Abstract
Myxofibrosarcoma remains obscure in molecular determinants of clinical aggressiveness, for which we elucidated implications of SKP2 amplification. Array comparative genomic hybridization was applied on samples and cell lines (NMFH-1 to OH931) to search causal genes of tumor progression. SKP2 gene dosage was determined in 82 independent tumors for clinical correlates. Stable SKP2 knockdown was achieved in myxofibrosarcoma cells to assess its oncogenic attributes and candidate mediators in prometastatic function. Pharmacologic assays were evaluated in vitro and in vivo for the therapeutic relevance of bortezomib. DNA gains frequently involved 5p in which three amplicons were differentially overrepresented in samples behaving unfavorably, encompassing mRNA-upregulated TRIO, SKP2, and AMACR genes. Detected in NMFH-1 cells and 38% of tumors, SKP2 amplification was associated with SKP2 immunoexpression and adverse prognosticators and independently predictive of worse outcomes. Nevertheless, SKP2-expressing OH931 cells and 14% of such tumors lacked gene amplification. Knockdown of SKP2 suppressed proliferation, anchorage-independent growth, migration, and invasion of sarcoma cells and downregulated motility-promoting genes, including ITGB2, ACTN1, IGF1, and ENAH. In vitro, bortezomib downregulated SKP2 expression at the mRNA level with p27(kip1) accumulation, induced caspase activation, and decreased cell viability in myxofibrosarcoma cells but not in fibroblasts. In vivo, bortezomib inhibited growth of NMFH-1 xenografts, the cells of which displayed decreased SKP2 expression but increased p27(kip1) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). As a predominant mechanism driving protein overexpression, SKP2 amplification confers tumor aggressiveness in myxofibrosarcoma. The sensitivity of myxofibrosarcoma cells to bortezomib with SKP2-repressing effect indicates the potentiality of ubiquitin-proteasome pathway as a therapeutic target.
Highlights
Myxofibrosarcoma, a common soft tissue sarcoma affecting the extremities of the elderly, is characterized by increased metastases after relentless local recurrences [1, 2]
The sensitivity of myxofibrosarcoma cells to bortezomib with S-phase kinase-associated protein 2 (SKP2)-repressing effect indicates the potentiality of ubiquitin-proteasome pathway as a therapeutic target
To validate the implication of SKP2 amplification, gene dosage was successfully quantified in 82 independent primary myxofibrosarcomas, excluding those used for array comparative genomic hybridization (aCGH) profiling or receiving neoadjuvant radiation or chemotherapy
Summary
Myxofibrosarcoma, a common soft tissue sarcoma affecting the extremities of the elderly, is characterized by increased metastases after relentless local recurrences [1, 2]. The cumulative overall survival rate is approximately 75% at 5 years and few series analyzing myxofibrosarcomas provided incongruent values for various clinicopathologic prognosticators [3,4,5]. We and others previously addressed the importance of clear margins, which predicted better local control and translated into final survival benefits [3, 5]. Little is understood about the molecular determinants accounting for the clinical aggressiveness of myxofibrosarcoma. Genome-wide approaches with derived targeted therapies are prompting increasing efforts to characterize
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