To search for differentially expressed gene products in selected
cancers of endodermal origin, cDNA libraries derived from
mRNA in human
hepatocellular carcinoma and adjacent grossly normal tissue were generated. From these parent libraries, subtracted cDNA libraries of
tumor minus normal and normal minus
tumor tissues were constructed. After screening these subtracted libraries by +/- hybridization, a
cDNA clone that is overexpressed in
hepatocellular carcinoma and encodes the human acidic
ribosomal phosphoprotein P0 (P0) was identified. We then evaluated the expression of this
phosphoprotein P0 in human colon
carcinoma samples. Surgical specimens of primary
tumors and liver
metastases were examined by Northern hybridization of total
RNA with one of 2 32P-labeled P0 probes. The
mRNA level of the P0 was greater in primary colon
carcinoma than in paired adjacent normal colonic epithelium in 36 of 38 cases; the mean
tumor/normal ratio was 2.7 (range, up to 13). The
tumor/normal ratio, when plotted against the Dukes' stage of disease, gave evidence for increasing P0 expression with increasing stage of colon
carcinoma (P = 0.02). In all 8 cases of paired colon
carcinoma metastatic to liver and 2 cases of paired primary
hepatocellular carcinoma, the P0
mRNA level was greater in
tumor than in adjacent normal liver tissue. The mean
tumor/normal ratio was 4.0 (range, up to 11) for the
colon cancers metastatic to liver and 4.2 for the primary
hepatocellular carcinoma samples. These findings support a common increased expression of selected gene products in different
tumors of endodermal origin and suggest that increased P0 expression, in line with certain other
ribosomal proteins, may be associated with human
colorectal cancer progression and
biological aggressiveness.