The dengue virus NS1 is a multifunctional protein that forms part of replication complexes. NS1 is also secreted, as a hexamer, to the extracellular milieu. Circulating NS1 has been associated with dengue pathogenesis by several mechanisms. Cell binding and internalization of soluble NS1 result in endothelial hyperpermeability and in the downregulation of the innate immune response. In this work, we report that the HDL scavenger receptor B1 (SRB1) in human hepatic cells and a scavenger receptor B1-like in mosquito C6/36 cells act as cell surface binding receptors for dengue virus NS1. The presence of the SRB1 on the plasma membrane of C6/36 cells, as well as in Huh7 cells, was demonstrated by confocal microscopy. The internalization of NS1 can be efficiently blocked by anti-SRB1 antibodies and previous incubation of the cells with HDL significantly reduces NS1 internalization. Significant reduction in NS1 internalization was observed in C6/36 cells transfected with siRNAs specific for SRB1. In addition, the transient expression of SRB1 in Vero cells, which lacks the receptor, allows NS1 internalization in these cells. Direct interaction between soluble NS1 and the SRB1 in Huh7 and C6/36 cells was demonstrated in situ by proximity ligation assays and in vitro by surface plasmon resonance. Finally, results are presented indicating that the SRB1 also acts as a cell receptor for Zika virus NS1. These results demonstrate that dengue virus NS1, a bona fide lipoprotein, usurps the HDL receptor for cell entry and offers explanations for the altered serum lipoprotein homeostasis observed in dengue patients. Importance Dengue is the most common viral disease transmitted to humans by mosquitoes. The dengue virus NS1 is a multifunctional glycoprotein necessary for viral replication. NS1 is also secreted as a hexameric lipoprotein and circulates in high concentrations in the sera of patients. Circulating NS1 has been associated with dengue pathogenesis by several mechanisms, including favoring of virus replication in hepatocytes and dendritic cells and disruption of the endothelial glycocalyx leading to hyperpermeability. Those last actions require NS1 internalization. Here, we identify the scavenger cell receptor B1, as the cell-binding receptor for dengue and Zika virus NS1, in cultured liver and in mosquito cells. The results indicate that flavivirus NS1, a bona fide lipoprotein, usurps the human HDL receptor and may offer explanations for the alterations in serum lipoprotein homeostasis observed in dengue patients.

15Dengue is the most common virus disease transmitted to humans by 16 mosquitoes. The dengue virus NS1 is a multifunctional protein that form part of 17 replication complexes. In addition, NS1 is also secreted, as a hexamer, to the 18 extracellular milieu. Circulating NS1 has been associated with dengue 19 pathogenesis by several different mechanisms. Cell binding and internalization 20 of soluble NS1 result in the disruption of tight junctions and in down regulation 21 of the innate immune response. In this work, we report that the HDL scavenger 22 receptor B1 (SRB1) in human hepatic cells, and a scavenger receptor B1-like in 23 mosquito C6/36 cells act as cell surface binding receptor for dengue virus NS1. 24 The presence of the SRB1 on the plasma membrane of C6/36 cells, as well as 25 in Huh-7 cells, was demonstrated by confocal microcopy. Internalization of NS1 26 can be efficiently blocked by anti-SRB1 antibodies and previous incubation of 27 the cells with HDL significantly reduces NS1 internalization. In addition, the 28 transient expression of SRB1 in Vero cells, which lack the receptor, renders 29 these cells susceptible to NS1 entry. Direct interaction between soluble NS1 30 and the SRB1 in Huh7 and C6/36 cells was demonstrated in vivo by proximity 31 ligation assays an in vitro by surface plasmon resonance. Finally, data is 32 presented indicating that the SRB1 also act as cell receptor for zika virus NS1. 33 These results demonstrate that dengue virus NS1, a bonna fide lipoprotein, 34 usurps the HDL receptor for cell entry and offers explanations for the altered 35 serum lipoprotein homeostasis observed in dengue patients.36 37 Key words: dengue, dengue virus, zika virus, NS1, scavenger receptor B-1. 38 39 The Flavivirus genus, belonging to the Flaviviridae family, includes a group of 40 vector borne viruses of importance in human public health as dengue virus 41 (DENV), Zika virus (ZIKV), yellow fever virus (YFV), Japanese encephalitis virus 42 (JEV) and West Nile virus (WNV). DENV and ZIKV are transmitted by the same 43 arthropods of the Aedes genus and share a similar geographical distribution 44 (Paixão et al 2018). It is estimated that almost half of the world population, 45 distributed in tropical and subtropical zones, is at risk of contracting these 46 diseases (WHO, 2018). The initial symptoms of both DENV and ZIKV infections 47 manifest as a febrile syndrome. Infections with DENV can evolve to 48 hemorrhagic syndrome accompanied of hypovolemic shock, systemic failure 49 and death, mainly in children. In turn, ZIKV infections when acquired during 50 pregnancy, are associated with the occurrence of microcephaly and other 51 neurological severe injuries in the fetus brain (Rather et al 2017). In adults, 52 ZIKV has been associated with the occurrence of Guillan-Barré syndrome which 53 is highly disabling (Song et al., 2017). DENV and ZIKV virions are spherical 54 particles of about 50nm in diameter. The positive RNA genome is about 11Kb in 55 length encoding for 3 structural (Membra...