INVESTIGATION OF THE RB-1 TUMOR-SUPPRESSOR GENE IN A UNITED-KINGDOM SERIES OF NON-HODGKINS-LYMPHOMAS

We have investigated the RB-1 tumour suppressor genes in a series of 2 0 non-Hodgkin's lymphomas (NHL). Polymerase chain reaction (PCR) ampli fication of polymorphic alleles indicated that there was evidence of a llelic imbalance around 13q14, the site of the RB-1 gene, in at least 5 NHL. Immunohistochemical analysis of the RB-1 protein demonstrated w ide variations in the percentage of cells exhibiting positive staining but these usually correlated with differences in the proliferation in dex as indicated by staining of Ki67. Only 3/35 NHL exhibited signific antly fewer cells expressing RB-1 protein than expressed Ki167. A comp rehensive analysis of the mutation status of RB-1 in 20 NHL was carrie d out using PCR based strategies involving single strand conformationa l polymorphism (SSCP) gels. Most of the protein coding region was stud ied by analysing cDNA derived from its mRNA and the remaining 5'-end o f the coding region investigated by analysing exon I of the gene. We a lso examined the promoter region of the gene. In none of the 20 NHL in vestigated were we able to identify a mutation; the only abnormal migr ating fragment observed proved to be a polymorphism in exon I of the g ene in 5 NHL. In one other case we detected instability at an intron r epeat sequence, which had occurred during progression of the disease, but again no mutation of the protein coding region was found. The low levels of RB-1 protein expression that we had observed in a few of our NHL therefore did not appear to be due to mutation of the gene. These data suggest that mutation of RB-1 is not a common event in the evolu tion of NHL, but that there may be another, as yet unidentified, tumou r suppressor gene near the RB-1 locus which is associated with NHL.