Patients with respiratory syncytial virus (RSV) infection exhibit enhanced susceptibility to subsequent pneumococcal infections. However, the underlying mechanisms involved in this increased susceptibility remain unclear. Here, we identified potentially novel cellular and molecular cascades triggered by RSV infection to exacerbate secondary pneumococcal pneumonia. RSV infection stimulated the local production of growth arrest–specific 6 (Gas6). The Gas6 receptor Axl was crucial for attenuating pneumococcal immunity in that the Gas6/Axl blockade fully restored antibacterial immunity. Mechanistically, Gas6/Axl interaction regulated the conversion of alveolar macrophages from an antibacterial phenotype to an M2-like phenotype that did not exhibit antibacterial activity, and the attenuation of caspase-1 activation and IL-18 production in response to pneumococcal infection. The attenuated IL-18 production failed to drive both NK cell–mediated IFN-γ production and local NO and TNF-α production, which impair the control of bacterial infection. Hence, the RSV-mediated Gas6/Axl activity attenuates the macrophage-mediated protection against pneumococcal infection. The Gas6/Axl axis could be a potentially novel therapeutic target for RSV-associated secondary bacterial infection.

Claudin-4 (CLDN4) is a key component of tight junctions (TJs) in epithelial cells. CLDN4 is overexpressed in many epithelial malignancies and correlates with cancer progression. Changes in CLDN4 expression have been associated with epigenetic factors (such as hypomethylation of promoter DNA), inflammation associated with infection and cytokines, and growth factor signaling. CLDN4 helps to maintain the tumor microenvironment by forming TJs and acts as a barrier to the entry of anticancer drugs into tumors. Decreased expression of CLDN4 is a potential marker of epithelial-mesenchymal transition (EMT), and decreased epithelial differentiation due to reduced CLDN4 activity is involved in EMT induction. Non-TJ CLDN4 also activates integrin beta 1 and YAP to promote proliferation, EMT, and stemness. These roles in cancer have led to investigations of molecular therapies targeting CLDN4 using anti-CLDN4 extracellular domain antibodies, gene knockdown, clostridium perfringens enterotoxin (CPE), and C-terminus domain of CPE (C-CPE), which have demonstrated the experimental efficacy of this approach. CLDN4 is strongly involved in promoting malignant phenotypes in many epithelial cancers and is regarded as a promising molecular therapeutic target.

Cancer dormancy is a state characterized by the quiescence of disseminated cancer cells, and tumor recurrence occurs when such cells re-proliferate after a long incubation period. These cancer cells tend to be treatment resistant and one of the barriers to successful therapeutic intervention. We have previously reported that long-term treatment of cancer cells with linoleic acid (LA) induces a dormancy-like phenotype. However, the mechanism underpinning this effect has not yet been clarified. Here, we investigate the mechanism of LA-induced quiescence in cancer cells. We first confirmed that long-term treatment of the mouse colorectal cancer cell line CT26 with LA induced quiescence. When these cells were inoculated subcutaneously into a syngeneic mouse and fed with an LA diet, the inoculated cancer cells maintained the quiescent state and exhibited markers of dormancy. LA-treated CT26 cells showed reduced oxidative phosphorylation, glycolysis, and energy production as well as reduced expression of the regulatory factors Pgc1α and MycC. MicroRNA expression profiling revealed that LA induced an upregulation in miR-494. The expression of Pgc1α and MycC were both induced by an miR-494 mimic, and the LA-induced decrease in gene expression was abrogated by an miR-494 inhibitor. The expression of miR-494 was enhanced by the mitochondrial oxidative stress produced by LA. In a syngeneic mouse subcutaneous tumor model, growth suppression by an LA diet and growth delay by LA pretreatment + LA diet were found to have similar effects as administration of an miR-494 mimic. In contrast, the effects of LA were abrogated by an miR-494 inhibitor. Analysis of human colorectal cancer tissue revealed that miR-494 was present at low levels in non-metastatic cases and cases with simultaneous liver metastases but was expressed at high levels in cases with delayed liver metastases, which also exhibited reduced expression of PGC1α and MYCC. These results suggest that miR-494 is involved in cancer dormancy induced by high levels of LA intake and that this microRNA may be valuable in targeting dormant cancer cells.

