Modulation of protein S and growth arrest specific 6 protein signaling inhibits pancreatic cancer cell survival and proliferation

Galectins Are Central Mediators of Immune Escape in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers and is highly immune tolerant. Although there is immune cell infiltration in PDAC tissues, most of the immune cells do not function properly and, therefore, the prognosis of PDAC is very poor. Galectins are carbohydrate-binding proteins that are intimately involved in the proliferation and metastasis of tumor cells and, in particular, play a crucial role in the immune evasion of tumor cells. Galectins induce abnormal functions and reduce numbers of tumor-associated macrophages (TAM), natural killer cells (NK), T cells and B cells. It further promotes fibrosis of tissues surrounding PDAC, enhances local cellular metabolism, and ultimately constructs tumor immune privileged areas to induce immune evasion behavior of tumor cells. Here, we summarize the respective mechanisms of action played by different Galectins in the process of immune escape from PDAC, focusing on the mechanism of action of Galectin-1. Galectins cause imbalance between tumor immunity and anti-tumor immunity by coordinating the function and number of immune cells, which leads to the development and progression of PDAC.

Protein S: function, regulation, and clinical perspectives

PURPOSE OF REVIEW

Protein S (PS) is an essential natural anticoagulant. PS deficiency is a major contributor to acquired hypercoagulability. Acquired hypercoagulability causes myocardial infarction, stroke, and deep vein thrombosis in millions of individuals. Yet, despite its importance in hemostasis, PS is the least understood anticoagulant. Even after 40 years since PS was first described, we are still uncovering information about how PS functions. The purpose of this review is to highlight recent findings that advance our understanding of the functions of PS and explain hypercoagulability caused by severe PS deficiency.

RECENT FINDINGS

PS has long been described as a cofactor for Activated Protein C (APC) and Tissue Factor Pathway Inhibitor (TFPI). However, a recent report describes direct inhibition of Factor IXa (FIXa) by PS, an activity of PS that had been completely overlooked. Thrombophilia is becoming a more frequently reported disorder. Hereditary PS deficiency is an anticoagulant deficiency that results eventually in thrombophilia. In addition, PS deficiency is a predisposing factor for venous thromboembolism (VTE), but an effect of PS deficiency in arterial thrombosis, such as arterial ischemic stroke, is uncertain. Plasma PS concentration decreases in pregnant women. Inherited thrombophilias are important etiologies for recurrent pregnancy loss, and anticoagulation therapy is of benefit to women with recurrent pregnancy loss who had documented only PS deficiency.Hypoxia is a risk factor for VTE, and hypoxia downregulates plasma PS level. Importantly, COVID-19 can lead to hypoxemia because of lung damage from IL6-driven inflammatory responses to the viral infection. Because hypoxia decreases the abundance of the key anticoagulant PS, we surmise that the IL6-induced cytokine explosion combined with hypoxemia causes a drop in PS level that exacerbates the thrombotic risk in COVID-19 patients.

SUMMARY

This review is intended to advance understanding of the anticoagulant function of an important plasma protein, PS. Despite 40+ years of research, we have not had a complete description of PS biology as it pertains to control of blood coagulation. However, the picture of PS function has become sharper with the recent discovery of FIXa inhibition by PS. Hemostasis mediated by PS now includes regulation of FIXa activity alongside the cofactor activities of PS in the TFPI/APC pathways. In addition, the direct inhibition of FIXa by PS suggests that PS, particularly a small derivative of PS, could be used to treat individuals with PS deficiencies or abnormalities that cause thrombotic complications.