Metastasis-Suppressing Potential of Ribonucleotide Reductase Small Subunit p53R2 in Human Cancer Cells

Abstract

Purpose: Previous gene transfection studies have shown that the accumulation of human ribonucleotide reductase small subunit M2 (hRRM2) enhances cellular transformation, tumorigenesis, and malignancy potential. The latest identified small subunit p53R2 has 80% homology to hRRM2. Here, we investigate the role of p53R2 in cancer invasion and metastasis. Experimental Design: The immunohistochemistry was conducted on a tissue array including 49 primary and 59 metastatic colon adenocarcinoma samples to determine the relationship between p53R2 expression and metastasis. A Matrigel invasive chamber was used to sort the highly invasive cells and to evaluate the invasion potential of p53R2. Results: Univariate and multivariate analyses revealed that p53R2 is negatively related to the metastasis of colon adenocarcinoma samples (odds ratio, 0.23; P < 0.05). The decrease of p53R2 is associated with cell invasion potential, which was observed in both p53 wild-type (KB) and mutant (PC-3 and Mia PaCa-2) cell lines. An increase in p53R2 expression by gene transfection significantly reduced the cellular invasion potential to 54% and 30% in KB and PC-3 cells, respectively, whereas inhibition of p53R2 by short interfering RNA resulted in a 3-fold increase in cell migration. Conclusions: Opposite regulation of hRRM2 and p53R2 in invasion potential might play a critical role in determining the invasion and metastasis phenotype in cancer cells. The expression level of ribonucleotide reductase small subunits may serve as a biomarker to predict the malignancy potential of human cancers in the future.Ribonucleoside diphosphate reductase (RR) plays an essential role in converting ribonucleoside diphosphate to 2 ¶-deoxyribonucleoside diphosphate. In a RR holoenzyme, large a and small h subunits form an a 2 h 2 heterotetramer that is required for RR activity (1). In humans, one large subunit (M1) and two small subunits (hRRM2 and p53R2) of RR have been identified (2). The large subunit M1 (hRRM1) contains substrate and allosteric effector sites that control the RR holoenzyme activity and substrate specificity (3 -5). The RR small subunits form two equivalent dinuclear iron centers that stabilize the tyrosyl free radical required for the initiation of electron transformation during catalysis (3,6). RR is essential as it provides deoxynucleotide triphosphate (dNTP) for DNA synthesis and DNA repair. The expression, subcellular localization, and function of RR are highly regulated (7). Because RR plays a critical role in DNA synthesis, it represents an important target for cancer therapy.Two RR small subunits, p53R2 and hRRM2, have an 80% similarity in protein sequence (2). An in vitro assay showed that recombinant p53R2 protein, as well as hRRM2, interacts with hRRM1 to form a holoenzyme with the ability to convert CDP to dCDP (8, 9). The diiron-dityrosyl radical cluster was identified as the RR activity center, located on the common binding pockets of p53R2 and hRRM2 (10). Using a synthetic heptapeptide to inhibit RR activity, p53R2...

Tumor suppressor FOXO3 regulates ribonucleotide reductase subunit RRM2B and impacts on survival of cancer patients

“…In previous studies, we have extensively investigated the functional and structural regulation of RR subunits including RRM1, RRM2, and RRM2B (also known as p53R2) [2-9]. RRM2B has been demonstrated to be a p53-inducible RR subunit that functions in cell cycle regulation, DNA repair, mitochondrial homeostasis, and the suppression of metastasis [3, 10-14]. Mutation of the RRM2B gene causes severe mitochondrial DNA (mtDNA) depletion, which indicates that RRM2B plays a crucial role in the supply of dNTPs used for mtDNA synthesis [15].…”

p53R2 expression as a prognostic biomarker in early stage non-small cell lung cancer

“…The invasion-suppressing ability of p53R2 was also found in oropharyngeal, prostate, pancreatic and colon cancer cell lines (15,16). In addition, these authors determined that the invasion-suppressing ability of p53R2 was not related to RR enzymatic activity (10). Plao et al concluded that p53R2 negatively modulates serum-induced MEK-ERK activity and inhibits the MEK-ERK-mediated malignancy potential to suppress invasion of human lung cancer cells (8).…”

“…A recent study concluded that the overexpression of RRM2 and p53R2, but not RRM1, in mice specifically induces lung neoplasms (12). p53R2 was also found to contain a malignancy-suppressing activity (10). The role of p53R2 expression in tumor formation has yet to be determined.…”

“…Overexpression of p53R2 is associated with clinical response in myelodysplatic syndrome/ acute myelogenous leukemia (9). It has been suggested that the opposite regulation of hRRM2 and p53R2 in the invasion potential may play a critical role in determining the invasion and metastasis phenotype in cancer cells (10). The implications of p53R2 expression, a regulatory subunit of RR, have yet to be determined and deserve further investigation.…”

Differential Expressions of p53, p53R2, hRRM2 and PBR in Chronic Lymphocytic Leukemia: A Correlation with Intracellular Cholesterol

“…Overexpression of p53R2 is associated with clinical response in myelodysplatic syndrome/acute myelogenous leukemia [25]. It has been suggested that the opposite regulation of hRRM2 and p53R2 in the invasion potential may play a critical role in determining the invasion and metastasis phenotype in cancer cells [26].…”