[Guidelines for gastroenteropancreatic neuroendocrine tumors--what is new? What should be incorporated in daily therapeutic decisions?]. / Leitlinien für gastroenteropankreatische neuroendokrine Tumoren--was ist neu? Was sollte in die Therapierichtlinien aufgenommen werden?

Neuroendocrine neoplasias are seldom, but increasing. This holds true for the incidence but even more for the prevalence, since patients are able to live with their disease for quite a long time. The European Neuroendocrine Tumor Society (ENETS) as well as other societies (NANETS: North American Neuroendocrine Tumor Society; NCCN: National Comprehensive Cancer Network; ESMO: European Society of Medical Oncology) have published diagnostic and therapeutic guidelines that we present in this review. We aim to summarize those actual guidelines in a practice-based diagnostic and therapeutic algorithm, but also wish to point to open questions that have to be discussed in a multidisciplinary approach.

[Neuroendocrine neoplasms of the breast]. / Neuroendokrine Neoplasien der Mamma.

Neuroendocrine neoplasms (NEN) of the breast are specific tumor entities. According to the literature up to 5% of breast neoplasms are malignant epithelial neoplasms of the breast. They are defined by a neuroendocrine (NE) architecture and cytology combined with an expression of the neuroendocrine vesicle markers chromogranin A and/or synaptophysin. The diagnosis is supplemented by the receptor status and the proliferative activity. According to the World Health Organization (WHO) classification of 2012 the following groups of NEN are distinguished: (1) invasive breast carcinoma with NE differentiation, (2) well-differentiated neuroendocrine tumor (NET) and (3) poorly differentiated small cell carcinoma (NEC). This review article focuses on (1) the definition and basic principles of diagnostics, (2) the history, nomenclature and WHO classification from 2003 and 2012, (3) the frequency of breast NEN, (4) the hereditary background and functional activity, (5) the expression of receptors and (6) the possible clinical implications. In addition, the first results of a retrospective single center study (n = 465 patients with breast cancer over a time period of 4 years) on the frequency of NEN of the breast at the Breast Center of the University Hospital Düsseldorf are presented. In this study a frequency of 4.5% of NEN was found based on a diagnostic cut-off of > 50% Chromogranin A and/or synaptophysin positive tumor cells.

[Neuroendocrine neoplasms of the distal jejunum and ileum]. / Neuroendokrine Neoplasien des distalen Jejunums und Ileums.

Neuroendocrine neoplasms (NEN) of the distal jejunum and ileum derive from serotonin-producing enterochromaffin (EC) cells. Due to their low proliferation rate and their infiltrative growth, they are often discovered at an advanced disease stage when metastasis has already occurred. The biology of these tumours is different from other NEN of the digestive tract. In order to standardise and improve diagnosis and therapy, the guidelines for the diagnosis and clinical management of jejuno-ileal NEN as well as for the management of patients with liver and other distant metastases from NEN were revised by the European Neuroendocrine Tumour Society (ENETS) in 2012. This review focuses on aspects relevant for surgical pathology.

[Hereditary syndromes of neuroendocrine tumours]. / Hereditäre Syndrome neuroendokriner Tumore.

Diffuse localised neuroendocrinal cells represent the largest population of endocrinally active cells and can degenerate to malignant neuroendocrine tumours (NET). In this review the most important hereditary syndromes that predispose for endocrine and neuroendocrine tumours are presented and discussed. NET occur mainly as sporadic tumours. Current investigations on the pathogenesis of sporadic neuroendocrine tumours have revealed a close relationship between hereditary and sporadic neuroendocrine tumours. In the course of hereditary syndromes, such as multiple endocrine neoplasia, endocrine and neuroendocrine tumours as well as non-endocrine neoplasias can occur. In order to recognise these syndromes in good time a knowledge of the predisposing syndromes and their cardinal symptoms is essential. In this way not only individualised diagnosis and therapy can be planned but also an appropriate early management of first degree relatives can be initiated.

[Pulmonary neuroendocrine neoplasms]. / Neuroendokrine Neoplasien der Lunge.

