Tumor Microenvironment and Metastasis Section, The Hormel Institute, University of Minnesota, Austin, MN, USA.
FASEB J. 2020 Jun;34(6):7345-7359. doi: 10.1096/fj.201903033R. Epub 2020 Apr 18.
TGFβ induces the differentiation of hepatic stellate cells (HSCs) into tumor-promoting myofibroblasts but underlying mechanisms remain incompletely understood. Because endocytosis of TGFβ receptor II (TβRII), in response to TGFβ stimulation, is a prerequisite for TGF signaling, we investigated the role of protein diaphanous homolog 1 (known as Diaph1 or mDia1) for the myofibroblastic activation of HSCs. Using shRNA to knockdown Diaph1 or SMIFH2 to target Diaph1 activity of HSCs, we found that the inactivation of Diaph1 blocked internalization and intracellular trafficking of TβRII and reduced SMAD3 phosphorylation induced by TGFβ1. Mechanistic studies revealed that the N-terminal portion of Diaph1 interacted with both TβRII and Rab5a directly and that Rab5a activity of HSCs was increased by Diaph1 overexpression and decreased by Diaph1 knockdown. Additionally, expression of Rab5aQ79L (active Rab5a mutant) increased whereas the expression of Rab5aS34N (inactive mutant) reduced the endosomal localization of TβRII in HSCs compared to the expression of wild-type Rab5a. Functionally, TGFβ stimulation promoted HSCs to express tumor-promoting factors, and α-smooth muscle actin, fibronection, and CTGF, markers of myofibroblastic activation of HSCs. Targeting Diaph1 or Rab5a suppressed HSC activation and limited tumor growth in a tumor implantation mouse model. Thus, Dipah1 and Rab5a represent targets for inhibiting HSC activation and the hepatic tumor microenvironment.
TGFβ 诱导肝星状细胞（HSCs）分化为促进肿瘤的肌成纤维细胞，但潜在机制仍不完全清楚。因为 TGFβ 受体 II（TβRII）的内吞作用，作为 TGF 信号的前提，我们研究了蛋白丝切蛋白同源物 1（称为 Diaph1 或 mDia1）在 HSCs 的肌成纤维细胞激活中的作用。使用 shRNA 敲低 Diaph1 或使用 SMIFH2 靶向 HSCs 的 Diaph1 活性，我们发现 Diaph1 的失活阻断了 TβRII 的内化和细胞内转运，并减少了 TGFβ1 诱导的 SMAD3 磷酸化。机制研究表明，Diaph1 的 N 端部分直接与 TβRII 和 Rab5a 相互作用，并且 Diaph1 的过表达增加了 HSCs 的 Rab5a 活性，而 Diaph1 的敲低则降低了 Rab5a 活性。此外，与野生型 Rab5a 的表达相比，Rab5aQ79L（活性 Rab5a 突变体）的表达增加，而 Rab5aS34N（非活性突变体）的表达减少了 TβRII 在 HSCs 中的内体定位。功能上，TGFβ 刺激促进 HSCs 表达促进肿瘤的因子，α-平滑肌肌动蛋白、纤维连接蛋白和 CTGF，这些都是 HSCs 肌成纤维细胞激活的标志物。靶向 Diaph1 或 Rab5a 抑制了 HSC 的激活，并在肿瘤植入小鼠模型中限制了肿瘤的生长。因此，Diaph1 和 Rab5a 是抑制 HSC 激活和肝肿瘤微环境的靶点。
