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Pheochromocytoma exhibit genetic instabilities of E-cadherin but not Adenomatous polyposis coli tumor suppressor gene

Pheochromocytomas are neuroendocrine tumors that produce catecholamines and originate from chromaffin cells, derived from neural crest. They are mostly located in the adrenal medulla, but also in ganglia of the sympathetic nervous system. Pheochromocytomas may be either sporadic or manifestation of a familial cancer syndrome. In the present study involvement of two tumor suppressor genes was investigated in human pheochromocytoma. Both genes: adenomatous polyposis coli, (APC) and E-cadherin (CDH1) are components of adherens junctions, but are also key molecules of the wnt signal transduction pathway. Our interest in elucidating the role of APC gene stemmed principally from the findings that wild type APC protein is highly expressed in the nervous system and is critically involved in neuronal differentiation (Dobashi Y et al, Biochem Biophys Res Commun, 2000, 279 ; 685-91). Fifteen sporadic pheochromocytomas together with corresponding normal tissues were tested for APC gene instability by PCR/loss of heterozygosity (LOH) using Restriction Fragment Length Polymorphism method. Prior to DNA extraction the pheochromocytoma samples were microdissected by a pathologist. The results of our analysis showed one allelic imbalance of the APC gene out of 11 heterozygous patients. The instability was confirmed on a high-resolution polyacrylamide gel/stained with silver. When we failed to detect frequent changes of APC gene, we broadened our investigation to another tumor suppressor gene, E-cadherin. CDH1 genetic changes were analyzed using PCR amplification of D16S752 marker (informativeness 91%, Pecina-Slaus N et al., Coll Antropol, 2002, 26 ; 85-8) linked to CDH1 gene. By Spreadex gel electrophoresis (Elchrom Scientific, Switzerland) one allelic imbalance of the CDH1 gene out of 13 heterozygous patients was discovered. Moreover, our marker revealed another type of genomic instability, characteristic of tumor cells (Ionov Y et al., Nature 1993, 363 ; 558-61) - replication error positive samples (RER+). Four out of 13 heterozygous samples were RER positive (30.8%). One of the target molecules in the wnt signalling cascade is the c-myc oncogene. We decided to test the level of c-myc protein expression immunohistochemistry. Six samples out of 7 available for IHC analysis, showed increased levels of myc protein in comparison to normal adrenal tissue. Our results suggest that alterations of E-cadhein gene may have a role in pheochromocytoma development and progression. Increased expression of c-myc oncogene, as well as allelic imbalance of APC gene, suggest that wnt pathway has a role in this neoplasm. Detected microsatellite genetic instabilities of the E-cadherin gene indicate that mismatch repair may also be targeted in pheochromocytoma.

pheochromocytoma; E-cadherin; adenomatous polyposis coli

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