The Hemagglutinin of Bat-Associated Influenza Viruses Is Activated by TMPRSS2 for pH-Dependent Entry into Bat but Not Human Cells

Hoffmann, Markus; Krüger, Nadine; Zmora, Pawel; Wrensch, Florian; Herrler, Georg; Pöhlmann, Stefan

Cleavage-activation of FLUAV-HA by host cell proteases is essential for FLUAV infectivity. Several TTSPs can cleave and activate HA in cell culture and recent studies demonstrated that TMPRSS2 is essential for FLUAV spread in mice [32, 33, 58, 59] . Moreover, polymorphisms in TMPRSS2 were shown to impact severity of influenza in humans [69] . Treatment of bat-FLUAV-HAL-expressing cells with trypsin led to proteolytic cleavage of HAL and exposure of HAL-bearing pseudotypes to trypsin was required for efficient transduction of target cells, indicating that proteolytic processing is also required for HAL function. Moreover, coexpression of batFLUAV-HAL with TMPRSS2, DESC-1 or MSPL resulted in proteolytic cleavage of HAL and rendered the particles infectious in the absence of trypsin treatment, suggesting that bat-FLUAV-HAL can utilize human proteases for their activation. Finally, titration of the amounts of TMPRSS2 had differential effects on the proteolytic cleavage of HAL17 and HAL18 and on infectivity of pseudotypes bearing these proteins, hinting towards subtle differences in the efficiency of TMPRSS2 use by these subtypes. Whether bat TMPRSS2 is also able to cleave and activate batFLUAV-HAL remains to be investigated.