Disease relevance of PHOX2A

• Main outcome measure: Presence or absence of mutation in PHOX2A gene in two siblings with exotropia and recessive CFEOM [1].
• CFEOM1, the classic familial form of congenital fibrosis of the extraocular muscles, is genetically heterogeneous but does not result from mutations in ARIX [2].
• Treatment of neuroblastoma cultures with PD98059 increases the interaction of Arix with DBH and NET genes, but not the TH gene [3].
• METHODS: Clinical examination of one patient with CFEOM1, one family with clinical features of CFEOM2, one family with recessive CFEOM3, one family with horizontal gaze palsy and progressive scoliosis (HGPPS), and four patients with various combinations of congenital cranial nerve abnormalities [4].
• Using mammalian one-hybrid and two-hybrid systems, we demonstrate that recruitment of Arix to the positions of homeodomain core recognition sites 1 and 2 at -153 to -166 of the DBH gene restores complete responsiveness of the promoter to PKA in SHSY-5Y neuroblastoma and HepG2 hepatoma cells [5].

High impact information on PHOX2A

• These findings confirm the hypothesis that CFEOM2 results from the abnormal development of nIII/nIV (ref. 7) and emphasize a critical role for ARIX in the development of these midbrain motor nuclei [6].
• We now have mapped a variant of CFEOM, exotropic strabismus fixus ("CFEOM2") [7].
• Two of the three families share a common disease-associated haplotype, suggesting a founder effect for CFEOM2 [7].
• We hypothesize that CFEOM2 results from an analogous developmental defect to CFEOM1, one that affects both the superior and inferior divisions of the oculomotor nerve and their corresponding alpha motoneurons and extraocular muscles [7].
• According to the known role of this gene, a transcription factor expressed during autonomic nervous system development, we have tested the transcriptional activity of WT and mutant PHOX2B expression constructs on the regulatory regions of two target genes, DbetaH and PHOX2A [8].

Biological context of PHOX2A

• This study was conducted to determine the incidence of KIF21A and PHOX2A mutations among individuals with the third CFEOM phenotype, CFEOM3 [9].
• Experimental procedure: Mutation analysis of the PHOX2A gene was performed using polymerase chain reaction amplification of the coding exons and direct sequencing of polymerase chain reaction products [1].
• Together, these results suggest that phosphorylation of Arix by ERK1/2 inhibits its ability to interact with target genes, and that both specificity of expression and modulation by external stimuli are monitored through the same transcription factor [3].
• Here, we demonstrate that Arix/Phox2a is phosphorylated by extracellular signal-related kinase (ERK)1/2 at two sites within the N-terminal transactivation domain [3].
• One patient with atrophy of the superior oblique muscle had a new change of T-4G in the promoter region of the ARIX gene [10].

Anatomical context of PHOX2A

• Consistent with the DNA binding activity of Arix, treatment of cultured cells with phosphatase inhibitors diminishes transcriptional activation with Arix plus forskolin [11].
• The recently described homeodomain protein ARIX is expressed specifically in noradrenergic cell types of the sympathetic nervous system, brain, and adrenal medulla [12].
• Human ARIX was positioned through analysis of somatic cell hybrids and fluorescence in situ hybridization of human metaphase chromosomes to chromosome 11q13.3-q13 [12].

Associations of PHOX2A with chemical compounds

• CONCLUSIONS: The 439C-->T mutation in this family changes a glutamine to a stop codon (Q90X) at the beginning of the PHOX2A homeodomain region [1].
• The homeodomain protein Arix/Phox2a plays a role in the development and maintenance of the noradrenergic cell type by regulating the transcription of genes involved in the biosynthesis and metabolism of noradrenaline [3].
• The homeodomain protein Arix interacts synergistically with cyclic AMP to regulate expression of neurotransmitter biosynthetic genes [13].
• The paired-like homeodomain protein, Arix, mediates protein kinase A-stimulated dopamine beta-hydroxylase gene transcription through its phosphorylation status [11].
• Amino acid analysis demonstrates the presence of phosphoserine within Arix [11].

Physical interactions of PHOX2A

• Arix coprecipitated with antisera directed against recombinant dHAND, demonstrating direct protein-protein interactions [14].
• Congenital fibrosis of the extraocular muscles type 2 (CFEOM2) is a complex strabismus syndrome that results from mutations in the homeodomain transcription factor PHOX2A [15].

Regulatory relationships of PHOX2A

• We have evaluated whether post-translational modification of Arix regulates PKA-mediated DBH gene transcription [11].

Other interactions of PHOX2A

• The phosphorylation level of Arix in cultured SH-SY5Y neuroblastoma cells is reduced when cells are treated with the mitogen activated protein kinase kinase 1 (MEK1) inhibitor UO126 [3].
• Our analysis only permitted the exclusion of the FEOM3 locus and the FEOM2 gene, ARIX [16].
• Thus, the present study demonstrates that Arix can integrate extrinsic signals through post-translational modification, regulating DBH gene transcription in response to activation of the PKA pathway [11].
• The dHAND-Arix complex was dissociated upon the addition of an unlabeled competitor containing a homeodomain, but not upon the addition of a competitor containing E-boxes [14].
• To assess the genetic mechanisms, we examined the transcription factor genes ARIX (recently identified as a causative gene for syndromic strabismus) and its paralogue, PMX2B [17].

Analytical, diagnostic and therapeutic context of PHOX2A

• Neither Arix nor cyclic AMP analogs alone effectively stimulate transcription from the DBH promoter in non-neuronal cell cultures [13].
• METHODS: The three exons of the ARIX gene were sequenced by genomic DNA amplification with polymerase chain reaction (PCR) and direct sequencing in 15 patients with superior oblique muscle palsy (13 with congenital and two with acquired palsy) and 54 normal individuals [18].
• Clinical presentation, neuroimaging and Phox2a-/- animal models all support the concept that CFEOM2 is a primary neurogenic abnormality with secondary myopathic changes [15].

References