Protein kinase F regulates the virulence of Mycobacterium tuberculosis

ABSTRACT The serine/threonine protein kinase F (PknF) of Mycobacterium tuberculosis (Mtb) has poorly defined targets and functions but is involved in limiting NLRP3 inflammasome activation in murine macrophages and dendritic cells in vitro . The importance of PknF for the virulence of Mtb in vivo is not known. Here, we demonstrate that the Mtb CDC1551 deletion mutant of pknF (∆ pknF ) expresses significantly increased levels of the lipid pthiocerol dimycoserosate (PDIM), a polyketide lipid with pro-virulence properties. The ∆ pknF mutant strain compared with the Mtb and complemented strains showed a 100-fold increase in growth at day 28 and about a 10-fold increase in growth at days 90–98 in the lungs of mice. The increase in pulmonary bacterial loads after infection with the ∆ pknF strain was conserved even in Nlrp3 -deficient mice, arguing that PknF modulates Mtb virulence independently of NLRP3-inflammasome activation in mice. Staining of lung sections revealed increased inflammation in the lungs of ∆ pknF strain-infected mice when compared with Mtb and the complemented mutant strain. Highly susceptible B6.Sst1 S mice displayed decreased host resistance, with significantly decreased survival when infected with the ∆ pknF strain compared to the complemented strain or Mtb. In conclusion, our data suggest that expression of PknF, as a modulator of multiple downstream effector proteins, restricts the virulence of Mtb in the lungs of mice through an NLRP3 inflammasome-independent mechanism, but potentially via suppressing production of the virulence lipid, PDIM.