Inhibition of neutrophil migration in mice by mouse formyl peptide receptors 1 and 2 dual agonist: indication of cross-desensitization in vivo

It has been reported that the stimulation of neutrophils with N‐formyl‐Met‐Leu‐Phe (fMLF), an agonist for formyl peptide receptor (Fpr) 1, renders cells unresponsive to other chemoattractants in vitro. This is known as cross‐desensitization, but its functional relevance in neutrophil migration in vivo has not been investigated. Here, we show that precedent stimulation of mouse neutrophils with compound 43, a non‐peptidyl agonist for mouse Fpr1 and Fpr2, rendered the cells unresponsive to a second stimulation with C5a, leukotriene B₄, or keratinocyte‐derived cytokine (KC) in calcium mobilization and chemotaxis assays in vitro. The expression of chemokine (C‐X‐C motif) receptor 2 (CXCR2) on the surface of neutrophils was concomitantly diminished by stimulating the cells with the compound. Moreover, oral administration of the compound to mice before they were exposed to lipopolysaccharide (LPS) aerosol resulted in a dose‐dependent reduction in the neutrophil count in bronchoalveolar lavage fluid. The expression of CXCR2 on blood neutrophils was also reduced in the compound‐administered mice. The recipient mice that underwent adoptive transfer of fluorescence‐labelled neutrophils that had been incubated with the compound showed a substantial decrease in neutrophil counts in bronchoalveolar lavage fluid after they were exposed to LPS, when compared with the control mice to which vehicle‐treated neutrophils had been transferred. These results are consistent with the idea that the agonist for Fpr1 and Fpr2 induced cross‐desensitization in neutrophils and attenuated neutrophil migration into the airways. Our results also revealed the unpredicted effect of an Fpr1 and Fpr2 dual agonist, which may act as a functional antagonist for multiple chemoattractant receptors in vivo.     

Prosaposin,tumor‐secreted protein,promotes pancreatic cancer progression by decreasing tumor‐infiltrating lymphocytes

Glycoproteins produced by tumor cells are involved in cancer progression, metastasis, and the immune response, and serve as possible therapeutic targets. Considering the dismal outcomes of pancreatic ductal adenocarcinoma (PDAC) due to its unique tumor microenvironment, which is characterized by low antitumor T‐cell infiltration, we hypothesized that tumor‐derived glycoproteins may serve as regulating the tumor microenvironment. We used glycoproteomics with tandem mass tag labeling to investigate the culture media of three human PDAC cell lines, and attempted to identify the key secreted proteins from PDAC cells. Among the identified glycoproteins, prosaposin (PSAP) was investigated for its functional contribution to PDAC progression. PSAP is highly expressed in various PDAC cell lines; however, knockdown of intrinsic PSAP expression did not affect the proliferation and migration capacities. Based on the immunohistochemistry of resected human PDAC tissues, high PSAP expression was associated with poor prognosis in patients with PDAC. Notably, tumors with high PSAP expression showed significantly lower CD8⁺ T‐cell infiltration than those with low PSAP expression. Furthermore, PSAP stimulation decreased the proportion of CD8⁺ T cells in peripheral blood monocytes. Finally, in an orthotopic transplantation model, the number of CD8⁺ T cells in the PSAP shRNA groups was significantly increased, resulting in a decreased tumor volume compared with that in the control shRNA group. PSAP suppresses CD8⁺ T‐cell infiltration, leading to the promotion of PDAC progression. However, further studies are warranted to determine whether this study contributes to the development of a novel immunomodulating therapy for PDAC.