Introduction: Five-year survival of metastatic renal cell carcinoma (mRCC) patients is < 10% and African American (AA) males have the highest incidence. Identification of the molecular determinants of mRCC and racial disparity in RCC is critical for biomarker development and targeted therapy. NaDC3 expressed in kidney epithelial cells is a succinate/citrate transporter, however its role has not been examined in any disease. We examined NaDC3 expression in normal and RCC tissues and correlated it with clinical outcome and racial disparity. We also evaluated biological functions and molecular signaling regulated by NaDC3 in RCC cells.
Methods: Differential gene expression in the matched normal and RCC tissues (n=6/category) was evaluated by microarray analysis; results were validated by QPCR and immunoblotting in tissues from 83 patients (White=46; Hispanic=24; AA=13). VHL+ and VHL- RCC cells were stably transfected with a NaDC3 construct. Transfectants were characterized for cell proliferation, cell cycle, motility, succinate/citrate transport and reactive oxygen species (ROS) measurement assays under normoxia and hypoxia. SDCT2 induction was evaluated following 5-azacytidine plus Trichostatin A treatment.
Results: NADC3 was 63- and 100-fold downregulated in low- and high-stage RCC tissues. Q-PCR validation showed 40-fold downregulation of NaDC3 in RCC tissues when compared to normal kidney (P < 0.0001). Downregulation was 40-fold in White and Hispanic patients, but 198-fold in AA patients (P=0.0049) and correlated with tumor stage and metastasis (P=0.009). Under hypoxia, NADC3 expression caused 3-4-fold inhibition of proliferation, cell-cycle, motility in both VHL+ and VHL- cells (P3-fold (P <0.001).
Conclusions: This is the first study on a functional biomarker in RCC, NADC3, that is a possible a novel tumor suppressor gene. NADC3 loss promotes RCC growth, survival and inhibits cellular senescence and its downregulation correlates with metastasis and racial disparity.
Source of Funding: 1R01CA227277-01A1 (VBL); Department of Defence -PRCRP (W81XWH1810277 (CA170470; PRCRP)