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Evidence against involvement of APC gene changes in pheochromocytoma.

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. Although several molecular studies have examined alterations in oncogenes and tumor suppressor genes in pheochromocytomas, much work is still required to give the final list of genes involved in this malignancy. In the present study involvement of adenomatous polyposis coli, APC gene was investigated in human pheochromocytomas. Our interest in elucidating the role of this 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 blood samples were tested for APC gene instability by polymerase chain reaction/loss of heterozygosity (LOH) using Restriction Fragment Length Polymorphism (RFLP) method. PCR amplification of exon 11 generated a 133 base pair fragment. RFLP of the digested PCR products revealed a Rsa I polymorphic site that is cleaved to 85 and 48 base pair fragments if the restriction site is present, and remains uncleaved if the site is absent. The results of our analysis showed no LOHs in all pheochromocytoma samples investigated when tumor DNA was compared to autologous constitutive DNA. One sample was suspicious of LOH, but when double-checked on a high-resolution polyacrylamide gel/stained with silver, faint bands appeared, demonstrating allelic imbalance in this sample. When we failed to detect changes of the APC gene in our sample, we went on to another tumor suppressor gene that is connected to APC both in adherens junctions, and also in the same signaling pathway. Pilot study using D16S752 marker linked to E-cadherin gene (informativity 91%) revealed another type of genomic instability, replication error (RER). Preliminary results in a small portion of sample (4), show two pheochromocytomas to be RER+. Our results suggest that alterations, in APC gene are not responsible for pheochromocytoma development and progression. Detected microsatellite genetic instability of the E-cadherin gene indicates direction of future studies, since it seems that another cellular mechanism, mismatch repair, is targeted in pheochromocytoma.

pheochromocytoma; APC

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