Archipelago/hCdc4/Fbw7 is the F-box protein specific for recognising and binding phosphorylated cyclin E and targeting it for ubiquitination. Mutations in Archipelago that prevent it from binding to phoshorylated cyclin E have been described in various human cancers including breast, ovarian and endometrial tumours. Previous studies have suggested that cyclin E is over-expressed in corticotroph tumours and other pituitary adenoma subtypes, and we postulated that this may be secondary to Archipelago under-expression, allowing cyclin E to accumulate. Therefore, RQ-PCR was used to investigate the mRNA expression of the two main transcript variants of Archipelago: AGO1 and AGO2 in 68 pituitary tumours (14 ACTH-secreting, 1 silent corticotroph, 13 GH-secreting, 27 non-functioning pituitary adenomas (NFPAs), 10 prolactin (PRL)-secreting, 2 FSH-secreting and one TSH-secreting tumour), as well as 13 normal pituitary samples. In addition, direct sequencing of the entire coding region of AGO1 and AGO2 was performed on 6 NFPAs, 6 GH-secreting, 3 PRL-secreting, and 11 ACTH-secreting tumours. RQ-PCR for both variants was also performed on normal human tissue from 25 other organ sites and a human lymphocyte cell line.
AGO1 was significantly over-expressed in ACTH-secreting (P=0.008), GH-secreting tumours (P=0.0016), and NFPAs (P=0.001) compared to normal pituitary. AGO2 was significantly over-expressed in GH-secreting (P=0.03), PRL-secreting tumours (P=0.03) and NFPAs (P=0.0006) compared to normal pituitary. No mutations of AGO1 or AGO 2 were found in any of the adenomas studied.
AGO1 and AGO2 mRNA have a widespread tissue distribution, and in most tissues except pituitary, adrenal and adipose tissue AGO1 appears to be the predominant transcript.
In summary, Archipelago mRNA is over-expressed in most pituitary tumours and no mutations were identified. We suggest this change is likely to be compensatory for the elevated cyclin E apparent in these tumours, and that there is no evidence, at the level of mRNA, for changes in Archipelago to be responsible for the elevated cyclin E levels seen in some pituitary tumours.
22 - 24 Mar 2004
British Endocrine Societies