Characterization of the human and mouse ETV1/ER81 transcription factor genes: Role of the two alternatively spliced isoforms in the human

The Ets transcription factors of the PEA3 group - E1AF/PEA3, ETV1/ER81 and ERM - are almost identical in the ETS DNA-binding and the transcriptional acidic domains. To accelerate our understanding of the molecular basis of putative diseases linked to ETV1 such as Ewing's sarcoma we characterized the human ETV1 and the mouse ER81 genes. We showed that these genes are both encoded by 13 exons in more than 90 kbp genomic DNA, and that the classical acceptor and donor splicing sites are present in each junction except for the 5' donor site of intron 9 where GT is replaced by TT. The genomic organization of the ETS and acidic domains in the human ETV1 and mouse ER81 (localized to chromosome 12) genes is similar to that observed in human ERM and human E1AF/PEA3 genes. Moreover, as in human ERM and human E1AF/PEA3 genes, a first untranslated exon is upstream from the first methionine, and the mouse ER81 gene transcription is regulated by a 1.8 kbp of genomic DNA upstream from this exon. In human, the alternative splicing of the ETV1 gene leads to the presence (ETV1α) or the absence (ETV1β) of exon 5 encoding the C-terminal part of the transcriptional acidic domain, but without affecting the alpha helix previously described as crucial for transactivation. We demonstrated here that the truncated isoform (human ETV1β) and the full-length isoform (human ETV1α) bind similarly specific DNA Ets binding sites. Moreover, they both activate transcription similarly through the PKA-transduction pathway, so suggesting that this alternative splicing is not crucial for the function of this protein as a transcription factor. The comparison of human ETV1α and human ETV1β expression in the same tissues, such as the adrenal gland or the bladder, showed no clear-cut differences. Altogether, these data open a new avenue of investigation leading to a better understanding of the functional role of this transcription factor.

Friedreich Ataxia

Friedreich's ataxia (FRDA) is the most common autosomal recessive hereditary ataxia in Caucasians. Neurological symptoms dominate the clinical picture. The underlying neuropathology affects the dorsal root ganglia, the spinal cord, and the deep cerebellar nuclei. In addition, most cases present a hypertrophic cardiomyopathy that may cause premature death. Other problems include a high risk of diabetes, skeletal abnormalities such as kyphoscoliosis, and pes cavus. Most patients carry a homozygous expansion of GAA trinucleotide repeat within the first intron of the FXN gene, leading to repressed transcription through epigenetic mechanisms. The encoded protein, frataxin, is localized in mitochondria and participates in the biogenesis of iron-sulfur clusters. Frataxin deficiency leads to mitochondrial dysfunction, altered iron metabolism, and oxidative damage. Thanks to progress in understanding pathogenesis and to the development of animal and cellular models, therapies targeted to correct frataxin deficiency or its downstream consequences are being developed and tested in clinical trials.

Friedreich Ataxia

Friedreich ataxia (FRDA) is an autosomal recessive disease characterized by progressive neurological and cardiac abnormalities. It has a prevalence of around 2×10⁵ in whites, accounting for more than one-third of the cases of recessively inherited ataxia in this ethnic group. FRDA may not exist in nonwhite populations.The first symptoms usually appear in childhood, but age of onset may vary from infancy to adulthood. Atrophy of sensory and cerebellar pathways causes ataxia, dysarthria, fixation instability, deep sensory loss, and loss of tendon reflexes. Corticospinal degeneration leads to muscular weakness and extensor plantar responses. A hypertrophic cardiomyopathy may contribute to disability and cause premature death. Other common problems include kyphoscoliosis, pes cavus, and, in 10% of patients, diabetes mellitus.The FRDA gene (FXN) encodes a small mitochondrial protein, frataxin, which is produced in insufficient amounts in the disease, as a consequence of the epigenetic silencing of the gene triggered by a GAA triplet repeat expansion in the first intron of the gene. Frataxin deficiency results in impaired iron-sulfur cluster biogenesis in mitochondria, in turn leading to widespread dysfunction of iron-sulfur center containing enzymes (in particular respiratory complexes I, II and III, and aconitase), impaired iron metabolism, oxidative stress, and mitochondrial dysfunction. Therapy aims to restore frataxin levels or to correct the consequences of its deficiency.