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Jo W M Höppener

Publications and source records attributed to Jo W M Höppener.

8 recordsLinked to original sources
PubMed2006

Menin links estrogen receptor activation to histone H3K4 trimethylation.

The product of the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor gene, menin, is an integral component of MLL1/MLL2 histone methyltransferase complexes specific for Lys4 of histone H3 (H3K4). We show that menin is a transcriptional coactivator of the nuclear receptors for estrogen and vitamin D. Activation of the endogenous estrogen-responsive TFF1 (pS2) gene results in promoter recruitment of menin and in elevated trimethylation of H3K4. Knockdown of menin reduces both activated TFF1 (pS2) transcription and H3K4 trimethylation. In addition, menin can directly interact with the estrogen receptor-alpha (ERalpha) in a hormone-dependent manner. The majority of disease-related MEN1 mutations prevent menin-ERalpha interaction. Importantly, ERalpha-interacting mutants are also defective in coactivator function. Our results indicate that menin is a critical link between recruitment of histone methyltransferase complexes and nuclear receptor-mediated transcription.

Animals↗
PubMed2006

Role of islet amyloid in type 2 diabetes mellitus.

Diabetes mellitus is one of the most common metabolic diseases worldwide and its prevalence is rapidly increasing. Due to its chronic nature (diabetes mellitus can be treated but as yet not cured) and its serious complications, it is one of the most expensive diseases with regard to total health care costs per patient. The elevated blood glucose levels in diabetes mellitus are caused by a defect in production and/or secretion of the polypeptide hormone insulin, which normally promotes glucose-uptake in cells. Insulin is produced by the pancreatic 'beta-cells' in the 'islets of Langerhans', which lie distributed within the exocrine pancreatic tissue. In type 2 diabetes mellitus, the initial defect in the pathogenesis of the disease in most of the patients is believed to be 'insulin resistance'. Hyperglycemia (clinically overt diabetes mellitus) will not develop as long as the body is able to produce enough insulin to compensate for the reduced insulin action. When this compensation fails ('beta-cell failure') blood glucose levels will become too high. In this review, we discuss one of the mechanisms that have been implicated in the development of beta-cell failure, i.e. amyloid formation in the pancreatic islets. This islet amyloid is a characteristic histopathological feature of type 2 diabetes mellitus and both in vitro and in vivo studies have revealed that its formation causes death of islet beta-cells. Being a common pathogenic factor in an otherwise heterogeneous disease, islet amyloidosis is an attractive novel target for therapeutic intervention in type 2 diabetes mellitus.

Amyloid↗
PubMed2005

Islet amyloid polypeptide inserts into phospholipid monolayers as monomer.

Amyloid deposits in the pancreatic islets of Langerhans are thought to be a main factor responsible for death of the insulin-producing islet beta-cells in type 2 diabetes. It is hypothesized that beta-cell death is related to interaction of the 37 amino acid residue human islet amyloid polypeptide (hIAPP), the major constituent of islet amyloid, with cellular membranes. However, the mechanism of hIAPP-membrane interactions is largely unknown. Here, we study the nature and the molecular details of the initial step of hIAPP-membrane interactions by using the monolayer technique. It is shown that both freshly dissolved hIAPP and the non-amyloidogenic mouse IAPP (mIAPP) have a pronounced ability to insert into phospholipid monolayers, even at lipid packing conditions that exceed the conditions that occur in biological membranes. In contrast, the fibrillar form of hIAPP has lost the ability to insert. These results, combined with the observations that both the insertion kinetics and the dependence of insertion on the initial surface pressure are similar for freshly dissolved hIAPP and mIAPP, indicate that hIAPP inserts into phospholipid monolayers most likely as a monomer. In addition, our results suggest that the N-terminal part of hIAPP, which is nearly identical with that of mIAPP, is largely responsible for insertion. This is supported by experiments with hIAPP fragments, which show that a peptide consisting of the 19 N-terminal residues of hIAPP efficiently inserts into phospholipid monolayers, whereas an amyloidogenic decapeptide, consisting of residues 20-29 of hIAPP, inserts much less efficiently. The results obtained here suggest that hIAPP monomers might insert with high efficiency in biological membranes in vivo. This process could play an important role as a first step in hIAPP-induced membrane damage in type 2 diabetes.

Amino Acid Sequence↗
PubMed2004

Islet amyloid polypeptide-induced membrane leakage involves uptake of lipids by forming amyloid fibers.

