression
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Viral infection: Epstein-Barr virus infection has been associated with aberrant UCK2 expression
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Epigenetic regulation: m6A RNA methylation modifications induced by METTL3 can affect UCK2 expression
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Hypoxic conditions: Hypoxia has been shown to induce UCK2 overexpression
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MicroRNA regulation: Downregulation of certain miRNAs can lead to increased UCK2 expression, as seen with miR-199a-3p which is sponged by LncRNA-NEAT1 in hepatocellular carcinoma
What are the metabolic and non-metabolic roles of UCK2 in cancer progression?
UCK2 contributes to cancer progression through both metabolic and non-metabolic mechanisms:
Metabolic functions:
UCK2 supports tumor development by providing sufficient nucleotides for enhanced DNA and RNA synthesis in rapidly dividing cancer cells . Inhibition of UCK2 has been shown to reduce 18S RNA expression in colorectal cancer cells, leading to cell cycle arrest . This impairment of RNA biosynthesis demonstrates UCK2's critical role in supporting the metabolic demands of cancer cells.
Non-metabolic functions:
Recent research has revealed several non-metabolic roles of UCK2 in tumor progression, particularly in hepatocellular carcinoma (HCC):
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STAT3-MMP2/9 signaling: UCK2 promotes in vitro migration and invasion and in vivo metastasis by activating the STAT3-MMP2/9 signaling axis in HCC
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EGFR-AKT pathway: UCK2 interacts with EGFR to block EGF-induced EGFR ubiquitination and degradation, thereby activating the EGFR-AKT signaling pathway
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Catalytic-independent functions: Studies using catalytic-dead UCK2 mutants (UCK2 D62A) showed that while these mutants failed to promote HCC cell proliferation, they still enhanced HCC metastasis, confirming UCK2's dual role in cancer progression
How can UCK2 be utilized as a diagnostic and prognostic biomarker in cancer?
UCK2 shows considerable promise as both a diagnostic and prognostic biomarker, particularly in lung cancer:
Diagnostic value:
Analysis of Gene Expression Omnibus (GEO) and Oncomine databases has revealed UCK2 overexpression in lung tumor tissues compared to adjacent non-tumor tissues or normal lung . This finding has been confirmed in clinical samples, with UCK2 showing particularly high expression in stage IA lung cancer with exceptional diagnostic accuracy (area under the receiver operating characteristic curve > 0.9) .
Prognostic value:
High UCK2 expression correlates with poorer clinicopathological features in lung cancer, including:
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Hepatocellular carcinoma (as part of macrophage-related four-gene or six-gene prognostic signatures)
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Endometrial cancer (as part of metabolism-related nine-gene or cell cycle-related five-gene signatures)
What experimental approaches can be used to study UCK2 function in cancer cells?
Several experimental approaches can be employed to investigate UCK2 function in cancer:
Gene expression manipulation:
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RNA interference (siRNA/shRNA): Knockdown of UCK2 has been shown to suppress proliferation and migration of lung cancer cells
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CRISPR-Cas9 gene editing: For complete knockout or targeted mutations
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Overexpression systems: Using wild-type or mutant UCK2 constructs to study specific functions
Protein-protein interaction studies:
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Co-immunoprecipitation: To identify binding partners such as EGFR
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Proximity ligation assay: For visualizing protein interactions in situ
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Yeast two-hybrid screening: To discover novel interacting proteins
Functional assays:
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Cell proliferation assays: MTT, BrdU incorporation, or colony formation
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Migration and invasion assays: Transwell, wound healing, or 3D matrix invasion
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In vivo metastasis models: Using fluorescently labeled or luciferase-expressing cells
Enzymatic activity measurements:
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Radiometric assays: Using radiolabeled substrates to measure phosphorylation
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Spectrophotometric coupled assays: For monitoring UCK2 activity in real-time
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Mass spectrometry: To quantify nucleotide metabolites
What approaches have been developed for targeting UCK2 in therapy?
UCK2 presents a promising therapeutic target with several approaches under investigation:
Direct inhibition strategies:
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Allosteric inhibitors: Structure-based drug prototyping has identified promising leads that non-competitively inhibit UCK2 activity by targeting a previously unknown allosteric site at the inter-subunit interface of this homotetrameric enzyme
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Active site inhibitors: Traditional competitive inhibitors targeting the enzyme's catalytic site
Combination therapy approaches:
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Dual pathway inhibition: Combined inhibition of dihydroorotate dehydrogenase (DHODH, involved in de novo pyrimidine biosynthesis) and UCK2 (critical for salvage pathway) has shown promise in attenuating viral replication in infected cells
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Synergistic targeting: Concurrent pharmacologic targeting of both metabolic and non-metabolic features of UCK2 using ECyd (metabolic inhibitor) and Erlotinib (targeting non-metabolic EGFR pathway) synergistically inhibits HCC growth and metastasis
Nucleoside analog development:
Several cytotoxic nucleoside analogs have been developed for cancer chemotherapy by leveraging UCK2's catalytic properties . These compounds are activated by UCK2 and subsequently interfere with cellular processes, leading to cancer cell death.
What is the relationship between UCK2 and response to nucleoside analog chemotherapies?
