Surface (S) Layer Proteins of Lactobacillus acidophilus Blocks Alphavirus and Flavivirus Infection via DC-SIGN Interaction

RUZAL SANDRA M.; MARTINEZ GUADALUPE; PRADO ACOSTA MARIANO; KIELIAN MARGARET

New Orleans

Congreso; American Society for Microbiology General Meeting 2017; 2017

ASM

Alphaviruses and flaviviruses are important human pathogens that include Chikungunya, Dengue and Zika virus, which can cause diseases in humans ranging from arthralgia to hemorrhagic fevers and microcephaly.We have previously shown that treatment with Surface (S) layer protein, present on the bacterial cell-envelope of Lactobacillus acidophilus, is able to inhibit Junin arenavirus and several bacterial infections by blocking the pathogen?s interaction with DC-SIGN, a trans-membrane protein that is a C-type calcium-dependent lectin. DC-SIGN is known to act an attachment factor for several viruses including alphaviruses and flaviviruses.In the present work we studied the inhibitory effect of S-layer protein in alphavirus and flavivirus infection. Furthermore, we used this viral system to dissect the mechanism of S-layer inhibition.To evaluate the protective effect of S-layer in DC-SIGN expressing cells, we used 3T3 Wild Type cells or 3T3 cells stably expressing DC-SIGN and we tested two alphaviruses [Semliki Forest virus (SFV), Chikungunya (CHIKV)], and two flaviviruses [Zika (ZIKV) and Dengue(DENV) virus].As expected, DC-SIGN expression significantly enhanced infection by all four viruses. Cells then were pretreated with S-layer for 1 hour prior to infection. Pretreatment decreased virus infectivity in cells expressing DC-SIGN to the low levels observed in non-DC-SIGN-expressing cells.To further investigate the mechanism of DC-SIGN-dependent S-layer inhibition we used the highly characterized SFV as a model system. Using confocal microscopy we showed that S-layer binds to cells expressing DC-SIGN and at somewhat lower levels to DC-SIGN-negative cells. Strikingly, S-layer prevented viral adsorption and internalization in DC-SIGN-expressing cells, but had no effect on virus binding to DC-SIGN-negative cells. Inhibition of virus binding occurred in a time dependent manner, with a significant reduction of infection requiring at least a 30 minute incubation of S-layer with DC-SIGN-expressing cells. We also showed that DC-SIGN endocytosis was not affected during S-layer treatment suggesting that it maintains its normal function. We propose that the interaction between S-layer and DC-SIGN inhibits the virus binding to this attachment factor, thus blocking the viral infection. Further characterization with DC-SIGN mutants will be used to address this question. The results of our research point out the importance of Lactobacillus acidophilus as a possible weapon against several emerging infectious diseases.