Formin homology proteins are a highly conserved family of cytoskeletal remodeling proteins best known for their ability to induce the formation of long unbranched actin filaments. They accomplish this by nucleating the de novo polymerization of F-actin and also by acting as F-actin barbed end "leaky cappers" that allow filament elongation while antagonizing the function of capping proteins. More recently, it has been reported that the FH2 domains of FRL1 and mDia2 and the plant formin AFH1 are able to bind and bundle actin filaments via distinct mechanisms. We find that like FRL1, FRL2 and FRL3 are also able to bind and bundle actin filaments. In the case of FRL3, this activity is dependent upon a proximal DAD/WH2-like domain that is found C-terminal to the FH2 domain. In addition, we show that, like other Diaphanousrelated formins, FRL3 activity is subject to autoregulation mediated by the interaction between its N-terminal DID and C-terminal DAD. In contrast, the DID and DAD of FRL2 also interact in vivo and in vitro but without inhibiting FRL2 activity. These data suggest that current models describing DID/ DAD autoregulation via steric hindrance of FH2 activity must be revised. Finally, unlike other formins, we find that the FH2 and N-terminal dimerization domains of FRL2 and FRL3 are able to form hetero-oligomers.Formin homology proteins (formins) are a highly conserved family of cytoskeletal regulatory proteins. Over 30 formins have been described to date, with more than 15 family members found in vertebrates (1). Formin activity is required in vivo for a diverse array of cellular functions, such as stress fiber formation, endosome motility, cell motility, cytokinetic ring formation, cell-cell junction assembly, filopodia formation, induction of cell polarity, and activation of the MAL/serum response factor signaling pathway (2-13). It is thought that at the core of all of these activities is the ability of formins to regulate actin cytoskeletal dynamics. This is achieved through the activity of two conserved formin homology domains, FH1 and FH2. FH1 consists of proline-rich repeats of varying sizes that can serve as ligands for Src homology 3 and WW domains as well as the small actin-binding protein profilin (14,15). FH2 domains form a dimer that induces the polymerization of long, unbranched filaments. It does this by nucleating de novo actin polymerization and by associating with the F-actin barbed end as a "leaky capper," allowing filament elongation while antagonizing the function of capping proteins (16). However, not all formins nucleate or elongate F-actin with equal potency. For example, mDia1 is an extremely efficient nucleator of polymerization, and its association with the barbed end of actin filaments accelerates elongation (16,17). In contrast, the isolated FH2 domain of FHOD1 does not induce actin polymerization in vivo (18). In addition, FH2 activity may also be influenced by the activity of adjacent domains. For example, in INF2, a WH2 G-actin binding motif antagonizes the nucleation activ...

Loss-of-function mutations in DJ-1 (PARK7) gene account for about 1% of all familial Parkinson's disease (PD). While its physiological function(s) are not completely clear, DJ-1 protects neurons against oxidative stress in both in vitro and in vivo models of PD. The molecular mechanism(s) through which DJ-1 alleviates oxidative stress-mediated damage remains elusive. In this study, we identified Paraoxonase-2 (PON2) as an interacting target of DJ-1. PON2 activity is elevated in response to oxidative stress and DJ-1 is crucial for this response. Importantly, we showed that PON2 deficiency hypersensitizes neurons to oxidative stress induced by MPP+ (1-methyl-4-phenylpyridinium). Conversely, over-expression of PON2 protects neurons in this death paradigm. Interestingly, PON2 effectively rescues DJ-1 deficiency-mediated hypersensitivity to oxidative stress. Taken together, our data suggest a model by which DJ-1 exerts its antioxidant activities, at least partly through regulation of PON2.

Mammalian cell-free systems are very useful for the biochemical and structural study of nuclear disassembly and assembly. Through experimental manipulations, the role of specific proteins in these processes can be studied. Recently, we intended to examine the involvement of integral and peripheral inner nuclear membrane proteins in nuclear disassembly and assembly. However, we could not achieve proper disassembly when isolated interphase HeLa nuclei were exposed to mitotic soluble extracts obtained from the same cell line and containing cyclin B1. Homogenates of synchronized mitotic HeLa cells left to reassemble their nuclei generated incomplete nuclear envelopes on chromatin masses. Digitonin-permeabilized mitotic cells also assembled incomplete nuclei, generating a lot of cytoplasmic inclusions of inner nuclear membrane proteins as an intermediate. These results were therefore used as a basis for a critical evaluation of mammalian cell-free systems. We present here evidence that cell synchronization itself can interfere with the progress of nuclear assembly, possibly by causing aberrant nuclear disassembly and/or by inducing the formation of an abnormal number of mitotic spindles.