Fibril formation of islet amyloid polypeptide (IAPP) is associated with cell death of the insulin-producing pancreatic beta-cells in patients with Type 2 Diabetes Mellitus. A likely cause for the cytotoxicity of human IAPP is that it destroys the barrier properties of the cell membrane. Here, we show by fluorescence confocal microscopy on lipid vesicles that the process of hIAPP amyloid formation is accompanied by a loss of barrier function, whereby lipids are extracted from the membrane and taken up in the forming amyloid deposits. No membrane interaction was observed when preformed fibrils were used. It is proposed that lipid uptake from the cell membrane is responsible for amyloid-induced membrane damage and that this represents a general mechanism underlying the cytotoxicity of amyloid forming proteins.

Amino Acid Sequence↗
PubMed2003

The spectrum of carcinoid tumours and carcinoid syndromes.

Carcinoids are neuroendocrine tumours of the gut which may also be found in the bronchus, pancreatic islets and retroperitoneum. They probably arise from gastrointestinal or bronchopulmonary pluripotential stem cells. Carcinoid tumours derived from these cells are potentially malignant; the strength of the tendency for aggressive growth correlates with the site of origin, depth of local penetration and the size of the tumour. Carcinoids occur sporadically or result from specific hereditary tumour syndromes. Mutations and/or aberrant expression of specific genes induce and promote tumour growth. Clinical features include local symptoms due to angulation or obstruction and hepatomegaly due to liver metastases. The carcinoid syndrome commonly involves flushing, diarrhoea, bronchospasm and hypotension. Other distinct syndromes may be caused by tumour release of products that may also be used as biochemical markers in diagnosis and follow-up. Scanning using radiolabelled octreotide, an analogue of somatostatin, sensitively identifies occult primary and metastatic deposits. Localized carcinoid tumours should be resected. Some patients benefit from hepatic resection. Palliation of symptoms is best achieved with octreotide. Hepatic artery chemoembolization may produce long-acting palliation. Further genetic characterization of the different types and stages of carcinoid development as well as assessment of gene expression profiles may improve differential diagnosis, prognosis and treatment.

Carcinoid Tumor↗
PubMed2002

Role of islet amyloid in type 2 diabetes mellitus: consequence or cause?

Type 2 diabetes mellitus (DM2) is characterized metabolically by defects in both insulin secretion and insulin action, resulting in hyperglycemia. Histopathologically, DM2 is characterized by depositions of protein in the pancreatic islets. This 'islet amyloid' is present in >90% of patients with DM2, as well as in monkeys and cats with DM2. The pathogenesis of DM2 is heterogeneous and multifactorial, although insulin resistance seems to be the predominant initiating factor for development of the disease. In the longer term, an insulin secretion defect is also revealed (referred to as 'beta-cell failure'), resulting in clinically manifest diabetes. Recent data, particularly from transgenic mouse studies, indicate that islet amyloidosis is a diabetogenic factor, which is both consequence (of insulin resistance) and cause (of beta-cell failure) of DM2. Available transgenic mouse models with islet amyloid formation in vivo will provide the opportunity to assess the effectiveness of novel anti-amyloidogenic therapies, for which promising results are emerging.

Amino Acid Sequence↗
PubMed2002

Inhibition of amyloid fibril formation of human amylin by N-alkylated amino acid and alpha-hydroxy acid residue containing peptides.

Amyloid deposits are formed as a result of uncontrolled aggregation of (poly)peptides or proteins. Today several diseases are known, for example Alzheimer's disease, Creutzfeldt-Jakob disease, mad cow disease, in which amyloid formation is involved. Amyloid fibrils are large aggregates of beta-pleated sheets and here a general method is described to introduce molecular mutations in order to achieve disruption of beta-sheet formation. Eight backbone-modified amylin derivatives, an amyloidogenic peptide involved in maturity onset diabetes, were synthesized. Their beta-sheet forming properties were studied by IR spectroscopy and electron microscopy. Modification of a crucial amide NH by an alkyl chain led to a complete loss of the beta-sheet forming capacity of amylin. The resulting molecular mutated amylin derivative could be used to break the beta-sheet thus retarding beta-sheet formation of unmodified amylin. Moreover, it was found that the replacement of this amide bond by an ester moiety suppressed fibrillogenesis significantly. Introduction of N-alkylated amino acids and/or ester functionalities-leading to depsipeptides-into amyloidogenic peptides opens new avenues towards novel peptidic beta-sheet breakers for inhibition of beta-amyloid aggregation.

Alkylation↗