Multiple Effects on Drug-Sensitivity, Genome Stability and Malignant Potential by Combinations of H-Ras, C-Myc and Mutant P53 Gene Overexpression

Huang, Ap; Jin, Hn; Wr, Taylor; Ja, Wright

doi:10.3892/ijo.7.1.57

Cited by 1 publication

(1 citation statement)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The RMP-6 mouse 10T1͞2 line, which has been transfected with a combination of activated H-ras, c-myc, and a mutated oncogenic form of p53, has been well characterized (26,32) and was used in these studies. Unlike the above R1 overexpressing cell lines studied, RMP͞mR1 cells (Table 1) did not show changes in tumorigenicity when compared with control RMP͞SHD cells (Table 2).…”

Section: Resultsmentioning

confidence: 99%

The R1 component of mammalian ribonucleotide reductase has malignancy-suppressing activity as demonstrated by gene transfer experiments

Fan

Huang

Villegas

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Our recent studies have shown that deregulated expression of R2, the rate-limiting component of ribonucleotide reductase, enhances transformation and malignant potential by cooperating with activated oncogenes. We now demonstrate that the R1 component of ribonucleotide reductase has tumor-suppressing activity. Stable expression of a biologically active ectopic R1 in ras-transformed mouse fibroblast 10T 1 ⁄2 cell lines, with or without R2 overexpression, led to significantly reduced colony-forming efficiency in soft agar. The decreased anchorage independence was accompanied by markedly suppressed malignant potential in vivo. In three ras-transformed cell lines, R1 overexpression resulted in abrogation or marked suppression of tumorigenicity. In addition, the ability to form lung metastases by cells overexpressing R1 was reduced by >85%. Metastasis suppressing activity also was observed in the highly malignant mouse 10T 1 ⁄2 derived RMP-6 cell line, which was transformed by a combination of oncogenic ras, myc, and mutant p53. Furthermore, in support of the above observations with the R1 overexpressing cells, NIH 3T3 cells cotransfected with an R1 antisense sequence and oncogenic ras showed significantly increased anchorage independence as compared with control ras-transfected cells. Finally, characteristics of reduced malignant potential also were demonstrated with R1 overexpressing human colon carcinoma cells. Taken together, these results indicate that the two components of ribonucleotide reductase both are unique malignancy determinants playing opposing roles in its regulation, that there is a novel control point important in mechanisms of malignancy, which involves a balance in the levels of R1 and R2 expression, and that alterations in this balance can significantly modify transformation, tumorigenicity, and metastatic potential.Ribonucleotide reductase is the only enzyme in the cell that is responsible for converting ribonucleotides into deoxyribonucleotides, the eventual substrates for DNA polymerase (1-3). In mammalian cells, this enzyme contains two dissimilar protein components, called R1 and R2, which are encoded by two different genes located on different chromosomes (4). Protein R1 is a homodimeric structure, with a molecular mass of 168 kDa, and has substrate sites and allosteric effector sites that control enzyme activity and substrate specificity (3, 5). Protein R2 is a homodimer, with a molecular mass of 88 kDa, and forms two equivalent dinuclear iron centers that stabilize a tyrosyl free radical required for the initiation of electron transformation during catalysis (5, 6). R1 and R2 proteins interact at their C-terminal ends to form an active holoenzyme (5, 7).Expression of ribonucleotide reductase is highly regulated (3,5,8). Nonproliferating cells do not contain ribonucleotide reductase activity. In proliferating cells the R2 protein is found primarily in S phase of the cell cycle (9). Although the R1 protein can be detected throughout the cell cycle, synthesis of R1 mRNA, like R2 mRNA...

show abstract

Section: Resultsmentioning

confidence: 99%