Squalene epoxidase promotes hepatocellular carcinoma development by
activating STRAP transcription and TGF-β/SMAD signaling
Abstract
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/PI, EdU assay, transwell, western blot, qRT-PCR, IHC staining,
RNA sequencing, dual-luciferase reporters and HE staining were evaluated
to investigate the pharmacological effects and possible mechanisms of
SQLE in vitro and in vivo. 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. SQLE expression is well
correlated with STRAP in HCC, and further, to amplify TGF-β/SMAD
signaling, SQLE even transcriptionally increased STRAP 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 a novel oncogene in HCC development by
activating TGF-β/SMAD signaling, and targeting SQLE could be useful in
drug development and therapy for HCC.