STAT3-YAP/TAZ signaling in endothelial cells promotes tumor angiogenesis.

The nuclear translocation and activity of the cotranscriptional activators YAP and TAZ (YAP/TAZ) in endothelial cells (ECs) are crucial during developmental angiogenesis. Here, we studied the role of YAP/TAZ signaling in ECs in tumor angiogenesis and found that the expression of YAP/TAZ and downstream target genes in ECs correlated with tumor vascularization in human colorectal carcinomas and skin melanoma. Treatment with the YAP/TAZ inhibitor verteporfin reduced vessel density and tumor progression in a mouse colorectal cancer (CRC) model. Conditional deletion of YAP/TAZ in ECs reduced tumor angiogenesis and growth in a mouse B16-F10 melanoma model. Using cultured ECs and mice with EC-specific ablation, we showed that signal transducer and activator of transcription 3 (STAT3) was required for the activation of YAP/TAZ in tumor-associated ECs. Moreover, we showed that STAT3-mediated signaling promoted YAP/TAZ activity and that the nuclear shuttling machinery for STAT3 was also required for YAP/TAZ nuclear translocation. Together, our data highlight the role of YAP/TAZ as critical players in ECs during tumor angiogenesis and provide insight into the signaling pathways leading to their activation.

Ochratoxin A induces ERK1/2 phosphorylation-dependent apoptosis through NF-κB/ERK axis in human proximal tubule HK-2 cell line.

Ochratoxin A (OTA) is a food contaminant mycotoxin with hazardous effects on human and animal health, primarily affecting the kidneys. OTA's mode of action is not well understood. OTA activates both MAPK/ERK and PI3K/Akt signaling pathways, which play role in apoptosis and cell survival, respectively. OTA is also known to induce toxicity by activating the NF-κB pathway in immune cells. However, its role in determining the cell fate upon OTA exposure in a human kidney cell line (HK-2) has not been fully explored. We made use of pharmacological inhibition of NF-κB to define its role in viability of OTA-treated HK-2 cells. We show that OTA-induced p65 NF-κB subunit translocation into the nucleus in a time-dependent manner using both Western blotting and immunofluorescence (IF). We also document the DNA-binding and reporter gene expression activities of NF-κB by electrophoretic mobility shift (EMSA) and luciferase reporter assays, respectively. Our results indicate that, following 6 h of exposure, OTA fully activates NF-κB pathway and its downstream effectors in HK-2 cells. In addition, Bay11-7085 treatment causes attenuation of the relative levels of OTA-mediated ERK1/2 phosphorylation, suggesting a cross-talk between NF-κB and the MAPK/ERK pathway. Critically, co-treatment of HK-2 cells with OTA and Bay11-7085 leads to the inhibition of OTA-induced apoptosis in a time-dependent manner. Our results support a robust association between NF-κB and the MAPK/ERK pathways in the modulation of apoptotic effects of OTA in HK-2 cells.

Acute inhibition of centriolar satellite function and positioning reveals their functions at the primary cilium.

Centriolar satellites are dynamic, membraneless granules composed of over 200 proteins. They store, modify, and traffic centrosome and primary cilium proteins, and help to regulate both the biogenesis and some functions of centrosomes and cilium. In most cell types, satellites cluster around the perinuclear centrosome, but their integrity and cellular distribution are dynamically remodeled in response to different stimuli, such as cell cycle cues. Dissecting the specific and temporal functions and mechanisms of satellites and how these are influenced by their cellular positioning and dynamics has been challenging using genetic approaches, particularly in ciliated and proliferating cells. To address this, we developed a chemical-based trafficking assay to rapidly and efficiently redistribute satellites to either the cell periphery or center, and fuse them into stable clusters in a temporally controlled way. Induced satellite clustering at either the periphery or center resulted in antagonistic changes in the pericentrosomal levels of a subset of proteins, revealing a direct and selective role for their positioning in protein targeting and sequestration. Systematic analysis of the interactome of peripheral satellite clusters revealed enrichment of proteins implicated in cilium biogenesis and mitosis. Importantly, induction of peripheral satellite targeting in ciliated cells revealed a function for satellites not just for efficient cilium assembly but also in the maintenance of steady-state cilia and in cilia disassembly by regulating the structural integrity of the ciliary axoneme. Finally, perturbing satellite distribution and dynamics inhibited their mitotic dissolution, and mitotic progression was perturbed only in cells with centrosomal satellite clustering. Collectively, our results for the first time showed a direct link between satellite functions and their pericentrosomal clustering, suggested new mechanisms underlying satellite functions during cilium assembly, and provided a new tool for probing temporal satellite functions in different contexts.