FREQUENT ALLELIC DELETIONS AND LOSS OF EXPRESSION CHARACTERIZE THE DCC GENE IN MALE GERM-CELL TUMORS

The DCC tumor suppressor gene has been shown to be frequently deleted or its expression reduced or absent in colorectal, gastro-intestinal, pancreatic, prostatic, and breast carcinomas, and glioblastomas. By al lelotype analysis using the DCC-flanking polymorphic marker D18S5 we h ave previously shown that allelic deletions at 18q21 occur in 40% of m ale germ cell tumors (Murty et al., 1994). In order to further underst and the role of DCC gene in germ cell tumorigenesis, we evaluated dele tions by loss of heterozygosity (LOH) and mRNA expression by RT-PCR in tumor tissues and cell lines. Analysis of 61 paired normal-tumor DNAs using the probes D18S5, JOSH 4.4 (a polymorphism within the DCC locus ) and a (CA)(n) polymorphism in an intron of DCC revealed that 45% of GCTs had allelic deletions. In addition, two homozygous deletions were found in the DCC gene among 91 (61 used in the LOH analysis and an ad ditional 30) tumor DNAs when screened with the cDNA probes (pDCC 1,65, pDCC 1.9 and pDCC 1.0). By RT-PCR analysis of four normal testes, nin e GCT cell lines and 14 tumor tissues, DCC gene expression was detecte d in all four normal testes, while four (45%) GCT cell lines and one ( 7%) tumor specimen showed lack of expression. In addition, DCC express ion was highly reduced in three (21%) tumor tissues. The high frequenc y of LOH at 18q21 was characteristic of seminomas as well as all subse ts of non-seminomas in primary as well as metastatic states. Frequent allelic loss in all histologic subsets, homozygous deletions, and loss of expression of DCC suggest that suppression of this gene's function is an early event in GCT development.