BAT-26, AN INDICATOR OF THE REPLICATION ERROR PHENOTYPE IN COLORECTALCANCERS AND CELL-LINES

Instability of microsatellites is a hallmark of the DNA replication er ror phenotype (RER+) due to the inactivation of mismatch repair genes, In humans, microsatellite instability has first been described in col orectal tumors developing in either hereditary nonpolyposis colorectal cancer or sporadic patients, Colorectal tumorigenesis in RER+ and RER - tumors is probably due to distinct mechanisms, and RER+ tumors have a better prognosis than RER- tumors, The study of the RER status of a tumor may thus be important in the future to determine biological prog nosis factors and investigate therapeutical strategies, The RER status of 134 primary tumors and 26 cell lines derived from colorectal cance rs was established by PCR amplification and analysis of a minimum of 3 2 microsatellite loci, This characterization allowed us to unambiguous ly classify 35 primary tumors and 7 cell lines as RER+, Typing of a si ngle poly(A) tract, BAT-26, was sufficient to confirm the RER status o f 159 of these 160 tumors and cell lines, Moreover, in DNA from unaffe cted individuals, normal tissues of a subset of the RER+ patients, and all RER- tumors or cell lines, BAT-26 was quasi-monomorphic, showing only minor size variations. BAT-26 alleles showing shortening from 4 t o 15 bp were observed in all but 1 of the RER+ tumors and cell lines, The size difference between the range of normal large alleles and unst able small alleles was sufficient to be detected by electrophoresis on conventional polyacrylamide gels stained with ethidium bromide, We th us propose a simple, low-cost, and rapid method to screen for the RER status of colorectal cancer primary tumors and cell lines, even in the absence of matching normal DNA and, in most cases, without the need f or radioactivity, This method could easily be set up in routine labora tories.