Login to Access Video or Poster Abstract: MP39-15
Sources of Funding: Grant NCI/NIH 5R01CA72821; 5R01CA176691

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. SDCT2 expressed in kidney epithelial cells is a succinate/citrate transporter, however its role has not been examined in any disease. We examined SDCT2 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 SDCT2 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 53 patients (White=21; Hispanic=19; AA=13). VHL+ and VHL- RCC cells were stablely transfected with a SDCT2 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 (5-AZA/TSA) treatment.

Results

SDCT2 was 63- and 100-fold downregulated in low- and high-stage RCC tissues. Q-PCR validation showed 40-fold downregulation of SDCT2 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, SDCT2 expression caused 3-4-fold inhibition of proliferation, cell-cycle, motility in both VHL+ and VHL- cells (P<0.01); only VHL+ cells were inhibited under normoxia. SDCT2 expression induced ROS levels and succinate transport by >3-fold (P<0.01) and activated p16INK4a-RB pathway and apoptosis (caspase-3 and PARP activation). 5-AZA+TSA treatment induced SDCT2 expression by 50-fold (P<0.001).

Conclusions

This is the first study on a functional biomarker in RCC, SDCT2, that is possibly a novel tumor suppressor gene. SDCT2 loss promotes RCC growth, survival and inhibits cellular senescence and its downregulation correlates with metastasis and racial disparity.

Funding

Grant NCI/NIH 5R01CA72821; 5R01CA176691