Perspectives on some recent studies on RAMPs.

This book on RAMPs covers a number of aspects on the biology of RAMPs. However, due to the uniqueness of some recent studies, they were not covered under a general title. Therefore, in this chapter, we describe three recent studies wherein RAMPs were found to be important players in cancer, hypertension and asthma.

Regulation of GPCR trafficking by RAMPs.

AM and CGRP receptors undergo differential intracellular receptor trafficking upon ligand stimulation. Intracellular trafficking of CLR/RAMP receptor complexes is regulated by posttranslational modifications and protein-protein interactions that differ for each cell type. Recent evidence is accumulating to suggest that the RAMP isoform in complex with CLR may play a role in determining the intracellular trafficking and fate of ligand-stimulated receptor complexes.

Introduction to RAMPs.

Receptor activity modifying proteins (RAMPs) are single transmembrane proteins discovered for their role in the regulation of translocation of certain G-protein coupled receptors (GPCRs) to the plasma membrane. Since its discovery in 1998, several pivotal advances have been made in understanding the function of this family of proteins. This chapter provides a basic introduction to RAMPs as well as details on the various chapters in this book.

Sex differences in inflammatory cytokine production in hepatic ischemia-reperfusion.

Background: The inflammatory response to hepatic ischemia-reperfusion (I/R) is associated with an increase in cytokine production. Studies have documented that sex hormones modulate both the innate and adaptive immune responses, and that females are more robust than males. The aim of this study was to determine whether a sex difference in cytokine response to hepatic I/R exists under normal pathophysiologic condition without hormone intervention.

RAMPs: The past, present and future.

The discovery of receptor-activity-modifying proteins (RAMPs) as accessory proteins required for the appropriate localization and function of certain G-protein coupled receptors (GPCRs) produced a paradigm shift in our understanding of GPCR regulation. Three RAMPs have now been demonstrated to be crucial for various aspects of the life cycle of calcitonin-like receptor (CLR) including endoplasmic reticulum-to-Golgi translocation, internalization and recycling. Although the RAMP-CLR interaction was the first to be identified, other GPCRs belonging to both the class B and C families of GPCRs also seem to be regulated by RAMPs.

Receptor activity-modifying protein (RAMP) isoform-specific regulation of adrenomedullin receptor trafficking by NHERF-1.

Receptor activity-modifying proteins (RAMPs 1-3) are single transmembrane accessory proteins critical to various G-protein coupled receptors for plasma membrane expression and receptor phenotype. A functional receptor for the vasodilatory ligand, adrenomedullin (AM), is comprised of RAMP2 or RAMP3 and calcitonin receptor-like receptor (CRLR). It is now known that RAMP3 protein-protein interactions regulate the recycling of the AM2 receptor.

Novel function for receptor activity-modifying proteins (RAMPs) in post-endocytic receptor trafficking.

RAMPs (1-3) are single transmembrane accessory proteins crucial for plasma membrane expression, which also determine receptor phenotype of various G-protein-coupled receptors. For example, adrenomedullin receptors are comprised of RAMP2 or RAMP3 (AM1R and AM2R, respectively) and calcitonin receptor-like receptor (CRLR), while a CRLR heterodimer with RAMP1 yields a calcitonin gene-related peptide receptor. The major aim of this study was to determine the role of RAMPs in receptor trafficking.

Okadaic acid stimulates caspase-like activities and induces apoptosis of cultured rat mesangial cells.

Glomerular mesangial cells play an important role in the development of glomerulosclerosis. Mesangial cell apoptosis has been shown to be involved in different stages of development of glomerulonephritis. The aim of the present study was to evaluate the effect of inhibition of serine/threonine phosphatases by okadaic acid, a shell fish toxin, on rat mesangial cell apoptosis and to examine the molecular mechanisms particularly the role of caspases.

Regulation of adrenomedullin signaling in kidney interstitial fibroblasts.

Adrenomedullin (AM), a potent vasodilatory peptide has beneficial effects in the kidney IN VIVO. The major aim of the present study was to determine the presence of AM receptor and the biological outcomes of AM on kidney interstitial fibroblasts in culture. Utilizing RT-PCR we found that NRK-49F cells express calcitonin receptor like receptor (CRLR) and receptor activity modifying protein 2 (RAMP2) but not RAMP3.

