PPIases Par14/Par17 Affect HBV Replication in Multiple Ways

Human parvulin 14 (Par14) and parvulin 17 (Par17) are peptidyl-prolyl cis/trans isomerases that upregulate hepatitis B virus (HBV) replication by binding to the conserved ¹³³Arg-Pro¹³⁴ (RP) motif of HBc and core particles, and ¹⁹RP²⁰-²⁸RP²⁹ motifs of HBx. In the absence of HBx, Par14/Par17 have no effect on HBV replication. Interaction with Par14/Par17 enhances the stability of HBx, core particles, and HBc. Par14/Par17 binds outside and inside core particles and is involved in HBc dimer-dimer interaction to facilitate core particle assembly. Although HBc RP motif is important for HBV replication, R133 residue is solely important for its interaction with Par14/Par17. Interaction of Par14 and Par17 with HBx involves two substrate-binding residues, Glu46/Asp74 (E46/D74) and E71/D99, respectively, and promotes HBx translocation to the nucleus and mitochondria. In the presence of HBx, Par14/Par17 are efficiently recruited to cccDNA and promote transcriptional activation via specific DNA-binding residues Ser19/44 (S19/44). S19 and E46/D74 of Par14, and S44 and E71/D99 of Par17, are also involved in the recruitment of HBc onto cccDNA. Par14/Par17 upregulate HBV replication via various effects that are mediated in part through the HBx-Par14/Par17-cccDNA complex and triple HBc, Par14/Par17, and cccDNA interactions in the nucleus, as well as via core particle-Par14/Par17 interactions in the cytoplasm.

FKBP51 and FKBP52 regulate androgen receptor dimerization and proliferation in prostate cancer cells

The growth of prostate cancer is dependent on the androgen receptor (AR), which serves as a ligand-specific transcription factor. Although two immunophilins, FKBP51 and FKBP52, are known to regulate AR activity, the precise mechanism remains unclear. We found that depletion of either FKBP51 or FKBP52 reduced AR dimer formation, chromatin binding, and phosphorylation, suggesting defective AR signaling. Furthermore, the peptidyl-prolyl cis/trans isomerase activity of FKBP51 was found to be required for AR dimer formation and cancer cell growth. Treatment of prostate cancer cells with FK506, which binds to the FK1 domain of FKBPs, or with MJC13, an inhibitor of FKBP52-AR signaling, also inhibited AR dimer formation. Finally, elevated expression of FKBP52 was associated with a higher rate of prostate-specific antigen recurrence in patients with prostate cancer. Collectively, these results suggest that FKBP51 and FKBP52 might be promising targets for prostate cancer treatment through the inhibition of AR dimer formation.

Sustained and targeted delivery of siRNA/DP7-C nanoparticles from injectable thermosensitive hydrogel for hepatocellular carcinoma therapy

Hepatocellular carcinoma (HCC) is one of the most lethal cancers in humans. The inhibition of peptidyl‐prolyl cis/trans isomerase (Pin1) gene expression may have great potential in the treatment of HCC. N‐Acetylgalactosamine (GalNAc) was used to target the liver. Cholesterol‐modified antimicrobial peptide DP7 (DP7‐C) acts as a carrier, the GalNAc‐siRNA/DP7‐C complex increases the uptake of GalNAc‐siRNA and the escape of endosomes in hepatocytes. In addition, DP7‐C nanoparticles and hydrogel‐assisted GalNAc‐Pin1 siRNA delivery can effectively enhance the stability and prolong the silencing effects of Pin1 siRNA. In an orthotopic liver cancer model, the GalNAc‐Pin1 siRNA/DP7‐C/hydrogel complex can potentially regulate Pin1 expression in hepatocellular carcinoma cells and effectively inhibit tumor progression. Our study proves that Pin1 siRNA is an efficient method for the treatment of HCC and provides a sustainable and effective drug delivery system for the suppression of liver cancer.

Targeting of parvulin interactors by diazirine mediated cross-linking discloses a cellular role of human Par14/17 in actin polymerization

The peptidyl-prolyl cis/trans isomerases (PPIases) Parvulin 14 (Par14) and Parvulin 17 (Par17) result from alternative transcription initiation of the PIN4 gene. Whereas Par14 is present in all metazoan, Par17 is only expressed in Hominidae. Par14 resides mainly within the cellular nucleus, while Par17 is translocated into mitochondria. Using photo-affinity labeling, cross-linking and mass spectrometry (MS) we identified binding partners for both enzymes from HeLa lysates and disentangled their cellular roles. Par14 is involved in biogenesis of ribonucleoprotein (RNP)-complexes, RNA processing and DNA repair. Its elongated isoform Par17 participates in protein transport/translocation and in cytoskeleton organization. Nuclear magnetic resonance (NMR) spectroscopy reveals that Par17 binds to β-actin with its N-terminal region, while both parvulins initiate actin polymerization depending on their PPIase activity as monitored by fluorescence spectroscopy. The knockdown (KD) of Par17 in HCT116 cells results in a defect in cell motility and migration.

