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18 recordsLinked to original sources
PubMed1977

Guanosine triphosphate: 5-hydroxylysine phosphotransferase in rat kidney cortex.

An enzyme which catalyzes the transfer of the gamma-phosphate from GTP onto 5-hydroxylysine was partially purified from rat kidney cortex by means of acid precipitation and DEAE-Sephadex A-50 column chromatography. The enzyme activity was assayed by measuring the transfer of [32P] from gamma-[32P]-GTP to materials not adsorbed by charcoal. This partially purified enzyme showed essentially no GTP phosphohydrolase activity and an optimal pH of 8.0. An apparent Km of about 23.8 mumol/1 was obtained with respect to 5-hydroxylysine. Mg2+ was required for the activity of this enzyme. Ethanolamine, L-lysine, L-ornithine and choline inhibited the enzyme but L-threonine, L-serine and hydroxy-L-proline did not. None of these compounds severed as substrate for this enzyme.

Animals↗
PubMed2002

Activation of Rac1 by shear stress in endothelial cells mediates both cytoskeletal reorganization and effects on gene expression.

Hemodynamic shear stress is a fundamental determinant of vascular remodeling and atherogenesis. Changes in focal adhesions, cytoskeletal organization and gene expression are major responses of endothelial cells to shear stress. Here, we show that activation of the small GTPase Rac is essential for gene expression and for providing spatial information for shear stress-induced cell alignment. Fluorescence resonance energy transfer (FRET) localizes activated Rac1 in the direction of flow. This directional Rac1 activation is downstream of shear-induced new integrin binding to extracellular matrix. Additionally, Rac1 mediates flow-induced stimulation of nuclear factor kappaB (NF-kappaB) and the subsequent expression of intercellular cell adhesion molecule 1 (ICAM-1), an adhesion receptor involved in the recruitment of leukocytes to atherosclerotic plaque. These studies provide a unifying model linking three of the main responses to shear stress that mediate both normal adaptation to hemodynamic forces and inflammatory dysfunction of endothelial cells in atherosclerosis.

Animals↗
PubMed2026

LncRNA H19 promotes vascular remodeling by inhibiting MFN2.

Neointimal hyperplasia, featuring excessive proliferation and migration of vascular smooth muscle cells (VSMCs), is crucial in vascular remodeling diseases. Long non-coding RNA (lncRNA) H19 promotes vascular remodeling, yet underlying mechanisms remain incompletely elucidated. Here, we investigated whether H19 acts via its derivative miR-675-5p. Bioinformatics found a conserved H19/miR-675-5p/MFN2 (mitofusin 2) axis. Cell assays were performed to evaluate the effects of H19 and miR-675-5p on VSMC proliferation and migration. The dual-luciferase reporter gene assay was used to assess the interaction between miR-675-5p and Mfn2 mRNA. The mouse model of common carotid artery ligation was used to evaluate the role of H19 in neointimal hyperplasia. Our data suggested that knockdown of H19 inhibited VSMC proliferation and migration, as well as neointimal hyperplasia. Mechanistically, H19 regulated MFN2 through miR-675-5p, leading to ERK1/2 (extracellular signal-regulated kinase 1/2) activation. In conclusion, we suggest that targeting the H19/miR-675-5p/MFN2/ERK1/2 axis may help to treat vascular remodeling diseases.

Animals↗
PubMed2026

DNM1L depletion leads to accelerated heteroplasmy shifting of m.10191C allele through ATG7-dependent pathways.

