Structural and Biochemical Analyses of the Core Components of the Hippo Pathway

Connexin 43 dephosphorylation mediates the Dchs1/YAP/TEAD signaling pathway to induce cardiac fibrosis

BACKGROUND

The gap junction protein connexin 43 (Cx43) has been implicated in the development of cardiac fibrosis. Our previous findings revealed that Cx43 dephosphorylation at serine 282 (S282) is related to cardiomyocyte apoptosis and arrhythmias in hearts damaged by ischemia/reperfusion. In this study, we investigated the role of Cx43 S282 phosphorylation in cardiac fibrosis.

METHODS

We used angiotensin II (Ang II) intervention in mice to establish an in vivo cardiac fibrosis model and transforming growth factor β-1 (TGF-β1) intervention in cardiac myofibroblasts to establish an in vitro fibrosis model. The expression of Cx43 S282 phosphorylation was examined in the in vivo and in vitro models. To further confirm the effect of Cx43 S282 phosphorylation on cardiac fibrosis, we transfected cardiac myofibroblasts with lentiviral bodies in vitro, and injected myocardium with adenovirus in vivo to establish the over-expression of phosphorylation of Cx43 S282 locus and mutant groups. We sequenced the mRNA of the in vitro group using gene set enrichment analysis (GSEA) and normalized enrichment scoring (NES) to investigate the signaling pathway by which p282-Cx43 affects myocardial fibrosis (MF). The role of the Hippo signaling pathway in phosphorylation at the Cx43 282 site was further validated.

RESULTS

In an in vivo and in vitro model of cardiac fibrosis, the level of phosphorylation of Cx43 S282 was reduced. Mutation of Cx43 S282 to a less phosphorylatable form (S282A) resulted in elevated levels of fibrosis markers, suggesting a critical antifibrotic role for phosphorylated Cx43 S282. Increased phosphorylation of Cx43 S282 produced an inhibitory effect on fibrosis. Enrichment analysis of mRNA sequencing in the mutant model group indicated that the Hippo signaling pathway was involved in the fibrosis process. Cx43 S282 phosphorylation increased the expression of Dchs1 gene, which activates the phosphorylation of yes-associated protein (YAP) and inhibits the YAP/TEAD signaling pathway to inhibit fibrosis development.

CONCLUSIONS

This study suggests that the phosphorylation of Cx43 S282 could be an effective antifibrotic target in cardiac fibroblasts. This indicates a novel mechanism and a molecular target that may hold promise for treating cardiac fibrosis.

Natural compound library screening to identify berberine as a treatment for rheumatoid arthritis

OBJECTIVE

Fibroblast-like synoviocytes (FLS) play a critical role on the exacerbation and deterioration of rheumatoid arthritis (RA). Aberrant activation of FLS pyroptosis signaling is responsible for the hyperplasia of synovium and destruction of cartilage of RA. This study investigated the screened traditional Chinese medicine berberine (BBR), an active alkaloid extracted from the Coptis chinensis plant, that regulates the pyroptosis of FLS and secretion of inflammatory factors in rheumatoid arthritis.

METHODS

First, BBR was screened using a high-throughput drug screening strategy, and its inhibitory effect on RA-FLS was verified by in vivo and in vitro experiments. Second, BBR was intraperitoneally administrated into the collagen-induced arthritis rat model, and the clinical scores, arthritis index, and joint HE staining were evaluated. Third, synovial tissues of CIA mice were collected, and the expression of NLRP3, cleaved-caspase-1, GSDMD-N, Mst1, and YAP was detected by Western blot.

RESULTS

The administration of BBR dramatically alleviated the severity of collagen-induced arthritis rat model with a decreased clinical score and inflammation reduction. In addition, BBR intervention significantly attenuates several pro-inflammatory cytokines (interleukin-1β, interleukin-6, interleukin-17, and interleukin-18). Moreover, BBR can reduce the pyroptosis response (caspase-1, NLR family pyrin domain containing 3, and gasdermin D) of the RA-FLS in vitro, activating the Hippo signaling pathway (Mammalian sterile 20-like kinase 1, yes-associated protein, and transcriptional enhanced associate domains) so as to inhibit the pro-inflammatory effect of RA-FLS.

CONCLUSION

These results support the role of BBR in RA and may have therapeutic implications by directly repressing the activation, migration of RA-FLS, which contributing to the attenuation of the progress of CIA. Therefore, targeting PU.1 might be a potential therapeutic approach for RA. Besides, BBR inhibited RA-FLS pyroptosis by downregulating of NLRP3 inflammasomes (NLRP3, caspase-1) and eased the pro-inflammatory activities via activating the Hippo signaling pathway, thereby improving the symptom of CIA.

A novel NF2 splicing mutant causes neurofibromatosis type 2 via liquid-liquid phase separation with large tumor suppressor and Hippo pathway

Neurofibromatosis type 2 is an autosomal dominant multiple neoplasia syndrome and is usually caused by mutations in the neurofibromin 2 (NF2) gene, which encodes a tumor suppressor and initiates the Hippo pathway. However, the mechanism by which NF2 functions in the Hippo pathway isn’t fully understood. Here we identified a NF2 c.770-784del mutation from a neurofibromatosis type 2 family. MD simulations showed that this mutation significantly changed the structure of the F3 module of the NF2-FERM domain. Functional assays indicated that the NF2 c.770-784del variant formed LLPS in the cytoplasm with LATS to restrain LATS plasma membrane localization and inactivated the Hippo pathway. Besides, this deletion partly caused a skipping of exon 8 and reduced the protein level of NF2, collectively promoting proliferation and tumorigenesis of meningeal cells. We identified an unrecognized mechanism of LLPS and splicing skipping for the NF2-induced Hippo pathway, which provided new insight into the pathogenesis of neurofibromatosis type 2.