The pulmonary neuroendocrine neoplasms originate from the enterochromaffin cells which are diffusely distributed in the body. The incidence of these tumors has increased significantly in recent decades due to the available diagnostics. They make up about 1-2% of all lung tumors and 20-30% of all neuroendocrine neoplasms. The current WHO classification from 2004 divides them into typical carcinoids (TC), atypical carcinoids (AC), large cell neuroendocrine carcinomas (LCNEC) and small cell carcinomas (SCLC). The major neuroendocrine biomarkers are chromogranin A, synaptophysin and CD56. TC have a low mitotic rate of <2 mitoses/2mm(2) (10 HPF), whereas the mitotic rate of the AC is 2-10 mitoses/2 mm(2) (10 HPF). The Ki-67 staining is helpful to distinguish typical and atypical carcinoids from the highly malignant LCNEC and SCLC. Clinically, the patient presents usually with cough, hemoptysis or bronchial obstruction. The occurrence of a carcinoid or Cushing's syndrome and a tumor-associated acromegaly are rare. Surgical resection with radical lymph node dissection is the treatment of choice for achieving long-term survival. Endoscopic resection of the endobronchial tumor growth is a good alternative for inoperable endobronchially localized tumors. Peptide receptor radionuclide therapy (PRRT) is a promising treatment option for patients with metastatic or unresectable pulmonary neuroendocrine tumors. New targeted therapies using angiogenesis inhibitors, mTOR inhibitors, and tyrosine kinase inhibitors are being tested for their effectiveness in many previous studies. Typical carcinoid tumors metastasize less frequently than AC, the 5-year survival rate of patients with TC being over 90%. Patients with AC have a 5-year survival rate between 35% and 87%. The highly malignant LCNEC and SCLC, on the other hand, have a 5-year survival rate between 15% and 57%, and <5% respectively. The increasing number of therapeutic options and diagnostic procedures requires a multidisciplinary approach and decision-making in multidisciplinary tumor conferences to ensure a personalized treatment approach. Therefore patients with a neuroendocrine neoplasm of the lung should be treated in specialized centers.

Treatment of advanced BP-NETS with lanreotide autogel/depot vs placebo: the phase III SPINET study.

Prospective data are lacking on early somatostatin analog (SSA) therapy in bronchopulmonary neuroendocrine tumors (BP-NETs; typical carcinoids and atypical carcinoids (TCs and ACs)). SPINET (EudraCT: 2015-004992-62; NCT02683941) was a phase III, double-blind study of lanreotide autogel/depot (LAN; 120 mg every 28 days) plus best supportive care (BSC) vs placebo plus BSC, with an optional open-label treatment phase (LAN plus BSC). Patients had metastatic/unresectable, somatostatin receptor (SSTR)-positive TCs or ACs. Recruitment was stopped early owing to slow accrual; eligible patients from the double-blind phase transitioned to open-label LAN. The adapted primary endpoint was progression-free survival (PFS) during either phase for patients receiving LAN. Seventy-seven patients were randomized (LAN, n = 51 (TCs, n = 29; ACs, n = 22); placebo, n = 26 (TCs, n = 16; ACs, n = 10)). Median (95% CI) PFS during double-blind and open-label phases in patients receiving LAN was 16.6 (11.3; 21.9) months overall (primary endpoint), 21.9 (12.8, not calculable (NC)) months in TCs, and 13.8 (5.4; 16.6) months in ACs. During double-blind treatment, median (95% CI) PFS was 16.6 (11.3; 21.9) months for LAN vs 13.6 (8.3; NC) months for placebo (not significant); corresponding values were 21.9 (13.8; NC) and 13.9 (13.4; NC) months, respectively, in TCs and 13.8 (5.4; 16.6) and 11.0 (2.8; 16.9) months, respectively, in ACs. Patients' quality of life did not deteriorate and LAN was well tolerated. Although recruitment stopped early and the predefined sample size was not met, SPINET is the largest prospective study to date of SSA therapy in SSTR-positive TCs and ACs and suggests clinical benefit in TCs.

The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours.

