Identification of a new class of PAX3-FKHR target promoters: a role of the Pax3 paired box DNA binding domain

Abstract

Alveolar rhabdomyosarcoma (aRMS), an aggressive skeletal muscle cancer, carries a unique t(2;13) chromosomal translocation resulting in the formation of a chimeric transcription factor PAX3-FKHR. This fusion protein contains the intact DNA-binding domains (PD: paired box binding domain; HD: paired-type homeodomain) of Pax3 fused to the activation domain of FKHR. Cells expressing Pax3 and PAX3-FKHR show vastly different gene expression patterns, despite that they share the same DNA-binding domains. We present evidence of a gain of function mechanism that allows the fusion protein to recognize and transcriptionally activate response elements containing a PD-specific binding site. This DNA recognition specificity is in contrast to the requirement for Pax3-specific target sequences that must contain a composite of PD-and HD-binding sites. Domain swapping studies suggest that an increased structural flexibility could account for the relaxed DNA targeting specificity in PAX3-FKHR. Here, we identify myogenin gene as a direct target of PD-dependent PAX3-FKHR activation pathway in vitro and in vivo. We demonstrate that PAX3-FKHR could induce myogenin expression in undifferentiated myoblasts by a MyoD independent pathway, and that PAX3-FKHR is directly involved in myogenin expression in aRMS cells.

AKT and PAX3-FKHR cooperation enforces myogenic differentiation blockade in alveolar rhabdomyosarcoma cell

“…In contrast, a previous study showed that PAX3-FKHR can transactivate myogenin independent of MyoD. 60 Moreover, a recent study demonstrated that PAX3-FKHR activates MyoD expression, but at the same time attenuates the MyoD-mediated terminal myogenic program. 15 Our data demonstrates that the restoration of PAX3-FKHR activity mediated induction of MyoD by dnAKT is incompetent in gene activation function in ARMS grown in DM, supporting that PAX3-FKHR activity mediated simultaneous induction and inhibition of MyoD regulated the myogenic program.…”

PAX-FKHR function as pangenes by simultaneously inducing and inhibiting myogenesis

“…Khan et al (1999) reported similar results using expression arrays. PAX3-FKHR has also been shown to transactivate myogenin directly, independent of MyoD (Zhang and Wang, 2007). Therefore, it is possible that PAX-FKHR also activate myogenin directly during ARMS formation.…”

Comparative expression profiling identifies an in vivo target gene signature with TFAP2B as a mediator of the survival function of PAX3/FKHR

“…Therefore, these experiments support the hypothesis that one of the oncogenic functions of PAX3/FKHR is to block terminal differentiation. Furthermore, they suggest that the cellular background has a profound effect on target genes bound and activated by PAX3 and/or that the target gene spectra of PAX3 and PAX3/ FKHR differs (Zhang and Wang, 2006).…”