Algal Toxin Azaspiracid-1 Induces Early Neuronal Differentiation and Alters Peripherin Isoform Stoichiometry.

Azaspiracid-1 is an algal toxin that accumulates in edible mussels, and ingestion may result in human illness as manifested by vomiting and diarrhoea. When injected into mice, it causes neurotoxicological symptoms and death. Although it is well known that azaspiracid-1 is toxic to most cells and cell lines, little is known about its biological target(s). A rat PC12 cell line, commonly used as a model for the peripheral nervous system, was used to study the neurotoxicological effects of azaspiracid-1. Azaspiracid-1 induced differentiation-related morphological changes followed by a latter cell death. The differentiated phenotype showed peripherin-labelled neurite-like processes simultaneously as a specific isoform of peripherin was down-regulated. The precise mechanism behind this down-regulation remains uncertain. However, this study provides new insights into the neurological effects of azaspiracid-1 and into the biological significance of specific isoforms of peripherin.

Increased interaction between DJ-1 and the Mi-2/ nucleosome remodelling and deacetylase complex during cellular stress.

DJ-1 was originally identified to be an oncogenic product, but has later been shown to be highly multifunctional. DJ-1 plays a role in oxidative stress response and transcriptional regulation, and loss of its function leads to an early onset of Parkinsonism. To further understand the mechanisms behind DJ-1's role in cell survival and death, we investigated alternations in endogenous DJ-1 protein-protein interaction in apoptotic cells exposed to the phosphatase inhibitor okadaic acid. By combining cellular stable isotopic labelling of amino acids in cell culture, sub-cellular fractionation, co-immunoprecipitation, and MS, we identified a novel group of DJ-1 interaction partners that increased their association to DJ-1 in okadaic acid-exposed cells. These proteins were integral components of the Mi-2/nucleosome remodelling and deacetylase (NuRD) complex. Knockdown of DJ-1 and MTA2, a core component of the NuRD complex, had a similar and pro-apoptotic effect on the transcriptional- and p53-dependent cell death induced by daunorubicin. On the other hand, MTA2 knockdown had no significant effect on the progression of p53-independent okadaic acid-induced apoptosis. Our data suggest that the increased DJ-1/NuRD interaction is a general anti-stress response regulated by okadaic acid-induced modifications of DJ-1. The observed interaction between DJ-1 and the NuRD complex may give new clues to how DJ-1 can protect cells from p53-dependent cell death.