UCK2 plays a crucial role in determining sensitivity to various nucleoside analog therapies:
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UCK2 expression levels correlate with sensitivity to several nucleoside analogs:
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Low expression of UCK2 (but not UCK1) is observed in cancer cells resistant to ECyd or EUrd
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Knockdown and upregulation of UCK2 are related to 5-FU resistance and sensitization, respectively, in colorectal cancer cells
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UCK2, rather than UCK1, is responsible for activation of RX-3117, a novel antimetabolite
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UCK2 serves as a biomarker of potential response to nucleoside analog treatments:
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UCK2 inhibition affects efficacy of certain therapies:
How does UCK2 contribute to viral replication and what are the implications for antiviral strategies?
UCK2's role in pyrimidine nucleotide biosynthesis makes it a promising target for antiviral therapies, particularly against RNA viruses:
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Pyrimidine nucleotide requirement for viral replication:
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RNA viruses require substantial amounts of pyrimidine ribonucleotides for genome replication
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By targeting UCK2, the salvage pathway for pyrimidine ribonucleotide production can be disrupted
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Combined inhibition strategy:
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Therapeutic implications:
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Newly developed allosteric inhibitors of UCK2 reduce the enzyme's kcat without altering its KM, potentially enabling "dialing" of the fractional inhibition of pyrimidine salvage
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This approach could achieve desired antiviral effects while minimizing host toxicity
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The COVID-19 pandemic has increased the urgency of developing such antiviral therapies with novel modes of action
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What methodologies are used to investigate the structural basis of UCK2 inhibition?
Several advanced structural biology and biochemical techniques are employed to study UCK2 inhibition:
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X-ray crystallography:
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Structure-based drug prototyping:
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Enzyme kinetics analysis:
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Site-directed mutagenesis:
How do circRNAs derived from UCK2 influence cancer biology?
Recent research has uncovered an interesting dimension to UCK2 biology through the identification of circular RNAs (circRNAs) derived from the UCK2 gene:
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CircUCK2 identification:
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Tumor suppressive functions:
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Molecular mechanism:
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Research implications:
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The opposing roles of UCK2 protein (oncogenic) and circUCK2 (tumor suppressive) suggest complex regulatory networks
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This duality presents challenges and opportunities in targeting UCK2 for cancer therapy
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UCK2 Expression in Lung Cancer vs Normal Tissue (Oncomine Analysis)
| Dataset | Cancer Type vs Normal | P-value | Fold Change |
|---|---|---|---|
| Hou et al, 2010 | Large Cell Carcinoma vs normal | 4.52E-12 | 5.239 |
| Hou et al, 2010 | Adenocarcinoma vs normal | 2.44E-12 | 2.427 |
| Hou et al, 2010 | Squamous Cell Carcinoma vs normal | 1.21E-18 | 4.289 |
Note: Analysis based on 538 samples from 5 Oncomine datasets with thresholds of two-fold change, P-value = .05, and top 10% gene rank .
UCK2 Functions in Tumor Development and Therapy
| Function Type | Mechanism | Effect on Cancer | Therapeutic Implications |
|---|---|---|---|
| Metabolic | Provides nucleotides for DNA/RNA synthesis | Supports rapid tumor cell proliferation | Target for nucleoside analog development |
| Non-metabolic | Activates STAT3-MMP2/9 signaling | Promotes migration, invasion, and metastasis | Potential for combination therapy approaches |
| Non-metabolic | Interacts with EGFR to block ubiquitination and degradation | Activates EGFR-AKT signaling pathway | Synergistic targeting with EGFR inhibitors |
| Circular RNA | circUCK2 acts as miRNA sponge for miR-767-5p | Relieves inhibition on TET1, reducing proliferation | Potential tumor suppressive mechanism |
Table synthesized from research findings presented in search result .
Product Science Overview
The UCK2 gene is located on chromosome 1q24.1 and encodes a protein that is approximately 261 amino acids long . The protein structure of UCK2 includes a five-stranded β-sheet surrounded by five α-helices and a β-hairpin loop, which forms a significant portion of the binding pocket for its substrates . The active site of UCK2 contains key residues such as His-117 and Tyr-112, which are crucial for substrate binding, and Asp-62, which is essential for its catalytic activity .
UCK2 catalyzes the phosphorylation of uridine and cytidine to uridine monophosphate (UMP) and cytidine monophosphate (CMP), respectively . This phosphorylation is the first step in the production of pyrimidine nucleoside triphosphates, which are necessary for RNA and DNA synthesis . UCK2 can utilize ATP or GTP as a phosphate donor and can also phosphorylate various nucleoside analogs, making it a versatile enzyme .
Recombinant UCK2 is produced through recombinant DNA technology, which involves inserting the UCK2 gene into an expression vector and introducing it into a host cell, such as E. coli, to produce the protein in large quantities. This recombinant form is used in various research and clinical applications, including studies on nucleotide metabolism and the development of antiviral and anticancer drugs .
UCK2 has been implicated in several clinical contexts. For instance, an allele of the UCK2 gene may play a role in mediating nonhumoral immunity to Hemophilus influenzae type B . Additionally, due to its role in nucleotide metabolism, UCK2 is a target for drug development, particularly in the context of cancer and viral infections .
