Genomic Amplification Of C-Jun Activates Genes That Promote Proliferation And Cell Migration In Liposarcoma

Introduction: Activating protein 1 (AP-1) is a dimeric transcription factor comprising proteins whose common denominator is the possession of basic leucine zipper (bZIP) domains that are essential for dimerization and DNA binding. Among this family, the c-Jun protein is a transcription factor that is activated among the earliest responses to mitogenic signaling. It can promote cell division and differentiation but also can act as a potent inducer of apoptosis in other contexts. Recently, c-Jun was directly implicated as a proto-oncogene in a human cancer when it was found to be genomically amplified in ∼30% of dedifferentiated liposarcomas (DDLPS). It was hypothesized that c-Jun overexpression might directly impair adipogenesis, thereby mediating the transition from well differentiated liposarcomas (WDLPS) to DDLPS. However, recent work from our lab has suggested that c-Jun may regulate other cellular processes in DDLPS, including proliferation. We are currently elucidating the precise mechanisms by which c-Jun amplification drives tumorigenesis in DDLPS. Methods We used lentiviral-mediated RNA interference to inhibit c-Jun in two DDLPS cell lines, one with c-Jun amplification and overexpression (LP6) and one with normal c-Jun copy number (LPS141). We then analyzed changes in mRNA levels by Affymetrix Exon array and changes in miRNA levels via Nanostring. Ingenuity Pathways (IPA) was used to screen the results for biological trends. We validated changes in gene expression via qRT-PCR and immunoblotting. Results: Analysis of 754 microRNAs revealed that 85 (11%) miRNAs exhibited a >2 fold decrease, and 23 (3%) exhibited >2 fold increase after c-Jun knockdown in LP6 cells. mRNA analysis showed that 116 genes were downregulated and 12 genes were upregulated >2 fold after c-Jun knockdown in LP6 cells. In LPS141 cells, 341 genes were downregulated and 57 upregulated. We identified only 10 common differentially expressed genes between these 2 cell lines, suggesting that c-Jun may acquire additional functions when genomically amplified. Pathway analysis showed that c-Jun promotes cell proliferation in both cell lines. However, genes involved in “cellular movement and connective tissue development” were significantly downregulated by c-Jun knockdown only in LP6 cells. We have validated these gene expression changes and are testing the hypothesis that c-Jun amplification promotes cell migration in DDLPS. Discussion: Liposarcomas exhibit nearly universal genomic amplification of MDM2 and CDK4, two oncogenes which are readily targeted by small molecules. Transcription factors such as c-Jun are difficult to target directly by small molecule inhibitors. Our studies suggest that amplified c-Jun may regulate genes that stimulate both proliferation and cell migration in DDLPS. We expect that this work will provide a starting point for developing targeted therapies for c-Jun-amplified DDLPS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-270. doi:1538-7445.AM2012-LB-270