The PED/PEA-15 diabetogene as a potential thiazolidinedione target in type 2 diabetes treatment

Mirra, Paola (2008) The PED/PEA-15 diabetogene as a potential thiazolidinedione target in type 2 diabetes treatment. [Tesi di dottorato] (Inedito)

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Abstract

The phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (PED/PEA-15) gene is over-expressed in tissues from individuals with type 2 diabetes. In cultured cells and in vivo, ped/pea-15 over-expression impairs insulin activation of protein kinase C zeta (PKCζ) and glucose disposal. Indeed, transgenic mice ubiquitously over-expressing ped/pea-15 feature impaired glucose tolerance and insulin resistance. However, it is still unknown how PED/PEA-15 gene expression is regulated. Recently, we have obtained evidence that Thiazolidinediones (TZDs), a class of peroxisome proliferator-activated receptor gamma (PPARγ) ligands, repress ped/pea-15 expression both at mRNA and protein levels. PPARγ is a member of the nuclear hormone receptor super-family that modulates gene expression upon ligand binding. Ligand-mediated activation of PPARγ has been linked to glucose homeostasis, cellular differentiation, apoptosis and anti-inflammatory responses. The aim of this work was to study whether and how TZD-activated PPARγ may exert its action on ped/pea-15 expression. In L6 skeletal muscle cells, rosiglitazone (RGTZ) decreased both ped/pea-15 mRNA and protein levels. This was paralleled by the RGTZ-dependent reduction of PKCα activation and a consequent increase of PKCζ activity. Consistent with the in vitro data, muscle tissue from control mice showed a 40% decrease of ped/pea-15 protein levels upon 10 days of treatment with RGTZ. HeLa cells treated with TPA, the prototypical AP1 activator, showed an increase in PED/PEA-15 mRNA levels. TPA induced also the activation of PED/PEA-15 promoter activity measured by luciferase assays. Interestingly, TPA effect was suppressed by RGTZ. EMSA and ChIP assays revealed that TPA caused an increased binding to the CRE-like site (a putative AP1 binding site) on the PED/PEA-15 promoter, and this binding was reduced by RGTZ. Since PPARγ activation by TZDs blocks AP1-mediated gene transcription, we hypothesized that PPARγ transrepression of the PED/PEA-15 gene could be due to a competition for limiting amounts of co-activators present in the cell. Indeed, the suppressive effect of rosiglitazone on PED/PEA-15 gene expression was blocked by over-expressing a dominant negative form of PPARγ, which lacks the ability to recruit the coactivator CBP/p300 (CREB-binding protein). The over-expression of p300 did not rescue the cells from the suppressive effect of PPARγ on PED/PEA-15 promoter activity, suggesting that PPARγ-mediated repression of AP1 transcriptional activity occurs in a CBP/p300-independent manner. Taken together, these results indicate that regulation through the CRE-like site on PED/PEA-15 promoter induces PED/PEA-15 transcription. This effect was blocked by treatment with TZDs. Finally, the results of this study identified PED/PEA-15 gene as a potential target for TZDs therapeutic action.

Tipologia di documento:Tesi di dottorato
Parole chiave:Type 2 diabetes; Thiazolidinediones; ped/pea-15
Settori scientifico-disciplinari MIUR:Area 06 Scienze mediche > MED/04 PATOLOGIA GENERALE
Coordinatori della Scuola di dottorato:
Coordinatore del Corso di dottoratoe-mail (se nota)
Vecchio, Giancarlovecchio@unina.it
Tutor della Scuola di dottorato:
Tutor del Corso di dottoratoe-mail (se nota)
Beguinot, Francescobeguino@unina.it
Stato del full text:Inedito
Data:09 Dicembre 2008
Numero di pagine:93
Istituzione:Università di Napoli, Federico II
Dipartimento o Struttura:Dipartimento di Biologia e Patologia Cellulare e Molecolare “L. Califano” - Università degli Studi di Napoli, “Federico II”
Tipo di tesi:Dottorato
Stato dell'Eprint:Inedito
Scuola di dottorato:Medicina Molecolare
Denominazione del dottorato:Dottorato di Ricerca in Oncologia ed Endocrinologia Molecolare
Ciclo di dottorato:XXI° ciclo
Numero di sistema:3408
Depositato il:17 Novembre 2009 10:49
Ultima modifica:17 Novembre 2009 10:49

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