Berberine (BBR) is a plant alkaloid that has various biological activities. The effects of BBR on gastrointestinal cancer (GIC) have also been investigated and anti-tumor effects such as induction of cell death have been reported. However, the mechanism of BBR-induced cell death has not been fully elucidated. To this end, we investigated the effects of BBR using three GIC cell lines. Our analyses revealed that BBR inhibited cell proliferation, invasion, sphere formation, and anticancer drug resistance in all of the cell lines. BBR also induced an increase in mitochondrial superoxide, lipid peroxide and Fe²⁺ levels, decreased mitochondrial membrane potential and respiration, decreased glutathione peroxidase 4 expression and glutathione and induced Parkin/PINK1-associated mitophagy. BBR, as well as rotenone, inhibited mitochondrial complex I and enhanced complex II, which were associated with autophagy, reactive oxidative species production, and cell death. Inhibition of complex II by malonate abrogated these changes. BBR-induced cell death was partially rescued by ferrostatin-1, deferoxamine, Z-VAD-FMK, and ATG5 knockdown. Furthermore, oral administration of BBR significantly reduced tumor weight and ascites in a syngeneic mouse peritoneal metastasis model using CT26 GIC cells. These findings suggest that BBR induced a combined type of cell death via complex I inhibition and autophagy. The marked anti-tumor and anti-stemness effects are expected to be useful as a new cell death-inducing agent for the treatment of GIC.

Resistance to anticancer drugs is a problem in the treatment of pancreatic ductal carcinoma (PDAC) and overcoming it is an important issue. Recently, it has been reported that statins induce apoptosis in cancer cells but the mechanism has not been completely elucidated. We investigated the antitumor mechanisms of statins against PDAC and their impact on resistance to gemcitabine (GEM). Lovastatin (LOVA) increased mitochondrial oxidative stress in PDAC cells, leading to apoptosis. LOVA reduced lipid rafts in the plasma membrane and mitochondria, suppressed the activation of epithelial growth factor receptor (EGFR) and AKT in plasma membrane rafts, and reduced B-cell lymphoma 2 (BCL2)-Bcl-2-associated X protein (BAX) binding and the translocation of F1F0 ATPase in mitochondrial rafts. In the three GEM-resistant cell lines derived from MIA and PANC1, the lipid rafts in the cell membrane and the mitochondria were increased to activate EGFR and AKT and to increase BCL2-BAX binding, which suppressed apoptosis. LOVA abrogated these anti-apoptotic effects by reducing the rafts in the resistant cells. By treating the resistant cells with LOVA, GEM sensitivity improved to the level of the parental cells. Therefore, cholesterol rafts contribute to drug resistance in PDAC. Further clinical research is warranted on overcoming anticancer drug resistance by statin-mediated intracellular cholesterol regulation.

Although gemcitabine (GEM) is widely used in chemotherapy for pancreatic ductal adenocarcinoma (PDA), drug resistance restricts its clinical effectiveness. To examine the mechanism of GEM resistance, we established two GEM-resistant cell lines from human PDA cells by continuous treatment with GEM and CoCl₂-induced chemical hypoxia. One resistant cell line possessed reduced energy production and decreased mitochondrial reactive oxygen species levels, while the other resistant cell line possessed increased stemness. In both cell lines, ethidium bromide-stained mitochondrial DNA levels decreased, suggesting mitochondrial DNA damage. Inhibition of hypoxia-inducible factor-1α in both cell lines did not restore the GEM sensitivity. In contrast, treatment of both cell types with lauric acid (LAA), a medium-chain fatty acid, restored GEM sensitivity. These results suggest that decreased energy production, decreased mitochondrial reactive oxygen species levels, and increased stemness associated with mitochondrial damage caused by GEM lead to GEM resistance, and that hypoxia may promote this process. Furthermore, forced activation of oxidative phosphorylation by LAA could be a tool to overcome GEM resistance. Clinical verification of the effectiveness of LAA in GEM resistance is necessary in the future.