This study was performed in 20 cases of squamous carcinoma of lung and 20 cases of control group. RNase activity was increased significantly in the squamous cell carcinoma tissue of the lung. Proteins in both lung cancer tissue and control lung tissue were isolated by a DEAE-cellulose column chromatography into 8 peaks, of which 5 peak proteins for the lung cancer tissue and 4 peak proteins for the control lung tissue exhibited a significant activity of RNase. RNase activity was markedly increased and RNase inhibitor activity was also increased, RNA/poly C ratio for the RNase activity being higher in the RNase isozyme I fraction isolated in the lung cancer tissue.
A considerable increase in the activity of the RNase isozyme I specific to the squamous cell carcinoma of the lung was observed following the pretreatmet of the lung cancer tissue extract with parahydroxymercurybenzoate(PHMB), showing higher RNA/poly C ratio for the RNase activity. This means that the RNase released from the RNase-inhibitor complex (the inhibitor free RNase) was found mostly in the RNase isoyzm I and that the inhibitor free RNase was more likely nonsecretory type RNase than the free RNase.
The inhibitor free RNase isozyme I isolated from the squanous cell carcinoma tissue of the lung was highly active toward poly C, AC and AU, the activity being decreased toward poly ACU, CIU, CI, CU, U, RNA, AGU in order. Nearly no activity was observed toward poly AG, GU and ACG. Substrate spectificity of the
free RNase isozyme I from the lung cancer tissue was similar in pattern to that of the inhibitor free RNase isozyme I, the activity toward poly U, RNA, poly CU, AG, CIU and ACU was lower in the free RNase isozyme I.
Observations that (1) RNase activity was unchanged, but RNase inhibitor activity was increased in the squamous cell carcinoma tissue of lung, (2) activities of free RNase and inhibitor free RNase in the RNase isozyme I fraction isolated from the lung cancer tissue was markedly increased, (3) the pretreatment of the lung cancer tissue extract with PHMB increased the activity of inhibitor free RNase isozyme I and its RNA/poly C ratio, (4) substrate specificity for the inhibitor free RNase isozyme I appeared to be different from that of the free RNase isozyme I in the lung cancer tissue suggested that the inhibitor free RNase isozyme I isolated from the squamous cell carcinoma tissue was specific to the lung cancer, could be regulated by RNase inhibitor and played an important role in RNA mediated tumorigenesis of the lung cancer.
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