14 research outputs found
Is uremia an example of acquired inhibition of receptor-mediated endocytosis?
Many factors that inhibit receptor-mediated endocytosis (RME) at postreceptor level in vitro have been described: (i) high concentration of urea, (ii) lowering of intracellular pH, (iii) hypotonic or hypertonic media, (iv) intracellular potassium depletion, (v) depletion of cellular ATP, (vi) inhibition of the enzyme transglutaminase, (vii) impairment of receptor recycling by rising of the endosomal pH, (viii) disruption of microtubules. Nearly all or all of the factors mentioned above are present as disturbances of homeostasis in uremia. The magnitude of the factors inhibiting RME in vitro is considerably greater than the deviations observed in uremia, but in vitro almost complete inhibition of RME is aimed and also in uremia all of the factors act together. The hypothesis that RME is inhibited in uremia is supported by the metabolism of macromolecules known or supposed to be internalized by this process. Although glucose intolerance in uremia is due to a postreceptor defect in insulin action, impaired RME at postreceptor level, to the best of my knowledge, has not been pointed as a general feature of uremia. In addition to uremia, there might be other clinical examples of inhibited RME at postreceptor level as well.Biomedical Reviews 1993; 2: 57-75
Nephrotic hyperlipidemia: is inhibition of receptor-mediated edocytosis involved?
Hyperlipidemia is a consistent feature of the nephrotic syndrome (NS) and is usually of the IIa or IIb Fredrickson type. In cases with severe hypoalbuminemia (15 g/l or less) very low density lipoproteins (VLDL) also increase and the ratio of cholesterol to triglyceride falls. The nephrotic hyperlipidemia is generally considered to be due to increased hepatic synthesis and secretion of lipoproteins, but there are also investigations showing altered lipoprotein clearance. Warwick et al have found a trend towards lower fractional catabolic rate of intermediate density lipoproteins (IDL) and low density lipoproteins (LDL) in nephrotic patients with relatively well maintained serum albumin despite the heavy proteinuria. In another group of nephrotic patients with lower plasma albumin levels, the amount of LDL cleared by receptor-mediated endocytosis (RME) was only 55% of the value seen in controls, while 60% more LDL were channeled into alternative catabolic pathways. In experimental NS, delayed removal of chylomicron remnants was revealed as well. Chylomicron remnants are taken up by the liver via the LDL receptor-related protein (LRP). Recently, evidences were provided that receptor for activated α2-macroglobulin (α2-macroglobulin-proteinase complex) and the LRP are one and the same entity. α2-macroglobulin seems to control the activity of proteinases not by active site-directed inhibition but by steric shielding and rapid clearance. The plasma levels of α2-macroglobulin are consistently elevated in NS, but to the best of my knowledge, there are insufficient data about the uptake of α2-macroglobulin-proteinase complexes. Asami et al reported a glomerular deposition of α2-macroglobulin in a child with steroid refractory NS, but such depositions were not detected in other nephrotic patients. Biochemical and clinical improvement was observed in this case after treatment with the synthetic proteinase inhibitor camostat mesylate, but the dynamics of α2-macroglobulin depositions was not examined.Biomedical Reviews 1994; 3: 77-79
Human TOP1 residues implicated in species specificity of HIV-1 infection are required for interaction with BTBD2, and RNAi of BTBD2 in old world monkey and human cells increases permissiveness to HIV-1 infection
<p>Abstract</p> <p>Background</p> <p>Host determinants of HIV-1 viral tropism include factors from producer cells that affect the efficiency of productive infection and factors in target cells that block infection after viral entry. TRIM5α restricts HIV-1 infection at an early post-entry step through a mechanism associated with rapid disassembly of the retroviral capsid. Topoisomerase I (TOP1) appears to play a role in HIV-1 viral tropism by incorporating into or otherwise modulating virions affecting the efficiency of a post-entry step, as the expression of human TOP1 in African Green Monkey (AGM) virion-producing cells increased the infectivity of progeny virions by five-fold. This infectivity enhancement required human TOP1 residues 236 and 237 as their replacement with the AGM counterpart residues abolished the infectivity enhancement. Our previous studies showed that TOP1 interacts with BTBD1 and BTBD2, two proteins which co-localize with the TRIM5α splice variant TRIM5Ύ in cytoplasmic bodies. Because BTBD1 and BTBD2 interact with one HIV-1 viral tropism factor, TOP1, and co-localize with a splice variant of another, we investigated the potential involvement of BTBD1 and BTBD2 in HIV-1 restriction.</p> <p>Results</p> <p>We show that the interaction of BTBD1 and BTBD2 with TOP1 requires <it>hu</it>-TOP1 residues 236 and 237, the same residues required to enhance the infectivity of progeny virions when <it>hu</it>-TOP1 is expressed in AGM producer cells. Additionally, interference with the expression of BTBD2 in AGM and human 293T target cells increased their permissiveness to HIV-1 infection two- to three-fold.</p> <p>Conclusions</p> <p>These results do not exclude the possibility that BTBD2 may modestly restrict HIV-1 infection via colocation with TRIM5 variants in cytoplasmic bodies.</p
