Functional analysis and clinical application of PHD3 in renal cell carcinoma

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VHL gene-mutant cell lines of renal cell carcinoma(RCC), SMKT-R2 and SMKT-R3 had stable overexpression of PHD3. In Caki-1, a VHL-wild type RCC cell line, PHD3 expression was induced in the non-confluent state. In Caki-1, in the nonconfluent state, the PI3K/Akt/mTOR pathway was activated, and inhibition of the pathway with LY294002 reduced PHD3 expression. Even in HIF-la/2a double-knockdown Caki-1, activation of the PI3k/Akt/mTOR pathway induced overexpression of PHD3. In addition, PHD3 siRNA promoted cell proliferation compared with control siRNA in Caki-1 without induction of HIF protein expression. Even in VHL-mutant SMKT-R2 and SMKT-R3, PHD3 siRNA showed the same effect. On the other hand, PHD3-expressing plasmid transfection into ACHN, a RCC cell line with no expression of PHD3 under normoxia, reduced cell proliferation compared with empty vector transfection.In 22 patients with RCC, preoperative serum anti-PHD3 Ab titers were significantly higher in RCC patients than in healthy volunteers. Both pre-and postoperative serum samples were obtained from 17 patients at least 1 month after tumor removal. In all 17 patients, titers of serum anti-PHD3 were decreased after the surgical resection compared with those before operation. The result suggests that the anti-PHD3 Ab may be a novel serological marker for RCC, and the titer may reflect the tumor burden in each individual.