# Regulation of Erythropoietin Activity in Clear Renal Cell Carcinoma

## TL;DR

This study explores how erythropoietin activity is regulated in clear-cell renal cell carcinoma, finding that low oxygen levels, not VHL mutations, drive EPO/EPOR activation.

## Contribution

The study reveals that hypoxia, not VHL status, primarily regulates EPO/EPOR in ccRCC, challenging prior assumptions.

## Key findings

- EPO and EPOR were significantly decreased in ccRCC without HIF1A expression.
- Hypoxia increased EPOR mRNA in Caki-1 cells but decreased it in 786-O cells under certain conditions.
- JAK2/STAT5A activity was increased only in HIF1A-positive tumors.

## Abstract

Clear-cell renal cell carcinoma (ccRCC) is associated with the mutated von Hippel–Lindau (VHL) gene leading to the activation of hypoxia-inducible factor 1A (HIF1A) and subsequent overexpression of erythropoietin (EPO). We analyzed tumor and healthy tissues from 43 ccRCC patients after radical nephrectomy and cultured 786-O (biallelic VHL inactivation) and Caki-1 (wild-type VHL) cells in normal (21% O2) and low oxygen (3% O2) with 10% and 2% fetal bovine serum (FBS). DNA sequencing, including Sanger sequencing, MLPA and LOH, revealed 27 somatic mutations of VHL in ccRCC. HIF1A protein showed decreased or no expression in tumors compared to healthy tissue, independent of VHL alteration. The 786-O cells showed increased HIF1A protein expression after 48 h under low oxygen and 10% FBS. EPO and erythropoietin receptor (EPOR) were significantly decreased in ccRCC without HIF1A expression. EPO mRNA increased in the 786-O cells at 3% O2 after 48 h, while the Caki-1 cells had low or no EPO expression. Hypoxia increased EPOR mRNA in the Caki-1 cells at 10% FBS, but decreased in the 786-O cells at 2% FBS after 48 h. JAK2/STAT5A activity was increased only in HIF1A-positive tumors. These results suggest that EPO/EPOR activation in ccRCC is mainly driven by low oxygen, not VHL regulation of hypoxia-related responses.