Peptide receptor radionuclide therapy (PRRNT) is a molecularly targeted radiation therapy involving the systemic administration of a radiolabelled peptide designed to target with high affinity and specificity receptors overexpressed on tumours. PRRNT employing the radiotagged somatostatin receptor agonists (90)Y-DOTATOC ([(90)Y-DOTA(0),Tyr(3)]-octreotide) or (177)Lu-DOTATATE ([(177)Lu-DOTA(0),Tyr(3),Thr(8)]-octreotide or [(177)Lu-DOTA(0),Tyr(3)]-octreotate) have been successfully used for the past 15 years to target metastatic or inoperable neuroendocrine tumours expressing the somatostatin receptor subtype 2. Accumulated evidence from clinical experience indicates that these tumours can be subjected to a high absorbed dose which leads to partial or complete objective responses in up to 30 % of treated patients. Survival analyses indicate that patients presenting with high tumour receptor expression at study entry and receiving (177)Lu-DOTATATE or (90)Y-DOTATOC treatment show significantly higher objective responses, leading to longer survival and improved quality of life. Side effects of PRRNT are typically seen in the kidneys and bone marrow. These, however, are usually mild provided adequate protective measures are undertaken. Despite the large body of evidence regarding efficacy and clinical safety, PRRNT is still considered an investigational treatment and its implementation must comply with national legislation, and ethical guidelines concerning human therapeutic investigations. This guidance was formulated based on recent literature and leading experts' opinions. It covers the rationale, indications and contraindications for PRRNT, assessment of treatment response and patient follow-up. This document is aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRNT and to deliver the treatment in a safe and effective manner. This document is largely based on the book published through a joint international effort under the auspices of the Nuclear Medicine Section of the International Atomic Energy Agency.

Pancreatic neuroendocrine neoplasms.

Pancreatic neuroendocrine tumors originate from the diffuse neuroendocrine system in the pancreatic region. These tumors exhibit a rising incidence despite their rareness and due to their benign behavior a considerable prevalence. Pathogenesis of pancreatic neuroendocrine tumors is characterized by common pathways of hereditary and sporadic tumors. Pancreatic neuroendocrine tumors may secrete peptide hormones or biogenic amines in an autonomous fashion as functional active tumors. Pathological grading and staging by TNM systems has been established in recent years classifying well and moderately differentiated pancreatice neuroendocrine tumors and poorly differentiated neuroendocrine carcinomas. Chromogranin A and less so pancreatic polypeptide are suitable tumor markers for pancreatic neuroendocrine tumors. Expression of receptors for somatostatin is the basis of treatment of pancreatic neuroendocrine tumors with somatostatin analogues as antisecretive and antiproliferative agents. In addition, somatostatin scintigraphy or PET/CT allows comprehensive diagnosis of pancreatic neuroendocrine tumors, which should be supported by (endoscopic and contrast enhanced) ultrasound, CT and MRI. Therapy of pancreatic neuroendocrine tumors consists of somatostatin analogues, chemotherapy, targeted therapy and peptide receptor radionuclide therapy. Two molecular substances hav been registered for pancreatic neuroendocrine tumors recently, sunitinib (Sutent®) and everolimus (Afinitor®). Predominant tumor load in the liver may be treated by local ablative therapy or liver transplantation. These treatment options have been included in guidelines of several professional societies and weighted for sequential therapy of patients with pancreatic neuroendocrine tumors according to effects and side effects.

[Expert dialogue: neuroendocrine tumours of the lungs and gastroenteropancreatic system]. / Expertendialog: Neuroendokrine Tumore der Lunge und des gastroenteropankreatischen Systems.

BACKGROUND: Neuroendocrine tumours of the lung exhibit an increasing incidence and prevalence. However, data on the diagnosis of and therapy for these tumours are sparse compared to neuroendocrine tumours of the gastroenteropancreatic system. METHODS: The present article reflects a dialogue between experts on neuroendocrine tumors of the lung and the gastroenteropancreatic system held on February 25th and 26th in Weimar, Germany. RESULTS: Many similarities exist between neuroendocrine tumours of the lung and the gastroenteropancreatic system but there are also significant differences. Similarities exist mainly concerning pathology, diagnosis and therapy. Differences exist regarding the systemic therapy and the significantly lower incidence of paraneoplastic syndromes. Somatostatin receptor PET/CT with gallium-68 labelled somatostatin analogues and peptide receptor radiotherapy are innovative methods for the diagnosis of and therapy for neuroendocrine tumours of the lung. The first treatment option remains complete resection of the tumour. Small molecules like everolimus (Afinitor®) have been tested in clinical trials and have been shown to prolong progression-free survival. CONCLUSIONS: Additional studies are necessary and efforts should be undertaken to establish a registry to increase data on methods suitable for he diagnosis of and therapy for neuroendocrine tumours of the lung.

