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Biomedical subjects

Micheline Misrahi

Publications and source records attributed to Micheline Misrahi.

8 recordsLinked to original sources
PubMed2006

[Wilson's disease].

Wilson's disease is an autosomal recessive disorder of copper excess. This illness results from mutations of the ATP7B gene chromosome 13. The discovery of the gene allowed a better understanding of cytosolic copper trafficking its relationship with ceruloplasmin synthesis. Symptomatic patients may present with hepatic, neurologic or psychiatric forms. Clinical and phenotypic evidences provide only presumptive arguments for this disease which can be routinely assessed by molecular analysis. This disease can be efficiently treated by chelation and zinc therapy. Liver transplantation is the therapy to patients with hepatic fulminant course, or in those with relentless progression of hepatic dysfunction in spite of medical therapy.

Hepatolenticular Degeneration↗
PubMed2006

Late onset of Wilson's disease in a family with genetic haemochromatosis.

We report the coexistence of Wilson's disease and genetic haemochromatosis in one family. The diagnosis of genetic haemochromatosis was established in a 52-year-old man. Among his siblings, one 57-year-old sister and one 55-year-old brother had decreased copper and ceruloplasmin levels in serum and increased urinary copper excretion. The sister shared the same human leucocyte antigen haplotypes and was homozygous for the HFE mutation C282Y, like the propositus. However, she had normal liver iron content and increased liver copper content. Her dietary copper intake was probably excessive. The association of Wilson's disease and genetic haemochromatosis is rare and has only been described twice. The onset of Wilson's disease after 50 years of age is rare; Wilson's disease should be considered in any patient with unexplained chronic liver disease; an excess in liver copper content might be induced by excessive dietary input in a susceptible individual.

Age of Onset↗
PubMed2005

Thyrotropin receptor trafficking relies on the hScrib-betaPIX-GIT1-ARF6 pathway.

G protein-coupled receptors are regulated by ligand stimulation, endocytosis, degradation of recycling to the cell surface. Little information is available on the molecular mechanisms underlying G protein-coupled receptors recycling. We have investigated recycling of the G protein-coupled thyroid stimulating hormone receptor (TSHR) and found that it relies on hScrib, a membrane-associated PDZ protein. hScrib directly binds to TSHR, inhibits basal receptor endocytosis and promotes recycling, and thus TSHR signalling, at the cell membrane. We previously demonstrated that hScrib is associated with a betaPIX-GIT1 complex comprised of a guanine nucleotide exchange factor and a GTPase-activating protein for ADP ribosylation factors that is involved in vesicle trafficking. We used dominant-negative constructs and small interfering RNA to show that TSHR recycling is regulated by the interaction between hScrib and betaPIX, and by the activity of GIT1. In addition, ARF6, a major target for GIT1, is activated during TSH stimulation of HEK293 and FRTL-5 thyroid cells, and plays a key role in TSHR recycling. Thus, we have uncovered an hScrib-betaPIX-GIT1-ARF6 pathway devoted to TSHR trafficking and function.

ADP-Ribosylation Factor 6↗
PubMed2005

Ovarian steroidogenesis and serum androgen levels in patients with premature ovarian failure.

Women with premature ovarian failure (POF) have been reported to have lower serum androgen levels compared with normal women. We reviewed the androgen profiles of 143 POF patients and found androgen levels above normal for postmenopausal women in 16% of these subjects. To determine the source of androgens in those women, we studied the available ovarian biopsy samples of 15 POF patients with increased androgen levels using immunohistochemistry, with a panel of antibodies directed against the main steroidogenic enzymes. Five of the ovarian biopsies exhibited abnormal follicles characterized by hypertrophied theca interna expressing steroidogenic enzymes involved in androgen synthesis. In five other biopsies, the steroidogenic activity was scarce and confined to a small number of ovarian stromal cells, sometimes situated in the proximity of follicular remnants. Finally, in five patients, we found no histological evidence of present or past follicular development beyond the quiescent follicular stage, and no steroidogenic cells were detected by immunohistochemistry. Our findings suggest that ovarian theca-derived cells are a source of androgens in some women with POF, whereas in others, as in most postmenopausal patients, the adrenals or the ovarian hilus cells may synthesize a significant quantity of androgens under LH stimulation.

Adolescent↗
PubMed2003

The basolateral sorting signals of the thyrotropin and luteinizing hormone receptors: an unusual family of signals sharing an unusual distal intracellular localization, but unrelated in their structures.