Adrenomedullin increases AP-1 expression in rat mesangial cells via activation of protein kinase-A and p38 MAPK.

Adrenomedullin (AM), a potent vasodilatory peptide, has anti-proliferative and pro-apoptotic effects in rat mesangial cells (RMCs). We have previously demonstrated that AM modulates activities of the members of MAPK family in RMCs. Because activation of MAPKs has been reported to induce AP-1 expression in other cell systems, the major aim of the present study was to examine the effects and mechanisms of AM on AP-1 member mRNA expression, in RMCs.

Negative growth effects of ciglitazone on kidney interstitial fibroblasts: role of PPAR-gamma.

Background/aims: Ciglitazone and other thiazolidinedione compounds are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligands and improve renal function in diabetic nephropathy independent of blood glucose control. Because interstitial fibroblasts and glomerular mesangial cells are important cell types affected in diabetic nephropathy, the major aim of the present study was to examine the effect of ciglitazone on apoptosis and growth of renal interstitial fibroblasts (NRKs) and glomerular mesangial cells (MMCs).

Methods: The effect of ciglitazone on apoptosis and cell growth of cultured NRKs and MMCs was done using DNA fragmentation and MTS cell-growth assays, respectively.

Mixed lineage kinase 3 inhibits phorbol myristoyl acetate-induced DNA synthesis but not osteopontin expression in rat mesangial cells.

Mixed lineage kinase 3 (MLK 3) (also called SPRK or PTK-1) is a recently described member of the family of the mixed lineage kinase subfamily of Ser/Thr protein kinases that interacts with mitogen-activated protein kinase pathways. In order to test the biological relevance and potential interaction of MLK 3 with protein kinase C-mediated signaling pathways, human MLK 3 was stably expressed in rat glomerular mesangial cells using a retroviral vector (LXSN) and the effects of phorbol myristoyl acetate (PMA) on DNA synthesis and osteopontin mRNA expression were examined. In control (vector-transfected) mesangial cells PMA increased [3H]-thymidine incorporation in a concentration-dependent manner.

Mixed lineage kinase 3 inhibits platelet-derived growth factor-stimulated DNA synthesis and matrix mRNA expression in mesangial cells.

Mixed lineage kinase 3 (MLK 3) is a recently described member of the MLK subfamily of Ser/Thr protein kinases that interacts with MAPK pathways. The aim of this study was to test the potential interaction of MLK 3 with signaling pathways stimulated by PDGF in rat mesangial cells. We have established a stable cell line expressing human MLK 3 in rat glomerular mesangial cells.

Novel regulation of adrenomedullin receptor by PDGF: role of receptor activity modifying protein-3.

Receptor activity modifying protein-3 (RAMP-3) has been shown to complex with the calcitonin receptor-like receptor, establishing a functional receptor for adrenomedullin (AM). AM exhibits potent antiproliferative and antimigratory effects on rat mesangial cells (RMCs). In this study we investigated the effect of platelet-derived growth factor (PDGF) on RAMP-3 expression in RMCs.

Cellular and molecular actions of adrenomedullin in glomerular mesangial cells.

Adrenomedullin (AM), a potent vasodilatory and hypotensive peptide produces several biological outcomes in glomerular mesangial cells. Mesangial cells are important in the pathogenesis of glomerulonephritis, and therefore the actions of AM on mesangial cells have important clinical and therapeutic implications. This minireview describes the various actions of AM on mesangial cell function and the signal transduction mechanisms involved.

Regulation of apoptosis by vasoactive peptides.

Although originally discovered because of their ability to affect hemodynamics, vasoactive peptides have been found to function in a variety of capacities including neurotransmission, endocrine functions, and the regulation of cell proliferation. A growing body of evidence describes the ability of vasoactive peptides to regulate cell death by apoptosis in either a positive or negative fashion depending on the peptide and the type of target cell. The available evidence to date is strongest for the peptides endothelin, angiotensin II, vasoactive intestinal peptide, atrial natriuretic peptide, and adrenomedullin.

FK506 promotes adenosine release from endothelial cells via inhibition of adenosine kinase.

The immunosuppressants, cyclosporin A and tacrolimus (FK506) induce an increase in plasma levels of adenosine and mimic ischemic preconditioning. However, the mechanism of action of the two drugs on adenosine metabolism is not clear. Since inhibition of adenosine kinase promotes an increase in endogenous adenosine release, we tested a hypothesis that FK506 induces adenosine release via inhibition of adenosine kinase activity.

