Submitted on July 14, 2008
Revised on September 6, 2008
Accepted on September 15, 2008
Differential expression of the regulated catecholamine secretory pathway in different hereditary forms of pheochromocytoma
Graeme Eisenhofer1*, Thanh-Truc Huynh2, Abdel Elkahloun3, John C Morris4, Gennady Bratslavsky4, W. Marston Linehan5, Zhengping Zhuang6, Brian M. Balgley7, Cheng S. Lee8, Massimo Mannelli, JW Lenders9, Stefan Bornstein10, and Karel Pacak4
1 University Hospital Carl Gustav Carus
2 National Institute of Child Health and Human Development
3 National Human Genome Research Institute
4 National Cancer Institute
5 Center for Cancer Resch NIC, NIH
6 NINDS, NIH
7 Calibrant Biosystems
8 University of Maryland
9 St. Radboud University Hospital
10 Medical Clinic III, University Clinic of Dresden
* To whom correspondence should be addressed. E-mail: Graeme.Eisenhofer{at}uniklinikum-dresden.de.
Pheochromocytomas in patients with von Hippel-Lindau (VHL) syndrome and multiple endocrine neoplasia type 2 (MEN 2) differ in the types and amounts of catecholamines produced and the resulting signs and symptoms. We hypothesized the presence of different processes of catecholamine release reflecting differential expression of components of the regulated secretory pathway amongst the two types of hereditary tumors. Differences in catecholamine secretion from tumors in patients with VHL syndrome (n=47) and MEN 2 (n=32) were examined using measurements of catecholamines in tumor tissue, urine and plasma, the latter under baseline conditions in all subjects and in a subgroup of patients who received intravenous glucagon to provoke catecholamine release. Microarray and proteomics analyses, quantitative PCR, and Western blotting were used to assess expression of tumor tissue secretory pathway components. The rate constant for baseline catecholamine secretion was 20-fold higher in VHL than in MEN 2 tumors (0.359±0.094 versus 0.018±0.009 day-1), but catecholamine release was only responsive to glucagon in MEN 2 tumors. Compared to tumors from MEN 2 patients, those from VHL patients were characterized by reduced expression of numerous components of the regulated secretory pathway (e.g., SNAP25, syntaxin, rabphilin 3A, annexin A7, calcium-dependent secretion activator). The mutation-dependent differences in expression of secretory pathway components indicate a more mature regulated secretory pathway in MEN 2 than VHL tumors. These data provide a unique mechanistic link to explain how variations in the molecular machinery governing exocytosis may contribute to clinical differences in the secretion of neurotransmitters or hormones and the subsequent presentation of a disease.
