Revisiting the interaction between complement lectin pathway protease MASP-2 and SARS-CoV-2 nucleoprotein.

Complement activation is considered to contribute to the pathogenesis of severe SARS-CoV-2 infection, mainly by generating potent immune effector mechanisms including a strong inflammatory response. Involvement of the lectin complement pathway, a major actor of the innate immune anti-viral defense, has been reported previously. It is initiated by recognition of the viral surface Spike glycoprotein by mannose-binding lectin (MBL), which induces activation of the MBL-associated protease MASP-2 and triggers the proteolytic complement cascade. A role for the viral nucleoprotein (N) has also been reported, through binding to MASP-2, leading to protease overactivation and potentiation of the lectin pathway. In the present study, we reinvestigated the interactions of the SARS-CoV-2 N protein, produced either in bacteria or secreted by mammalian cells, with full-length MASP-2 or its catalytic domain, in either active or proenzyme form. We could not confirm the interaction of the N protein with the catalytic domain of MASP-2 but observed N protein binding to proenzyme MASP-2. We did not find a role of the N protein in MBL-mediated activation of the lectin pathway. Finally, we showed that incubation of the N protein with MASP-2 results in proteolysis of the viral protein, an observation that requires further investigation to understand a potential functional significance in infected patients.

Targeting galectin-1 overcomes breast cancer-associated immunosuppression and prevents metastatic disease

Galectin-1 (Gal1), an evolutionarily conserved glycan-binding protein, contributes to the creation of an immunosuppressed microenvironment at sites of tumor growth. In spite of considerable progress in elucidating its role in tumor-immune escape, the mechanisms underlying the inhibitory functions of Gal1 remain obscure. Here, we investigated the contribution of tumor Gal1 to tumor growth, metastasis, and immunosuppression in breast cancer. We found that the frequency of Gal1(+) cells in human breast cancer biopsies correlated positively with tumor grade, while specimens from patients with benign hyperplasia showed negative or limited Gal1 staining. To examine the pathophysiologic relevance of Gal1 in breast cancer, we used the metastatic mouse mammary tumor 4T1, which expresses and secretes substantial amounts of Gal1. Silencing Gal1 expression in this model induced a marked reduction in both tumor growth and the number of lung metastases. This effect was abrogated when mice were inoculated with wild-type 4T1 tumor cells in their contralateral flank, suggesting involvement of a systemic modulation of the immune response. Gal1 attenuation in 4T1 cells also reduced the frequency of CD4(+)CD25(+) Foxp3(+) regulatory T (T(reg)) cells within the tumor, draining lymph nodes, spleen, and lung metastases. Further, it abrogated the immunosuppressive function of T(reg) cells and selectively lowered the expression of the T-cell regulatory molecule LAT (linker for activation of T cells) on these cells, disarming their suppressive activity. Taken together, our results offer a preclinical proof of concept that therapeutic targeting of Gal1 can overcome breast cancer-associated immunosuppression and can prevent metastatic disease(AU)