PAK in pathogen-host interactions

Mechanism by Which PF-3758309, a Pan Isoform Inhibitor of p21-Activated Kinases, Blocks Reactivation of HIV-1 Latency

The "block and lock" strategy is one approach that might elicit a sterilizing cure for HIV-1 infection. The "block" refers to a compound's ability to inhibit latent HIV-1 proviral transcription, while the "lock" refers to its capacity to induce permanent proviral silencing. We previously identified PF-3758309, a pan-isoform inhibitor of p21-activated kinases (PAKs), as a potent inhibitor of HIV-1 latency reversal. The goal of this study was to define the mechanism(s) involved. We found that both 24ST1NLESG cells (a cell line model of HIV-1 latency) and purified CD4+ naïve and central memory T cells express high levels of PAK2 and lower levels of PAK1 and PAK4. Knockdown of PAK1 or PAK2, but not PAK4, in 24ST1NLESG cells resulted in a modest, but statistically significant, decrease in the magnitude of HIV-1 latency reversal. Overexpression of PAK1 significantly increased the magnitude of latency reversal. A phospho-protein array analysis revealed that PF-3758309 down-regulates the NF-κB signaling pathway, which provides the most likely mechanism by which PF-3758309 inhibits latency reversal. Finally, we used cellular thermal shift assays combined with liquid chromatography and mass spectrometry to ascertain whether PF-3758309 off-target binding contributed to its activity. In 24ST1NLESG cells and in peripheral blood mononuclear cells, PF-3758309 bound to mitogen-activated protein kinase 1 and protein kinase A; however, knockdown of either of these kinases did not impact HIV-1 latency reversal. Collectively, our study suggests that PAK1 and PAK2 play a key role in the maintenance of HIV-1 latency.

Transcriptome analysis of Anopheles dirus and Plasmodium vivax at ookinete and oocyst stages

Malaria is transmitted by Plasmodium parasites through the bite of female Anopheles mosquitoes. One of the most important mosquito vectors in the Greater Mekong Subregion is Anopheles dirus. This study reports RNA sequencing (RNA-Seq) transcriptome analysis of An. dirus at 18 hours and 7 days after a P. vivax-infected blood meal, which represent infection at the ookinete and oocyst parasite developmental stages, respectively. Following infection, 582 An. dirus transcripts were modulated. The 2,408 P. vivax transcripts could be classified into ookinete-specific, two-stage, and oocyst-specific groups. Results were validated by quantitative reverse transcription polymerase chain reaction. Gene ontology analysis of the vector and parasite revealed several biological pathways for both, providing a better understanding of Anopheles-Plasmodium interactions at the ookinete and oocyst stages.

Subverting Host Cell P21-Activated Kinase: A Case of Convergent Evolution across Pathogens

Intracellular pathogens have evolved a wide range of strategies to not only escape from the immune systems of their hosts, but also to directly exploit a variety of host factors to facilitate the infection process. One such strategy is to subvert host cell signalling pathways to the advantage of the pathogen. Recent research has highlighted that the human serine/threonine kinase PAK, or p21-activated kinase, is a central component of host-pathogen interactions in many infection systems involving viruses, bacteria, and eukaryotic pathogens. PAK paralogues are found in most mammalian tissues, where they play vital roles in a wide range of functions. The role of PAKs in cell proliferation and survival, and their involvement in a number of cancers, is of great interest in the context of drug discovery. In this review we discuss the latest insights into the surprisingly central role human PAK1 plays for the infection by such different infectious disease agents as viruses, bacteria, and parasitic protists. It is our intention to open serious discussion on the applicability of PAK inhibitors for the treatment, not only of neoplastic diseases, which is currently the primary objective of drug discovery research targeting these enzymes, but also of a wide range of infectious diseases.

The PAKs come of age: Celebrating 18 years of discovery

Protein kinases are versatile signaling molecules that are involved in the regulation most physiological responses. The p21-activated kinases (PAKs) can be activated directly by the small GTPases Rac and Cdc42 and are among the best characterized downstream effectors of these Rho proteins. The structure, substrate specificity and functional role of PAKS are evolutionarily conserved from protozoa to mammals. Vertebrate PAKs are particularly important for cytoskeletal remodeling and focal adhesion assembly, thereby contributing to dynamic processes such as cell migration and synaptic plasticity. This issue of Cellular Logistics focuses on the PAK family of kinases, with ten reviews written by researchers currently working in the field. Here in this introductory overview we highlight some of the most interesting recent discoveries regarding PAK biochemistry and biology. The reviews in this issue cover a range of topics including the atomic structures of PAK1 and PAK4, their role in animals as assessed by knockout studies, and how PAKs are likely to contribute to cancer and neurodegenerative diseases. The promise remains that PAK inhibitors will emerge that validate current pre-clinical studies suggesting that blocking PAK activity will positively contribute to human health.

Developing an international Pseudomonas aeruginosa reference panel

Pseudomonas aeruginosa is a major opportunistic pathogen in cystic fibrosis (CF) patients and causes a wide range of infections among other susceptible populations. Its inherent resistance to many antimicrobials also makes it difficult to treat infections with this pathogen. Recent evidence has highlighted the diversity of this species, yet despite this, the majority of studies on virulence and pathogenesis focus on a small number of strains. There is a pressing need for a P. aeruginosa reference panel to harmonize and coordinate the collective efforts of the P. aeruginosa research community. We have collated a panel of 43 P. aeruginosa strains that reflects the organism's diversity. In addition to the commonly studied clones, this panel includes transmissible strains, sequential CF isolates, strains with specific virulence characteristics, and strains that represent serotype, genotype or geographic diversity. This focussed panel of P. aeruginosa isolates will help accelerate and consolidate the discovery of virulence determinants, improve our understanding of the pathogenesis of infections caused by this pathogen, and provide the community with a valuable resource for the testing of novel therapeutic agents.

Protein arrays as tool for studies at the host-pathogen interface

Pathogens and parasites encode a wide spectrum of multifunctional proteins interacting to and modifying proteins in host cells. However, the current lack of a reliable method to unveil the protein-protein interactions (PPI) at the host-pathogen interface is retarding our understanding of many important pathogenic processes. Thus, the identification of proteins involved in host-pathogen interactions is important for the elucidation of virulence determinants, mechanisms of infection, host susceptibility and/or disease resistance. In this sense, proteomic technologies have experienced major improvements in recent years and protein arrays are a powerful and modern method for studying PPI in a high-throughput format. This review focuses on these techniques analyzing the state-of-the-art of proteomic technologies and their possibilities to diagnose and explore host-pathogen interactions. Major technical advancements, applications and protocol concerns are presented, so readers can appreciate the immense progress achieved and the current technical options available for studying the host-pathogen interface. Finally, future uses of this kind of array-based proteomic tools in the fight against infectious and parasitic diseases are discussed.