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<p>Understanding the molecular mechanisms that govern hepatic stellate cell (HSC) fate is essential for developing effective antifibrotic therapies. Yes-associated protein (YAP) plays a pivotal role in organ fibrogenesis and HSC activation, but its upstream regulatory signals in liver fibrosis remain largely unknown. Here, we demonstrate the role of p21-activated kinase 4 (PAK4), an emerging therapeutic target, in the activating phosphorylation of YAP and subsequent HSC activation. PAK4 expression was markedly upregulated in activated HSCs from patients and mice with liver fibrosis and correlated with disease severity. Silencing PAK4 suppressed hallmark features of HSC activation, including fibrotic activity, proliferation, migration, and contractility. HSC-specific deletion of <i>Pak4</i> and oral administration of a selective PAK4 inhibitor attenuated hepatic fibrosis in mice. Mechanistically, PAK4 directly phosphorylated YAP at T428, a previously unrecognized site, leading to YAP stabilization, nuclear accumulation, and transcriptional activation, which in turn promoted HSC activation. Overexpression of a phospho-inactive YAP mutant in HSCs reduced fibrogenesis, validating the functional importance of PAK4-mediated YAP phosphorylation. Notably, T428-phosphorylated YAP levels were substantially elevated in livers from patients with fibrosis. Our findings reveal a new PAK4-YAP signaling axis in HSCs, whereby PAK4-mediated T428 phosphorylation of YAP promotes its activation and drives liver fibrosis. These insights highlight a potential therapeutic strategy targeting HSC activation.</p>

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p21-activated kinase 4 drives hepatic stellate cell activation and liver fibrosis through the phosphorylation of YAP at T428

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月30日

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  • Gil-Hwan Kim,
  • Hyunsoo Rho,
  • Chang Hun Lee,
  • You-Jung Hong,
  • Yongdo Park,
  • Hwang Chan Yu,
  • Mi-Young Song,
  • Hye Jin Jo,
  • Eun Joo Kang,
  • Ri Han,
  • Song Yi Yu,
  • Ekihiro Seki,
  • Yoonji Lee,
  • Sangkyu Lee,
  • Eun Ju Bae,
  • Byung-Hyun Park,
  • Chang Yeob Han

摘要

Understanding the molecular mechanisms that govern hepatic stellate cell (HSC) fate is essential for developing effective antifibrotic therapies. Yes-associated protein (YAP) plays a pivotal role in organ fibrogenesis and HSC activation, but its upstream regulatory signals in liver fibrosis remain largely unknown. Here, we demonstrate the role of p21-activated kinase 4 (PAK4), an emerging therapeutic target, in the activating phosphorylation of YAP and subsequent HSC activation. PAK4 expression was markedly upregulated in activated HSCs from patients and mice with liver fibrosis and correlated with disease severity. Silencing PAK4 suppressed hallmark features of HSC activation, including fibrotic activity, proliferation, migration, and contractility. HSC-specific deletion of Pak4 and oral administration of a selective PAK4 inhibitor attenuated hepatic fibrosis in mice. Mechanistically, PAK4 directly phosphorylated YAP at T428, a previously unrecognized site, leading to YAP stabilization, nuclear accumulation, and transcriptional activation, which in turn promoted HSC activation. Overexpression of a phospho-inactive YAP mutant in HSCs reduced fibrogenesis, validating the functional importance of PAK4-mediated YAP phosphorylation. Notably, T428-phosphorylated YAP levels were substantially elevated in livers from patients with fibrosis. Our findings reveal a new PAK4-YAP signaling axis in HSCs, whereby PAK4-mediated T428 phosphorylation of YAP promotes its activation and drives liver fibrosis. These insights highlight a potential therapeutic strategy targeting HSC activation.