EXPRESSION OF THE WILMS-TUMOR GENE-WT1 IN HUMAN-MALIGNANT MESOTHELIOMA CELL-LINES AND RELATIONSHIP TO PLATELET-DERIVED GROWTH FACTOR-A AND INSULIN-LIKE GROWTH FACTOR-2 EXPRESSION

Mutations in the WTI tumor suppressor gene are known to contribute to the development of Wilms' tumor (WT) and associated gonadal abnormalit ies. WTI is expressed principally in the fetal kidney, developing gona ds, and spleen and also in the mesothelium, which lines the coelomic c avities. These tissues develop from mesenchymal components that have s ubsequently become epithelialized, and it has therefore been proposed that WTI may play a role in this transition of cell types. To test the possible involvement of this gene in malignant mesothelioma, we have first studied its expression in a panel of human normal and malignant mesothelial cell lines. WTI mRNA expression levels varied greatly betw een the cell lines and no specific chromosomal aberration on I1p, whic h could be related to the variation in WTI expression in these cell li nes, was observed. Furthermore, no gross deletions, rearrangements, or functionally inactivating point mutations in the WTI coding region we re identified. All four WTI splice variants were observed at similar l evels in these cell lines. The WTI gene encodes a zinc-finger transcri ption factor and the four protein isoforms are each believed to act as transcriptional repressors of certain growth factor genes. Lack of WT I expression is thus predicted to result in growth stimulation of tumo r cells. Binding of one particular WTI isoform construct to the insuli n-like growth factor 2 (IGF2) and platelet-derived growth factor A (PD GFA) gene promoters has been demonstrated to result in repression of t hese genes in transient transfection studies. Analysis of IGF2 and PDG FA mRNA expression levels compared with WTI mRNA expression levels fai led to demonstrate an inverse correlation in the mesothelial cell line s, which endogenously express these genes. Finally, the putative role of WTI in the transition of cell types was investigated. No obvious co rrelation between WTI expression levels and cell morphology of the mal ignant mesothelial cell lines was evident from this study. Moreover, n o change in WTI expression was observed in normal mesothelial cells wh ich were, by alteration of culture conditions, manipulated to switch f rom the mesenchymal to epithelial morphology. (C) 1995 Wiley-Liss, Inc .