Telomerase activity in thymomas and mammary gland adenocarcinomas induced by polyoma virus in AKR mice

Telomerase is an enzyme that stabilizes telomere lenght in transformed cells and tumors. Its role in tumor development is far from clear. In this paper, a new experimental model to study telomerase activity during tumorigenesis is presented. After infection with Polyoma virus, AKR mice developed thymomas and mammary gland adenocarcinomas. Polyoma antigens were observed by the peroxidase-antiperoxidase technique on tissue sections, and by Western blot on tumor extracts. The TRAP assay was performed to detect telomerase activity. It was not present in normal mammary gland, but it was positive in mammary gland adenocarcinomas. A different pattern was seen in thymic tissues: normal thymus had higher telomerase activity than thymomas. The incubation of thymoma extracts with normal thymus extracts decreased telomerase activity in the latter. These results demonstrate two different patterns of telomerase activity in tumors induced by Polyoma virus, and suggest the presence of telomerase inhibitory factors in thymomas.

Transfer RNA nucleoside composition in 13762 rat adenocarcinoma

Abnormalities in patterns of RNA methylation and in the activities of tRNA methyltransferases are well-documented phenomena. In this study, we focused our attention on tRNA from adenocarcinoma, a 9,10-dimethyl-1,2-benznthracene-induced mammary tumor, because prior evidence has suggested the occurence of an abnormal pattern of tRNA methylation. Chemical postlabeling of tumor vs normal rat liver and mammary gland tRNAs revealed tumor specific differences in the modified nucleoside distribution, i.e., a 5.8-fold increase in tumor n-2-methylguanosine together with a 2.7-,2.8-,2.6-, and 2.8-fold decrease in tumor 1-methyladenosine, dihydrouridine, pseudoridine and 5-methylcytidyne, respectively. Class A tRNAs, a slower gel migrating group of tumor tRNAs, exhibited even lower 1-methyladenosine levels. Most of the remaining nucleosides in class A tRNAs showed molar ratios similar to those found in bulk tumor tRNA. However, N-2-methylguanosine levels class A tRNA are intermediate between bulk tumor tRNA (2.8%) and mammary gland tRNA (0.49%). The only qualitative difference found in tumor tRNA seems to be the absence of inosine usually present in tRNAs from liver and mammary tissues. In spite of its abnormal methylation pattern adenocarcinoma tRNA binds to glucocorticoid receptor protein from mouse AtT-20 cells, generating a 65 tRNA-protein complex, in a fashion similar to that previously described for the endogenous tRNA isolated from the same cells

Effect of hydrocortisone on arginase activity in ICRC mouse mammary tumours in vitro.

Three fold increase of arginase activity was observed in hydrocortisone treated mammary tumour tissue when compared to the untreated tissue in vitro. No change in succinic dehydrogenase activity was observed. It is likely that arginase present in mammary tumour is due to the presence of mammary tumour virus and it is tempting to speculate that the increase in arginase activity by hydrocortisone may be due to sustained viral production in the presence of hydrocortisone.