FREQUENT ALTERATIONS IN GENE-EXPRESSION IN COLON-TUMOR CELLS OF THE MICROSATELLITE MUTATOR PHENOTYPE

Tumors of the microsatellite mutator phenotype (MMP) are characterized by the accumulation of many thousands of somatic mutations in tracts of simple repeated sequences or microsatellites. Using arbitrarily pri med PCR fingerprinting of RNA (RAP-PCR), we have comparatively analyze d the overall gene expression patterns of several colorectal tumor cel l lines with and without the MMP. A reproducible pattern of 30-40 main products was obtained for each fingerprint with a total of about 200 cell transcripts analyzed. Differences in RAP-PCR fingerprints were de tected between these tumor cell lines. Some of these expression polymo rphisms appeared to be specific for tumor cells of the MMP because the y were present in two or more different MMP(+) cell lines but absent i n all MMP(-) cell lines analyzed. We also analyzed RNAs prepared from single cell clones isolated from these tumor cell lines. Reproducible differences in the fingerprints were detected between single cell clon es from each of the cell lines analyzed. Examples of single cell clone -specific fingerprint differences from one of the MMP tumor cell lines were cloned and sequenced. Differential expression of some of these s equences was confirmed by Northern analysis using the cloned fragments as probes. Similar fingerprint alterations were also observed among s ingle cell clones derived from single cell clones from mutator tumor c ell lines, which appeared to exhibit higher clonal variation in gene e xpression compared with MMP(-) cells. The detection of inter- and intr a-tumor alterations in gene expression by unbiased RAP-PCR show that t hese fluctuations occur with high frequency in tumor cells of the MMP. These results indicate that the profound genomic instability of tumor cells of the MMP is also reflected in a high incidence of alterations in their patterns of gene expression.