Differential regulation of insulin receptor substrates-1 and -2 (IRS-1 and IRS-2) and phosphatidylinositol 3-kinase isoforms in liver and muscle of the obese diabetic (ob/ob) mouse.

Intracellular insulin signaling involves a series of alternative and complementary pathways created by the multiple substrates of the insulin receptor (IRS) and the various isoforms of SH2 domain signaling molecules that can interact with these substrates. In this study, we have evaluated the roles of IRS-1 and IRS-2 in signaling to the phosphatidylinositol (PI) 3-kinase pathway in the ob/ob mouse, a model of the insulin resistance of obesity and non-insulin-dependent diabetes mellitus. We find that the levels of expression of both IRS-1 and IRS-2 are decreased approximately 50% in muscle, whereas in liver the decrease is significantly greater for IRS-2 (72%) than for IRS-1 (29%). This results in differential decreases in IRS-1 and IRS-2 phosphorylation, docking of the p85alpha regulatory subunit of PI 3-kinase, and activation of this enzyme in these two insulin target tissues. In ob/ob liver there is also a change in expression of the alternatively spliced isoforms of the regulatory subunits for PI 3-kinase that was detected at the protein and mRNA level. This resulted in a 45% decrease in the p85alpha form of PI 3-kinase, a ninefold increase in the AS53/p55alpha, and a twofold increase in p50alpha isoforms. Thus, there are multiple alterations in the early steps of insulin signaling in the ob/ob mouse, with differential regulation of IRS-1 and IRS-2, various PI 3-kinase regulatory isoforms, and a lack of compensation for the decrease in insulin signaling by any of the known alternative pathways at these levels.

Glucose-dependent insulinotropic polypeptide is a growth factor for beta (INS-1) cells by pleiotropic signaling.

Activation of the G-protein-coupled receptor for glucose-dependent insulinotropic polypeptide facilitates insulin-release from pancreatic beta-cells. In the present study, we examined whether glucose-dependent insulinotropic polypeptide also acts as a growth factor for the beta-cell line INS-1. Here, we show that glucose-dependent insulinotropic polypeptide induced cellular proliferation synergistically with glucose between 2.5 mM and 15 mM by pleiotropic activation of signaling pathways. Glucose-dependent insulinotropic polypeptide stimulated the signaling modules of PKA/cAMP regulatory element binder, MAPK, and PI3K/protein kinase B in a glucose- and dose-dependent manner. Janus kinase 2 and signal transducer and activators of transcription 5/6 pathways were not stimulated by glucose-dependent insulinotropic polypeptide. Activation of PI3K by glucose-dependent insulinotropic polypeptide and glucose was associated with insulin receptor substrate isoforms insulin receptor substrate-2 and growth factor bound-2 associated binder-1 and PI3K isoforms p85alpha, p110alpha, p110beta, and p110gamma. Downstream of PI3K, glucose-dependent insulinotropic polypeptide-stimulated protein kinase Balpha and protein kinase Bbeta isoforms and phosphorylated glycogen synthase kinase-3, forkhead transcription factor FKHR, and p70S6K. These data indicate that glucose-dependent insulinotropic polypeptide functions synergistically with glucose as a pleiotropic growth factor for insulin-producing beta-cells, which may play a role for metabolic adaptations of insulin-producing cells during type II diabetes.

Differential signaling by regulatory subunits of phosphoinositide-3-kinase influences cell survival in INS-1E insulinoma cells.

Class 1A phosphoinositide 3-kinase (PI3K) is essential for beta-cell growth and survival. Although PI3K has been studied extensively in diabetes the effect of alternatively spliced isoforms of the catalytic subunit p85α on beta cell proliferation and survival remains to be defined.We examined expression and signaling of alternatively spliced PI3K regulatory subunits p85α, p55α and p50α in insulinoma cells (INS-1E), an insulin-producing beta cell line. PI3K regulatory isoforms were knocked down by siRNA transfection or overexpressed by adenoviral gene delivery.Knockdown of p85α elevated PI3K activation determined by Akt phosphorylation at baseline and after stimulation with growth factors. In contrast, Akt phosphorylation was inhibited by overexpression of all isoforms of p85α. Correspondingly, p55α and p85α overexpression decreased downstream kinase GSK-3 phosphorylation as well, whereas p50α overexpression resulted in an activation of GSK-3. Moreover, overexpression of p50α and p85α lead to retinoblastoma protein hyperphosphorylation and S-phase entry. Upon challenge of INS-1E cells with a cytotoxic cytokine cocktail, levels of p85α were reduced and p50α was upregulated. Selective overexpression of p50α prevented cytokine induced apoptosis in INS-1E cells.In conclusion, signalling of p50α, p55α and p85α is similar at the level of Akt, but differentially influence downstream GSK-3 activation and cell cycle entry. PI3K isoform p50α induction by cytokines provides a link between regeneration and cell survival under cytotoxic stress in insulin-producing pancreatic beta-cells.

