Prof Ashley B Grossman
|Research Area:||Cell and Molecular Biology|
|Keywords:||cushing's disease, adrenal, pituitary, acromegaly, Ghrelin, AMPK, AIP and neuroendocrine tumours|
My original interest lay on uncovering the control and regulatory mechanisms for the hypothalamus and pituitary, and this amongst others established the importance of cytokines and gaseous neurotransmitters in neuroregulation, specifically mediating the neurohormonal consequences of inflammation and infection.
More recently, I have explored the molecular pathogenesis of a variety of different endocrine tumours, including pituitary tumours and especially those responsible for Cushing’s disease, where over several years my group has demonstrated many perturbations of the cell cycle which appear to be secondary to altered trafficking in cytoplasmic signalling pathways, especially the Akt-mTOR and MAPK pathways. However, no specific mutations likely to be pathogenic have been identified to date, and it is most likely that these changes are in turn secondary to membrane-associated defects. With my collaborator Prof. Marta Korbonits we have been exploring the role of the tumour suppressor gene product, AIP, to which is responsible for many cases of familial acromegaly and prolactinomas, to see how this is involved in the process of pituitary tumorigenesis.
In terms of adrenocortical tumours, especially malignant ones, we have shown promoter-methylation dependent changes in several signalling pathways, while studies of neuroendocrine tumours have revealed specific targets for intervention. More recent studies on phaeochromocytomas and paragangliomas have shown how abnormal signalling in such pathways can only be interrupted successfully if several if not all such pathways are interrupted or antagonised simultaneously. My aim has been to translate these molecular findings into novel therapies.
|Prof Rajesh V Thakker||OCDEM||University of Oxford||United Kingdom|
|Prof Marta Korbonits||William Harvey Research Institute, Barts and the London School of Medicine and Dentistry||United Kingdom|
The pathogenesis of tumour formation in the anterior pituitary including adrenocorticotropic hormone (ACTH)-secreting tumours has been intensively studied, but the causative mechanisms involved in pituitary cell transformation and tumourigenesis remain unclear. Hide abstract
Gigantism results when a growth hormone-secreting pituitary adenoma is present before epiphyseal fusion. In 1909, when Harvey Cushing examined the skeleton of an Irish patient who lived from 1761 to 1783, he noted an enlarged pituitary fossa. We extracted DNA from the patient's teeth and identified a germline mutation in the aryl hydrocarbon-interacting protein gene (AIP). Four contemporary Northern Irish families who presented with gigantism, acromegaly, or prolactinoma have the same mutation and haplotype associated with the mutated gene. Using coalescent theory, we infer that these persons share a common ancestor who lived about 57 to 66 generations earlier. Hide abstract
Pituitary adenomas present with a variety of clinical endocrine manifestations and arise in a sporadic setting or rarely as part of hereditary genetic syndromes. Molecular analysis of familial pituitary adenomas has provided significant insight into pituitary tumorigenesis. Some specific genes have been identified that predispose to pituitary neoplasia, but these are rarely involved in the pathogenesis of sporadic tumors. The number of identified genes involved in pituitary tumorigenesis is progressively increasing. The possible resulting mechanisms of action involve abnormalities in signal transduction pathways, cell cycle regulators, growth factors, chromosome stability and others. Further studies are needed to evaluate the clinical significance of genetic alterations and their implications for patient prognosis, as well as to identify targets for existing and new therapeutic options. The aim of this review is to focus on the molecular pathology of pituitary adenomas from a practical perspective and discuss the possible clinical implications which may relate to particular molecular alterations. We have summarised familial syndromes related to pituitary adenomas and considered the prognostic value of selected molecular alterations in these tumors. Hide abstract
Pheochromocytomas and paragangliomas are genetically heterogeneous neural crest-derived neoplasms. We recently identified germline mutations of the novel transmembrane-encoding gene FP/TMEM127 in familial and sporadic pheochromocytomas consistent with a tumor suppressor effect. Hide abstract
