STK25 and MST3 Have Overlapping Roles to Regulate Rho GTPases during Cortical Development

Expression analysis of type I ARF small GTPases ARF1-3 during mouse brain development

BACKGROUND

ARF (ADP-ribosylation factor) GTPases are major regulators of intracellular trafficking, and classified into 3 groups (Type I - III), among which the type I group members, ARF1 and 3, are responsible genes for neurodevelopmental disorders.

METHODS

In this study, we analysed the expression of Type I ARFs ARF1-3 during mouse brain development using biochemical and morphological methods.

RESULTS

Western blotting analyses revealed that ARF1-3 are weakly expressed in the mouse brain at embryonic day 13 and gradually increase until postnatal day 30. ARF1-3 appear to be abundantly expressed in various telencephalon regions. Biochemical fractionation studies detected ARF1-3 in the synaptosome fraction of cortical neurons containing both pre- and post-synapses, however ARF1-3 were not observed in post-synaptic compartments. In immunohistochemical analyses, ARF1-3 appeared to be distributed in the cytoplasm and dendrites of cortical and hippocampal neurons as well as in the cerebellar molecular layer including dendrites of Purkinje cells and granule cell axons. Immunofluorescence in primary cultured hippocampal neurons revealed that ARF1-3 are diffusely distributed in the cytoplasm and dendrites with partial colocalization with a pre-synaptic marker, synaptophysin.

CONCLUSIONS

Overall, our results support the notion that ARF1-3 could participate in vesicle trafficking both in the dendritic shaft (excluding spines) and axon terminals (pre-synaptic compartments).

Beyond the exome: utility of long-read whole genome sequencing in exome-negative autosomal recessive diseases

BACKGROUND

Long-read whole genome sequencing (lrWGS) has the potential to address the technical limitations of exome sequencing in ways not possible by short-read WGS. However, its utility in autosomal recessive Mendelian diseases is largely unknown.

METHODS

In a cohort of 34 families in which the suspected autosomal recessive diseases remained undiagnosed by exome sequencing, lrWGS was performed on the Pacific Bioscience Sequel IIe platform.

RESULTS

Likely causal variants were identified in 13 (38%) of the cohort. These include (1) a homozygous splicing SV in TYMS as a novel candidate gene for lethal neonatal lactic acidosis, (2) a homozygous non-coding SV that we propose impacts STK25 expression and causes a novel neurodevelopmental disorder, (3) a compound heterozygous SV in RP1L1 with complex inheritance pattern in a family with inherited retinal disease, (4) homozygous deep intronic variants in LEMD2 and SNAP91 as novel candidate genes for neurodevelopmental disorders in two families, and (5) a promoter SNV in SLC4A4 causing non-syndromic band keratopathy. Surprisingly, we also encountered causal variants that could have been identified by short-read exome sequencing in 7 families. The latter highlight scenarios that are especially challenging at the interpretation level.

CONCLUSIONS

Our data highlight the continued need to address the interpretation challenges in parallel with efforts to improve the sequencing technology itself. We propose a path forward for the implementation of lrWGS sequencing in the setting of autosomal recessive diseases in a way that maximizes its utility.

STK25: a viable therapeutic target for cancer treatments?

Serine/threonine protein kinase 25 (STK25) is a critical regulator of ectopic lipid storage, glucose and insulin homeostasis, fibrosis, and meta-inflammation. More and more studies have revealed a strong correlation between STK25 and human diseases. On the one hand, STK25 can affect glucose and fatty acid metabolism in normal cells or tumors. On the other hand, STK25 participates in autophagy, cell polarity, cell apoptosis, and cell migration by activating various signaling pathways. This article reviews the composition and function of STK25, the energy metabolism and potential drugs that may target STK25, and the research progress of STK25 in the occurrence and development of tumors, to provide a reference for the clinical treatment of tumors.

STE20-type kinases MST3 and MST4 promote the progression of hepatocellular carcinoma: Evidence from human cell culture and expression profiling of liver biopsies

Hepatocellular carcinoma (HCC) is one of the most fatal and fastest growing malignancies. Recently, nonalcoholic steatohepatitis (NASH), characterized by liver steatosis, inflammation, cell injury (hepatocyte ballooning), and different stages of fibrosis, has emerged as a major catalyst for HCC. Because the STE20-type kinases, MST3 and MST4, have been described as critical molecular regulators of NASH pathophysiology, we here focused on determining the relevance of these proteins in human HCC. By analyzing public datasets and in-house cohorts, we found that hepatic MST3 and MST4 expression was positively correlated with the incidence and severity of HCC. We also found that the silencing of both MST3 and MST4, but also either of them individually, markedly suppressed the tumorigenesis of human HCC cells including attenuated proliferation, migration, invasion, and epithelial-mesenchymal transition. Mechanistic investigations revealed lower activation of STAT3 signaling in MST3/MST4-deficient hepatocytes and identified GOLGA2 and STRIPAK complex as the binding partners of both MST3 and MST4. These findings reveal that MST3 and MST4 play a critical role in promoting the progression of HCC and suggest that targeting these kinases may provide a novel strategy for the treatment of liver cancer.

