The prokaryotic ubiquitin-like protein presents poor cleavage sites for proteasomal degradation.

In an event reminiscent of eukaryotic ubiquitination, the bacterial prokaryotic ubiquitin-like protein (Pup)-proteasome system (PPS) marks target proteins for proteasomal degradation by covalently attaching Pup, the bacterial tagging molecule. Yet, ubiquitin is released from its conjugated target following proteasome binding, whereas Pup enters the proteasome and remains conjugated to the target. Here, we report that although Pup can be degraded by the bacterial proteasome, it lacks favorable 20S core particle (CP) cleavage sites and is thus a very poor 20S CP substrate. Reconstituting the PPS in vitro, we demonstrate that during pupylated protein degradation, Pup can escape unharmed and remain conjugated to a target-derived degradation fragment. Removal of this degradation fragment by Dop, a depupylase, facilitates Pup recycling and re-conjugation to a new target. This study thus offers a mechanistic model for Pup recycling and demonstrates how a lack of protein susceptibility to proteasome-mediated cleavage can play a mechanistic role in a biological system.

The Expression Levels and Cellular Localization of Pigment Epithelium Derived Factor (PEDF) in Mouse Testis: Its Possible Involvement in the Differentiation of Spermatogonial Cells.

Pigment epithelium derived factor (PEDF) is a multifunctional secretory soluble glycoprotein that belongs to the serine protease inhibitor (serpin) family. It was reported to have neurotrophic, anti-angiogenic and anti-tumorigenic activity. Recently, PEDF was found in testicular peritubular cells and it was assumed to be involved in the avascular nature of seminiferous tubules. The aim of this study was to determine the cellular origin, expression levels and target cells of PEDF in testicular tissue of immature and adult mice under physiological conditions, and to explore its possible role in the process of spermatogenesis in vitro. Using immunofluorescence staining, we showed that PEDF was localized in spermatogenic cells at different stages of development as well as in the somatic cells of the testis. Its protein levels in testicular homogenates and Sertoli cells supernatant showed a significant decrease with age. PEDF receptor (PEDF-R) was localized within the seminiferous tubule cells and in the interstitial cells compartment. Its RNA expression levels showed an increase with age until 8 weeks followed by a decrease. RNA levels of PEDF-R showed the opposite trend of the protein. Addition of PEDF to cultures of isolated cells from the seminiferous tubules did not changed their proliferation rate, however, a significant increase was observed in number of meiotic/post meiotic cells at 1000 ng/mL of PEDF; indicating an in vitro differentiation effect. This study may suggest a role for PEDF in the process of spermatogenesis.

The Use of Tamoxifen as a Potential Treatment for Bipolar Disorder.

Bipolar disorder (BD) is a chronic mental disease that substantially affects the patient's quality of life and causes significant morbidity and mortality. Although there are a variety of available treatments, therapeutic intervention is not beneficial in many cases and recurrence rates remain high. Recent data suggested tamoxifen, a drug with a wide range of activities, as a potential treatment for reducing manic symptoms of BD. Tamoxifen's therapeutic effect on bipolar mania has not been fully elucidated, but it is believed to biochemically operate on protein kinase C (PKC) inhibition. In this article, we review preclinical and clinical studies investigating the efficacy of tamoxifen as a potential treatment for bipolar manic patients.