Human TMPRSS2 Expression Vectors

Human TMPRSS2 (transmembrane protease serine 2) is a type II transmembrane serine protease (TTSP) protein containing four subunits: an N-terminal transmembrane domain, and a large ectodomain comprised of an LDLA (low-density lipoprotein receptor A) subunit, a group A scavenger receptor domain, and a trypsin-like serine protease domain in C-terminal [1]. TTSPs activation requires cleavage following a basic amino acid residue (Arg for TMPRSS2) in a conserved activation motif preceding the catalytic domain [1]. 

TMPRSS2 has been found to cleave the hemagglutinin (HA) glycoprotein from the influenza virus, and the Spike glycoprotein of MERS-CoV, SARS-CoV, and SARS-CoV-2, to generate unlocked, fusion-catalyzing HA and Spike at the target cell surface [2-4].

In the context of SARS-CoV-2 infection, TMPRSS2 exerts a crucial proteolytic activation of the S protein bound to ACE2 to facilitate the viral entry into target cells [2, 6, 7]. The Spike glycoprotein harbors two distinct cleavage sites, known as S1/S2 and S2’, at the intersection its S1 and S2 domains, and inside the S2 domain, respectively. While the exact timing and location for Spike binding, cleavage, and fusion processes to take place remain to be determined, it has been proposed that the S protein is cleaved into two subunits (S1 and S2) by proteases, including furin and TMPRSS2 [2, 8, 9]. S1 binds to ACE2, and S2 is further cleaved and activated by the TMPRSS2 [2, 8]. Together these actions result in host-viral membrane fusion and the viral RNA genome is released into the host cell cytoplasm.

Interestingly, while TTSPs are believed to remain membrane-associated after activation because of a disulfide bond linking the pro-domain and the catalytic domain [1], TMPRSS2 has been found to be autoactivated, cleaved and its serine protease domain released in the tissues, cell line cultures, and mouse serum [10]. 

Two spliced transcript variants encoding a long (1) and a short (2) isoform have been found for the TMPRSS2 gene, and both isoforms have been found to cleave the Spike protein of SARS-CoV for cathepsin L-independent entry into target cells [3].

Camostat and Nafamostat are two clinically-proven inhibitors of TMPRSS2 [1, 11].

References

1. Bugge T.H. et al. 2009. Type II transmembrane serine proteases. J. Biol. Chem. 284(35) :23177-23181.
2. Hoffmann M.  et al. 2020. SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor. Cell. 181:1-16.
3. Zmora P.  et al. 2015. TMPRSS2 isoform 1 activates respiratory viruses and is expressed in viral target cells. PLoS ONE 10(9):e0138380.
4. Matsuyama S. et al. 2010. Efficient activation of the severe acute respiratory syndrome coronavirus spike protein by the transmembrane protease TMPRSS2. J. Virol. 84:12658-12664.
5. Hamming I.  et al. 2004. Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. J. Pathol. 203:631-637.
6. Li W.  et al. 2003. Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature. 426(6965):450-454.
7. Zhou P.  et al. 2020. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature. 579(7798):270-273.
8. Walls A.C.,  et al. 2020. Structure, function, and antigenicity of the SARS-CoV-2 spike glycoprotein. Cell. 181(2):281-292.e6.
9. Hoffmann M.  et al., 2020. A multibasic cleavage site in the Spike protein of SARS-CoV-2 is essential for infection of human lung cells. Molecular Cell. 78:1-6.
10. Afar, D.E.H. et al. 2001. Catalytic cleavage of the androgen-regulated TMPRSS2 protease results in its secretion by prostate and prostate cancer epithelia. Cancer Res.  61(4):1686-1692.
11. Vincent, M.J.  et al. 2005. Chloroquine is a potent inhibitor of SARS coronavirus infection and spread. Virol J 2, 69.