Cell cycle dysregulation is one of the defining features of cancer. Cyclin-dependent kinase 4 (CDK4), together with its regulatory subunit cyclin D, governs cell cycle progression through the G1 phase. Cyclin-dependent kinase inhibitors, including p16(INK4A) (encoded by CDKN2A), in turn regulate CDK4. In particular, dysregulation of the p16/CDK4/cyclin D complex has been established in a variety of types of human tumours. Dominant activating mutations affecting codon 24 of the CDK4 gene (replacement of Arg24 by Cys or His) render CDK4 insensitive to p16(INK4) inhibition and are responsible for melanoma susceptibility in some kindreds. However, 'knock-in' mice homozygous for the CDK4(R24C) mutation were noted to develop multiple neoplasia, most commonly including endocrine tumours: pituitary adenomas, insulinomas and Leydig cell testicular tumours. We therefore speculated that sporadic human endocrine tumours might also harbour such mutations. The aim of the current study was to analyze the CDK4 gene for the two characterized activating mutations, R24C and R24H, in sporadic human pituitary adenomas, insulinomas and Leydig cell tumours. We used DNA extracted from 61 pituitary adenomas, and paired tumorous and neighboring normal genomic DNA extracted from 14 insulinoma and 6 Leydig cell tumour samples. Genomic DNA from patients with familial melanoma harbouring the R24C or the R24H mutations served as positive controls. All samples were subjected to PCR, mutation-specific restriction digests and/or sequencing. Both methodologies failed to detect mutations at these two sites in any of the sporadic endocrine tumours including pituitary adenomas, benign or malignant insulinomas or Leydig cell tumours, while the positive controls showed the expected heterozygote patterns. Protein expression of CDK4 was demonstrated by immunohistochemistry and Western blotting in pituitary and pancreatic samples. These data suggest that the changes in the regulatory 'hot-spot' on the CDK4 gene, causing various endocrine tumours in CDK4(R24C/R24C )mice, are not a major factor in sporadic pituitary, insulin beta-cell or Leydig cell tumorigenesis.
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- Author: M Gueorguiev x
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VV Vax, R Bibi, S Diaz-Cano, M Gueorguiev, B Kola, N Borboli, B Bressac-de Paillerets, GJ Walker, Dedov II, AB Grossman, and M Korbonits
ME Pyle, M Korbonits, M Gueorguiev, S Jordan, B Kola, DG Morris, A Meinhardt, MP Powell, FX Claret, Q Zhang, C Metz, R Bucala, and AB Grossman
Macrophage migration inhibitory factor (MIF) is an essential regulator of the macrophage responses to endotoxin. MIF also has the ability to override the anti-inflammatory actions of glucocorticoids during an immune response, and is thus an important pro-inflammatory factor. The presence of MIF in cells of the anterior pituitary has been described, and high levels of MIF in other rapidly proliferating tIssues have also been demonstrated. It has been hypothesised that MIF release from these cells is influenced by the hypothalamo-pituitary-adrenal axis, and that ACTH and MIF are released simultaneously to exert counter-regulatory effects on cortisol. However, another intracellular role for MIF has also been suggested as it has been shown that MIF exerts an effect on the inhibitory cell cycle control protein p27 through an interaction with Jab1, a protein implicated in p27 degradation. We studied MIF expression in different normal and adenomatous human pituitary samples using immunohistochemistry and RT-PCR. There was evidence of co-immunoprecipitation of MIF with Jab1, suggesting an interaction of the two proteins. Our results showed that there is increased expression of MIF protein in the nuclei of all pituitary adenomas compared with normal tIssue (P=0.0067), but there was no statistically significant difference in nuclear MIF expression between the different adenoma types. Nuclear MIF expression correlated positively with p27 and its phosphorylated form in normal tIssue (P=0.0028 and P<0.0001); however, this relationship was not seen in the adenoma samples. Cytoplasmic expression of MIF was found to be variable both in normal and adenomatous samples, with no consistent pattern. MIF mRNA was demonstrated to be present in all tumour and normal samples studied. Somatotroph tumours showed higher MIF mRNA expression compared with normal pituitary or other types of adenomas. In conclusion, MIF is expressed in cell nuclei in pituitary adenomas to a greater extent than in normal pituitary tIssue. We speculate that it may play a role in the control of the cell cycle, but whether its higher level in adenomas is a cause or a consequence of the tumorigenic process remains to be clarified.