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.
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