[57] Recurrent Amplification at 11q13.5-14.1 Targets PAK1 as a Tumor-Promoting Oncogene in Primary Myxofibrosarcomas

Chien-Feng Li, Jui Lan, Hui-Chun Tai, Tzu-Ju Chen, Hsuan-Ying Huang. Chi-Mei Medical Center, Tainan, Taiwan; Southern Taiwan University of Science and Technology, Tainan, Taiwan; Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan; Changhua Christian Hospital, Changhua, Taiwan

Background: Myxofibrosarcoma is genetically complex and obscure in molecular determinants of clinical aggressiveness. By using array comparative genomic hybridization to profile 12 fresh samples and 3 cell lines, one of the recurrent gained regions seen in at least 20% of samples was mapped to 11q13.5-14.1, encompassing amplified PAK1 (p21 protein-activated kinase 1) oncogene with mRNA upregulation seen in published transcriptome (GSE21122), among others.
Design: To evaluate significance of PAK1 gene status, mRNA abundance, and protein expression, FISH, branched-chain DNA (bDNA), and immunohistochemical assays were performed in independent myxofibrosarcoma samples, yielding 75, 79, and 98 informative cases, respectively. The results were correlated with clincopathological and tested variables, disease-specific survival (DSS), and metastasis-free survival (MFS). The oncogenic functions of PAK1 were elucidated with (1) transfection of wild-type PAK1 and hyperactivating T423E mutant (PAK1T423E) in low PAK1-expressing NMFH-2 myxofibrosarcoma cells and (2) short-hairpin RNA interference in PAK1-overexpressing OH931 cells.
Results: Defined as 5-fold increased signals relative to reference probe and present in 14.7% (11/75) of cases, high-level PAK1 amplification was significantly related to higher mRNA abundance (p=0.011, bDNA assay) and immunoexpression (p=0.004), with the latter two also associated with each other and deep-seated tumors. High-level PAK1 amplification highly correlated with higher grades (p=0.009), together with increased mRNA abundance (p=0.011) and immunoexpression (p<0.011) of PAK1. Apart from higher grades, only high-level PAK1 amplification independently portended adverse outcomes (DSS, p=0.018, hazard ratio=3.929; MFS, hazard ratio=5.772, p=0.016). Stable PAK1-knockdown OH931 cells displayed significantly attenuated cell migration/invasion in transwell and matrigel assays and decreased cell proliferation in Brdu assay. Conversely, these aggressive phenotypes were enhanced in NMFH-2 cells transfected with wild-type PAK1 and even more drastic with PAK1T423E mutant.
Conclusions: High-level PAK1 amplification contributes to mRNA and protein upregulation and promotes tumor aggressiveness via enhancing cell proliferation and migration/invasion in myxofibrosarcomas.
Category: Bone & Soft Tissue

Monday, March 4, 2013 1:00 PM

Poster Session II # 27, Monday Afternoon


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