[Peptide receptor radionuclide therapy for patients with somatostatin receptor expressing tumours. German Guideline (S1)]. / Peptidrezeptor-Radionuklidtherapie Somatostatinrezeptor-exprimierender Tumore. DGN-Leitlinie (S1).

This document describes the guideline for peptide receptor radionuclide therapy (PRRT) published by the German Society of Nuclear Medicine (DGN) and accepted by the Association of the Scientific Medical Societies in Germany (AWMF) to be included in the official AWMF Guideline Registry. These recommendations are a prerequisite for the quality management in the treatment of patients with somatostatin receptor expressing tumours using PRRT. They are aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRT and to deliver the treatment in a safe and effective manner. The recommendations are based on an interdisciplinary consensus. The document contains background information and definitions and covers the rationale, indications and contraindications for PRRT. Essential topics are the requirements for institutions performing the therapy, e. g. presence of an expert for medical physics, intense cooperation with all colleagues involved in the treatment of a patient, and a certificate of instruction in radiochemical labelling and quality control are required. Furthermore, it is specified which patient data have to be available prior to performance of therapy and how treatment has to be carried out technically. Here, quality control and documentation of labelling are of great importance. After treatment, clinical quality control is mandatory (work-up of therapy data and follow-up of patients). Essential elements of follow-up are specified in detail. The complete treatment inclusive after-care has to be realised in close cooperation with the involved medical disciplines. Generally, the decision for PRRT should be undertaken within the framework of a multi-disciplinary tumour board.

Region-specific mRNA expression of phosphatidylinositol 3-kinase regulatory isoforms in the central nervous system of C57BL/6J mice.

Activation of phosphatidylinositol 3-kinase (PI 3-kinase) by receptor tyrosine kinases for growth factors is crucial for neuronal cell survival and proliferation. This class of kinases is comprised of heterodimers, each consisting of one regulatory and one catalytic subunit. Multiple isoforms of regulatory subunits exist, including p85alpha and its alternative splice products p50alpha and AS53/p55alpha, and p85beta and p55(PIK), which are derived from different genes. The regional distribution of these PI 3-kinase regulatory isoforms was mapped in the adult murine brain by in situ hybridization histochemistry. All isoforms were demonstrated in abundance in choroid plexus and anterior pituitary. In neuronal compartments, however, PI 3-kinase isoforms were distributed in a regionally specific manner. In general, the mRNAs for p85alpha, p50alpha, AS53, and p85beta were widespread, with the highest level in the olfactory system, in neuronal groups of the forebrain and hypothalamus, in the hippocampus, cortex, inferior and superior colliculus, pituitary, and cerebellum. However, each isoform had specific variations. Lower expression levels of these isoforms were found in the thalamus, diencephalon, mesencephalon, and brainstem. In contrast, abundant mRNA expression of p55(PIK) was limited to cerebellum and anterior pituitary, with moderate levels of p55(PIK) in the olfactory bulb and hippocampus and low levels elsewhere. The distribution pattern of PI 3-kinase isoforms in the brain indicates pluripotent signaling properties for PI 3-kinase isoforms p85alpha, p50alpha, AS53/p55alpha, and p85beta for a variety of receptor tyrosine kinases, whereas the restricted expression of p55(PIK) implies a regionally specific role for this isoform in neuronal signaling. The unique integrated expression profiles of PI 3-kinase isoforms in distinct neuronal compartments denote complex intracellular signaling pathways for each neuronal region to ensure specificity of receptor tyrosine kinase signal transduction.

Regional specificities in the distribution, chemical phenotypes, and coexistence patterns of neuropeptide containing nerve fibres in the human anal canal.

