LILRB2 promotes immune escape in breast cancer cells via enhanced HLA-A degradation.

PURPOSE: Increased expression of leukocyte immunoglobulin-like receptor subfamily B member 2 (LILRB2) is associated with immune evasion in breast cancer (BC). The aim of this study to elucidate the role of LILRB2 in BC progression. METHODS: LILRB2 expression in tumor tissues was detected by immunohistochemical staining. Human leukocyte antigen A (HLA-A) expression in BC cells was detected by Western blotting, and HLA-A ubiquitination was detected by immunoprecipitation and histidine pulldown assay. An in-situ tumor model was established in nude BALB/c mice to verify the role of LILRB2 in immune escape. Finally, the functions and potential mechanisms of LILRB2 in BC progression were explored using in silico data. RESULTS: LILRB2 was upregulated in BC tissues and cells, and correlated positively with poor prognosis. LILRB2 promoted BC progression by downregulating HLA-A expression. Mechanistically, LILRB2 facilitates the ubiquitination and subsequent degradation of HLA-A by promoting the interaction between the ubiquitin ligase membrane-associated ring finger protein 9 (MARCH9) and HLA-A. In syngeneic graft mouse models, LILRB2-expressing BC cells evaded CD8 + T cells and inhibited the secretion of cytokines by the cytotoxic CD8 + T cells. CONCLUSION: LILRB2 downregulates HLA-A to promote immune evasion in BC cells and is a promising new target for BC treatment.

TGF-ß-Induced FLRT3 Attenuation Is Essential for Cancer-Associated Fibroblast-Mediated Epithelial-Mesenchymal Transition in Colorectal Cancer.

Cancer-associated fibroblasts (CAF) constitute a major component of the tumor microenvironment. The effects of CAFs on the progression of colorectal cancer remain controversial. In this study, we found the ectopic overexpression of Fibronectin leucine-rich transmembrane protein 3 (FLRT3) inhibited the process of epithelial-mesenchymal transition (EMT), as well as the proliferation, migration, invasion, and promote apoptosis of colorectal cancer cells, whereas silencing FLRT3 expression resulted in the opposite phenomenon. FLRT3 downregulation was associated with a poor prognosis in colorectal cancer. Also, FLRT3 expression was significantly related to some clinicopathologic factors, including T stage (P = 0.037), N stage (P = 0.042), and E-cadherin (P = 0.002) level. Via univariate and multivariate analyses, M stage (P < 0.0001), FLRT3 (P = 0.044), and E-cadherin (P = 0.003) were associated with overall survival and were independent prognostic factors for it. Mechanistically, CAFs secreted TGF-ß, which downregulated FLRT3 expression by activating SMAD4 to promote aggressive phenotypes in colorectal cancer cells. Moreover, FLRT3 repressed tumorigenesis and lung metastasis, which could be reversed by LY2109761, a dual inhibitor of TGF-ß receptor type I and II. Treatment with LY2109761 increased IFN-γ expression in CD8+ T cells and reduced the number of regulatory T cells in the tumor microenvironment. Taken together, we revealed the metastasis-suppressive function of FLRT3, which was attenuated during the CAFs-mediated activation of the TGF-ß/SMAD4 signaling pathway to promote EMT in colorectal cancer. LY2109761 that significantly inhibited metastasis could be a new treatment option for advanced colorectal cancer. IMPLICATIONS: CAFs enhance colorectal cancer aggressiveness by reducing FLRT3 expression through activating TGF-ß/SMAD4 signaling pathway. CAF-targeted therapy and/or LY2109761 were promising treatments for colorectal cancer.

FGF15 Activates Hippo Signaling to Suppress Bile Acid Metabolism and Liver Tumorigenesis.