Adrenal failure secondary to hypothalamo-pituitary disease is a common clinical problem which has serious repercussions. It is essential to perform validated diagnostic procedures and manage such patients with clear objectives and based on well-established replacement programs. Hide abstract
Familial pituitary adenomas can occur in MEN1 and Carney complex, as well as in the recently characterized familial isolated pituitary adenoma (FIPA) syndrome. FIPA is an autosomal dominant disease with incomplete penetrance, characterized by early-onset disease, often aggressive tumor growth and a predominance of somatotroph and lactotroph adenomas. In 20% of FIPA families, heterozygous mutations have been described in the aryl hydrocarbon receptor interacting (AIP) gene, whereas in other families the causative gene(s) are unknown. It has been suggested that AIP is a tumor suppressor gene and although experimental data support this hypothesis, the exact molecular mechanism by which its disruption leads to tumorigenesis is unclear. Here we discuss the clinical, genetic and molecular features of patients with FIPA. Hide abstract
EUROPEAN JOURNAL OF ENDOCRINOLOGY, 162 (6), pp. 1165-1165. | Read more2010. Diagnosis and localisation of insulinoma: the value of modern magnetic resonance imaging in conjunction with calcium stimulation catheterisation (vol 162, 971, 2010)
Familial isolated pituitary adenoma (FIPA) is an autosomal dominant condition with variable genetic background and incomplete penetrance. Germline mutations of the aryl hydrocarbon receptor interacting protein (AIP) gene have been reported in 15-40% of FIPA patients. Limited data are available on the functional consequences of the mutations or regarding the regulation of the AIP gene. We describe a large cohort of FIPA families and characterize missense and silent mutations using minigene constructs, luciferase and beta-galactosidase assays, as well as in silico predictions. Patients with AIP mutations had a lower mean age at diagnosis (23.6+/-11.2 years) than AIP mutation-negative patients (40.4+/-14.5 years). A promoter mutation showed reduced in vitro activity corresponding to lower mRNA expression in patient samples. Stimulation of the protein kinase A-pathway positively regulates the AIP promoter. Silent mutations led to abnormal splicing resulting in truncated protein or reduced AIP expression. A two-hybrid assay of protein-protein interaction of all missense variants showed variable disruption of AIP-phosphodiesterase-4A5 binding. In summary, exonic, promoter, splice-site, and large deletion mutations in AIP are implicated in 31% of families in our FIPA cohort. Functional characterization of AIP changes is important to identify the functional impact of gene sequence variants. Hide abstract
Neuroendocrinology, 91 (4), pp. 326-332. | Read more2010. ENETS consensus guidelines for the management of brain, cardiac and ovarian metastases from neuroendocrine tumors.
Raf/MEK/ERK and phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) cascades are key signalling pathways interacting with each other to regulate cell growth and tumourigenesis. We have previously shown B-Raf and Akt overexpression and/or overactivation in pituitary adenomas. The aim of this study is to assess the expression of their downstream components (MEK1/2, ERK1/2, mTOR, TSC2, p70S6K) and effectors (c-MYC and CYCLIN D1). We studied tissue from 16 non-functioning pituitary adenomas (NFPAs), six GH-omas, six prolactinomas and six ACTH-omas, all collected at transsphenoidal surgery; 16 normal autopsy pituitaries were used as controls. The expression of phospho and total protein was assessed with western immunoblotting, and the mRNA expression with quantitative RT-PCR. The expression of pSer217/221 MEK1/2 and pThr183 ERK1/2 (but not total MEK1/2 or ERK1/2) was significantly higher in all tumour subtypes in comparison to normal pituitaries. There was no difference in the expression of phosphorylated/total mTOR, TSC2 or p70S6K between pituitary adenomas and controls. Neither c-MYC phosphorylation at Ser 62 nor total c-MYC was changed in the tumours. However, c-MYC phosphorylation at Thr58/Ser62 (a response target for Akt) was decreased in all tumour types. CYCLIN D1 expression was higher only in NFPAs. The mRNA expression of MEK1, MEK2, ERK1, ERK2, c-MYC and CCND1 was similar in all groups. Our data indicate that in pituitary adenomas both the Raf/MEK/ERK and PI3K/Akt/mTOR pathways are upregulated in their initial cascade, implicating a pro-proliferative signal derangement upstream to their point of convergence. However, we speculate that other processes, such as senescence, attenuate the changes downstream in these benign tumours. Hide abstract