Gadd45β dimerization does not affect MKK7 binding

摘要

The Gadd45 family comprises three small acidic proteins, α,β, and γ, largely involved in cellular response to genotoxic stress and DNA damage. They exert and mediate a large number of functions, including regulation of cell cycle, indeed, it has been demonstrated that, depending on cell type or tissues, Gadd45α and Gadd45γ have strong pro-apoptotic properties, whereas, Gadd45β is a potent mediator of the protective effects of NF-kB against the TNFα induced apoptosis [1,2]. Gadd45β fulfils this function by strongly interacting with MKK7, an essential JNK activator, and blocking its catalytic activity [1,2] and this mechanism has been largely investigated elucidating key residues on both the kinase [1] and the Gadd45 protein [2]. The regions 132-156 of MKK7, containing the ATP-binding K149, and 60-86 of Gadd45β, containing a large acidic stretch, participate in this interaction and the corresponding synthetic peptides strongly block the Gadd45β/MKK interaction and promote apoptosis when administered to RelA~(-/-) cells [1,2]. Based on large biochemical and site-directed mutagenesis data, a 3D model of the MKK7/Gadd45β has been proposed, corroborating the view that the acidic loop D61-169 of Gadd45β enters the kinase catalytic pocket and prevents access to the ATP, thereby inactivating the enzyme. However, Gadd45 proteins interact with several other partners and in addition, it has been reported that they all can homo-and/or hetero-dimerize or oligomerize [3]. With the aim of studying the influence that Gadd45β oligomerization can have on MKK7 binding and, therefore, on the mechanism by which NF-kB counteracts the TNFα-mediated programmed cell death, we have here investigated the Gadd45β regions involved in self-association.