The mechanisms of the basolateral targeting of G protein-coupled receptors remain largely unknown. Mutagenesis experiments have allowed us to identify the basolateral sorting signals of the TSH and LH receptors expressed in Madin-Darby canine kidney cells and thyroid follicular FRT cells. Unexpectedly these signals (amino acids 731-746 and 672-689, respectively) share an unusual localization in the distal part of the intracellular domain of the receptors at a marked distance from the membrane. When grafted onto the p75-neurotropin receptor, these signals redirect this normally apically expressed protein to the basolateral cell surface. They are independent of the endocytosis signal. The basolateral sorting signals of TSH, LH, and FSH receptors do not exhibit primary sequence homology with each other or with any other known signal. Furthermore, circular dichroism studies show that the three signals exhibit distinct secondary structures. The TSH receptor has a stable helical structure, the LH receptor has both helix and beta-sheet structures, and the FSH receptor sorting signal has a main random coil structure. This means that even in closely-related receptors different secondary structures can be found for basolateral signals unrelated to internalization signals. This observation contrasts with what is known about basolateral signals related to internalization signals for which a common beta-turn structure has been described. Deletion of the basolateral sorting signals results in apical targeting of the receptors, suggesting the existence of apical sorting information. However, a soluble form of the TSH receptor, which harbors all N- and putative O-linked oligosaccharides, is secreted in a nonpolarized fashion. This implies that apical sorting information must be located elsewhere, either in the transmembrane or in the intracellular domains of the receptor.

Amino Acid Sequence↗
PubMed2003

Role of cleavage and shedding in human thyrotropin receptor function and trafficking.

The thyrotropin receptor (TSHR) undergoes a cleavage at the cell membrane, leading to a heterodimer, comprising an alpha extracellular and a beta-transmembrane and intracellular subunits, held together by disulfide bonds. Moreover, part of the alpha-subunit of the receptor is shed from thyroid and transfected L cells. To understand the role of cleavage and shedding, we constructed deletion mutants starting, respectively, at the most N-terminal (S314), and C-terminal (L378) cleavage sites previously mapped, corresponding to free beta1 or beta2-subunits without further modification of receptor structure. Functional studies performed in COS-7 cells showed that both mutants display an increased basal activation of the cAMP pathway when compared with the wild-type receptor. By contrast, deletion of almost the entire extracellular domain of the receptor (TM409 mutant) totally impairs receptor function, thus confirming a role of the juxtamembrane extracellular region in receptor function. The beta1 mutant receptor exhibited an increased internalization when compared with the hormone-activated holoreceptor. Furthermore, no recycling was observed in the case of the beta1 mutant receptor. These observations strongly argue for a different conformation between the receptor activated by cleavage and shedding on the one hand, and the receptor activated by the ligand on the other hand. Cleavage and shedding of a receptor already activated by a transmembrane activating mutation M453T further increase its activity, showing that the extracellular domain still exerts a negative effect in the M453T holoreceptor. An increased internalization of the M453T receptor was observed when compared with the wild-type receptor, which was increased further in the corresponding truncated beta1-M453T receptor. Thus cleavage and shedding yield TSHR activation but also increase internalization of the free beta-subunits of the receptor, the latter mechanism limiting simultaneously excessive receptor signaling. The combined effects may be responsible for the limited basal constitutive activation of the cAMP pathway that is detected for the TSHR.

Animals↗
PubMed2002

Functional characterization of the human FSH receptor with an inactivating Ala189Val mutation.

An Ala189Val mutation of the human FSH receptor (FSHR) has been found to cause hypergonadotrophic ovarian failure with arrest of follicular maturation in women, and suppressed spermatogenesis in men. We have now characterized the molecular mechanisms of the receptor inactivation. Wild-type and mutant FSHR cDNAs were expressed in monkey kidney (COS-7) cells and murine granulosa tumour (KK-1) cells. Similar steady-state levels of FSHR mRNA were found in COS-7 and KK-1 cells transfected with both types of FSHR cDNA. Conspicuously, immunofluorescence and confocal microscopy studies revealed that whereas the wild-type receptor could be readily detected on the plasma membrane, most of the mutated protein was intracellularly sequestered. Ligand binding studies confirmed the greatly reduced cell surface expression of the mutant FSHR. A low level of mutated receptors were expressed at the cell surface, as shown by ligand binding and cAMP response. The capacity of these receptors to evoke another second messenger response, that of inositol trisphosphate (IP3), was almost totally lost. This finding may be related to the clinical picture of the patients, i.e. blockade of follicular maturation. There is a highly conserved stretch of five amino acids (Ala-Phe-Asn-Gly-Thr) in the region of the mutation in all glycoprotein hormone receptors. We therefore created the same Ala to Val transition in the human LHR and studied its functional consequences. Similar functional alterations, i.e. intracellular sequestration and attenuated signal transduction, were found, as with mutated FSHR. Hence, this particular mutation in the conserved extracellular region of glycoprotein hormone receptors induces a conformational change that suppresses cell membrane targeting of the mutated receptor, probably through altered intracellular folding.

Animals↗