Ribonuclease has been known to be involved in processes of carcinogenesis and cancer suppression. The present study was to isolate and purify the RNase isozymes in the adenocarcinoma tissue of lung and to investigate the property of isozyme V activated and exhibiting secretory nature of the enzyme in the cancer tissue. Also studied was effect of RNase inhibitor and polynucleotides on the isozyme to investigate how the isozyme was regulated in the cancer tissue.
RNase activity was unchanged, but RNase inhibitor activity was significantly increased in the adenocarcinoma tissue of the lung, showing increase in inhibitor/RNase ratio. This indicates that both RNase inhibitor activity and ratio of inhibitor/RNase activity could be used as biochemical markers for the adenocarcinoma of the lung. RNases in the cancer tissue was isolated by a DEAE-cellulose column chromatography into 7 ioszymes, of which three isozymes(isozyme Ⅰ, Ⅵ and Ⅶ) were not found in the control lung tissue and one isozyme (isozyme Ⅴ) was greatly increased in the activity. The results indicated that RNase isozymes Ⅰ, Ⅵ and Ⅶ were specific to the lung cancer and the isozyme Ⅴ was activated in the cancer tissue. Activity of RNase inhibitor complexed with the isozyme Ⅴ activated was increased and ratio of inhibitor/RNase was also increased. The ratio of RNA/poly C for the RNase isozyme Ⅴ was far less than 1.0 exhibiting strong secretory nature of the enzyme.
The RNase isozyme Ⅴ isolated from the adenocarcinoma tissue of lung was further isolated and purified by HPLC. The purified RNase isozyme Ⅴ (Ⅴ-4) was active toward poly C and far less active toward purine polyribonucleotides and RNA. The purified isozyme was highly active toward poly ACU and AC and substrate specificity toward these two heteropolyribonucleotides appeared to be different from that of control lung tissue. The RNase isozyme Ⅴ (Ⅴ-4) isolated from the lung cancer tissue was inhibited by nucleic acids and polynucleotides, the degree of inhibition being different from one polynucletide to other.
The results indicated that RNase isozyme Ⅴ (Ⅴ-4) was activated in the adenocarcinoma tissue of the lung, exhibited strong secretory nature of the enzyme and was regulated not only by protein inhibitor, RNase inhibitor but also base sequence of polynucleotides.
Substrate specificity for the RNase isozyme Ⅴ (Ⅴ-4) appeared to be different from that of control lung tissue, suggesting that the isozyme might be sepcific to the adenocarcinoma of the lung and that the isozyme might play a role in carcinogenesis and cancer suppression of the lung.
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