Biomedical subjects

M Potier

Publications and source records attributed to M Potier.

At least 19 recordsLinked to original sources

PubMed2006

Combined AGE inhibition and ACEi decreases the progression of established diabetic nephropathy in B6 db/db mice.

The accumulation of advanced glycation end products (AGE) is a key factor in diabetic nephropathy (DN). Pyridoxamine inhibits AGE formation and protects against type I DN. Herein we tested: (1) whether C57BL6 db/db mice as a model of established type II DN resembled patients treated with drugs which inhibit angiotensin II action; (2) whether pyridoxamine was effective as a single therapy; and (3) whether pyridoxamine would add to the benefit of angiotensin-converting enzyme inhibition (ACEi) by enalapril. In first set of experiments mice were treated with ACEi (benazepril) and an angiotensin II receptor blocker (valsartan) combination for 16 weeks after the onset of diabetes. In second group, mice with established DN were treated with pyridoxamine for 8 weeks. In a third set, mice with established DN were treated with pyridoxamine and enalapril combination for 16 weeks. Benazepril and valsartan combination partially prevented the development and progression of DN. Pyridoxamine treatment, as single therapy, decreased the progression of albuminuria and glomerular lesions. The combination of pyridoxamine with enalapril reduced both mortality and the progression of DN. In conclusion, (1) C57 BL6 db/db mice are a model of progressive type II DN; (2) The combination of pyridoxamine with enalapril decreased progression of type 2 DN and overall mortality. Thus, pyridoxamine could be a valuable adjunct to the current treatment of established type II DN.

Albuminuria↗

PubMed2006

Concentrations of isoflavones in plasma and urine of post-menopausal women chronically ingesting high quantities of soy isoflavones.

Soy food or food supplements based on soy containing isoflavones (Isos) are increasingly available in Western countries. However, the variability of Isos levels in urine and plasma in humans during chronic ingestion is poorly documented. Nevertheless, this is the way these compounds will most probably be used in the future, especially if the soy-based supplements market goes on increasing. Here, glycosilated Isos in an enriched extract of Prevastein equal to 100 mg of equivalent Isos aglycone was given daily to 27 post-menopausal women for 30 days and to 12 post-menopausal women for 60 days. Volunteers were given Prevastein in a cereal bar (25 mg Isos) and in a yoghurt (25 mg Isos) both at breakfast and dinner. Plasma samples were collected after overnight fasting. Urine samples were aliquots of a 24 h collection checked on volume and creatinin excretion levels. Genistein, daidzein and equol were measured at day 0 and every 15 days afterwards, using original specific ELISAs. Constant levels were reached from the 15th day. About 59.2% of the volunteers were significant equol producers in the first experiment and 58.3% in the second. A large variability in plasma and urine levels was observed among post-menopausal women consuming 100 mg Isos per day, although remaining relatively stable in each individual subject. This could partly account for the controversial effects of Isos recorded so far in clinical studies. So Isos plasma levels would have to be assayed during chronic exposures, and could help to better understand the large variability of the effects classically observed in clinical studies. ELISA techniques could be easily exported to analytical laboratories to help physicians and nutritionists with their prescriptions.

Aged↗

PubMed2000

Matrix accumulation in mesangial cells exposed to cyclosporine A requires a permissive genetic background.

BACKGROUND: Chronic nephrotoxicity is an important adverse effect of cyclosporine A (CsA) therapy. Tubulo-interstitial lesions and arteriolopathy are common histologic findings. Glomerular lesions are also described, but they are of variable severity. The aim of our study is to determine whether CsA has a direct effect on mesangial cells and whether the cellular response depends on the genetic background. METHODS: We studied mesangial cells isolated from mice susceptible (ROP/Le-+Es1(b)+Es1(a), ROP) and resistant to glomerulosclerosis (B6SJLF1, C57). We previously showed that sclerosis-prone and sclerosis-resistant phenotypes are maintained in vitro. We examined whether CsA exposure directly affected extracellular matrix turnover in mesangial cells and whether the response is determined by the genetic background. Extracellular matrix synthesis and degradation were studied by proline incorporation, ELISA, reverse transcription-polymerase chain reaction, zymography, and reverse zymography. We chose a CsA dose that induced neither cytotoxicity nor apoptosis (1 microg/ml). RESULTS: At the dose of 1 microg/ml total collagen accumulation was increased in ROP but not in C57 cells. Matrix metalloproteinase (MMP)-2 activity and mRNA levels were selectively decreased in ROP cells. CsA exposure did not affect tissue inhibitors of MMP (TIMP)-1 and -2 activity or TGF-beta1 mRNA expression and protein synthesis in either cell line. CONCLUSION: CsA increases total collagen accumulation in mesangial cells from sclerosis-prone mice by decreasing MMP-2 activity, but does not affect cells from sclerosis-resistant mice. Thus, CsA directly affects mesangial cells, but only those with a permissive genetic background for glomerulosclerosis.

