VHL Inactivation Is an Important Pathway for the Development of Sporadic Pancreatic Endocrine Tumors
AM Schmitt, S Schmid, T Rudolph, M Anlauf, G Kloppel, H Moch, PU Heitz, P Komminoth, A Perren. University Hospital Zurich, Zurich, Switzerland; City Hospital Triemli, Zurich, Switzerland; Klinikum Rechts der Isar, Technische Universitt Mnchen, Munich, Germany; University of Kiel, Kiel, Germany
Background: A small subset of familial pancreatic endocrine tumors (PET) arises in patients with von-Hippel-Lindau syndrome. A loss of function of the VHL gene can lead directly to an accumulation of the Hypoxia-Inducible Factor alpha (HIF-1), resulting in the transcription of a series of hypoxia inducible genes such as CA-9 and GLUT-1. Sporadic PET very rarely harbour somatic VHL mutations, but the chromosomal location of the VHL gene is frequently deleted in sporadic PET and a subset of sporadic PET shows active hypoxia signals on mRNA and protein level. The aim of the present study was to correlate epigenetic and genetic VHL alterations to hypoxia signalling in order to identify the frequency of functional VHL inactivation in sporadic PET.
Design: A total of 152 paraffin-embedded sporadic PET were included in the study and used for immunohistochemistry and FISH analysis. Fresh frozen tissue of 37 of these tumors was available for RNA and DNA analyses. VHL gene mutation, VHL deletion as well as promoter methylation analyses were performed. Quantitative RNA expression levels of VHL and CA-9 were studied. The HIF target proteins CA-9 and GLUT-1 were investigated by semiquantitative immunohistochemistry.
Results: VHL mutations were absent in all 37 PET examined. In 14 of 79 cases (18%) VHL deletion by FISH and in 2 of 35 cases (6%) methylation of the VHL promoter region was detected. CA-9 and GLUT-1 protein was expressed in 27% and 30% of the tumors, respectively. Protein expression of the HIF-1 downstream target CA-9 correlated significantly with the expression of CA-9 mRNA (p < 0.05) and VHL loss (p < 0.001). Moreover, CA-9 immunohistochemistry correlated significantly with GLUT-1 immunohistochemistry (p < 0.001).
Conclusions: We conclude that VHL gene inactivation by promoter methylation and VHL hemizygous deletion in nearly 25% of PET leads to an activation of the HIF-pathway. Our data suggest that VHL inactivation is an important mechanism for the development of a subset of sporadic PET.
Tuesday, March 10, 2009 8:15 AM
Platform Session: Section H1, Tuesday Morning