Endocrine Abstracts (2002) 3 P120

Expression of the F-box protein Skp-2 in normal and tumorous human pituitary

M Musat1,2, M Korbonits1, M Pyle1, M Gueorguiev1, M Powell1, C Dumitrache2, C Poiana2 & AB Grossman1

1Department of Endocrinology, St Bartholomew's and the Royal London School of Medicine and Dentistry,London,UK; 2Department of Endocrinology I, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania.

Disruption of the normal cell cycle is one of the most frequent alterations in tumour cells, contributing to uncontrolled cell proliferation during tumour development. The CDK inhibitor p27 plays a pivotal role in controlling cell proliferation during development and tumourigenesis, and has been implicated in tumorigenesis in rats. Previous studies have demonstrated changes in p27 protein expression, in human pituitary tumours,especially in corticotroph tumours, where p27 protein(but not RNA)expression is particulary low. It seems probable that the fall in p27 is due to increased degradation through the ubiquitin-proteasome pathway. Skp2 (S-phase kinase-interacting protein) is a specific F-box protein that allows the recognition and binding of phosphorylated p27 to the ubiquitin complex. There are recent reports that Skp2 is oncogenic and over-expressed in colorectal cancers and oral epithelial carcinomas, and it has been suggested that the destabilization of p27 observed in many types of aggressive human cancers is due to a corresponding increase in the levels of Skp2. The aim of our study was to investigate the possible role of Skp2 in pituitary tumourigenesis, and correlations with our previous data on p27.

A total of 59 human pituitary samples, 7 normal and 52 adenomas, and a further 24 non-pituitary tissues, were assessed for transcriptional expression of Skp2; 41 pituitary samples were assessed for protein expression. Gene expression was determined by PCR and the sequence of the PCR product was confirmed by direct sequencing. 'Real-time' RT-PCR was then performed for relative quantification of the Skp2 transcript, using a TaqMan Gold assay. Immunostaining was performed using mouse monoclonal anti-Skp2 antibody. Skp2 mRNA and protein was detectable in every sample studied. Our results showed no significant difference between the different pituitary tumours and normal pituitary tissue in Skp2 transcript quantification, and no significant increase in nuclear immunohistochemical staining. Our data suggest that increased p27 degradation through the ubiquitin-proteasome pathway is unlikely to be regulated in pituitary tumours by changes in Skp2 expression.

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