Squalene epoxidase promotes hepatocellular carcinoma development by activating STRAP transcription and TGF-β/SMAD signaling

Background and Purpose Squalene epoxidase (SQLE) is a key enzyme involved in cholesterol biosynthesis, but increasing evidence reveals that SQLE is abnormally expressed in some types of malignant tumors, and the underlying mechanism remains poorly understood. Experimental Approach Bioinformatics analysis and RNA sequencing were applied to detect to differentially expressed genes in clinical HCC tumors. AnnexinV-FITC/PI, EdU assay, transwell, IHC staining, cytoskeleton F-actin filaments assay, RNA sequencing, dual-luciferase reporters and HE staining were evaluated to investigate the pharmacological effects and possible mechanisms of SQLE. Key Results We found that SQLE expression is specifically elevated in HCC tumors, correlating with poor clinical outcomes. SQLE promoted HCC growth, EMT, and metastasis both in vitro and in vivo. In contrast, silencing of SQLE expression prevented HCC development. Both RNA-seq and functional experiments revealed that the protumorigenic effect of SQLE on HCC is closely related to the activation of cellular TGF-β/SMAD signaling, but interestingly, the stimulatory effect of SQLE on TGF-β/SMAD signaling and HCC development is also critically dependent on STRAP, a serine and threonine kinase. SQLE expression is well correlated with STRAP in HCC, and further, to amplify TGF-β/SMAD signaling, SQLE even transcriptionally increased STRAP gene expression mediated by the trans-acting factor AP-2α. Finally, as a chemical inhibitor of SQLE, NB-598 markedly inhibited HCC cell growth and tumor development in mouse models. Conclusions and Implications Taken together, SQLE serves as an oncogene in HCC development by activating TGF-β/SMAD signaling, and targeting SQLE could be useful in drug development and therapy for HCC.

Deformation of the nucleus by TGFβ1 via the remodeling of nuclear envelope and histone isoforms

The cause of nuclear shape abnormalities which are often seen in pre-neoplastic and malignant tissues is not clear. In this study we report that deformation of the nucleus can be induced by TGFβ1 stimulation in several cell lines including Huh7. In our results, the upregulated histone H3.3 expression downstream of SMAD signaling contributed to TGFβ1-induced nuclear deformation, a process of which requires incorporation of the nuclear envelope (NE) proteins lamin B1 and SUN1. During this process, the NE constitutively ruptured and reformed. Contrast to lamin B1 which was relatively stationary around the nucleus, the upregulated lamin A was highly mobile, clustering at the nuclear periphery and reintegrating into the nucleoplasm. The chromatin regions that lost NE coverage formed a supra-nucleosomal structure characterized by elevated histone H3K27me3 and histone H1, the formation of which depended on the presence of lamin A. These results provide evidence that shape of the nucleus can be modulated through TGFβ1-induced compositional changes in the chromatin and nuclear lamina.

Honokiol Acts as a Potent Anti-Fibrotic Agent in the Liver through Inhibition of TGF-β1/SMAD Signaling and Autophagy in Hepatic Stellate Cells

Chronic liver injury may result in hepatic fibrosis, which can progress to cirrhosis and eventually liver failure. There are no drugs that are specifically approved for treating hepatic fibrosis. The natural product honokiol (HNK), a bioactive compound extracted from Magnolia grandiflora, represents a potential tool in the management of hepatic fibrosis. Though HNK has been reported to exhibit suppressive effects in a rat fibrosis model, the mechanisms accounting for this suppression remain unclear. In the present study, the anti-fibrotic effects of HNK on the liver were evaluated in vivo and in vitro. In vivo studies utilized a murine liver fibrosis model, in which fibrosis is induced by treatment with carbon tetrachloride (CCl4). For in vitro studies, LX-2 human hepatic stellate cells (HSCs) were treated with HNK, and expression of markers of fibrosis, cell viability, the transforming growth factor-β (TGF-β1)/SMAD signaling pathway, and autophagy were analyzed. HNK was well tolerated and significantly attenuated CCl4-induced liver fibrosis in vivo. Moreover, HNK decreased HSC activation and collagen expression by downregulating the TGF-β1/SMAD signaling pathway and autophagy. These results suggest that HNK is a new potential candidate for the treatment of hepatic fibrosis through suppressing both TGF-β1/SMAD signaling and autophagy in HSCs.

Phosphatidylserine eversion regulated by phospholipid scramblase activated by TGF-β1/Smad signaling in the early stage of kidney stone formation

The mechanism underlying phosphatidylserine eversion in renal tubule cells following calcium oxalate-mediated damage remains unclear; therefore, we investigated the effects of TGF-β1/Smad signaling on phosphatidylserine eversion in the renal tubule cell membrane during the early stage of kidney stone development. In a rat model of early stage of calcium oxalate stone formation, phosphatidylserine eversion on the renal tubular cell membrane was detected by flow cytometry, and the expression of TGF-β1 (transforming growth factor-β1), Smad7, and phospholipid scramblase in the renal tubular cell membrane was measured by western blotting. We observed that the TGF-β1/Smad signaling pathway increased phosphatidylserine eversion at the organism level. The results of in vitro studies demonstrated that oxalate exposure to renal tubule cells induced TGF-β1 expression, increasing phospholipid scramblase activity and phosphatidylserine eversion in the renal tubule cell membrane. These results indicate that TGF-β1 stimulates phosphatidylserine eversion by increasing the phospholipid scramblase activity in the renal tubule cell membrane during the early stage of kidney stone development. The results of this study form a basis for further detailed research on the development of therapeutic agents that specifically treat urolithiasis and exert fewer adverse effects.