The external factors that modulate Hippo signaling remain elusive. Here, we report that FGF15 activates Hippo signaling to suppress bile acid metabolism, liver overgrowth, and tumorigenesis. FGF15 is induced by FXR in ileal enterocytes in response to increased amounts of intestinal bile. We found that circulating enterohepatic FGF15 stimulates hepatic receptor FGFR4 to recruit and phosphorylate NF2, which relieves the inhibitory effect of Raf on the Hippo kinases Mst1/2, thereby switching FGFR4's role from pro-oncogenic to anti-tumor signaling. The activated Mst1/2 subsequently phosphorylates and stabilizes SHP to downregulate the key bile acid-synthesis enzyme Cyp7a1 expression, thereby limiting bile acid synthesis. In contrast, Mst1/2 deficiency impairs bile acid metabolism and remarkably increases Cyp7a1 expression and bile acid production. Importantly, pharmacological depletion of intestinal bile abrogates Mst1/2-mutant-driven liver overgrowth and oncogenesis. Therefore, FGF15-Hippo signaling along the gut-liver axis acts as a sensor of bile acid availability to restrain liver size and tumorigenesis.

Hippo Signaling Suppresses Cell Ploidy and Tumorigenesis through Skp2.

Polyploidy can lead to aneuploidy and tumorigenesis. Here, we report that the Hippo pathway effector Yap promotes the diploid-polyploid conversion and polyploid cell growth through the Akt-Skp2 axis. Yap strongly induces the acetyltransferase p300-mediated acetylation of the E3 ligase Skp2 via Akt signaling. Acetylated Skp2 is exclusively localized to the cytosol, which causes hyper-accumulation of the cyclin-dependent kinase inhibitor p27, leading to mitotic arrest and subsequently cell polyploidy. In addition, the pro-apoptotic factors FoxO1/3 are overly degraded by acetylated Skp2, resulting in polyploid cell division, genomic instability, and oncogenesis. Importantly, the depletion or inactivation of Akt or Skp2 abrogated Hippo signal deficiency-induced liver tumorigenesis, indicating their epistatic interaction. Thus, we conclude that Hippo-Yap signaling suppresses cell polyploidy and oncogenesis through Skp2.

Integration of Hippo signalling and the unfolded protein response to restrain liver overgrowth and tumorigenesis.

The role of the unfolded protein response (UPR) in tissue homeostasis remains largely unknown. Here we find that loss of Mst1/2, the mammalian Hippo orthologues, or their regulator WW45, leads to a remarkably enlarged endoplasmic reticulum (ER) size-associated UPR. Intriguingly, attenuation of the UPR by tauroursodeoxycholic acid (TUDCA) diminishes Mst1/2 mutant-driven liver overgrowth and tumorigenesis by promoting nuclear exit and degradation of Hippo downstream effector Yap. Yap is required for UPR activity and ER expansion to alleviate ER stress. During the adaptive stage of the UPR, PERK kinase-eIF2α axis activates Yap, while prolonged ER stress-induced Hippo signalling triggers assembly of the GADD34/PP1 complex in a negative feedback loop to inhibit Yap and promote apoptosis. Significantly, the deregulation of UPR signals associated with Yap activation is found in a substantial fraction of human hepatocellular carcinoma (HCC). Thus, we conclude Yap integrates Hippo and UPR signalling to control liver size and tumorigenesis.

The Ets transcription factor GABP is a component of the hippo pathway essential for growth and antioxidant defense.

The transcriptional coactivator Yes-associated protein (YAP) plays an important role in organ-size control and tumorigenesis. However, how Yap gene expression is regulated remains unknown. This study shows that the Ets family member GABP binds to the Yap promoter and activates YAP transcription. The depletion of GABP downregulates YAP, resulting in a G1/S cell-cycle block and increased cell death, both of which are substantially rescued by reconstituting YAP. GABP can be inactivated by oxidative mechanisms, and acetaminophen-induced glutathione depletion inhibits GABP transcriptional activity and depletes YAP. In contrast, activating YAP by deleting Mst1/Mst2 strongly protects against acetaminophen-induced liver injury. Similar to its effects on YAP, Hippo signaling inhibits GABP transcriptional activity through several mechanisms. In human liver cancers, enhanced YAP expression is correlated with increased nuclear expression of GABP. Therefore, we conclude that GABP is an activator of Yap gene expression and a potential therapeutic target for cancers driven by YAP.