The papillary renal cell carcinoma (RCC)-associated (X;1)(p11;q21) translocation fuses the genes PRCC and TFE3 and leads to cancer by an unknown molecular mechanism. We here demonstrate that the mitotic checkpoint protein MAD2B interacts with PRCC. The PRCC-TFE3 fusion protein retains the MAD2B interaction domain, but this interaction is impaired. In addition, we show that two t(X;1)-positive RCC tumor cell lines are defective in their mitotic checkpoint. Transfection of PRCCTFE3, but not the reciprocal product TFE3PRCC, disrupts the mitotic checkpoint in human embryonic kidney cells. Our results suggest a dominant-negative effect of the PRCCTFE3 fusion gene leading to a mitotic checkpoint defect as an early event in papillary RCCs.
Chromosomal translocations often occur as tumor-specific abnormalities, suggesting that the underlying molecular alterations are crucial for tumor development (1, 2). In a subset of renal cell carcinomas (RCCs) with chromophilic histology and a mainly papillary growth pattern, referred to as papillary RCCs, chromosomal translocations involving the Xp11 region, usually t(X;1)(p11;q21), are recurrently encountered (3-11). Positional cloning of the Xp11 breakpoint by us and others revealed that the t(X;1)(p11;q21) translocation results in an in-frame fusion of the transcription factor TFE3 gene on the X-chromosome to the PRCC gene on chromosome 1 (12-14). Consequently, two fusion genes are formed, TFE3PRCC and PRCCTFE3, both of which are expressed in t(X;1)-positive tumor cells (13).TFE3 is a ubiquitously expressed transcription factor characterized by the presence of a basic region followed by helix-loophelix and leucine zipper domains, both of which are needed for dimerization and DNA binding of the transcription factor (15-17). The fusion protein PRCCTFE3 retains all these domains. PRCC is also ubiquitously expressed and characterized by a relatively high proline content. We have shown that the Nterminal 156 amino acids of PRCC, when fused to TFE3, significantly elevate the transactivating capacity of this fusion protein as compared with wild-type TFE3 (18). Moreover, transfection studies with conditionally immortalized mouse renal proximal epithelial cells, from which chromophilic tumors are thought to arise, showed that PRCCTFE3 could bypass temperature-induced growth arrest and differentiation (19). On the basis of the limited functional information available, we chose to further characterize PRCC via the identification of interacting proteins through yeast two-hybrid screening. This resulted in the identification of MAD2B, member of a family of genes involved in processes of mitotic checkpoint control mechanisms (20-22). Our results indicate that PRCCTFE3 expression may contribute to RCC development through a mechanism that affects the PRCC-MAD2B interaction.
Materials and MethodsYeast Two-Hybrid Analysis. Yeast two-hybrid analysis and filter lift assays were basically performed as described by the manufacturer (Stratagene). In short, yeast cells (pJ69-4A), kindly provided by Phi...