Animals↗

PubMed2000

Renal synthesis of leukaemia inhibitory factor (LIF), under normal and inflammatory conditions.

Leukaemia inhibitory factor (LIF) is a pleiotropic cytokine that is particularly involved in nephrogenesis and repair of the extracellular matrix. Transgenic mice overexpressing LIF have mesangial proliferative glomerulonephritis. Also, during local inflammatory reactions, such as kidney graft rejection or urinary tract infections, urinary LIF excretion is enhanced. The aim of the study therefore was to study LIF production by normal and inflammatory diseased kidneys (glomerulonephritis or graft rejection), maintained in short cultures. To determine the responsibility of the kidney itself in LIF synthesis, we measured LIF secretion into the culture supernatants of human mesangial or renal tubular epithelial cells. Fragments from diseased kidneys, whether grafts or not, released more LIF than normal human kidney fragments, mesangial or renal tubular epithelial cells. However, LIF production was delayed in renal transplants compared to glomerulonephritic samples taken from untreated patients. In every case, LIF production was enhanced by interleukin 1beta (IL-1beta) and inhibited by IL-4 or dexamethasone, except in two severe rejection episodes. So, LIF appeared to respond to pro- and anti-inflammatory stimuli, in vitro and in vivo. Considering its biological effects, LIF could play a role in inflammatory renal diseases.

Animals↗

PubMed2000

Protein gamma-radiolysis in frozen solutions is a macromolecular surface phenomenon: fragmentation of lysozyme, citrate synthase and alpha-lactalbumin in native or denatured states.

PURPOSE: To test whether radiolysis-induced fragmentation in frozen aqueous protein solution is dependent on solvent access to the surface of the protein or to the molecular mass of the polypeptide chain. MATERIALS AND METHODS: 60Co gamma-irradiation of three proteins at -78 degrees C: lysozyme, citrate synthase and alpha-lactalbumin in their native state, with or without bound substrate, or denatured (random coil in urea/acid-denatured state). RESULTS: By SDS-polyacrylamide gel electrophoresis/analysis of the protein-fragmentation process, it was found that for a given protein D37 values (dose to decrease the measured amount of protein, with an unaltered polypeptidic chain, to 37% of the initial amount) varied according to the state of the protein. D37 for denatured proteins was always much smaller than for native states, indicating a greater susceptibility to fragmentation. In urea, contrary to the native state, no well-defined fragments were observed. Radiolysis decay constants (K= 1/D37) increased with solvent-accessible surface area of these proteins estimated from their radii of gyration in the various states. This is shown also in previous data on native or SDS-denatured proteins. Denatured proteins which have a large surface area exposed to the solvent compared with native ones are more fragmented at equal doses. CONCLUSIONS: It is concluded that D37 is directly related to the exposed surface area and not to the molecular mass of the polypeptide chain.

Animals↗

PubMed1999

Purification, cDNA cloning, and expression of a new human blood plasma glutamate carboxypeptidase homologous to N-acetyl-aspartyl-alpha-glutamate carboxypeptidase/prostate-specific membrane antigen.

We describe the identification, cDNA cloning, and biochemical characterization of a new human blood plasma glutamate carboxypeptidase (PGCP). PGCP was co-purified from human placenta with lysosomal carboxypeptidase, cathepsin A, lysosomal endopeptidase, cathepsin D, and a gamma-interferon-inducible protein, IP-30, using an affinity chromatography on a Phe-Leu-agarose column. A PGCP cDNA was obtained as an expressed sequence tag clone and completed at 5'-end by rapid amplification of cDNA ends polymerase chain reaction. The cDNA contained a 1623-base pair open reading frame predicting a 541-amino acid protein, with five putative Asn glycosylation sites and a 21-residue signal peptide. PGCP showed significant amino acid sequence homology to several cocatalytic metallopeptidases including a glutamate carboxypeptidase II also known as N-acetyl-aspartyl-alpha-glutamate carboxypeptidase or as prostate-specific membrane antigen and expressed glutamate carboxypeptidase activity. Expression of the PGCP cDNA in COS-1 cells, followed by Western blotting and metabolic labeling showed that PGCP is synthesized as a 62-kDa precursor, which is processed to a 56-kDa mature form containing two Asn-linked oligosaccharide chains. The mature form of PGCP was secreted into the culture medium, which is consistent with its intracellular localization in secretion granules. In humans, PGCP is found principally in blood plasma, suggesting a potential role in the metabolism of secreted peptides.

