The PAX3-FKHR fusion gene of rhabdomyosarcoma cooperates with loss of p16INK4A to promote bypass of cellular senescence.
Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence. Despite advances in therapy, patients with a histologic variant of rhabdomyosarcoma known as alveolar rhabdomyosarcoma (ARMS) have a 5-year survival of <30%. ARMS is characterized by a chromosomal translocation generating the PAX3-FKHR fusion gene. However, ectopic expression of PAX3-FKHR often induces inhibition of cell proliferation, or cell death, when expressed in nonmuscle cells. This prompted us to explore the effect of expressing PAX3-FKHR in more relevant cells, specifically primary human skeletal muscle cells because these cells can be converted to a tumorigenic state that mimics rhabdomyosarcoma. PAX3-FKHR expression promoted both fetal and postnatal primary human skeletal muscle cell precursors to bypass the senescence growth arrest checkpoint. This bypass was accompanied by epigenetic DNA methylation of the p16(INK4A) promoter and correspondingly a loss of expression of this tumor suppressor. Knockdown of p16(INK4A) cooperated with PAX3-FKHR to drive proliferation past senescence, whereas reintroduction of wild-type p16(INK4A) in post-senescent cells caused growth arrest. Thus, PAX3-FKHR acts in concert with loss of p16(INK4A) to promote inappropriate proliferation of skeletal muscle cells. This association between PAX3-FKHR expression and p16(INK4A) loss was seen in human ARMS tumor tissue, as both human rhabdomyosarcoma cell lines and tissue microarrays showed a trend toward down-regulation of p16(INK4A) protein in alveolar subsets. We surmise that the generation of the PAX3-FKHR fusion protein may require loss of p16(INK4A) to promote malignant proliferation of skeletal muscle cells as an early step in ARMS tumorigenesis.
Linardic
Corinne M
CM
Department of Pediatrics, Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA. linar001@mc.duke.edu
Naini
Sarasija
S
Herndon
James E
JE
Kesserwan
Chimen
C
Qualman
Stephen J
SJ
Counter
Christopher M
CM
D045744:Cell Line, Tumor; D049109:Cell Proliferation; D016922:Cellular Senescence; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism*; D019175:DNA Methylation; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology; D020411:Oligonucleotide Array Sequence Analysis; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins; D012208:Rhabdomyosarcoma / Q000378:metabolism*
D019941:Cyclin-Dependent Kinase Inhibitor p16; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051761:Paired Box Transcription Factors; D011993:Recombinant Fusion Proteins