Somatostatin Regulates the Extracellular Regulated Kinase Cascade of Human Rheumatoid Arthritis Synoviocytes
Date of Award
Somatostatin, Kinase cascade, Human rheumatoid arthritis synoviocytes
Somatostatin (SRIF, somatotropin release inhibitory factor) is a ubiquitously expressed neuropeptide, interacting with cells via five SRIF receptor subtypes (sst.-sst.), belonging to the guanine nucleotide binding protein-coupled receptor (GPCR) superfamily. SRIF receptors have been well documented for their ability to inhibit cell proliferation and secretion in a variety of animal tissues. Over the past l S years, pre-clinical and clinical studies implicate that SRIF and SRIF analog therapy improve symptoms in patients suffering from rheumatoid arthritis (RA). In this study, we investigate SRIF's effects on intracellular signaling in the synovium, the cellular layer that lines synovial joints, using in vitro cultures of human synovial fibroblasts. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis of synovial isolated mRNA established the presence of sst, in these cells. The sst, receptor links somatostatin action to control of synovial intracellular signaling. We have examined SRIF effects on the synoviocyte extracellular regulated kinase pathway (ERK). Using phospho-specific antisera, we demonstrate that SRIF and SRIF analogs decrease phospho-ERK.1/2 levels, suggesting basal ERK.1/2 is upregulated in RA synoviocytes. SRIF also suppressed basal levels of activated Raf and MEKl/2, two upstream regulatory kinases ofERKl/2. Furthermore, SRIF suppressed 1NFa stimulated activation ofERK.112 in RA synoviocytes. We also observed that SRIF increases a sodium vanadate-sensitive intracellular protein phosphatase activity in RA synoviocytes, indicating a possible intracellular mechanism by which SRIF controls the phosphorylation status of the ERK.112 kinases. Fluorescent confocal scanning microscopy reveals that TNF-o. stimulated the localization of phospho-ERK.112 in the nuclei of RA synoviocytes, which was inhibited upon co-treatment with SRIF. Taken together our results demonstrate that SRIF regulates intracellular signaling in rheumatoid synoviocytes.
West, Frances Mae, "Somatostatin Regulates the Extracellular Regulated Kinase Cascade of Human Rheumatoid Arthritis Synoviocytes" (2006). Seton Hall University Dissertations and Theses (ETDs). 2470.