In order to investigate the substrate specificity for ribonucleases (R se) in cervical cancer, activities of acid, neutral and alkaline RNases were determined using RNA or polyribonucleotides as the substrate in extracts of cervical cancer tissue and serum of patients with cervical cancer. Also studied were effects of DNA on the activity of the acid RNase measured with a variety of substrates so as to elucidate the mechanism by which acid RNase activity in cervical cancer tissues wase regulated by nucleic acids.
1) The acid RNase in cervical cancer tissues exhibited the greatest activity against RNA or polyuridylate (poly U) and the least activity was observed against purine polyribonucleotides,, polyadenylate (poly A) or polyguanylate (poly G). These results indicate that acid RNase in cervical cancer tissues is mainly composed of the type I RNase classified according to Neuwelt and preferentially hydrolyzes the uridine internucleotide linkages.
2) Degradation of RNA by the extracts from cervical cancer tissues at both neutral and alkaline pH appeared to be catalyzed by the same enzyme, since the substrate specificities for RNase activities determined at the two pH media were observed to be. very similar with each other. The RNase activity measured at the two pH media was highly active against polycytidylate (poly C), indicating that neutral and alkaline RNases in cervical cancer tissues fall mostly into the type II RNase and show greater affinity to the cytidine internucleotide linkages.
3) The acid DNase activity in cervical cancer tissues was inhibited by poly G to greater extent and by poly A or RNA to lesser extent. The acid DNase activity was, however, not changed at. all in the presence of poly C and was even activated by poly U. These results suggested that the acid DNase activity in cervical cancer tissues was regulated not only by the amount of RNA present, but also by the nature of RNA.
4) Activities of RNase measured at acidic, neutral and alkaline pH in serum of patients with cervical cancer exhibited the greatest activity against poly C and the least- activity against poly A or poly G. These results indicated that, in the serum of patients with cervical cancer, the type l[ RNase predominated over the type j RNase and that the RNase in the cancer serum showed greater affinity to the cytidine internucleotide linkages.
|