Id2 is a HLH factor with well established role in cellular proliferation and differentiation. Traditionally Id2 is classified as a dominant negative member of the HLH family, yet it shows broad association with proteins from other families. Changes in its expression in response to hormonal and growth signal differs greatly between cell types though little is known about its regulation in macrophages. In this study the regulation of Id2 protein expression by glucose and hormones is studied in J774.2 macrophages. In J774.2 cells glucose induces increases in protein levels of Id2. Up regulation of Id2 requires glutamine, is mimicked by glucosamine and is inhibited by azaserine, an inhibitor of glutamine:fructose-6-phosphate amidotransferase (GFAT). Further, adenoviral mediated overexpression of GFAT increases levels of Id2. We conclude that hexosamine pathway mediate changes in Id2 level. Effect of glucose is cell type specific. While a similar effect is observed in Hepatocyte, little or no changes occur in L6 Myocytes and 3T3-L1 Adipocytes. Id2 acts as negative regulator of transcription by forming inactive heterodimer with other members of the HLH family such as SREBP-1. Previously, work in the laboratory has shown that high levels of glucose prime J774.2 macrophages in such a way that insulin and leptin are able to reduce expression of hormone sensitive lipase (HSL). Here we observe that activity of mouse HSL promotor is increased when co-expressed with SREBP-1. The SREBP-1 induced increase in HSL promoter activity is attenuated upon co-expression with Id2, indicating that increased Id2 levels can mimic the effects of high glucose. Id2 expression in J774.2 cells is affected by intracellular cAMP raising agents and insulin. Effect of cAMP is mediated by Epac through PI3 kinase dependent pathway. GSK3 is the end effector of both cAMP and insulin effect, its inactivation leads to up regulation of Id2 protein level.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:423099 |
| Date | January 2006 |
| Creators | Tingsabadh, Rommaneeya |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1445872/ |
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