MLN64 and MENTHO, two mediators of endosomal cholesterol transport

2006 ◽  
Vol 34 (3) ◽  
pp. 343-345 ◽  
Author(s):  
F. Alpy ◽  
C. Tomasetto
Keyword(s):  
Metastatic Lymph Node ◽  
Regulatory Protein ◽  
Steroidogenic Acute Regulatory Protein ◽  
Cholesterol Transport ◽  
Lipid Transfer ◽  
Transmembrane Helices ◽  
Late Endosomes ◽  
Start Domain ◽  
Steroidogenic Acute Regulatory

MLN64 (metastatic lymph node 64) and MENTHO (MLN64 N-terminal homologue) are two late-endosomal proteins that share a conserved region of four transmembrane helices with three short intervening loops called the MENTAL domain (MLN64 N-terminal domain). This domain mediates MLN64 and MENTHO homo- and hetero-interactions, targets both proteins to late endosomes and binds cholesterol in vivo. In addition to the MENTAL domain, MLN64 contains a cholesterol-specific START domain [StAR (steroidogenic acute regulatory protein)-related lipid transfer domain]. The START domain is a protein module of approx. 210 residues that binds lipids, including sterols, and is present in 15 distinct proteins in mammals. Thus MLN64 and MENTHO define discrete cholesterol-containing subdomains within the membrane of late endosomes where they may function in cholesterol transport. The MENTAL domain might serve to maintain cholesterol at the membrane of late endosomes prior to its shuttle to cytoplasmic acceptor(s) through the START domain.

scholarly journals Molecular basis for the recognition of steroidogenic acute regulatory protein by the 14-3-3 protein family

2020 ◽  
Author(s):  
Kristina V. Tugaeva ◽  
James Titterington ◽  
Dmitriy V. Sotnikov ◽  
Eugene G. Maksimov ◽  
Alfred A. Antson ◽  
...  
Keyword(s):  
Biochemical Analysis ◽  
Structural Transition ◽  
Molten Globule ◽  
Regulatory Protein ◽  
Steroidogenic Acute Regulatory Protein ◽  
Cholesterol Transport ◽  
Peptide Cleavage ◽  
Partial Unfolding ◽  
Start Domain ◽  
Steroidogenic Acute Regulatory

ABSTRACTSteroidogenesis in adrenals and gonads starts from cholesterol transport to mitochondria by the steroidogenic acute regulatory protein STARD1, containing a mitochondrial import sequence followed by a cholesterol-binding START domain. Although mutations in this protein have been linked to lipoid congenital adrenal hyperplasia, the mechanism of steroidogenesis regulation by the STARD1 remains debatable, hypothetically involving a molten-globule structural transition and interaction with 14-3-3 proteins. We show that, while the isolated START domain does not interact with 14-3-3, interaction is enabled by STARD1 phosphorylation at Ser57, close to the mitochondrial peptide cleavage site. Biochemical analysis of the STARD1 affinity towards 14-3-3 and crystal structures of 14-3-3 complexes with Ser57 and Ser195 phosphopeptides, suggest distinct roles of site-specific phosphorylations in recruiting 14-3-3, to modulate STARD1 activity, processing and import to mitochondria. Phosphorylation at Ser195 creates a unique conditional site, that could only bind to 14-3-3 upon partial unfolding of the START domain.

scholarly journals StarD7 Gene Expression in Trophoblast Cells: Contribution of SF-1 and Wnt-β-Catenin Signaling

2011 ◽  
Vol 25 (8) ◽  
pp. 1364-1375 ◽  
Author(s):  
Viviana Rena ◽  
Jésica Flores-Martín ◽  
Sofía Angeletti ◽  
Graciela M. Panzetta-Dutari ◽  
Susana Genti-Raimondi
Keyword(s):  
Gene Expression ◽  
Intracellular Transport ◽  
Regulatory Protein ◽  
Steroidogenic Acute Regulatory Protein ◽  
Regulatory Sequences ◽  
Physical Interaction ◽  
Lipid Transfer ◽  
Amino Acid Mutations ◽  
Steroidogenic Acute Regulatory