Amino Acid Sequence↗

PubMed1999

Clinical spectrum of infantile free sialic acid storage disease.

Infantile free sialic acid storage disease (ISSD) is a rare autosomal recessive metabolic disorder caused by a lysosomal membrane transport defect, resulting in accumulation of free sialic acid within lysosomes. Only a few cases have been described. We report on three new cases of ISSD with different modes of presentation: an infant with nephrotic syndrome, a case of fetal and neonatal ascites with heart failure, and a case of fetal ascites with esophageal atresia type III. From these patients and a review of the literature (27 cases total) we draw the following conclusions. 1) "Coarse facies," fair complexion, hepatosplenomegaly, and severe psychomotor retardation are constant findings in this disorder. 2) Nephrotic syndrome occurred in most cases (four in seven) in which renal evaluation was performed. Therefore, ISSD is an important cause of nephrosis in infants with a storage disorder phenotype. 3) Fetal/neonatal ascites or hydrops was the mode of presentation in 13 (60%) of 21 cases. Thus, ISSD enters in the differential diagnosis of hydrops fetalis with a storage disease phenotype. 4) Cardiomegaly was evident in nine cases. 5) Corneae were always clear, and albinoid fundi were reported in five cases. 6) Dysostosis multiplex was not prominent. 7) Bone marrow aspiration could be negative. 8) Death ensued in early infancy with a mean age of 13.1 months. All reported deaths were caused by respiratory infections.

Ascites↗

PubMed1999

Identification of UDP-N-acetylglucosamine-phosphotransferase-binding sites on the lysosomal proteases, cathepsins A, B, and D.

A key step in the targeting of soluble lysosomal enzymes is their recognition and phosphorylation by a 540 kDa multisubunit enzyme, UDP-N-acetylglucosamine-phosphotransferase (phosphotransferase). The molecular mechanism of recognition is still unknown, but previous experiments suggested that the phosphotransferase-binding sites on lysosomal proteins are represented by structurally conserved surface patches of amino acids. We identified four such regions on nonhomologous lysosomal enzymes, cathepsins A, B, and D, which were superimposed by rotating their structures around the Calpha atom of the glycosylated Asn residue. We proposed that these regions represent putative phosphotransferase-binding sites and tested synthetic peptides, derived from these regions on the basis of surface accessibility, for their ability to inhibit in vitro phosphorylation of purified cathepsins A, B, and D. Our results indicate that cathepsin A and cathepsin D have one closely related phosphotransferase recognition site represented by a structurally and topologically conserved beta-hairpin loop, similar to that previously identified in lysosomal beta-glucuronidase. The most potent inhibition of phosphorylation was demonstrated by homologous peptides derived from the regions located on cathepsin molecules opposite the oligosaccharide chains which are phosphorylated by the phosphotransferase. We propose that recognition and catalytic sites of the phosphotransferase are located on different subunits, therefore, providing an effective mechanism for binding and phosphorylation of lysosomal proteins of different molecular size.

Animals↗

PubMed1999

[The anatomic lobulation of the prostate, a controversial description].

Vésalius, in 1543, described, for the first time, the prostate as an unique organ. But, in the 19th century, two schools confronted; for Cruveilhier and Testut, the prostate was made of several lobes, when Cloquet and Sappey thought it as a unique zone. Albarran, in 1902, described the sub-uretral glands. Thereafter, Cuneo, in 1911 and Franks, in 1954, described two zones, one, internal, formed by the Albarran's glands, and the other, external, concerning the whole prostatic gland. On the contrary, Lowsley, in 1912, and Gil Vernet, in 1953, described several lobes, 5 for Lowsley, 3 for Gil Vernet. Recently, in 1968, and 1978, McNeal had made the proof that the prostate is histologically and anatomically heterogeneous, with three zones, transitional, central and peripheral ones.

Anatomy↗

PubMed1999

Role of sphingolipids in the transport of prosaposin to the lysosomes.

