OVER-EXPRESSION OF THE S13 RIBOSOMAL-PROTEIN IN ACTIVELY GROWING CELLS

In order to define biological markers of aggressiveness, 2 rat colon-c arcinoma cell lines differing by their tumorigenicity were used to clo ne genes over-expressed in colon carcinoma as compared with normal epi thelial cells. A progressive rat colon-carcinoma clone (PROb) cDNA lib rary was hybridized with 32P-cDNA synthesized from mRNA prepared from these PROb cells, or from regressive cells (REGb) derived from the sam e tumor. Several clones were isolated after the initial screening. The specificity of each clone was confirmed by RNA blotting. One of these (B9) was found to hybridize to an mRNA 30-fold more abundant in PROb cells than in normal adult rat colon, and was therefore selected for f urther study. No gene amplification was detected by Southern blot anal ysis, indicating that the difference in mRNA content was most likely d ue to an increased transcription of this gene. Sequencing of the cDNA revealed approximately 98% homology with the rat S13 ribosomal protein . The expression level of this gene was determined in a series of rat cell lines with different growth rates. A good correlation was found b etween these 2 parameters. Our data suggest that the S13 ribosomal-pro tein gene can be used to evaluate the growth rate of tumor cells, whic h might be correlated with their aggressiveness. In an initial trial e xperiment, S13 ribosomal-protein mRNA was detected in a series of huma n colorectal tumors by in situ hybridization. A strong signal was seen in the 4 tumors analyzed. (C) 1993 Wiley-Liss, Inc.