Sporadic pituitary tumours are generally benign tumours in which the none of the oncogenes or tumour suppressor genes classically mutated in other cancers are commonly mutated, nor are there frequent changes in genes associated with genetic endocrine neoplasia syndromes. Such tumours are associated with excessive but not completely unregulated proliferation, implicating a possible abnormality in a cell signalling pathway in their pathogenesis. Recently, the serine/threonine kinase BRAF, which is interpolated between the tyrosine kinase receptor, Ras and the MAPK system, has been shown to function as an oncogene in the majority of sporadic melanomas, and in a significant minority of thyroid papillary carcinomas, when mutated at position V599E in exon 15. We therefore investigated BRAF expression and the possible presence of the V599E mutation in sporadic pituitary tumours.
Thirty-seven pituitary tumours of varying types were assessed for the presence of the V599E mutation in reverse-transcribed mRNA, using direct sequencing of the PCR-derived product including the 599 position, by conventional methodology. We also assessed 3 positive 'controls' (melanomas) known to be heterozygous for this mutation. We then carried out an analysis of the quantitative expression of the BRAF transcript using 'real-time' PCR on 10 normal autopsy pituitaries and 27 pituitary adenomas
The 3 control melanoma samples were confirmed to be V599E mutation-positive, but we were unable to demonstrate a mutation in any of the 37 pituitary tumours. BRAF expression was significantly increased in the pituitary adenoma samples compared to the normal pituitaries (P<0.034): subtype analysis showed that this was principally due to marked over-expression in the non-functioning pituitary adenomas (NFPAs).
We conclude that mutations of BRAF are not a common finding in pituitary adenomas, but that BRAF mRNA is significantly over-expressed in pituitary adenomas, especially in NFPAs. Thus, a number of potentially oncogenic pathways are over-expressed in pituitary tumours.
04 - 06 Apr 2005
British Endocrine Societies