Nucleotide composition bias in mitochondrial DNA (mtDNA) makes the heavy strand prone to form a DNA secondary structure called a guanine quadruplex (G4). This secondary structure has been shown to inhibit polymerase processivity in vitro. We previously identified pathogenic mtDNA variants that lead to increased G4-forming propensity, including a T to C mutation at m.10191 (m.10191 T > C) that causes Leigh syndrome. Cells treated with G4 binding agent (G4BA) berberine show a reduction in m.10191C pathogenic heteroplasmy levels. To help better understand the underlying mechanism behind berberine-induced heteroplasmy shift, we examined the relationship between mitochondrial fission and berberine-mediated shift. Here we show that knockdown of the fission factor DNM1L leads to an accelerated heteroplasmy shift towards the healthy mtDNA allele, lowering m.10191C by 10% in 3 weeks, compared to the 5 weeks required for berberine alone. The specific mechanism involves ATG7, as knockdown of ATG7 is able to partially delay this accelerated heteroplasmy shift. Taken together, we show that DNM1L knockdown is able to accelerate berberine-induced m.10191C heteroplasmy shifting through an autophagy-related mechanism.

Humans↗
PubMed1979

Mechanisms of action of cholera and Escherichia coli enterotoxins.

Current information is reviewed on the mechanism of secretion in small intestine, including how it is altered by cyclic 3',5'-adenosine monophosphate and on the structures and properties of cholera and both heat-labile and heat-stable Escherichia coli enterotoxins. Two separate active ion transport processes are altered by cyclic 3',5'-adenosine monophosphate: 1) coupled absorption of NaCl is inhibited in villus cells and 2) active anion secretion is stimulated, probably in crypt cells. Cholera and heat-labile E. coli toxins exert their secretory effect by stimulating intestinal mucosal adenylate cyclase. This stimulation results from the A1 subunit catalyzed transfer of adenosine diphosphate ribose from NAD to a membrane-bound guanosine triphosphatase, thereby inhibiting the enzyme, which normally represses adenylate cyclase. Heat-stable E. coli enterotoxin stimulates intestinal mucosal guanylate cyclase, which appears to be the basis for its enterotoxicity.

Animals↗
PubMed2026

HRAS promotes mutant NRAS-driven transformation with codon and allele specificity.

Wild-type RAS family members determine the signaling and therapeutic response in cancers driven by mutant HRAS and KRAS because they activate alternate RAS effector pathways. Here, we found that the requirement for wild-type RAS to support mutant NRAS-driven transformation correlated with codon-specific differences in GTP hydrolysis. NRAS with mutations at either Gly12 (G12X) or Gly13 (G13X), which retained the GDP-GTP cycling function, had modest autonomous transforming potential. In contrast, NRAS with GTP-locking mutations at Gln61 (Q61X mutants) was uncoupled from receptor tyrosine kinase (RTK) input, rendering wild-type RAS an obligate partner for RTK-stimulated signaling and oncogenesis. In RASless cells expressing mutant NRAS, reintroduction of wild-type HRAS was sufficient to restore signaling and transformation. Global dependency mapping in human cancer cells revealed functional partitioning, wherein mutant NRAS promoted MAPK signaling and wild-type HRAS promoted PI3K-AKT survival signaling. Consequently, allele-specific or pan-RAS(ON) inhibitors synergized with inhibitors of proximal RTK signaling or of wild-type HRAS or KRAS to overcome this signaling plasticity. Pan-RAS(ON) and HRAS inhibition was synergistic for all NRAS mutants tested, with Q61X mutants showing greater sensitivity. These findings define the signaling partnership between mutant NRAS and wild-type HRAS as a targetable vulnerability and provide a biochemical blueprint for dual RAS inhibition in NRAS-mutated malignancies.

Humans↗
PubMed2025

Ras-MAPK pathway in patients with lupus nephritis.

