Carney complex (CNC) is an autosomal dominant multiple neoplasia syndrome featuring cardiac, endocrine, cutaneous and neural tumours, as well as a variety of pigmented lesions of the skin and mucosa. Pituitary GH-secreting tumours are found in approximately 10% of patients with CNC. One of the genes responsible for CNC, the PRKAR1A gene, located on human chromosome 17q22-24, has recently been cloned. This represents a putative tumour suppressor gene, coding for the type 1alpha regulatory subunit of PKA, which is found to be mutated in approximately half of the patients with CNC. However, it is currently unclear as to whether similar mutations occur in sporadic pituitary tumours. We have therefore investigated a series of GH-secreting and other pituitary tumours for sequence abnormalities in the PRKAR1A gene. The mRNA produced by the PRKAR1A undergoes decay if it codes for a truncated protein; we therefore also determined PRKAR1A mRNA levels in the tumours, and compared them with known mutant PRKAR1A-carrying lymphocyte samples.
We extracted RNA from a series of pituitary tumours, reverse transcribed it to cDNA, and directly sequenced the PRKAR1A coding-sequence in 44 pituitary tumours. Lymphocyte and tumour tissue RNA from 2 patients with CNC was used as positive controls. Using duplex PCR with the PRKAR1A and the 'housekeeping' gene GAPDH, we determined the relative expression of the PRKAR1A gene in the unknown as well as in the positive control samples.
No mutations were found in any of the exons sequenced. Relative mRNA expression was not decreased in any of the sporadic pituitary tumour samples while decreased RNA expression was seen in cell lines derived from CNC1 patients, which could be restored by an RNA degradation inhibitor while cells derived from a pituitary tumour from a CNC1 patient showed grossly diminished amount of PRKAR1A mRNA. The present data thus do not suggest a major role for the PRKAR1A tumour suppressor gene in sporadic GH-secreting or other pituitary tumours.
24 - 26 Mar 2003
British Endocrine Societies