Overexpression of ribosomal proteins L4 and L5 and the putative alternative elongation factor PTI-1 in the doxorubicin resistant human colon cancer cell line LoVoDxR.

A better understanding of the regulatory network underlying cellular drug resistance and stress response may be helpful to overcome the phenomenon of therapy-induced cross-resistances against a variety of antineoplastic agents. Two new powerful molecular techniques, mRNA differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) and subtractive suppressive hybridisation were applied for the comparative analysis of the gene expression profile of a doxorubicin resistant and its corresponding sensitive parental colon carcinoma cell line (LoVo H67P). DDRT-PCR generated partial cDNAs from the doxorubicin resistant, sensitive and stress (dexamethasone, doxorubicin, cadmium chloride or heat) exposed sensitive cells, were size-separated on polyacrylamide gels. The expression patterns of more than 9000 bands of the resistant, sensitive and stressed sensitive cell populations were identical by more than 95%. Of the differentially expressed mRNAs, 20 cDNA fragments were reamplified after isolation from the gel, used as probes for Northern blot analysis to verify their differential expression and sequenced after cloning. Among the differentially expressed cDNAs, homologies of 96% and 87%, respectively, were found to the human proto-oncogene PTI-1 and the human ribosomal protein L4. Subtractive suppressive hybridisation revealed overexpression of the ribosomal protein L5 in the doxorubicin resistant line. These data point to the control of gene expression at the translational level as an important mechanism involved in cellular stress response.