Cases were wild type for MYOD1 and no other mutations or rearrangements characteristic of a known subtype of rhabdomyoma or rhabdomyosarcoma were identified.
We investigated 30 cases of MYOD1-mutant rhabdomyosarcoma (12 previously reported and 18 newly diagnosed) with an age range of 2-94 years, including 15 children.
Our data support unappreciated and dominant oncogenic roles for MYF5 and MYOD convergence on common transcriptional targets to regulate human RMS growth.
Furthermore, while all 10 MYOD1 mutant spindle cell and sclerosing rhabdomyosarcoma samples showed diffuse and strong MYOD1 immunoexpression, 7 of 31 samples of rhabdomyosarcoma with wild-type MYOD1 were negative forMYOD1 expression.
From the investigated 17 samples, seven (41%) showed homozygous mutation of MYOD1, indicating a critical role in this rare subtype of adult spindle cell RMS, while no mutations were found in any of the other genes involved in myogenic differentiation.
Amongst the transcripts differentially expressed in the RD cells, MYOD and MYOG (2 fold, p<0.05), and six MYOD downstream targets were up-regulated in RD but not C2C12 cells.
We report here that MyoD1 mRNA is not specific for RMS, but can be amplified from ex vivo samples of many other childhood tumors and some normal tissues.
Our data suggest that the methylation status of the MyoD1 upstream CpG sites may be related to rhabdomyosarcoma tumorigenesis and may have valuable implications for its differential diagnosis.
We detected the MyoD1 transcript in normal skeletal muscle and in almost all RMSs, whereas no expression was found in non-RMS samples or in normal hematopoietic tissues.
Furthermore, the regulatory-gene analyses indicated that these 2 sublines represented 2 distinct differentiation stages of myoblasts, and that MyoD1 and myogenin could serve as the lineage marker and the differentiation marker, respectively, of human rhabdomyosarcoma.
Further, these analyses identify two syntenic clusters of muscle-associated genes on the short arm of human chromosome 11, one in the region of rhabdomyosarcoma locus that includes IGF2 and TH and the second the tightly linked MYOD1 and LDHA loci, which have been evolutionarily conserved in homologous regions of both the mouse and the rat genomes.
Transfection of the mouse MyoD1 gene into the human rhabdomyosarcoma cell line RD increased the ability of the tumor cells to differentiate into multinucleated myotubes and enhanced myosin heavy-chain gene expression but did not decrease tumorigenicity in nude mice.