Emerging evidence indicates that the neuronal guidance molecule SLIT plays a role in tumor suppression, as SLIT-encoding genes are inactivated in several types of cancer, including lung cancer; however, it is not clear how SLIT functions in lung cancer. Here, our data show that SLIT inhibits cancer cell migration by activating RhoA and that myosin 9b (Myo9b) is a ROBO-interacting protein that suppresses RhoA activity in lung cancer cells. Structural analyses revealed that the RhoGAP domain of Myo9b contains a unique patch that specifically recognizes RhoA. We also determined that the ROBO intracellular domain interacts with the Myo9b RhoGAP domain and inhibits its activity; therefore, SLIT-dependent activation of RhoA is mediated by ROBO inhibition of Myo9b. In a murine model, compared with control lung cancer cells, SLIT-expressing cells had a decreased capacity for tumor formation and lung metastasis. Evaluation of human lung cancer and adjacent nontumor tissues revealed that Myo9b is upregulated in the cancer tissue. Moreover, elevated Myo9b expression was associated with lung cancer progression and poor prognosis. Together, our data identify Myo9b as a key player in lung cancer and as a ROBO-interacting protein in what is, to the best of our knowledge, a newly defined SLIT/ROBO/Myo9b/RhoA signaling pathway that restricts lung cancer progression and metastasis. Additionally, our work suggests that targeting the SLIT/ROBO/Myo9b/RhoA pathway has potential as a diagnostic and therapeutic strategy for lung cancer.

The role of IL‐10 in malignant pleural effusion (MPE) remains unknown. By using murine MPE models, we observed that an increase in pleural IL‐10 was a significant predictor of increased risk of death. We noted that TH1‐ and TH17‐cell content in MPE was higher in IL‐10–/– mice than in WT mice, and IL‐10 deficiency promoted differentiation into TH1 but not into TH17 cells. A higher fraction of TH1 and TH17 cells in the MPE of IL‐10–/– mice expressed CXCR3 compared with WT mice. We also demonstrated that Lewis lung cancer and colon adenocarcinoma cells secreted large amounts of CXCL10, a ligand of CXCR3, which induced the migration of TH1 and TH17 cells into the MPE, and IFN‐γ could promote this signaling cascade. Furthermore, intrapleural injection of mice with CXCL10‐deficient tumor cells led to decreased TH1‐ and TH17‐cell content in MPE, increased MPE volume, and reduced survival of MPE‐bearing mice. Taken together, we demonstrated that IL‐10 deficiency promoted T‐cell differentiation into TH1 cells and upregulated the CXCR3‐CXCL10 signaling pathway that recruits TH1 and TH17 cells into MPE, ultimately resulting in decreased MPE formation and longer survival time of mice‐bearing MPE.

Inflammatory signaling networks between tumor cells and immune cells contribute to the development of malignant pleural effusion (MPE). B cells have been found in MPE; however, little is known about their roles there. In the present study, by using mouse MPE models, we noted that although the total B cells in MPE were decreased as compared with the corresponding blood and spleen, the percentage of activated naïve B cells expressing higher levels of CD80, CD86, myosin heavy chain-II, CD44, CD69, and programmed cell death-ligand 1 (PD-L1) molecules were increased in wild-type mouse MPE. Compared with wild-type mice, decreased T helper (T)1 cells and increased T17 cells were present in B cell-deficient mouse MPE, which paralleled to the reduced MPE volume and longer survival time. Adoptive transfer of activated naïve B cells into B cell-deficient mice was able to increase T1 cells and decrease T17 cells in MPE and shorten the survival of mice bearing MPE. Furthermore, we demonstrated that activated naïve B cells inhibited T17-cell expansion via the PD-1/PD-L1 pathway and promoted naïve CD4 T-cell differentiation into T1/T17 cells through secreting IL-27/IL-6 independent of the PD-1/PD-L1 pathway. Collectively, our data uncovered a mechanism by which naïve B cells promote MPE formation by regulating T1/T17 cell responses, making these B cells an attractive target for therapeutic intervention in the fight against cancer.