BACKGROUND: Pathogenic mutations in genes encoding components of the Ras/mitogen-activated protein kinase (Ras-MAPK) pathway cause RASopathy. Here, we describe five unrelated patients with SLE carrying mutations associated with RASopathy and investigate the activity of the Ras-MAPK pathway. METHODS: Pathogenic variants were identified by whole-exome/whole-genome sequencing. The activity of the Ras-MAPK pathway in peripheral blood mononuclear cells (PBMC) and kidneys was evaluated using RNA sequencing and datasets from the nephroseq database, respectively. RESULTS: Five (likely) pathogenic variants in four Ras-MAPK genes were identified, including NRAS: c.G38A: p.G13D; ARAF: c.C1435T: p.R479C; KRAS: c.T341C: p.V114A; PTPN11: c.G455A: p.R152H and NRAS: c.G34A: p.G12S. Kidney injury is the main feature, presenting with nephrotic syndrome (2/5), proteinuria and haematuria (2/5). Acute kidney injury and rapidly progressive nephritic syndrome were noted in one patient each. Other clinical features included mucocutaneous lesions (5/5), cardiac involvement (4/5) and arthralgia (3/5). Laboratory abnormalities included hypocomplementaemia (5/5), presence of antiphospholipid antibodies (4/5), decreased regulatory T cells (3/3), pancytopenia (3/5) and persistent monocytosis (2/5). Kidney biopsy revealed lupus nephritis. Most patients responded well to standard therapy, with the exception of the patient with the NRAS p.G13D mutation who died. The Ras-MAPK pathway was activated in both PBMC and kidney of patients with LN as indicated by increased expression of NRAS, KRAS, RIT1, MRAS, PPP1CB, SHOC2, SOS2 and MAP2K1, as well as decreased expression of negative regulators of the Ras-MAPK pathway, CBL, LZTR1 and NF1. CONCLUSION: Kidney involvement may be the main feature of the clinical spectrum of RASopathy. Genetic screening should be considered for patients with early onset lupus.

Humans↗
PubMed2025

In-depth assessment of BRAF, NRAS, KRAS, EGFR, and PIK3CA mutations on cell-free DNA in the blood of melanoma patients receiving immune checkpoint inhibition.

INTRODUCTION: Circulating tumor DNA (ctDNA) holds promise for guiding immune checkpoint inhibitor (ICI) therapy and stratifying responders from non-responders. While tumor-informed ctDNA detection approaches are sensitive and mutation-inclusive, they require tumor tissue, which limits applicability in real-world settings. Conversely, tumor-agnostic methods often have limited genomic coverage. In this study, we evaluated a tumor-agnostic, broad-panel ctDNA assay in patients with advanced melanoma treated with ICI. METHODS: We conducted a prospective analysis of 241 longitudinal samples from 39 patients with unresectable stage III/IV melanoma using a SYSMEX targeted NGS panel covering 1,114 COSMIC mutations. Plasma samples were collected at baseline and during ICI therapy. The assay's sensitivity reached seven mutant molecules, corresponding to a 0.07% mutation allele frequency (MAF). ctDNA profiles were compared with matched tumor tissue and correlated with clinical features and survival. RESULTS: At baseline, ctDNA was detected in 64.5% of patients. Common mutations included BRAFV600E (43.8%) and NRASG12D (36.4%), followed by KRAS, EGFR, and PIK3CA variants. Overall tissue-plasma concordance was 51.6%, with more extended biopsy-plasma intervals associated with discordance (p = 0.0105). Notably, 12.2% of cases exhibited partial concordance, characterized by shared mutations and additional plasma-only alterations, underscoring the complementary value of blood-based profiling. Persistent or re-emerging ctDNA positivity post-therapy correlated with shorter progression-free survival (PFS, p = 0.003), while ctDNA-negative patients showed significantly improved outcomes. Patients that remained ctDNA-negative had significantly longer progression-free survival (median not reached) compared to those with persistent ctDNA positivity (median 3 months) or those converting to positive (median 7.5 months; p = 0.0073). Early NRAS and KRAS ctDNA levels strongly predicted poor response (p = 0.0069 and p = 0.028). The prognostic impact extended beyond canonical drivers, as non-hotspot variants also correlated with the outcome. Notably, even low-level ctDNA persistence (5-10 MM/mL) carried adverse prognostic implications (p = 0.0054). Concerning a shorter PFS, ctDNA positivity was also associated with elevated S100 levels (p = 0.047). Organ-specific mutation enrichment (e.g., KRASG12D in brain, EGFRG719A in lymph nodes) suggested possible metastatic tropism. CONCLUSION: Broad tumor-agnostic ctDNA analysis effectively identified clinically relevant mutations and predicted outcomes in ICI-treated melanoma patients. This approach enables tissue-independent and real-time ctDNA monitoring and may inform patient selection and therapeutic strategies in future interventional trials.

