Characterization of gene amplification-driven SKP2 overexpression in myxofibrosarcoma: potential implications in tumor progression and therapeutics.
OBJECTIVE
Myxofibrosarcoma remains obscure in molecular determinants of clinical aggressiveness, for which we elucidated implications of SKP2 amplification.


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Department of Pathology, National Institute of Cancer Research, Taiwan.
Chien-Feng
CF
Li
Ju-Ming
JM
Wang
Hong-Yo
HY
Kang
Chiung-Kuei
CK
Huang
Jun-Wen
JW
Wang
Fu-Min
FM
Fang
Yu-Hui
YH
Wang
Wen-Ren
WR
Wu
Shau-Hsuan
SH
Li
Shih-Chen
SC
Yu
Jen-Chieh
JC
Lee
Jui
J
Lan
Yow-Ling
YL
Shiue
Li-Ching
LC
Wu
Hsuan-Ying
HY
Huang
D000818:Animals; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D045744:Cell Line, Tumor; D055028:Comparative Genomic Hybridization; D005260:Female; D005354:Fibrosarcoma / Q000235:genetics*; D005784:Gene Amplification; D018628:Gene Dosage; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics; D006801:Humans; D008297:Male; D051379:Mice; D016513:Mice, SCID; D008875:Middle Aged; D011379:Prognosis; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D011719:Pyrazines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D019998:Racemases and Epimerases / Q000235:genetics; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics*; D015854:Up-Regulation; D023041:Xenograft Model Antitumor Assays
D001897:Boronic Acids; D020662:Guanine Nucleotide Exchange Factors; D011719:Pyrazines; D012333:RNA, Messenger; D044786:S-Phase Kinase-Associated Proteins; D000069286:Bortezomib; D017346:Protein Serine-Threonine Kinases; C099628:TRIO protein, human; D019998:Racemases and Epimerases; C108352:alpha-methylacyl-CoA racemase