Peptidyl-Prolyl-cis/trans-Isomerases Mip and PpiB of Legionella pneumophila Contribute to Surface Translocation, Growth at Suboptimal Temperature, and Infection

The gammaproteobacterium Legionella pneumophila is the causative agent of Legionnaires' disease, an atypical pneumonia that manifests itself with severe lung damage. L. pneumophila, a common inhabitant of freshwater environments, replicates in free-living amoebae and persists in biofilms in natural and man-made water systems. Its environmental versatility is reflected in its ability to survive and grow within a broad temperature range as well as its capability to colonize and infect a wide range of hosts, including protozoa and humans. Peptidyl-prolyl-cis/trans-isomerases (PPIases) are multifunctional proteins that are mainly involved in protein folding and secretion in bacteria. In L. pneumophila the surface-associated PPIase Mip was shown to facilitate the establishment of the intracellular infection cycle in its early stages. The cytoplasmic PpiB was shown to promote cold tolerance. Here, we set out to analyze the interrelationship of these two relevant PPIases in the context of environmental fitness and infection. We demonstrate that the PPIases Mip and PpiB are important for surfactant-dependent sliding motility and adaptation to suboptimal temperatures, features that contribute to the environmental fitness of L. pneumophila Furthermore, they contribute to infection of the natural host Acanthamoeba castellanii as well as human macrophages and human explanted lung tissue. These effects were additive in the case of sliding motility or synergistic in the case of temperature tolerance and infection, as assessed by the behavior of the double mutant. Accordingly, we propose that Mip and PpiB are virulence modulators of L. pneumophila with compensatory action and pleiotropic effects.

Activation and Polarity Control of PIN-FORMED Auxin Transporters by Phosphorylation

Auxin controls almost every aspect of plant development. Auxin is distributed within the plant by passive diffusion and active cell-to-cell transport. PIN-FORMED (PIN) auxin efflux transporters are polarly distributed in the plasma membranes of many cells, and knowledge about their distribution can predict auxin transport and explain auxin distribution patterns, even in complex tissues. Recent studies have revealed that phosphorylation is essential for PIN activation, suggesting that PIN phosphorylation needs to be taken into account in understanding auxin transport. These findings also ask for a re-examination of previously proposed mechanisms for phosphorylation-dependent PIN polarity control. We provide a comprehensive summary of the current knowledge on PIN regulation by phosphorylation, and discuss possible mechanisms of PIN polarity control in the context of recent findings.

Regulation of Microtubule Assembly by Tau and not by Pin1

The molecular mechanism by which the microtubule-associated protein (MAP) tau regulates the formation of microtubules (MTs) is poorly understood. The activity of tau is controlled via phosphorylation at specific Ser/Thr sites. Of those phosphorylation sites, 17 precede a proline, making them potential recognition sites for the peptidyl-prolyl isomerase Pin1. Pin1 binding and catalysis of phosphorylated tau at the AT180 epitope, which was implicated in Alzheimer's disease, has been reported to be crucial for restoring tau's ability to promote MT polymerization in vitro and in vivo [1]. Surprisingly, we discover that Pin1 does not promote phosphorylated tau-induced MT formation in vitro, refuting the commonly accepted model in which Pin1 binding and catalysis on the A180 epitope restores the function of the Alzheimer's associated phosphorylated tau in tubulin assembly [1, 2]. Using turbidity assays, time-resolved small angle X-ray scattering (SAXS), and time-resolved negative stain electron microscopy (EM), we investigate the mechanism of tau-mediated MT assembly and the role of the Thr231 and Ser235 phosphorylation on this process. We discover novel GTP-tubulin ring-shaped species, which are detectable in the earliest stage of tau-induced polymerization and may play a crucial role in the early nucleation phase of MT assembly. Finally, by NMR and SAXS experiments, we show that the tau molecules must be located on the surface of MTs and tubulin rings during the polymerization reaction. The interaction between tau and tubulin is multipartite, with a high affinity interaction of the four tubulin-binding repeats, and a weaker interaction with the proline-rich sequence and the termini of tau.