Prosaposin is the precursor of four lysosomal saposins that promote the degradation of glycosphingolipids (GSLs) by acidic hydrolases. GSLs contain a hydrophobic ceramide moiety, which acts as a membrane anchor, and a hydrophilic oligosaccharide chain that faces the lumen of the Golgi apparatus and extracellular spaces. By using fumonisin B1, PDMP and D609, we tested the hypothesis that sphingolipids mediate the transport of prosaposin to the lysosomes. Fumonisin B1 interferes with the synthesis of ceramide, PDMP blocks the formation of glucosylceramide and D609 blocks the formation of sphingomyelin. Fumonisin B1 produced a 59;-85% decrease in the density of gold particles in the lysosomes of CHO and NRK cells immunolabeled with anti-prosaposin antibody, and a 55% reduction in the lysosomes of CHO cells stably transfected with an expression vector containing a human prosaposin cDNA. To examine whether the mannose 6-phosphate receptor pathway was affected by this treatment, NRK and CHO cells treated or not with fumonisin B1 were labeled with anti-cathepsin A antibody. The results showed no significant differences in labeling of the lysosomes, suggesting that the effect of fumonisin B1 was specific. When fumonisin B1 and D609 were added to the media of transfected CHO cells, a decrease in immunofluorescence with anti-prosaposin antibody was observed by confocal microscopy. PDMP did not cause any reduction in immunoreactivity, indicating that sphingolmyelin appears to be involved in this process. In conclusion, our data support the hypothesis that sphingolipids, possibly sphingomyelin, are involved in the transport of prosaposin to the lysosomes.

Animals↗

PubMed1998

Two sequence-ready contigs spanning the two copies of a 200-kb duplication on human 21q: partial sequence and polymorphisms.

Physical mapping across a duplication can be a tour de force if the region is larger than the size of a bacterial clone. This was the case of the 170- to 275-kb duplication present on the long arm of chromosome 21 in normal human at 21q11.1 (proximal region) and at 21q22.1 (distal region), which we described previously. We have constructed sequence-ready contigs of the two copies of the duplication of which all the clones are genuine representatives of one copy or the other. This required the identification of four duplicon polymorphisms that are copy-specific and nonallelic variations in the sequence of the STSs. Thirteen STSs were mapped inside the duplicated region and 5 outside but close to the boundaries. Among these STSs 10 were end clones from YACs, PACs, or cosmids, and the average interval between two markers in the duplicated region was 16 kb. Eight PACs and cosmids showing minimal overlaps were selected in both copies of the duplication. Comparative sequence analysis along the duplication showed three single-basepair changes between the two copies over 659 bp sequenced (4 STSs), suggesting that the duplication is recent (less than 4 mya). Two CpG islands were located in the duplication, but no genes were identified after a 36-kb cosmid from the proximal copy of the duplication was sequenced. The homology of this chromosome 21 duplicated region with the pericentromeric regions of chromosomes 13, 2, and 18 suggests that the mechanism involved is probably similar to pericentromeric-directed mechanisms described in interchromosomal duplications.

Cell Line↗

PubMed1998

Molecular mechanism of lysosomal sialidase deficiency in galactosialidosis involves its rapid degradation.

Galactosialidosis is an inherited lysosomal storage disease caused by the combined deficiency of lysosomal sialidase and beta-galactosidase secondary to the deficiency of cathepsin A/protective protein, which is associated with sialidase and beta-galactosidase in a high-molecular weight (1.27MDa) complex. Clinical phenotypes of patients as well as the composition of compounds which are stored in patient's tissues implicate sialidase deficiency as the underlying pathogenic defect. The recent cloning and sequencing of lysosomal sialidase [Pshezhetsky, Richard, Michaud, Igdoura, Wang, Elsliger, Qu, Leclerc, Gravel, Dallaire and Potier (1997), Nature Genet. 15, 316-320] allowed us to study the molecular mechanism of sialidase deficiency in galactosialidosis. By Western blotting, using antibodies against the recombinant human enzyme, and by NH2-terminal sequencing, we showed that sialidase is synthesized as a 45.5 kDa precursor and after the cleavage of the 47-amino acid signal peptide and glycosylation becomes a 48.3 kDa mature active enzyme present in the 1.27 kDa complex. Transgenic expression of sialidase in cultured skin fibroblasts from normal controls and from galactosialidosis patients, followed by immunofluorescent and immunoelectron microscopy showed that in both normal and affected cells the expressed sialidase was localized on lysosomal and plasma membranes, but the amount of sialidase found in galactosialidosis cells was approximately 5-fold reduced. Metabolic labelling studies demonstrated that the 48.3 kDa mature active form of sialidase was stable in normal fibroblasts (half-life approximately 2.7 h), whereas in galactosialidosis fibroblasts the enzyme was rapidly converted (half-life approximately 30 min) into 38.7 and 24 kDa catalytically inactive forms. Altogether our data provide evidence that the molecular mechanism of sialidase deficiency in galactosialidosis is associated with abnormal proteolytic cleavage and fast degradation.

