Ste20-like kinase, SLK, activates the heat shock factor 1 - Hsp70 pathway

Role of the Ste20-like kinase SLK in podocyte adhesion

SLK controls the cytoskeleton, cell adhesion, and migration. Podocyte-specific deletion of SLK in mice leads to podocyte injury as mice age and exacerbates injury in experimental focal segment glomerulosclerosis (FSGS; adriamycin nephrosis). We hypothesized that adhesion proteins may be substrates of SLK. In adriamycin nephrosis, podocyte ultrastructural injury was exaggerated by SLK deletion. Analysis of a protein kinase phosphorylation site dataset showed that podocyte adhesion proteins-paxillin, vinculin, and talin-1 may be potential SLK substrates. In cultured podocytes, deletion of SLK increased adhesion to collagen. Analysis of paxillin, vinculin, and talin-1 showed that SLK deletion reduced focal adhesion complexes (FACs) containing these proteins mainly in adriamycin-induced injury; there was no change in FAC turnover (focal adhesion kinase Y397 phosphorylation). In podocytes, paxillin S250 showed basal phosphorylation that was slightly enhanced by SLK; however, SLK did not phosphorylate talin-1. In adriamycin nephrosis, SLK deletion did not alter glomerular expression/localization of talin-1 and vinculin, but increased focal adhesion kinase phosphorylation modestly. Therefore, SLK decreases podocyte adhesion, but FAC proteins in podocytes are not major substrates of SLK in health and disease.

The Ste20-like kinase - a Jack of all trades?

Over the past 20 years, the Ste20-like kinase (SLK; also known as STK2) has emerged as a central regulator of cytoskeletal dynamics. Reorganization of the cytoskeleton is necessary for a plethora of biological processes including apoptosis, proliferation, migration, tissue repair and signaling. Several studies have also uncovered a role for SLK in disease progression and cancer. Here, we review the recent findings in the SLK field and summarize the various roles of SLK in different animal models and discuss the biochemical mechanisms regulating SLK activity. Together, these studies have revealed multiple roles for SLK in coupling cytoskeletal dynamics to cell growth, in muscle repair and in negative-feedback loops critical for cancer progression. Furthermore, the ability of SLK to regulate some systems appears to be kinase activity independent, suggesting that it may be an important scaffold for signal transduction pathways. These various findings reveal highly complex functions and regulation patterns of SLK in development and disease, making it a potential therapeutic target.

Cellular stress and redox activity proteins are involved in gastric carcinogenesis associated with Helicobacter pylori infection expressing high levels of thioredoxin-1

Helicobacter pylori infection is related to the development of gastric diseases. Our previous studies showed that high thioredoxin-1 (Trx1) expression in H. pylori can promote gastric carcinogenesis. To explore the underlying molecular mechanisms, we performed an isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis of stomach tissues from Mongolian gerbil infected with H. pylori expressing high and low Trx1. Differences in the profiles of the expressed proteins were analyzed by bioinformatics and verified using Western blot analysis. We found three candidate proteins, 14-3-3α/β, glutathione-S-transferase (GST), and heat shock protein 70 (HSP70), in high Trx1 tissues compared with low Trx1 tissues and concluded that cellular stress and redox activity-related proteins were involved in the pathogenesis of gastric cancer associated with H. pylori Trx1.

Proteostasis as a therapeutic target in glomerular injury associated with mutant α-actinin-4

Mutations in α-actinin-4 (actinin-4) result in hereditary focal segmental glomerulosclerosis (FSGS) in humans. Actinin-4 mutants induce podocyte injury because of dysregulation of the cytoskeleton and proteotoxicity. Injury may be associated with endoplasmic reticulum (ER) stress and polyubiquitination of proteins. We assessed if the chemical chaperone 4-phenylbutyrate (4-PBA) can ameliorate the proteotoxicity of an actinin-4 mutant. Actinin-4 K255E, which causes FSGS in humans (K256E in the mouse), showed enhanced ubiquitination, accelerated degradation, aggregate formation, and enhanced association with filamentous (F)-actin in glomerular epithelial cells (GECs). The mutant disrupted ER function and stimulated autophagy. 4-PBA reduced actinin-4 K256E aggregation and its tight association with F-actin. Transgenic mice that express actinin-4 K256E in podocytes develop podocyte injury, proteinuria, and FSGS in association with glomerular ER stress. Treatment of these mice with 4-PBA in the drinking water over a 10-wk period significantly reduced albuminuria and ER stress. Another drug, celastrol, which enhanced expression of ER and cytosolic chaperones in GECs, tended to reduce actinin-4 aggregation but did not decrease the tight association of actinin-4 K256E with F-actin and did not reduce albuminuria in actinin-4 K256E transgenic mice. Thus, chemical chaperones, such as 4-PBA, may represent a novel therapeutic approach to certain hereditary glomerular diseases.

Whole genome sequencing of an African American family highlights toll like receptor 6 variants in Kawasaki disease susceptibility

Kawasaki disease (KD) is the most common acquired pediatric heart disease. We analyzed Whole Genome Sequences (WGS) from a 6-member African American family in which KD affected two of four children. We sought rare, potentially causative genotypes by sequentially applying the following WGS filters: sequence quality scores, inheritance model (recessive homozygous and compound heterozygous), predicted deleteriousness, allele frequency, genes in KD-associated pathways or with significant associations in published KD genome-wide association studies (GWAS), and with differential expression in KD blood transcriptomes. Biologically plausible genotypes were identified in twelve variants in six genes in the two affected children. The affected siblings were compound heterozygous for the rare variants p.Leu194Pro and p.Arg247Lys in Toll-like receptor 6 (TLR6), which affect TLR6 signaling. The affected children were also homozygous for three common, linked (r² = 1) intronic single nucleotide variants (SNVs) in TLR6 (rs56245262, rs56083757 and rs7669329), that have previously shown association with KD in cohorts of European descent. Using transcriptome data from pre-treatment whole blood of KD subjects (n = 146), expression quantitative trait loci (eQTL) analyses were performed. Subjects homozygous for the intronic risk allele (A allele of TLR6 rs56245262) had differential expression of Interleukin-6 (IL-6) as a function of genotype (p = 0.0007) and a higher erythrocyte sedimentation rate at diagnosis. TLR6 plays an important role in pathogen-associated molecular pattern recognition, and sequence variations may affect binding affinities that in turn influence KD susceptibility. This integrative genomic approach illustrates how the analysis of WGS in multiplex families with a complex genetic disease allows examination of both the common disease–common variant and common disease–rare variant hypotheses.