Using mouse xenograft models, we found that the co-overexpression of MDM2 and CDK4 in 5H cells with five additional oncogenic mutations can cause proliferative sarcoma with a DDLPS-like morphology in vivo.
In the present study, we report that CDK4 is highly expressed in human synovial sarcoma, and high CDK4 expressions are associated with poor prognosis in sarcomas patients and the clinical stage and the TNM grade in synovial sarcoma patients.
Our results also indicate that the increase in sarcoma incidence in Polμ<sup>-/-</sup>P53<sup>-/-</sup> mice could be associated with Cdk4 and Kub3 amplification and overexpression.
We compared sensitivity and specificity of p16 IHC to MDM2 and CDK4 IHC in the differential diagnosis of ALT-WDLPS (n=19) versus benign adipocytic tumors (n=44) and DDLPS (n=18) versus mimicking sarcomas (n=20).
Gene silencing of <i>CIC-DUX4</i> as well as <i>Ccnd2, Ret</i>, and <i>Bcl2</i> effectively inhibited CDS tumor growth <i>in vitro</i> The CDK4/6 inhibitor palbociclib and the soft tissue sarcoma drug trabectedin also blocked the growth of mouse CDS.
Palbociclib is also active in vivo against sarcomas displaying high levels of CDK4 but not against sarcomas displaying low levels of CDK4 and high levels of p16ink4a.
Genes that are frequently amplified in sarcoma include CDK4, YEATS4, HMGA2, MDM2, JUN, DNM3, FLT4, MYCN, MAP3K5, GLI1 and the microRNAs miR-214 and miR-199a2.
Chromosomal enrichment analysis of genes showed a highly significant impact at cytoband 7q22 (chromosome 7) which included mouse double minute (MDM2) and cyclin-dependant kinase (CDK4) as well as other genes associated with human sarcomas.
In conclusion, MDM2 and CDK4 immunostainings, which correlate with gene amplification, are helpful adjuncts to differentiate ALT-WDLPS from benign adipose tumors and to separate DDLPS from poorly differentiated sarcomas.
The three cases in which CGH showed gains in the 12q region were studied specifically for amplifications of MDM2 and CDK4, two genes that have been shown to be amplified in other soft tissue sarcomas.
Overexpression and amplification of several genes (MDM2, CDK4 and SAS) located on chromosome 12q13-15 have been noted to occur in various human sarcomas.
The region q13-15 of chromosome 12 frequently is altered in human sarcomas, and several genes, such as SAS, CDK4, and MDM2, have been found to be amplified in bone and soft tissue sarcomas.
Amplification of the cyclin-dependent kinase 4 (CDK4) gene, located at 12q13-q14, has been found as an alternative genetic alteration to CDKN2A inactivation in various human tumors including malignant gliomas and sarcomas.
However, alterations in other components of the pRh/p16INK4A/ CDK4/cyclin D1/E2F pathway have been proven crucial for tumourigenesis in human sarcomas.
Our results suggest that: (a) alteration of the p16 gene is infrequent in primary soft-tissue sarcoma; (b) Cdk4 may act as an oncogene in soft-tissue sarcoma; and (c) elevated p16 and RB levels might be the result of compensatory up-regulation of these proteins to counteract CDK4 overexpression in these tumors.
However, CGH analysis detected amplification of 12q14 also in some tumors where neither MDM2 nor CDK4 was amplified, suggesting that another as yet unknown gene(s) may drive amplification of this region in sarcomas.