Animals↗

PubMed1998

Molecular pathology of galactosialidosis in a patient affected with two new frameshift mutations in the cathepsin A/protective protein gene.

Galactosialidosis is a recessively inherited lysosomal storage disease characterized by the combined deficiency of neuraminidase and beta-galactosidase secondary to the genetic deficiency of cathepsin A/protective protein. In lysosomes, cathepsin A forms a high-molecular-weight complex with beta-galactosidase and neuraminidase that protects these enzymes against intralysosomal proteolysis. In a patient affected with late infantile form of galactosialidosis, we found two new cathepsin A mutations, a two-nucleotide deletion, c517delTT and an intronic mutation, IVS8+9C-->G resulting in abnormal splicing and a five-nucleotide insertion in the cathepsin A cDNA. Both mutations cause frameshifts and result in the synthesis of truncated cathepsin A proteins, which, as suggested by structural modeling, are incapable of dimerization, complex formation, and catalysis. However, enzymatic assays, gel-filtration, and Western blot analysis of the patient's cultured skin fibroblast extracts showed the presence of a small amount of normal-size, catalytically active cathepsin A and cathepsin A-beta-galactosidase 680 kDa complex, suggesting that a low amount of cathepsin A mRNA is spliced normally and produces the wild-type protein. This may contribute to the relatively mild phenotype of the patient and illustrates the importance of critically comparing molecular results with clinical and biochemical phenotypes.

Adolescent↗

PubMed1998

Cloning of the cDNA and gene encoding mouse lysosomal sialidase and correction of sialidase deficiency in human sialidosis and mouse SM/J fibroblasts.

Lysosomal sialidase occurs in a multienzyme complex that also contains beta-galactosidase and cathepsin A. We previously cloned the human lysosomal sialidase cDNA and characterized mutations in human sialidosis patients. Here, we report the cloning and expression of the mouse lysosomal sialidase cDNA and gene. The 1.77 kb cDNA encodes an open reading frame of 408 amino acids which shows high homology to the human lysosomal sialidase (80%), the rat cytosolic sialidase (65%) and viral and bacterial sialidases (50-55%). The sialidase gene is approximately 4 kb long and contains six exons. The five introns range in size from 96 to 1200 bp. Northern blot analysis revealed high expression of multiple sialidase transcripts in kidney and epididymis, moderate levels in brain and spinal cord, and low levels in adrenal, heart, liver, lung and spleen. Transient expression of the cDNA clone in sialidase-deficient SM/J mouse fibroblasts and human sialidosis fibroblasts restored normal levels of sialidase activities in both cell types. Immunocytochemically expressed sialidase co-localized with a lysosomal marker, LAMP2, confirming its lysosomal nature. Since sialidase activity requires its association with beta-galactosidase and cathepsin A, the expression of mouse sialidase within human sialidosis cells underlines the structural similarity between mouse and human enzymes and suggests that the mechanism for complex formation and function is highly conserved.

Amino Acid Sequence↗

PubMed1998

Comparative study of cyclosporin A, cyclosporin G, and the novel cyclosporin derivative IMM 125 in isolated glomeruli and cultured rat mesangial cells: a morphometric analysis.

BACKGROUND: One adverse side-effect of the immunosuppressive drug cyclosporin A (CsA) is a decrease in glomerular filtration rate (GFR). This effect might be the result of increased glomerular contractions. The present study compared the contractile effects of CsA, cyclosporin G (CsG) and the novel cyclosporin derivative IMM 125 in isolated rat glomeruli and primary cultures of rat mesangial cells. METHODS: Interactive image analysis was used to measure glomerular and mesangial cell contraction. RESULTS: CsA, CsG, and IMM 125 at concentrations of 0, 10(-9), 10(-8), 10(-7), 10(-6) and 10(-5) M caused a time-dependent and a concentration-dependent contraction of isolated glomeruli and mesangial cells 30 min after incubation. In glomeruli, CsA was more potent than CsG and IMM 125. In mesangial cells, IMM 125 also exhibited the lowest contractile activity, while CsA and CsG were almost equally myoreactive. The absolute degree of the glomerular contraction was proportional to the number of contracting mesangial cells in one glomeruli. The number of responding cells after incubation with IMM 125 and CsG were lower compared to CsA, which might explain the different response with CsG and CsA in both models. CONCLUSIONS: Since the concentrations used in these experiments were close to that reached in rat serum after treatment with CsA, the present results suggest that the contractile effects of IMM 125 and CsG in isolated glomeruli were clearly smaller compared to CsA, which might reflect the cyclosporins induced GFR changes in vivo.

