Myxoid/round cell liposarcomas (MLS/RCLS) are characterized by chromosome translocations that result in formation of FUS-CHOP or EWSR1-CHOP fusion oncogenes. More than 95% of the tumors carry one of these fusion genes. FUS-CHOP transforms 3T3 cells and causes MLS/RCLS-like tumors in transgenic mice. The fusion oncoproteins act as abnormal transcription factors and are believed to induce abnormal expression of growth controlling genes as part of their transforming activities. The aim of this study was to search for recurrent abnormal expression patterns of cell cycle regulating proteins and growth factor receptors. A series of 14 MLS/RCLS, 2 MLS/RCLS derived cell lines and a FUS-CHOP transfected human sarcoma cell line were analyzed using immunohistochemistry, Western blotting, and cDNA microarray based screening. The results revealed a highly abnormal expression pattern of several growth controlling proteins. The G1 cyclins D1 and E and their associated kinases CDK4 and CDK2 were strongly overexpressed in all of the tumors. High expression levels were also found for Cdk4/6 inhibitor P16 and CDK2 inhibitors P27 and P57. The growth factor tyrosine kinase receptors PDGFRB and EGFR were present in most cells of all investigated tumors. We conclude that deregulation of G1 controlling proteins is common in MLS/RCLS and that aberrant expression of these proteins is of importance in the pathogenesis of this tumor type.

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