Collagen I-DDR1 signaling promotes hepatocellular carcinoma cell stemness via Hippo signaling repression.

Cancer stem cells (CSCs) are a minority population of cancer cells with stemness and multiple differentiation potentials, leading to cancer progression and therapeutic resistance. However, the concrete mechanism of CSCs in hepatocellular carcinoma (HCC) remains obscure. We found that in advanced HCC tissues, collagen I was upregulated, which is consistent with the expression of its receptor DDR1. Accordingly, high collagen I levels accompanied by high DDR1 expression are associated with poor prognoses in patients with HCC. Collagen I-induced DDR1 activation enhanced HCC cell stemness in vitro and in vivo. Mechanistically, DDR1 interacts with CD44, which acts as a co-receptor that amplifies collagen I-induced DDR1 signaling, and collagen I-DDR1 signaling antagonized Hippo signaling by facilitating the recruitment of PP2AA to MST1, leading to exaggerated YAP activation. The combined inhibition of DDR1 and YAP synergistically abrogated HCC cell stemness in vitro and tumorigenesis in vivo. A radiomic model based on T2 weighted images can noninvasively predict collagen I expression. These findings reveal the molecular basis of collagen I-DDR1 signaling inhibiting Hippo signaling and highlight the role of CD44/DDR1/YAP axis in promoting cancer cell stemness, suggesting that DDR1 and YAP may serve as novel prognostic biomarkers and therapeutic targets in HCC.

Rapamycin Upregulates Connective Tissue Growth Factor Expression in Hepatic Progenitor Cells Through TGF-ß-Smad2 Dependent Signaling.

Rapamycin (sirolimus) is a mTOR kinase inhibitor and is widely used as an immunosuppressive drug to prevent graft rejection in organ transplantation currently. However, some recent investigations have reported that it had profibrotic effect in the progression of organ fibrosis, and its precise role in the liver fibrosis is still poorly understood. Here we showed that rapamycin upregulated connective tissue growth factor (CTGF) expression at the transcriptional level in hepatic progenitor cells (HPCs). Using lentivirus-mediated small hairpin RNA (shRNA) we demonstrated that knockdown of mTOR, Raptor, or Rictor mimicked the effect of rapamycin treatment. Mechanistically, inhibition of mTOR activity with rapamycin resulted in a hyperactive PI3K-Akt pathway, whereas this activation inhibited the expression of CTGF in HPCs. Besides, rapamycin activated the TGF-ß-Smad signaling, and TGF-ß receptor type I (TGFßRI) serine/threonine kinase inhibitors completely blocked the effects of rapamycin on HPCs. Moreover, Smad2 was involved in the induction of CTGF through rapamycin-activated TGF-ß-Smad signaling as knockdown completely blocked CTGF induction, while knockdown of Smad4 expression partially inhibited induction, whereas Smad3 knockdown had no effect. Rapamycin also induced ROS generation and latent TGF-ß activation which contributed to TGF-ß-Smad signaling. In conclusion, this study demonstrates that rapamycin upregulates CTGF in HPCs and suggests that rapamycin has potential fibrotic effect in liver.

Autocrine transforming growth factor-ß/activin A-Smad signaling induces hepatic progenitor cells undergoing partial epithelial-mesenchymal transition states.

Hepatic progenitor cells (HPCs) are a subpopulation of cells which was usually expanded in chronic liver injury and are contributed to liver regeneration through differentiating into hepatocytes and cholangiocytes. Epithelial-mesenchymal transition is a dynamic process which is important for the progression of liver fibrosis and cancer initiation. This study demonstrated that LE/6 and WB-F344 cells, both of which were HPC derived cell lines, were undergoing partial epithelial-mesenchymal transition states, which was indicated by the co-expression of epithelial markers (E-cadherin and zona occludin 1), and mesenchymal markers (vimentin, fibronectin, collagen 1and α-SMA). Furthermore, autocrine TGF-ß and activin A signaling contributed to the maintenance of partial EMT in HPCs. In addition, Smad signaling, a classic downstream signaling cascade of both TGF-ß and activin A, also participated in the partial EMT. These findings revealed the existence of partial EMT states in HPCs and confirmed some partial EMT related autocrine signaling cascades, and may help to further the understanding and explore the functional role of HPCs in the process of hepatic fibrosis and liver cancer initiation.