Animals↗

PubMed1997

P-glycoprotein is a dimer in the kidney and brain capillary membranes: effect of cyclosporin A and SDZ-PSC 833.

Radiation-inactivation studies were performed in order to elucidate the oligomeric nature of P-glycoprotein (P-gp) expressed in brain capillaries and renal brush border membranes (BBMs). Irradiation of renal BBMs resulted in a dose-dependent loss of P-gp, which corresponded to a target size (TS) of 255 and 211 kDa, as detected by Western blot and [125I]arylazidoprazosin labeling, respectively. Similar TSs were determined for P-gp expressed in brain capillaries. These TSs correspond to approximately twice the size (120 kDa) of deglycosylated P-gp. Furthermore, the estimated TS for P-gp was not significantly different when renal BBMs were incubated with SDZ-PSC 833 (PSC) prior and during exposure to ionizing radiation. To confirm these results, the size of P-gp was evaluated from its mobility on blue-native polyacrylamide gels followed by Western blot analysis. Using this method, an apparent molecular size of 334 and 264 kDa was determined for P-gp in brain capillaries and renal BBMs, respectively. This corresponds to approximately twice the size of the glycosylated monomeric subunit of P-gp in brain capillaries (162 kDa) or renal BBMs (140 kDa). P-gp expressed in renal BBMs isolated from rats which had been treated daily with cyclosporin A (CsA) or PSC also migrated as a 264 kDa protein. These results suggest that P-gp exists mainly as a dimer in normal tissues and that resistance modulators such as CsA and PSC do not alter its oligomeric state.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1997

Endogenous basic fibroblast growth factor isoforms involved in different intracellular protein complexes.

Four forms of basic fibroblast growth factor (bFGF or FGF-2) result from an alternative initiation of translation involving one AUG (155-amino acid form) and three CUGs (210-, 201- and 196-amino acid forms). These different forms of bFGF show different intracellular biological activities. To identify their intracellular targets, the 210- and 155-amino acid forms of bFGF were independently transfected into CHO cells and their correct subcellular localizations were verified, the 155-amino acid bFGF form being essentially cytoplasmic whereas the 210-amino acid protein was nuclear. The radiation fragmentation method was used to determine the target size of the different bFGF isoforms in the transfected CHO cells and to show that the 210- and 155-amino acids bFGF isoforms were included in protein complexes of 320 and 130 kDa respectively. Similar results were obtained using the SK-Hep1 cell line, which naturally expressed all forms of bFGF. Co-immunoprecipitation assays using different chimaeric bFGF-chloramphenicol acetyltransferase proteins showed that different cellular proteins are associated with different parts of the bFGF molecule. We conclude that bFGF isoforms are involved in different molecular complexes in the cytosol and nucleus, which would reflect different functions for these proteins.

Animals↗

PubMed1997

mRNP3 and mRNP4 are phosphorylatable by casein kinase II in Xenopus oocytes, but phosphorylation does not modify RNA-binding affinity.

mRNP3 and mRNP4 (also called FRGY2) are two mRNA-binding proteins which are major constituents of the maternal RNA storage particles of Xenopus laevis oocytes. The phosphorylation of mRNP3-4 has been implicated in the regulation of mRNA masking. In this study, we have investigated their phosphorylation by casein kinase II and its consequence on their affinity for RNA. Comparison of the phosphopeptide map of mRNP3-4 phosphorylated in vivo with that obtained after phosphorylation in vitro by purified Xenopus laevis casein kinase II strongly suggests that casein kinase II is responsible for the in vivo phosphorylation of mRNP3-4 in oocytes. The phosphorylation occurs on a serine residue in a central domain of the proteins. The affinity of mRNP3-4 for RNA substrates remained unchanged after the treatment with casein kinase II or calf intestine phosphatase in vitro. This suggests that phosphorylation of these proteins does not regulate their interaction with RNA but rather controls their interactions with other proteins.

Amino Acid Sequence↗