Cell Proliferation and Glucose Transport: The Intracellular Signal Transduction Pathways that Mediate the Early Phase of Growth Factor-Stimulated Glucose Transport

Biochemistry

Merrall, Nicola Wendy

University:University of Glasgow

关键词: Biochemistry;   

Others  :  http://theses.gla.ac.uk/75815/1/13818551.pdf

来源: University of Glasgow

【 摘 要 】

Growth factors stimulate glucose transport; the increase in the rate is biphasic, with the early phase occurring immediately and lasting up to two hours. 3T3-L1 fibroblasts are a murine cell line which express a single facilitative monosaccharide transporter, Glut1. Insulin and platelet-derived growth factor (PDGF) stimulate cell proliferation in 3T3-L1 fibroblasts. These growth factors and the tumour promoter, 4beta-phorbol 12-myristate, 13-acetate (PMA), all stimulate 2-deoxyglucose uptake, in a similar manner. These effects are not additive, so the effects of these ligands on the rate of glucose transport may be mediated by a similar signal transduction pathway. The role of sn-1,2-diacylglycerol (DAG) and protein kinase C (PKC) in the early phase of insulin-, PDGF- and PMA-stimulated glucose transport was examined in 3T3-L1 fibroblasts. Insulin has no effect on either DAG accumulation or PKC activity, so neither DAG nor PKC is necessary for insulin-stimulated glucose transport. PDGF stimulates both DAG accumulation and PKC activity; however, PDGF-stimulated glucose transport is unaffected by the down-regulation or the inhibition of PKC, so PKC is not necessary for PDGF-stimulated glucose transport. PMA also stimulates both DAG accumulation and PKC activity, and PMA-stimulated glucose transport is abolished by the down-regulation and the inhibition of PKC, so PKC is necessary for PMA-stimulated glucose transport. Thus, a signal transduction pathway involving PKC is not necessary for the early phase of insulin- or PDGF-stimulated glucose transport, but it is necessary for the early phase of PMA-stimulated glucose transport. The role of mitogen-activated protein kinase (MARK) in the early phase of insulin-, PDGF- and PMA-stimulated glucose transport was also examined in 3T3-L1 fibroblasts. Insulin, PDGF and PMA stimulate MAPK activity with the same dependancy on PKC as for the increase in the rate of glucose transport. In addition, insulin-, PDGF- and PMA-stimulated activation of MAPK precedes the increase in the rate of glucose transport.Therefore, given that the activation of MAPK and the increase in the rate of glucose transport have the same dependency on PKC, and that the activation of MAPK precedes the increase in the rate of glucose transport, it is possible that the early phase of growth factor-stimulated glucose transport is mediated by a signal transduction pathway involving MAPK in 3T3-L1 fibroblasts. Xenopus laevis oocytes also only express Glut1. Insulin-like growth factor-I (IGF-I) stimulates both glucose transport and MAPK activity in X. laevis oocytes. Again, the activation of MAPK precedes the increase in the rate of glucose transport. In addition, the microinjection into X laevis oocytes of recombinant p42mapk, purified MAPK kinase (MAPKK) or p39mos fusion protein, results in an increase in the rate of glucose transport. Since p39mos activates MAPKK, which in turn activates MAPK, it seems that components of a signal transduction pathway involving MAPK are able to stimulate glucose transport in X. laevis oocytes. Furthermore, IGF-I-stimulated glucose transport is inhibited by the microinjection of CLIOO, a protein tyrosine/ threonine phosphatase that is specific for MAPK. Therefore, given that IGF-I stimulates both glucose transport and MAPK activity, that components of a signal transduction pathway involving MAPK also stimulate glucose transport, and that inhibition of MAPK activity abolishes IGF-I-stimulated glucose transport, it is likely that IGF-I-stimulated glucose transport is mediated by a signal transduction pathway involving MAPK in X. laevis oocytes. The insulin and IGF-I receptors are tyrosine protein kinases of a similar structure, and either ligand can bind to either receptor, so it is likely that insulin- and IGF-I- stimulated glucose transport are mediated by a similar signal transduction pathway. Therefore, given that it is possible that the early phase of growth factor-stimulated glucose transport is mediated by a signal transduction pathway involving MAPK in 3T3-L1 fibroblasts, that it is likely that IGF-I-stimulated glucose transport is mediated by a signal transduction pathway involving MAPK in X. laevis oocytes, and that it is likely that insulin- and IGF-I-stimulated glucose transport are mediated by a similarsignal transduction pathway, it seems that the early phase of insulin-stimulated glucose transport in 3T3-L1 fibroblasts is, in fact, mediated by a pathway involving MAPK. Furthermore, PDGF, which also binds to a tyrosine protein kinase receptor, has similar effects to insulin on the rate of glucose transport and the activation of MAPK in 3T3-L1 fibroblasts. Therefore, it is also likely that the early phase of PDGF-stimulated glucose transport is also mediated by a signal transduction pathway involving MAPK. This thesis concludes that the early phase of growth factor-stimulated glucose transport is mediated by a signal transduction pathway involving MAPK.