Fusion of Non-Muscle Myosin MYH9 to the USP6Oncogene in Nodular Fasciitis.
Michele R Erickson-Johnson, Margaret M Chou, Barbara R Evers, Christopher W Roth, Amber R Seys, Long Jin, Xiaoke Wang, Ying Ye, Alan W Lau, Andre M Oliveira. Univeristy of Pennsylvania School of Medicine, Philadelphia; Mayo Clinic, Rochester, MN
Background: Nodular fasciitis (NF) is a self limited mesenchymal lesion of uncertain etiology that commonly affects younger individuals. Rapid growth, rich cellularity and brisk mitotic activity often lead to a misdiagnosis of sarcoma. Only rare putative cases of NF have been characterized at the cytogenetic level but no consistent anomaly has been identified. While studying the biology of the USP6 oncogene, we observed that subcutaneous xenografts of MC3T3 pre-osteoblasts overexpressing USP6 produced lesions with clinical and histologic features similar to human NF. These observations led us to investigate whether USP6 transcriptional upregulation could be involved in the pathogenesis of NF arising in humans.
Design: Stable cell lines expressing USP6 were generated in MC3T3-E1 pre-osteoblasts and injected into nude mice. Two frozen samples and 13 additional paraffin-embedded tissues from classic examples of human NF were retrieved from the Mayo Clinic tumor archives (n=15). USP6 mRNA expression profile was performed using semi-quantitative RT-PCR. Fusion gene identification was carried out using 5' RACE RT-PCR. Fluorescence is situ hybridization (FISH) was performed for the following loci: USP6, CDH11, COL1A1 and MYH9. Confirmatory specific RT-PCR and direct sequencing for MYH9-USP6 was performed in all 15 cases and 16 non-NF controls.
Results: Xenograph-induced tumors showed clinico-pathologic features similar to those seen in human NF. USP6 mRNA transcriptional upregulation was identified in the two index cases of human NF. FISH analysis showed a balanced rearrangement of the USP6 locus in 14 of 15 human NF cases (93%). 5'RACE, RT-PCR and direct sequencing identified the fusion of MYH9 exon 1 to either exon 1 or 2 of USP6. MYH9 locus rearrangement was found in 13/15 (87%) of the NF cases. One case showed rearrangement of USP6 only (without MYH9), and one case showed no rearrangement of either gene. No rearrangement of COL1A1 or CDH11 was found. RT-PCR and sequencing confirmed the fusion MYH9-USP6 in 11 of 15 NF (73%). Non-NF tumors were negative for MYH9-USP6 fusion.
Conclusions: Our study provides new insight into the biology of NF, which can be viewed as a self-limited form of neoplasia. The mechanism seems to involve USP6 transcriptional upregulation due to its fusion with a strong ectopic promoter, akin to what was seen previously in aneurysmal bone cyst. The identification of a sensitive and specific abnormality in NF may also provide a novel diagnostic avenue for these lesions.
Category: Bone & Soft Tissue
Monday, February 28, 2011 8:00 AM
Platform Session: Section F, Monday Morning