Modification in the inherent mode of allelic replication in lymphocytes ofpatients suffering from renal cell carcinoma: A novel genetic alteration associated with malignancy

Using fluorescence in situ hybridization (FISH) to interphase nuclei, we ex amined the replication timing of I allele relative to its counterpart in PH A-stimulated peripheral blood lymphocytes of normal subjects and patients s uffering from a solid tumor (renal cell carcinoma). In the FISH assay, an u nreplicated DNA sequence is identified by a single dot-like hybridization s ignal, whereas a replicated region gives rise to a duplicated, bipartite si gnal. Accordingly, lymphocytes of normal individuals show 2 patterns of all elic replication: (i) synchronized replication of allelic counterparts, as exemplified by the biallelically expressed loci TP53 and D21S55; and (ii) n on-synchronized replication of allelic partners, as exemplified by the earl y and late replicating alleles of GABRB3, an imprinted locus subjected to m onoallelic expression. However, when present in lymphocytes of the cancer p atients, all 3 loci change their replication mode: alleles of TP53 and D21S 55 become asynchronous, whereas the early replicating allele of GABRB3 dela ys replication, leading to relaxation in the imprinted mode of replication. Based on the tight relationship between temporal order of allelic replicat ion and allelic mode of expression, the modified order of allelic replicati on observed in nonmalignant cells of individuals diagnosed with cancer repr esents a novel genetic alteration associated with malignancy. This alterati on detected by simple cytogenetic means, applied to peripheral blood lympho cytes, offers a potential test for cancer identification. (C) 2000 Wiley-Li ss, Inc.