Desensitization and resensitization of adrenomedullin-sensitive receptor in rat mesangial cells.

Adrenomedullin is a potent adenylate cyclase activator and a vasodilatory peptide, that has anti-proliferative and apoptotic effects in rat mesangial cells. The present study was designed to determine the mechanisms of desensitization and resensitization of adrenomedullin-sensitive receptor in mesangial cells. Adrenomedullin caused a rapid desensitization of cAMP response evident within 5 min that was almost complete by 1 h of treatment.

Microalbuminuria in urban Zimbabwean women.

The prevalence of microalbuminuria (MAU) in African populations has not been reported, nor has the relationship between MAU and hypertension been reported for these populations. We collected spot urine samples from 370 women, 25 years and older as a part of a population-based, cross-sectional blood pressure survey in an urban community in Zimbabwe and analysed the samples for albumin and beta2-microglobulin. The age-adjusted prevalence of hypertension was 30% for women 25 years and older in this community.

Activation of multiple mitogen-activated protein kinases by recombinant calcitonin gene-related peptide receptor.

Calcitonin gene-related peptide is a 37-amino-acid neuropeptide and a potent vasodilator. Although calcitonin gene-related peptide has been shown to have a number of effects in a variety of systems, the mechanisms of action and the intracellular signaling pathways, especially the regulation of mitogen-activated protien kinase (MAPK) pathway, is not known. In the present study we investigated the role of calcitonin gene-related peptide in the regulation of MAPKs in human embryonic kidney (HEK) 293 cells stably transfected with a recombinant porcine calcitonin gene-related peptide-1 receptor.

Adrenomedullin decreases extracellular signal-regulated kinase activity through an increase in protein phosphatase-2A activity in mesangial cells.

Adrenomedullin is a recently identified peptide hormone that has receptors in a number of different systems including renal mesangial cells. We reported recently that adrenomedullin can cause a decrease in extracellular signal-regulated kinase (ERK) activity and increase jun amino-terminal kinase (JNK) and P38 mitogen-activated protein kinase (P38 MAPK) acitivities in rat mesangial cells. Associated with these responses we also reported that adrenomedullin can decrease proliferation and increase apoptosis in mesangial cells.

Regulation of glomerular mesangial cell proliferation in culture by adrenomedullin.

Adrenomedullin is a recently discovered vasodilatory peptide that has been shown to be a potent activator of adenylate cyclase in a variety of cell systems, including rat mesangial cells. The major aim of the present study was to determine the regulation of rat mesangial cell proliferation (using [3H]thymidine incorporation as an index), apoptosis (using nucleosome-associated cytoplasmic DNA fragmentation as an index) and mitogen-activated protein kinase (MAPK) cascade, specifically extracellular signal-regulated kinase (ERK), jun-amino terminal kinase (JNK) and P38 mitogen-activated protein kinase (P38 MAPK) activities, by adrenomedullin-stimulated cyclic AMP-protein kinase-A pathway. Adrenomedullin increased cAMP levels significantly above basal and the response was inhibited by the adrenomedullin receptor antagonist, adrenomedullin-(22-52).

SB203580 reverses adrenomedullin's effect on proliferation and apoptosis in cultured mesangial cells.

Adrenomedullin is a potent vasodilatory peptide that has a variety of effects in a number of different systems including kidney. In cultured rat glomerular mesangial cells adrenomedullin increases cAMP, decreases proliferation and increases apoptosis. Associated with the anti-proliferative and apoptotic effects, adrenomedullin also causes a decrease in extracellular signal-regulated kinase2 (ERK2) and an increase in cJun N-terminal kinase 1 (JNK1) and P38 mitogen-activated protein kinase (P38 MAPK) activities.

Mechanism of adrenomedullin-stimulated hyaluronic acid release in rat mesangial cells.

Adrenomedullin is a potent vasodilatory peptide that increases cAMP in a number of different systems including rat mesangial cells. Since mesangial cells play a significant role in glomerular matrix production, we evaluated the effects and molecular mechanisms of adrenomedullin action on hyaluronic acid release, an important extracellular matrix component. Adrenomedullin increased hyaluronic acid release in mesangial cells in a concentration-dependent manner.