A Role for IFITM Proteins in Restriction of Mycobacterium tuberculosis Infection

Ranjbar, Shahin; Haridas, Viraga; Jasenosky, Luke D.; Falvo, James V.; Goldfeld, Anne E.

IFITM3's antiviral activity has been associated with its distribution to late endosomal/ lysosomal membranes and its ability to promote increases in the number and size of acidic intracellular compartments (Feeley et al., 2011; Mudhasani et al., 2013; Wee et al., 2012) . To determine if a similar mechanism was involved in IFITM3's modulation of MTb infection, we investigated the association of IFITM3 and MTb with endosomal compartments in A549 human lung alveolar carcinoma cells. A549 cells transcribe IFITM1-3 in response to IFN-b stimulation ( Figure S5 ) and are a long-standing model for MTb infection of the airway epithelium (Bermudez and Goodman, 1996; McDonough and Kress, 1995) , and they have been used extensively to examine IFITM antiviral activity (Brass et al., 2009; Huang et al., 2011; John et al., 2013) . Furthermore, as we found in THP-1 cells, shRNA-mediated depletion of the IFITMs in A549 cells led to greater MTb growth at 24 (57%) and 48 (30%) hr post-infection ( Figure S6 ), and overexpression of IFITM1, 2, or 3 in A549 cells inhibited MTb growth, with IFITM3 exhibiting the strongest effect ( Figures S6C and S6D) , supporting the relevance of A549 cells for examination of IFITM3-MTb intracellular association by confocal microscopy.