Humans↗
PubMed1977

Characterization of the m7G(5')pppN-pyrophosphatase activity from HeLa cells.

The m7(G(5')pppN-pyrophosphatase activity previously detected in HeLa cells has been further characterized. Results from DEAE-cellulose column chromatography and polyacrylamide gel electrophoresis under nondenaturing conditions revealed only one enzyme activity in HeLa cell extracts which was capable of selectively hydrolyzing m7G(5')pppN to yield m7pG + ppN (where N = 2'-O-methylated or unmethylated ribonucleosides or oligonucleotides of up to 8 to 10 nucleosides in length). The majority (approximately 95%) of this activity was found in the cytoplasmic extract but appeared not to be associated with the lysosomal fraction. m7G(5')pppG was hydrolyzed by the partially purified enzyme in the absence of divalent cations at a pH optimum of 7.5 and a temperature optimum of 45 degrees, with a Michaelis constant (Km) of 1.7 micronM. Sedimentation analysis and gel filtration showed the molecular weight of the enzyme as approximately 81,000. Inhibition studies testing the effect of a number of prospective substrates on the rate of m7G(5')pppG hydrolysis have confirmed the importance of the methyl moiety at the N7 position of guanosine for enzyme-substrate interaction. Furthermore, the trimethylated guanosine-containing 5'-terminal structure derived from U-2 RNA was found not to serve as substrate, and 7-methylinosine, unlike 7-methylguanosine, was not an effective inhibitor of m7G(5')pppG hydrolysis. Thus, the 2-amino group of the 7-methylguanosine portion of m7G(5')pppN is also important for substrate interaction with this specific pyrophosphatase.

Cytoplasm↗
PubMed1978

[Guanyl cyclase in Escherichia coli. II. Identification and characteristics on the enzyme inhibitor].

The activity of guanylate cyclase and that of its inhibitor present in E. coli extract, have been separated through a linear KCl gradient on DEAE-cellulose column. The activity of the inhibitor is lost after ribonuclease treatment, whereas is strengthened by addition of poly (C). Other types of RNA synthetic homopolymers do not affect the inhibitor's activity. Chromatographic analysis of the products of guanylate cyclase measured in the presence of FI and FI plus poly (C), indicated that the inhibitor has a poly (C) dependent GTPase activity.

Deoxyribonucleases↗
PubMed1978

[Guanylate cyclase in E. coli. III. Purification and possible physiological role of GTPase].

A phosphohydrolase with a preferential activity for GTP has been isolated and partially purified from E. coli extracts. The enzyme purification has been achieved through precipitation by ammonium sulfate and chromatography on DEAE-cellulose, DEAE-Sephadex, Ultragel and a second DEAE-cellulose column. The phosphohydrolase activity is poly (C) dependent. The chromatographic analysis on PEI-cellulose has shown that the main product of GTP hydrolysis is GDP. The possibility that the enzyme partially purified in this work has an important role in the control of GTP availability as substrate for guanylate cyclase into the cells has been discussed.

Chromatography, DEAE-Cellulose↗
PubMed1979

Acidic ribosomal proteins from eukaryotic cells. Effect on ribosomal functions.

