In Vitro studies of non poly alanine PHOX2B mutations argue against a loss-of-function mechanism for congenital central hypoventilation.
A wide range of autonomic dysfunctions, i.e. Central Hypoventilation Syndromes, Hirschsprung disease and Tumours of the Sympathetic Nervous System have been ascribed to heterozygous PHOX2B mutations in man. The PHOX2B mutations reported include polyalanine expansions in a 20 alanines tract, missense, frameshift mutations and nonsense mutation. Some genotype/phenotype correlations have been drawn, but the molecular mechanism(s) underlying them remain(s) unclear. So far, loss-of-function, gain-of-function and dominant negative effects have been proposed as disease-causing mechanisms for polyalanine expansions. Indeed, mutant with an expanded polyalanine tract result in decreased transactivation of known target genes and protein misfolding leading to oligomerisation in vitro for all expansions and to cytoplasmic protein aggregation for longer expansions. We extended the molecular studies to other non-polyalanine expansion mutations and show that most PHOX2B protein mutants oligomerize even in the absence of the normal 20 alanines tract. Conversely, a premature stop codon mutation in a CHS patient leads to the production of an N-terminally truncated protein by re-initiation of translation that does not form oligomers. Therefore, PHOX2B misfolding is not the only mechanism leading to dysfunction of the ventilatory autonomic system.
Trochet
Delphine
D
INSERM U781 et Département de Génétique, Hôpital Necker-Enfants Malades, Université Paris Descartes, Faculté de Médecine, Assistance Publique-Hôpitaux de Paris (AP-HP), Paris, France.
Mathieu
Yves
Y
Pontual
Loïc de
Ld
Savarirayan
Ravi
R
Munnich
Arnold
A
Brunet
Jean-François
JF
Lyonnet
Stanislas
S
Goridis
Christo
C
Amiel
Jeanne
J
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001483:Base Sequence; D002850:Chromatography, Gel; D003062:Codon / Q000235:genetics; D018389:Codon, Nonsense; D016368:Frameshift Mutation; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D007040:Hypoventilation / Q000151:congenital* / Q000235:genetics*; D008156:Luciferases / Q000378:metabolism; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D010455:Peptides / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D055503:Protein Multimerization; D055550:Protein Stability; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics*; D015533:Transcriptional Activation / Q000235:genetics
D003062:Codon; D018389:Codon, Nonsense; D018398:Homeodomain Proteins; D050505:Mutant Proteins; C109220:NBPhox protein; D010455:Peptides; D014157:Transcription Factors; C019529:polyalanine; D008156:Luciferases