Steroidogenic acute regulatory protein-related lipid transfer domain containing 7 (StarD7) is a poorly characterized member of the steroidogenic acute regulatory protein-related lipid transfer proteins, up-regulated in JEG-3 cells, involved in intracellular transport and metabolism of lipids. Previous studies dealing with the mechanisms underlying the human StarD7 gene expression led us to define the cis-acting regulatory sequences in the StarD7 promoter using as a model JEG-3 cells. These include a functional T cell-specific transcription factor 4 (TCF4) site involved in Wnt-β-catenin signaling. To understand these mechanisms in more depth, we examined the steroidogenic factor 1 (SF-1) contribution to StarD7 expression. Cotransfection experiments in JEG-3 cells point out that the StarD7 promoter is activated by SF-1, and this effect is increased by forskolin. EMSA using JEG-3 nuclear proteins demonstrated that SF-1 binds to the StarD7 promoter. Additionally, chromatin immunoprecipitation analysis indicated that SF-1 and β-catenin are bound in vivo to the StarD7 promoter. Reporter gene assays in combination with mutations in the SF-1 and TCF4 binding sites revealed that the StarD7 promoter is synergistically activated by SF-1 and β-catenin and that the TCF4 binding site (−614/−608) plays an important role in this activation. SF-1 amino acid mutations involved in the physical interaction with β-catenin abolished this activation; thus demonstrating that the contact between the two proteins is necessary for an efficient StarD7 transcriptional induction. Finally, these data suggest that β-catenin could function as a bridge between SF-1 and TCF4 forming a ternary complex, which would stimulate StarD7 expression. The SF-1 and β-catenin pathway convergence on StarD7 expression may have important implications in the phospholipid uptake and transport, contributing to the normal trophoblast development.

scholarly journals Complex Role of the Mitochondrial Targeting Signal in the Function of Steroidogenic Acute Regulatory Protein Revealed by Bacterial Artificial Chromosome Transgenesis in Vivo

2008 ◽  
Vol 22 (4) ◽  
pp. 951-964 ◽  
Author(s):  
Goro Sasaki ◽  
Tomohiro Ishii ◽  
Pancharatnam Jeyasuria ◽  
Youngah Jo ◽  
Assaf Bahat ◽  
...  
Keyword(s):  
Bacterial Artificial Chromosome ◽  
Adrenal Cortex ◽  
Regulatory Protein ◽  
Artificial Chromosome ◽  
Steroidogenic Acute Regulatory Protein ◽  
Mitochondrial Targeting ◽  
Targeting Signal ◽  
Steroidogenic Cells ◽  
Steroidogenic Acute Regulatory

The steroidogenic acute regulatory protein (StAR) stimulates the regulated production of steroid hormones in the adrenal cortex and gonads by facilitating the delivery of cholesterol to the inner mitochondrial membrane. To explore key aspects of StAR function within bona fide steroidogenic cells, we used a transgenic mouse model to explore the function of StAR proteins in vivo. We first validated this transgenic bacterial artificial chromosome reconstitution system by targeting enhanced green fluorescent protein to steroidogenic cells of the adrenal cortex and gonads. Thereafter, we targeted expression of either wild-type StAR (WT-StAR) or a mutated StAR protein lacking the mitochondrial targeting signal (N47-StAR). In the context of mice homozygous for a StAR knockout allele (StAR−/−), all StAR activity derived from the StAR transgenes, allowing us to examine the function of the proteins that they encode. The WT-StAR transgene consistently restored viability and steroidogenic function to StAR−/− mice. Although the N47-StAR protein was reportedly active in transfected COS cells and mitochondrial reconstitution experiments, the N47-StAR transgene rescued viability in only 40% of StAR−/− mice. Analysis of lipid deposits in the primary steroidogenic tissues revealed a hierarchy of StAR function provided by N47-StAR: florid lipid deposits were seen in the adrenal cortex and ovarian theca region, with milder deposits in the Leydig cells. Our results confirm the ability of StAR lacking its mitochondrial targeting signal to perform some essential functions in vivo but also demonstrate important functional defects that differ from in vitro studies obtained in nonsteroidogenic cells.

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