MOLECULAR SCREENING FOR SOMATIC MUTATIONS IN CORTICOTROPIC ADENOMAS OF DOGS WITH PITUITARY-DEPENDENT HYPERADRENOCORTICISM

Pituitary tumorigenesis is now generally regarded as a multistep proce ss of genomic damage leading to uncoupling of interdependent systems t hat control cell proliferation and differentiation. The alterations in clude mutations in genes encoding for proteins involved in signal tran sduction pathways, such as G-proteins and the p21 protein encoded for by the ras genes. Apart from their excessive secretion of ACTH, cortic otropic adenomas are characterized by decreased sensitivity to inhibit ion by glucocorticoids. Therefore, mutations in the glucocorticoid rec eptor leading to decreased sensitivity to glucocorticoids may contribu te to corticotropic tumor formation. In this study, 16 corticotropic a denomas of dogs with pituitary-dependent hyperadrenocorticism were scr eened for mutations in the Gs alpha, H-, K-, N-ras genes and the codin g region of the DNA-binding domain of the glucocorticoid receptor. The cDNA fragment of the Gs alpha gene encompassed codons 159-240. The K- , and N-ras fragments spanned codons 1-71, The H-ras gene was only scr eened for mutations in codons 12/13 by direct sequencing of the PCR pr oduct. The cDNA fragment of the DNA-binding domain of the glucocortico id receptor encompassed codons 410-500. The Gs alpha, K-ras, N-ras gen es and the DNA-binding domain of the glucocorticoid receptor were scre ened by single-strand conformation polymorphism analysis. No mutations were found in the Gs alpha gene, the ras genes and the DNA-binding do main of the glucocorticoid receptor. It is concluded that mutations in the Gs alpha gene (codons 159-240), the K- and N-ras genes (codons 1- 71), the H-ras gene (codons 12/13) and mutations in the DNA-binding do main of the glucocorticoid receptor do not play a role in the tumorige nesis of canine corticotropic adenomas. (C) 1997, Editrice Kurtis.