The c-erbB-2/neu proto-oncogene in human pituitary tumours.

Abstract

The aetiology of most pituitary tumours remains unknown. We have examined the potential role of neu receptor proto-oncogene in human pituitary tumorigenesis. Ten non-tumorous pituitary glands and 16 morphologically characterized functional and clinically non-functioning pituitary adenomas were studied. Protein expression was examined by immunohistochemistry, mRNA expression by RT-PCR and competitive PCR, gene amplification by differential PCR, and point mutations by DNA sequencing. Cytoplasmic positivity for neu was identified in a few scattered cells of the non-tumorous adenohypophysis using an antibody to the intracytoplasmic domain of neu, but no membrane staining was found with an antibody to the extracellular domain; the latter is said to reflect gene amplification. mRNA transcript signals of the expected size were identified in the normal adenohypophysis and in all 16 adenomas examined. No increase in the degree of mRNA expression, however, was noted in the different tumour types compared to normal human pituitary tissue as determined by competitive PCR. As neu can be activated to an oncogene by a point mutation in the transmembrane region, nucleotide substitutions in this domain were investigated. Direct sequencing of codon 659 revealed no point mutations in any of the tumours. Furthermore, since amplification of neu has been noted in various human malignancies, DNA from these tumours was examined by differential PCR. No detectable differences were noted between the neu gene and the single-copy reference gene IFN-gamma. The neu gene is expressed in adenohypophysial cells and their tumours. In pituitary adenomas, this expression is not associated with gene amplification or activating mutations to suggest a direct role in pituitary tumorigenesis.