The role of PAX3-FOXO1 in the pathogenesis of alveolar rhabdomyosarcoma

Rhabdomyosarcomas, malignant tumors of mesenchymal origin, are the most common soft tissue sarcomas in children. Of the two subtypes, alveolar tumors (ARMS) portend the worst prognosis. Most ARMS are characterized by a balanced reciprocal chromosomal translocation t(2;13) that fuses the PAX3 to the FOXO1 gene. Expression of the fusion gene is a negative prognostic factor independent of tumor subtype. Despite the overwhelming data implicating the PAX3-FOXO1 chimeric protein in the pathogenesis of ARMS, little is known about its function. To study its function in its endogenous context, myogenic precursor cells were isolated from transgenic mice. These cells express PAX3- FOXO1 under the control of the PAX3 promoter. The absence of any additional genetic lesions enabled us to dissect the effect of PAX3-FOXO1 alone without the contribution of the additional genetic abnormalities in cells derived from tumors. Chapter 1 introduces alvoleolar rhabdomyosarcomas and summarizes current knowledge of PAX3-FOXO1 function. Chapter 2 describes the characterization of PAX3-FOXO1 transgenic myoblasts and details the discovery of a novel mechanisms by which PAX3-FOXO1 regulates p57Kip2 transcription through the degradation of EGR1. Chapter 3 details the regulation of Mdm2 transcription by PAX3-FOXO1 and discusses how this attenuation of TP53 function likely contributes to the relative resistance of ARMS to treatment. Chapter 4 summarizes the progress made in this dissertation and examines future direction

The role of PAX3-FOXO1 in the pathogenesis of alveolar rhabdomyosarcoma

Rhabdomyosarcomas, malignant tumors of mesenchymal origin, are the most common soft tissue sarcomas in children. Of the two subtypes, alveolar tumors (ARMS) portend the worst prognosis. Most ARMS are characterized by a balanced reciprocal chromosomal translocation t(2;13) that fuses the PAX3 to the FOXO1 gene. Expression of the fusion gene is a negative prognostic factor independent of tumor subtype. Despite the overwhelming data implicating the PAX3-FOXO1 chimeric protein in the pathogenesis of ARMS, little is known about its function. To study its function in its endogenous context, myogenic precursor cells were isolated from transgenic mice. These cells express PAX3- FOXO1 under the control of the PAX3 promoter. The absence of any additional genetic lesions enabled us to dissect the effect of PAX3-FOXO1 alone without the contribution of the additional genetic abnormalities in cells derived from tumors. Chapter 1 introduces alvoleolar rhabdomyosarcomas and summarizes current knowledge of PAX3-FOXO1 function. Chapter 2 describes the characterization of PAX3-FOXO1 transgenic myoblasts and details the discovery of a novel mechanisms by which PAX3-FOXO1 regulates p57Kip2 transcription through the degradation of EGR1. Chapter 3 details the regulation of Mdm2 transcription by PAX3-FOXO1 and discusses how this attenuation of TP53 function likely contributes to the relative resistance of ARMS to treatment. Chapter 4 summarizes the progress made in this dissertation and examines future direction

Genomic Duplication and Overexpression of TJP2/ZO-2 Leads to Altered Expression of Apoptosis Genes in Progressive Nonsyndromic Hearing Loss DFNA51

Age-related hearing loss is due to death over time, primarily by apoptosis, of hair cells in the inner ear. Studies of mutant genes responsible for inherited progressive hearing loss have suggested possible mechanisms for hair cell death, but critical connections between these mutations and the causes of progressive hearing loss have been elusive. In an Israeli kindred, dominant, adult-onset, progressive nonsyndromic hearing loss DFNA51 is due to a tandem inverted genomic duplication of 270 kb that includes the entire wild-type gene encoding the tight junction protein TJP2 (ZO-2). In the mammalian inner ear, TJP2 is expressed mainly in tight junctions, and also in the cytoplasm and nuclei. TJP2 expression normally decreases with age from embryonic development to adulthood. In cells of affected family members, TJP2 transcript and protein are overexpressed, leading to decreased phosphorylation of GSK-3β and to altered expression of genes that regulate apoptosis. These results suggest that TJP2- and GSK-3β-mediated increased susceptibility to apoptosis of cells of the inner ear is the mechanism for adult-onset hearing loss in this kindred and may serve as one model for age-related hearing loss in the general population

Reduced transcript expression of genes affected by inherited and de novo CNVs in autism

Individuals with autism are more likely to carry rare inherited and de novo copy number variants (CNVs). However, further research is needed to establish which CNVs are causal and the mechanisms by which these CNVs influence autism. We examined genomic DNA of children with autism (N=41) and healthy controls (N=367) for rare CNVs using a high-resolution array comparative genomic hybridization platform. We show that individuals with autism are more likely to harbor rare CNVs as small as ∼10 kb, a threshold not previously detectable, and that CNVs in cases disproportionately affect genes involved in transcription, nervous system development, and receptor activity. We also show that a subset of genes that have known or suspected allele-specific or imprinting effects and are within rare-case CNVs may undergo loss of transcript expression. In particular, expression of CNTNAP2 and ZNF214 are decreased in probands compared with their unaffected transmitting parents. Furthermore, expression of PRODH and ARID1B, two genes affected by de novo CNVs, are decreased in probands compared with controls. These results suggest that for some genes affected by CNVs in autism, reduced transcript expression may be a mechanism of pathogenesis during neurodevelopment