The fine-tuning of TRAF2-GSTP1-1 interaction: effect of ligand binding and in situ detection of the complex.

A. De Luca, G. Mei, N. Rosato, E. Nicolai, L. Federici, C. Palumbo, A. Pastore, M. Serra, A. M. Caccuri

Research output: Contribution to journalArticlepeer-review

Abstract

We provide the first biochemical evidence of a direct interaction between the glutathione transferase P1-1 (GSTP1-1) and the TRAF domain of TNF receptor-associated factor 2 (TRAF2), and describe how ligand binding modulates such an equilibrium. The dissociation constant of the heterocomplex is K(d)=0.3 μM; however the binding affinity strongly decreases when the active site of GSTP1-1 is occupied by the substrate GSH (K(d)≥2.6 μM) or is inactivated by oxidation (Kd=1.7 μM). This indicates that GSTP1-1's TRAF2-binding region involves the GSH-binding site. The GSTP1-1 inhibitor NBDHEX further decreases the complex's binding affinity, as compared with when GSH is the only ligand; this suggests that the hydrophobic portion of the GSTP1-1 active site also contributes to the interaction. We therefore hypothesize that TRAF2 binding inactivates GSTP1-1; however, analysis of the data, using a model taking into account the dimeric nature of GSTP1-1, suggests that GSTP1-1 engages only one subunit in the complex, whereas the second subunit maintains the catalytic activity or binds to other proteins. We also analyzed GSTP1-1's association with TRAF2 at the cellular level. The TRAF2-GSTP1-1 complex was constitutively present in U-2OS cells, but strongly decreased in S, G2 and M phases. Thus the interaction appears regulated in a cell cycle-dependent manner. The variations in the levels of individual proteins seem too limited to explain the complex's drastic decline observed in cells progressing from the G0/G1 to the S-G2-M phases. Moreover, GSH's intracellular content was so high that it always saturated GSTP1-1. Interestingly, the addition of NBDHEX maintains the TRAF2-GSTP1-1 complex at low levels, thus causing a prolonged cell cycle arrest in the G2/M phase. Overall, these findings suggest that a reversible sequestration of TRAF2 into the complex may be crucial for cell cycle progression and that multiple factors are involved in the fine-tuning of this interaction.

Original languageEnglish
JournalCell Death and Disease
Volume5
DOIs
Publication statusPublished - 2014

ASJC Scopus subject areas

  • Medicine(all)

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