Endothelial MPL knockdown inhibited tumor growth and angiogenesis and decreased the prevalence of Tregs and alternatively activated macrophages in a xenograft model of NSCLC.
Endothelial MPL promotes tumor angiogenesis and modulates the tumor microenvironment by facilitating Treg recruitment, suggesting it as a potential dual anti-angiogenic and immunomodulatory target for lung cancer therapy.
Abstract Background Tumor endothelial cells (TECs) are in a chronically altered state that affects tumor immunity through various mechanisms, including increased vascularity (tumor angiogenesis) and altered recruitment of inflammatory cells. Vascular endothelial growth factor (VEGF) is one of the main cytokines driving the tumor endothelial phenotype. We had previously shown that thrombopoietin receptor (MPL) is targeted by microRNA-1, a ubiquitous tumor suppressor downregulated by VEGF. MPL has been extensively studied in megakaryocytes, where, upon thrombopoietin (TPO) binding, it associates with Jak2 and activates STAT3 and -5. Less is known about the role of MPL in TECs. Both STAT3 and STAT5 play critical roles in angiogenesis, especially in response to hypoxia. STAT3 also induces the expression of P-selectin (SELP) in TECs. SELP, the main ligand for PSGL-1, mediates immune cell adhesion to ECs and has immunomodulatory effects on Tregs and dendritic cells. Here, we examined the contribution of endothelial MPL to tumor angiogenesis and immunity. Methods MPL expression was measured in lung ECs (CD31+ CD45−) isolated from KrasLSL-G12D; Trp53fl/fl (KP) mice and from human non-small-cell lung cancer (NSCLC) specimens. Human umbilical vein ECs (HUVECs) were transduced with MPL-shRNA or control vectors and stimulated with VEGF for functional studies. To assess vascular-specific MPL function in vivo, VE-cadherin-driven lentiviral vectors were used for EC-specific MPL knockdown or overexpression. These constructs were delivered to Lewis lung carcinoma (LLC) implants to evaluate tumor growth and angiogenesis. Immune cell infiltration in LLC tumors was assessed by immunohistochemistry and gene-expression profiling. Results MPL levels in TECs from NSCLC patients are significantly higher than non-cancerous human pulmonary microvascular ECs (HPMECs). MPL levels are also significantly elevated in ECs from KP mouse tumor-bearing lungs compared to controls. MPL knockdown in endothelial cells (ECs) inhibited VEGFR2 and STAT3 phosphorylation and decreased SELP levels at the endothelial surface. MPL overexpression had the opposite effects. In a xenograft model of NSCLC, EC-specific MPL knockdown post-implantation inhibited tumor growth and angiogenesis and decreased the prevalence of Tregs and alternatively activated macrophages in tumors. Again, EC-specific overexpression had the opposite effects. A gene expression analysis of TECs from this model showed altered adhesion molecule (decreased SELP, MAdCAM-1, and ALCAM) and chemokine/cytokine levels (decreased CCL2, CXCL10, and 11) with MPL knockdown. Conclusion Endothelial MPL promotes tumor angiogenesis through VEGFR2-JAK2-STAT3 pathway and modulates the tumor microenvironment by facilitating Treg recruitment. Targeting endothelial MPL can be used as a dual anti-angiogenic and immunomodulatory strategy for lung cancer therapy. This abstract is funded by: None
Korde et al. (2026) studied Non-Small Cell Lung Cancer. Endothelial MPL knockdown vs. Control vectors was evaluated on Tumor growth, angiogenesis, and immune cell infiltration. Endothelial MPL knockdown inhibited tumor growth and angiogenesis and decreased the prevalence of Tregs and alternatively activated macrophages in a xenograft model of NSCLC.