Molecular mechanisms involved in regulating protein activity and biological function of MST3

Mammalian sterile 20-like (Ste20-like) protein kinase 3 (MST3) or serine/threonine-protein kinase 24 (STK24) is a serine/threonine protein kinase that belongs to the mammalian STE20-like protein kinase family. MST3 is a pleiotropic protein that plays a critical role in regulating a variety of events, including apoptosis, immune response, metabolism, hypertension, tumor progression, and development of the central nervous system. The MST3-mediated regulation is intricately related to protein activity, post-translational modification, and subcellular location. Here, we review the recent progress on the regulatory mechanisms against MST3 and its-mediated control of disease progression.

Novel kinome profiling technology reveals drug treatment is patient and 2D/3D model dependent in glioblastoma

Glioblastoma is the deadliest brain cancer. One of the main reasons for poor outcome resides in therapy resistance, which adds additional challenges in finding an effective treatment. Small protein kinase inhibitors are molecules that have become widely studied for cancer treatments, including glioblastoma. However, none of these drugs have demonstrated a therapeutic activity or brought more benefit compared to the current standard procedure in clinical trials. Hence, understanding the reasons of the limited efficacy and drug resistance is valuable to develop more effective strategies toward the future. To gain novel insights into the method of action and drug resistance in glioblastoma, we established in parallel two patient-derived glioblastoma 2D and 3D organotypic multicellular spheroids models, and exposed them to a prolonged treatment of three weeks with temozolomide or either the two small protein kinase inhibitors enzastaurin and imatinib. We coupled the phenotypic evidence of cytotoxicity, proliferation, and migration to a novel kinase activity profiling platform (QuantaKinome™) that measured the activities of the intracellular network of kinases affected by the drug treatments. The results revealed a heterogeneous inter-patient phenotypic and molecular response to the different drugs. In general, small differences in kinase activation were observed, suggesting an intrinsic low influence of the drugs to the fundamental cellular processes like proliferation and migration. The pathway analysis indicated that many of the endogenously detected kinases were associated with the ErbB signaling pathway. We showed the intertumoral variability in drug responses, both in terms of efficacy and resistance, indicating the importance of pursuing a more personalized approach. In addition, we observed the influence derived from the application of 2D or 3D models in in vitro studies of kinases involved in the ErbB signaling pathway. We identified in one 3D sample a new resistance mechanism derived from imatinib treatment that results in a more invasive behavior. The present study applied a new approach to detect unique and specific drug effects associated with pathways in in vitro screening of compounds, to foster future drug development strategies for clinical research in glioblastoma.

GCKIII (Germinal Center Kinase III) Kinases STK24 and STK25 (Serine/Threonine Kinase 24 and 25) Inhibit Cavernoma Development

BACKGROUND

Cavernous cerebral malformations can arise because of mutations in the CCM1, CCM2, or CCM3 genes, and lack of Cdc42 has also been reported to induce these malformations in mice. However, the role of the CCM3 (cerebral cavernous malformation 3)-associated kinases in cavernoma development is not known, and we, therefore, have investigated their role in the process.

METHODS

We used a combination of an in vivo approach, using mice genetically modified to be deficient in the CCM3-associated kinases STK24 and STK25 (serine/threonine kinases 24 and 25), and the in vitro model of human endothelial cells in which expression of STK24 and STK25 was inhibited by RNA interference.

RESULTS

Mice deficient for both Stk24 and Stk25, but not for either of them individually, developed aggressive vascular lesions with the characteristics of cavernomas at an early age. Stk25 deficiency also gave rise to vascular anomalies in the context of Stk24 heterozygosity. Human endothelial cells deficient for both kinases phenocopied several of the consequences of CCM3 loss, and single STK25 deficiency also induced KLF2 expression, Golgi dispersion, altered distribution of β-catenin, and appearance of stress fibers.

CONCLUSIONS

The CCM3-associated kinases STK24 and STK25 play a major role in the inhibition of cavernoma development.

New Strategies for the Treatment of Neuropsychiatric Disorders Based on Reelin Dysfunction

Reelin is an extracellular matrix protein that is mainly produced in Cajal-Retzius cells and controls neuronal migration, which is important for the proper formation of cortical layers in the developmental stage of the brain. In the adult brain, Reelin plays a crucial role in the regulation of N-methyl-D-aspartate receptor-dependent synaptic function, and its expression decreases postnatally. Clinical studies showed reductions in Reelin protein and mRNA expression levels in patients with psychiatric disorders; however, the causal relationship remains unclear. Reelin-deficient mice exhibit an abnormal neuronal morphology and behavior, while Reelin supplementation ameliorates learning deficits, synaptic dysfunctions, and spine loss in animal models with Reelin deficiency. These findings suggest that the neuronal deficits and brain dysfunctions associated with the down-regulated expression of Reelin are attenuated by enhancements in its expression and functions in the brain. In this review, we summarize findings on the role of Reelin in neuropsychiatric disorders and discuss potential therapeutic approaches for neuropsychiatric disorders associated with Reelin dysfunctions.