Abstract
Inactivation of the von Hippel‐Lindau (VHL) tumor‐suppressor gene causes both the familial cancer syndrome VHL disease and corresponding sporadic tumor types, including renal‐cell carcinoma. Subcellular localization of VHL gene products was determined by indirect immunofluorescence. Both native and exogenously expressed VHL proteins displayed a cytoplasmic peri‐nuclear immunostaining pattern, which co‐localized with markers for the endoplasmic reticulum (ER). In addition, subcellular fractionation indicated that both native and exogenously expressed VHL products are found predominantly in the cytosolic compartment. Deletion analyses demonstrated that a 64–amino acid region of VHL (residues 114–177) is responsible for cytosolic as well as ER subcellular localization. Taken together, the immunostaining and biochemical fractionation studies suggest that VHL localizes to the cytosolic face of the ER. The relationship between VHL subcellular localization and VHL‐associated ubiquitination was examined. Chimeric VHL‐green fluorescent protein (GFP) products, which localized to the peri‐nuclear region, were shown to undergo ubiquitination. VHL amino acids 114–177 were necessary and sufficient for this modification. Consistent with a role of VHL in ubiquitination, expression of VHL led to enhanced ubiquitination of cellular proteins, and amino acids 114–177 were also critical for this effect. Therefore, amino acids 114–177 were required for accurate VHL subcellular localization, ubiquitination of VHL‐GFP products and VHL‐dependent increases in cellular ubiquitination. Since mutations in this region of VHL are frequently detected in renal‐cell carcinomas, these results suggest that proper VHL subcellular localization and associated ubiquitination functions may be necessary for VHL‐mediated tumor suppression.