Expression of Human CD4 and chemokine receptors in cotton rat cells confers permissiveness for productive HIV infection
<p>Abstract</p> <p>Background</p> <p>Current small animal models for studying HIV-1 infection are very limited, and this continues to be a major obstacle for studying HIV-1 infection and pathogenesis, as well as for the urgent development and evaluation of effective anti-HIV-1 therapies and vaccines. Previously, it was shown that HIV-1 can infect cotton rats as indicated by development of antibodies against all major proteins of the virus, the detection of viral cDNA in spleen and brain of challenged animals, the transmission of infectious virus, albeit with low efficiency, from animal to animal by blood, and an additional increase in the mortality in the infected groups.</p> <p>Results</p> <p>Using <it>in vitro </it>experiments, we now show that cotton rat cell lines engineered to express human receptor complexes for HIV-1 (hCD4 along with hCXCR4 or hCCR5) support virus entry, viral cDNA integration, and the production of infectious virus.</p> <p>Conclusion</p> <p>These results further suggest that the development of transgenic cotton rats expressing human HIV-1 receptors may prove to be useful small animal model for HIV infection.</p
Cytokine Effects on the Entry of Filovirus Envelope Pseudotyped Virus-Like Particles into Primary Human Macrophages
Macrophages are one of the first and also a major site of filovirus replication and, in addition, are a source of multiple cytokines, presumed to play a critical role in the pathogenesis of the viral infection. Some of these cytokines are known to induce macrophage phenotypic changes in vitro, but how macrophage polarization may affect the cell susceptibility to filovirus entry remains largely unstudied. We generated different macrophage subsets using cytokine pre-treatment and subsequently tested their ability to fuse with beta-lactamase containing virus-like particles (VLP), pseudotyped with the surface glycoprotein of Ebola virus (EBOV) or the glycoproteins of other clinically relevant filovirus species. We found that pre-incubation of primary human monocyte-derived macrophages (MDM) with interleukin-10 (IL-10) significantly enhanced filovirus entry into cells obtained from multiple healthy donors, and the IL-10 effect was preserved in the presence of pro-inflammatory cytokines found to be elevated during EBOV disease. In contrast, fusion of IL-10-treated macrophages with influenza hemagglutinin/neuraminidase pseudotyped VLPs was unchanged or slightly reduced. Importantly, our in vitro data showing enhanced virus entry are consistent with the correlation established between elevated serum IL-10 and increased mortality in filovirus infected patients and also reveal a novel mechanism that may account for the IL-10-mediated increase in filovirus pathogenicity
Constitutive cell surface association between CD4 and CCR5
HIV-1 entry into cells involves formation of a complex between gp120 of the viral envelope glycoprotein (Env), a receptor (CD4), and a coreceptor. For most strains of HIV, this coreceptor is CCR5. Here, we provide evidence that CD4 is specifically associated with CCR5 in the absence of gp120 or any other receptor-specific ligand. The amount of CD4 coimmunoprecipitated with CCR5 was significantly higher than that with the other major HIV coreceptor, CXCR4, and in contrast to CXCR4 the CD4âCCR5 coimmunoprecipitation was not significantly increased by gp120. The CD4âCCR5 interaction probably takes place via the second extracellular loop of CCR5 and the first two domains of CD4. It can be inhibited by CCR5- and CD4-specific antibodies that interfere with HIV-1 infection, indicating a possible role in virus entry. These findings suggest a possible pathway of HIV-1 evolution and development of immunopathogenicity, a potential new target for antiretroviral drugs and a tool for development of vaccines based on EnvâCD4âCCR5 complexes. The constitutive association of a seven-transmembrane-domain G protein-coupled receptor with another receptor also indicates new possibilities for cross-talk between cell surface receptors