Activin receptor‑like kinases (ALKs), members of the type I activin receptor family, belong to the serine/threonine kinase receptors of the transforming growth factor‑β (TGF‑β) superfamily. ALKs mediate the roles of activin/TGF‑β in a wide variety of physiological and pathological processes, ranging from cell differentiation and proliferation to apoptosis. For example, the activities of ALKs are associated with an advanced tumor stage in prostate cancer and the chondrogenic differentiation of mesenchymal stem cells. Therefore, potent and selective small molecule inhibitors of ALKs would not only aid in investigating the function of activin/TGF‑β, but also in developing treatments for these diseases via the disruption of activin/TGF‑β. In recent studies, several ALK inhibitors, including LY‑2157299, SB‑431542 and A‑83‑01, have been identified and have been confirmed to affect stem cell differentiation and tumor progression in animal models. This review discusses the therapeutic perspective of small molecule inhibitors of ALKs as drug targets in tumor and stem cells.

Natural killer (NK) cells can migrate quickly to the tumor site to exert cytotoxic effects on tumors, and some chemokines, including CXCL8, CXCL10 or and CXCL12, can regulate the migration of NK cells. Activin A, a member of the transforming growth factor β (TGF-β) superfamily, is highly expressed in tumor tissues and involved in tumor development and immune cell activation. In this study, we focus on the effects of activin A on NK cell migration. In vitro, activin A induced NK cell migration and invasion, promoted cell polarization and inhibited cell adhesion. Moreover, activin A increased Ca²⁺, p-SMAD3 and p-AKT levels in NK cells. An AKT inhibitor and Ca²⁺ chelator partially blocked activin A-induced NK cell migration. In vivo, exogenous activin A increased tumor-infiltrating NK cells in NS-1 cell solid tumors and inhibited tumor growth, and blocking endogenous activin A with anti-activin A antibody reduced tumor-infiltrating NK cells in 4T-1 cell solid tumors. These results suggest that activin A induces NK cell migration through AKT signaling and calcium signaling and may enhance the antitumor effect of NK cells by increasing tumor-infiltrating NK cells.

Activin A levels are elevated during multiple severe infections and associated with an increased risk of death. However, the role of activin A in bacterial infection is still unclear. Here, we found that activin A levels were increased during S. aureus skin infection in mice. Administration of activin A increased the bacterial burden and promoted the spread of bacteria in vivo. Moreover, activin A inhibited neutrophil chemotaxis to N-formylmethionine-leucyl-phenylalanine via the type IIA activin receptor (ActRIIA) in vitro and impaired ActRIIA+ neutrophil recruitment to infection foci in vivo. Additionally, we identified a novel subpopulation of neutrophils, ActRIIA+ neutrophils, which exhibit superior phagocytic capacity compared to ActRIIA− neutrophils and possess an N2-like immunoregulatory activity via secreting IL-10 and TGF-β. Taken together, these findings indicate that activin A inhibits the recruitment of ActRIIA+ neutrophils to infected foci, leading to the impairment of bacterial clearance, and thus may hamper early infection control.

Follistatin (FST) as a gonadal protein is central to the establishment and maintenance of pregnancy. Trophoblasts’ migration and invasion into the endometrium are critical events in placental development. This study aimed to elucidate the role of FST in the migration and invasion of placental trophoblasts of mice. We found that FST increased the vitality and proliferation of primary cultured trophoblasts of embryonic day 8.5 (E8.5) mice and promoted wound healing of trophoblasts. Moreover, FST significantly induced migration of trophoblasts in a microfluidic device and increased the number of invasive trophoblasts by Matrigel-coated transwell invasion assay. Being treated with FST, the adhesion of trophoblasts was inhibited, but intracellular calcium flux of trophoblasts was increased. Western blotting results showed that FST had no significant effects on the level of p-Smad3 or the ratio of p-Smad3/Smad3 in trophoblasts. Interestingly, FST elevated the level of p-JNK; the ratio of p-JNK/JNK; and expression of migration-related proteins N-cadherin, vimentin, ezrin and MMP2 in trophoblasts. Additionally, the migration of trophoblasts and expression of N-cadherin, vimentin, and MMP2 in trophoblasts induced by FST were attenuated by JNK inhibitor AS601245. These findings suggest that the elevated FST in pregnancy may act as a chemokine to induce trophoblast migration and invasion through the enhanced JNK signaling to maintain trophoblast function and promote placental development.

Background: Chronic atrophic gastritis (CAG) is a severe condition characterized by inflammation and loss of appropriate mucosal glands in the stomach. The underlying mechanisms of CAG development remain unclear. Exploring immune-related circular RNAs (circRNAs) could provide insights for potential diagnostic and therapeutic strategies. Methods: Samples from 40 patients with CAG and non-CAG (CNAG) underwent high-throughput sequencing, and EdgeR analysis identified differentially expressed circRNAs and mRNAs. Gene Ontology (GO) analysis elucidated biological functions, while Immune Cell Abundance Identifier (ImmuCellAI) estimated immune cell abundance. Flow cytometry analyzed immune cell infiltration. Weighted gene co-expression network analysis (WGCNA) identified hub genes related to the immune response in CAG. CircRNA-mRNA networks were constructed, and qRT-PCR validated findings. Results: A total of 163 differentially expressed immune-related genes (DEIRGs) were identified between CAG and CNAG. The upregulated immune-related mRNAs in CAG were significantly enriched in antimicrobial humoral response, viral entry into host cells, neutrophil activation, and leukocyte migration. Conversely, downregulated immune-related mRNAs were linked to regulation of natural killer cell-mediated cytotoxicity, positive regulation of adaptive immune response, antigen receptor-mediated signaling pathway, and B cell activation. Immune Cell Abundance Identifier (ImmuCellAI) and flow cytometry confirmed increased neutrophil infiltration in CAG compared to CNAG. WGCNA identified 56 hub immune-related genes. Additionally, circRNA expression profiles in CNAG and CAG were explored, with 19 upregulated and 23 downregulated circRNAs identified in CAG. The upregulated circRNAs were associated with biological processes like carnitine metabolic process and regulation of B cell receptor signaling pathway. A circRNA-mRNA co-expression network was constructed based on five circRNAs highly related to hub immune-related genes. Furthermore, the expression of eight immune-related mRNAs and five circRNAs were validated in CAG. Conclusion: This study is the first systematic analysis of circRNA profiles in CAG and provide important insights for potential immunotherapeutic strategies and early diagnostic biomarkers in CAG treatment.