Precipitation of Saccharomyces cerevisiae ribosomes by ethanol under experimental conditions that do not release the ribosomal proteins can affect the activity of the particles. In the presence of 0.4 M NH4Cl and 50% ethanol only the most acidic proteins from yeast and rat liver ribosomes are released. At 1 M NH4Cl two more non-acidic proteins are lost from the ribosomes. The release of the acidic proteins causes a small inactivation of the polymerizing activity of the particles, additional to that caused by the precipitation itself. The elongation-factor-2-dependent GTP hydrolysis of the ribosomes is, however, more affected by the loss of acidic proteins. These proteins can stimulate the GTPase but not the polymerising activity when added back to the treated particles. Eukaryotic proteins cannot be substituted for bacterial acidic proteins L7 and L12. We have not detected immunological cross-reaction between acidic proteins from Escherichia coli and those from yeast, Artemia salina and rat liver or between acidic proteins from these eukaryotic ribosomes among themselves.

GTP Phosphohydrolase-Linked Elongation Factors↗
PubMed1979

The proton-translocating adenosine triphosphatase of the obligately anaerobic bacterium Clostridium pasteurianum. 1. ATP phosphohydrolase activity.

1. The cell-membrane ATP phosphohydrolase of vegetatively grown Clostridium pasteurianum was specifically Mg2+-dependent, but demonstrated significant activity with GTP, CTP and UTP. It displayed approximate Michaelis-Menten kinetics only in the presence of certain effectors (e.g. phosphoenolpyruvate, fructose 1,6-bis-phosphate) which decreased the Km for ATP (to below 2 mM) but also V, whilst extending to pH 5.8 the effective pH range of activity of the enzyme. 2. ATP phosphohydrolase activity of the membrane ATPase (BF0F1) was inhibited by N,N'-dicyclohexylcarbodiimide, butyricin 7423, Dio-9, 4-chloro-7-nitrobenzofurazan, efrapeptin, leucinostatin and quercetin, and to a lesser degree by aurovertin and citreoviridin. The enzyme was not inhibited by oligomycin, spegazzinine, tributyl tin, triethyl tin or venturicidin. The soluble ATPase (BF1) component differed in not being inhibited by N,N'-dicyclohexylcarbodiimide, butyricin 7423 or leucinostatin. 3. The ATPase (BF0F1) complex and its soluble (BF1) component were separately purified. 4. Dodecylsulphate/polyacrylamide gel electrophoresis separated only four polypeptide components in the purified ATPase (BF0F1), with approximate molecular weights (+/- 10%) as follows: subunit a, 65 500; subunit c, 57 500; subunit da, 43 000; subunit fa, 15 000. The soluble (BF1 component contained only the three polypeptide subunits a, c and da. These were present in the BF0F1 preparation in the ratio 2 : 1 : 2; the contribution of subunit fa could not satisfactorily be quantified. 5. Subunit a was identified as the component binding 4-chloro-7-nitrobenzofurazan and subunit fa as the component binding N,N'-dicyclohexylcarbodiimide. The ATP phosphohydrolase activity of the membrane ATPase was not activated by trypsin treatment and the ATPase (BF0F1) contained no trypsin-sensitive inhibitor protein subunit. 6. Purified ATPase (BF0F1) was incorporated into artificial proteoliposomes which demonstrated ATP-dependent enhancement of 8-anilinonaphthalene-1-sulphonate fluorescence and ATP-dependent proton influx. These reactions were abolished by proton conductors (e.g. carbonylcyanide m-chlorophenylhydrazone) by valinomycin in the presence of a high external concentration of K+, or by N,N'-dicyclohexylcarbodiimide, butyricin 7423, Dio-9, 4-chloro-7-nitrobenzofurazan or leucinostatin. Oligomycin, tributyl tin, triethyl tin and venturicidin were not inhibitory. 7. When stripped of the soluble BF1 component, such ATPase-proteoliposomes demonstrated nil ATP phosphohydrolase activity and did not display ATP-dependent enhancement of 8-anilino-naphthalene-1-sulphonate fluorescence or ATP-dependent protein influx. All of these activities were restored by incubation of the BF1-depleted proteoliposomes with a purified preparation of the soluble BF1 component.

Adenosine Triphosphatases↗