[55] Recurrent (2;2) and (2;8) Translocations in Rhabdomyosarcoma without the Canonical PAX-FOXO1 Fuse PAX3 to Members of the Nuclear Receptor Transcriptional Coactivator (NCOA) Family

JA Bridge, R Streblow, RW Frayer, P Dal Cin, A Rosenberg, A Meloni-Ehrig, J Sumegi. University of Nebraska Medical Center, Omaha, NE; Cincinnati Children's Hospital Medical Center, Cincinnati, OH; Harvard Medical School, Boston, MA; Massachusetts General Hospital, Boston, MA; Quest Diagnostics Nichols Institute, Chantilly, VA

Background: The fusion oncoproteins PAX3-FOXO1 [t(2;13)(q35;q14)] and PAX7-FOXO1 [t(1;13)(p36;q14)] typify alveolar rhabdomyosarcoma (ARMS); however, 20-30% of cases lack these specific translocations.
Design: Cytogenetic and/or molecular characterization to include FISH, RT-PCR and sequencing analyses were conducted on four ARMS and one embryonal rhabdomyosarcoma (ERMS) exhibiting a 2q35 or PAX3 rearrangement but lacking a PAX-FOXO1 transcript.
Results: Novel, recurrent t(2;2)(p23;q35) or t(2;8)(q35;q13) translocations fusing PAX3 to NCOA1 or NCOA2 respectively were identified. The PAX3-NCOA1 and PAX3-NCOA2 transcripts encode chimeric proteins composed of the paired-box and homeodomain DNA-binding domains of PAX3, and the CID domain, the Q-rich region and the AD2 domain of NCOA1 or NCOA2. To investigate the biological function of these recurrent variant translocations, the coding regions of PAX3-NCOA1 and PAX3-NCOA2 cDNA constructs were introduced into expression vectors with tetracycline-regulated expression. Both fusion proteins showed transforming activity in the soft agar assay. Deletion of the AD2 portion of the PAX3-NCOA fusion proteins reduced the transforming activity of each chimeric protein. Similarly, but with greater impact, CID domain deletion fully abrogated the transforming activity of the chimeric protein.
Conclusions: These studies: (1) expand our knowledge of PAX3 variant translocations in RMS with identification of a novel PAX3-NCOA2 fusion; (2) show that both PAX3-NCOA1 and PAX3-NCOA2 represent recurrent RMS rearrangements; (3) confirm the transforming activity of both translocation events and demonstrate the essentiality of intact AD2 and CID domains for optimal transforming activity; and, (5) provide alternative approaches (FISH and RT-PCR) for detecting PAX-NCOA fusions in nondividing cells of RMS. The latter could potentially be utilized as aids in diagnostically challenging cases.
Category: Bone & Soft Tissue

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 2, Tuesday Morning

 

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