Despite the pivotal clinical significance of the human anal canal, little is known about its total and specific innervation. This study assessed the comparative distribution and histotopology of nerve fibres immunoreactive for neural markers and a variety of regulatory active neuropeptides in the human anal canal by light microscopic immunohistochemistry. Depending on the epithelial zone and region of the anal canal, the neural elements were differentially immunoreactive for the pan-neural marker protein gene product 9.5, the catecholamine marker tyrosine hydroxylase, the neuroendocrine marker chromogranin A, and various neuropeptides. Protein gene product 9.5-immunoreactive nerve fibres were ubiquitously abundant in the anal canal. In the anal transitional zone, ectopic epithelial types were supplied by the same pattern of peptidergic nerves as the respective type of epithelium in normotopic location. In the dermis of the squamous zone and in the perianal epidermis, unusual distribution patterns of nerve fibres, referred to as areas of high nerve fibre density, were encountered. Double immunohistochemistry revealed region-specific coexistence patterns of neuropeptidergic nerve fibres, and novel peptide coexistence patterns were detected in anal nerve fibres. Subsets of nerve fibres formed close spatial relationships with chromogranin A-positive neuroendocrine cells, most frequently in the anal transitional zone. Chromogranin-A positive cells were shown to be present in the epithelium of perianal eccrine sweat glands. The differential distribution, peptide phenotypes and coexistence patterns of different nerve fibre populations in the human anal canal may reflect topospecific regulatory functions of neurally released neuropeptides in health and disease.

Mechanisms of mitogenic and anti-apoptotic signaling by glucose-dependent insulinotropic polypeptide in beta(INS-1)-cells.

Glucose-dependent insulinotropic polypeptide (GIP) acts as a glucose-dependent growth factor for beta-cells. Here we show that GIP and glucose also act synergistically as anti-apoptotic factors for beta-cells, using the well-differentiated beta-cell line, INS-1. Mitogenic and anti-apoptotic signaling of GIP were dependent upon pleiotropic activation of protein kinase A (PKA)/cAMP regulatory element binder (CREB), mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-kinase)/PKB signaling modules. The signaling modules activated by GIP were dependent on glucose metabolism and calcium influx and were tightly linked by multiple activating and inhibiting cross-talk. These interactions included: (i) a central role of tyrosine phosphorylation for stimulation of PKA/CREB, MAPK and PI3-kinase/PKB, (ii) inhibition of PKA/CREB by the MAPK pathway at the level of MAPK kinase-1 or downstream, (iii) activation of MAPK signaling by PI3-kinase and PKA at the level of extracellular-signal regulated kinase 1/2 or upstream, and (iv) activation of PKB by MAPK and PKA signaling at the level of PKB or upstream. Furthermore, we demonstrated inhibition of CREB signaling by Ca(2+)/calmodulin kinase I/IV. These results indicated that GIP acts as a mitogenic and anti-apoptotic factor for beta-cells by pleiotropic activation of tightly linked signaling pathways in beta-cells.

Integrative mitogenic role of protein kinase B/Akt in beta-cells.

Protein kinase B/Akt (PKB/Akt) is activated by phosphatidylinositol 3-kinase (PI 3-K) and is a central mediator of cellular proliferation and protection against apoptosis. Insulin, insulin-like growth factor (IGF-1), and glucagon-like peptide-1 (GLP-1) act as glucose-dependent growth factors for pancreatic beta-cells. We assessed signaling pathways and stimulation patterns of PKB/Akt activation by these ligands in the beta-cell line INS-1. Insulin, IGF-1, and GLP-1 induced distinctive time dependent, dose dependent, and glucose dependent phosphorylation of PKB/Akt. Insulin and IGF-1 stimulated PI 3-K activity was mainly associated with insulin receptor substrate (IRS) isoforms IRS-1 and IRS-2 and less so with the IRS-isoform Grb-2 associated binder-1 (Gab-1). In contrast, GLP-1 induced PI 3-K activity mainly in Gab-1 and also in IRS-2 immunoprecipitates, although in an attenuated kinetic. Thus, activation pathways of PKB/Akt by insulin, IGF-1, and GLP-1 converge at the level of IRS-isoforms and PI 3-K inducing differential activation of PKB/Akt. These data indicate an essential role of PKB/Akt in regulation of beta-cell proliferation.