No abstract

A survey of PDE4 inhibitors reveals that some compounds trigger intracellular aggregation of PDE4A4 into accretion foci through association with the ubiquitin-binding scaffold protein p62 (SQSTM1). We show that this effect is driven by inhibitor occupancy of the catalytic pocket and stabilization of a "capped state" in which a sequence within the enzyme's upstream conserved region 2 (UCR2) module folds across the catalytic pocket. Only certain inhibitors cause PDE4A4 foci formation, and the structural features responsible for driving the process are defined. Switching to the UCR2-capped state induces conformational transition in the enzyme's regulatory N-terminal portion, facilitating protein association events responsible for reversible aggregate assembly. PDE4-selective inhibitors able to trigger relocalization of PDE4A4 into foci can therefore be expected to exert actions on cells that extend beyond simple inhibition of PDE4 catalytic activity and that may arise from reconfiguring the enzyme's protein association partnerships.

Cohesins are a group of proteins that function to mediate correct chromosome segregation, DNA repair and meiotic recombination. This report presents the amino acid sequence for the Schizosaccharomyces pombe cohesin Psc3 based on the translation of the cDNA sequence, showing that the protein is smaller than previously predicted. Interestingly, comparison of the amino acid and DNA coding sequences of Psc3 with fission yeast Rec11 meiotic region-specific recombination activator shows that both intron positioning within the genes and the amino-terminal half of the two proteins are highly conserved. We demonstrate that although the intergenic region upstream of the psc3+ start codon contains a consensus sequence for the cell-cycle regulatory MluI cell-cycle box, psc3+ transcription is not differentially regulated during the mitotic cell cycle. Finally, we demonstrate that an epitope-tagged version of Psc3 undergoes no major changes during the mitotic cell cycle. However, instead we identify at least three distinct isoforms of Psc3, suggesting that post-translational modification of Psc3 contributes to the regulation of cohesion function.