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NF2 c.770-784 deletion is a novel mutation related to Neurofibromatosis type 2

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NF2 variant forms LLPS in the cytoplasm with LATS and inhibits the Hippo pathway

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NF2 variant causes an aberrant skipping of exon 8 and reduces NF2 protein level

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NF2 variant promotes proliferation and tumorigenesis of meningeal cells

Activation of the tumor suppressive Hippo pathway by triptonide as a new strategy to potently inhibit aggressive melanoma cell metastasis

Metastatic melanoma has a very high mortality rate despite the availability of chemotherapy, radiotherapy, and immunotherapy; therefore, more effective therapeutics are needed. The Hippo pathway plays an inhibitory role in melanoma progression, but the tumor suppressors Salvador homolog-1 (SAV1) and large tumor suppressor 1 (LATS1) in this pathway are down-regulated in melanoma. As a result, the downstream oncogenic Yes-associated protein (YAP) is active, resulting in uncontrolled melanoma growth and metastasis. Therapeutics for remedying SAV1 and LATS1 deficiency in melanoma have not yet been reported in the literature. Here, we show that the small molecule triptonide (MW 358 Da) robustly suppressed melanoma cell tumorigenicity, migration, and invasion. Furthermore, triptonide markedly reduced tumor growth and melanoma lung metastasis in tumor-bearing mice with low toxicity. Molecular mechanistic studies revealed that triptonide promoted SAV1 and LATS1 expression, strongly activated the tumor-suppressive Hippo pathway, degraded oncogenic YAP via the lysosomal pathway, and reduced levels of tumorigenic microphthalmia-associated transcription factor (MITF) in melanoma cells. Triptonide also strongly inhibited activation of AKT, a SAV1-binding signaling protein. Collectively, our results conceptually demonstrate that induction of SAV1 and LATS1 expression and activation of the tumor-suppressive Hippo pathway by triptonide potently inhibits aggressive melanoma cell growth and metastasis. These findings suggest a new strategy for developing therapeutics to treat metastatic melanoma and highlight a novel drug candidate against aggressive melanoma.

Correction of the tumor suppressor Salvador homolog-1 deficiency in tumors by lycorine as a new strategy in lung cancer therapy

Salvador homolog-1 (SAV1) is a tumor suppressor required for activation of the tumor-suppressive Hippo pathway and inhibition of tumorigenesis. SAV1 is defective in several cancer types. SAV1 deficiency in cells promotes tumorigenesis and cancer metastasis, and is closely associated with poor prognosis for cancer patients. However, investigation of therapeutic strategies to target SAV1 deficiency in cancer is lacking. Here we found that the small molecule lycorine notably increased SAV1 levels in lung cancer cells by inhibiting SAV1 degradation via a ubiquitin-lysosome system, and inducing phosphorylation and activation of the SAV1-interacting protein mammalian Ste20-like 1 (MST1). MST1 activation then caused phosphorylation, ubiquitination, and degradation of the oncogenic Yes-associated protein (YAP), therefore inhibiting YAP-activated transcription of oncogenic genes and tumorigenic AKT and NF-κB signal pathways. Strikingly, treating tumor-bearing xenograft mice with lycorine increased SAV1 levels, and strongly inhibited tumor growth, vasculogenic mimicry, and metastasis. This work indicates that correcting SAV1 deficiency in lung cancer cells is a new strategy for cancer therapy. Our findings provide a new platform for developing novel cancer therapeutics.

Clostridium perfringens enterotoxin induces claudin-4 to activate YAP in oral squamous cell carcinomas

Claudin (CLDN)-4 expression has been associated with malignancy in various cancers. When CLDN4 expression was examined in oral squamous cell carcinoma (OSCC), 22 out of 57 (39%) cases showed immunoreactivity in the nucleus. Nuclear CLDN4-positive cases showed a stronger correlation with cancer progression than the negative cases. Intratumoral anaerobic bacterial DNA examination revealed nuclear CLDN4 expression in 81% of Clostridium perfringens-positive cases. Treatment of human oral squamous cell carcinoma cell lines HSC3 and HSC4 with Clostridium perfringens enterotoxin (CPE), induced CLDN4 nuclear translocation to enhance epithelial-mesenchymal transition (EMT), stemness, cell proliferation and invasive ability. In addition, CPE treatment suppressed phosphorylation of yes-associated protein-1 (YAP1) and promoted YAP1 nuclear translocation, resulting in increased expression of YAP1 target genes; cyclin D1 and connective tissue growth factor. Moreover, it was revealed that the complex of YAP1, CLDN4 and zona occludens-2 (ZO-2) was formed by CPE treatment, further suppressing YAP1 phosphorylation by LATS1 and activating it. Thus YAP activation in OSCC was regarded important in promoting malignant phenotypes. Our research suggested that the control of oral anaerobic bacteria may suppress YAP activation and in turn tumor progression.