-20pt?>Mycobacterium tuberculosis (Mtb) is a pathogenic bacterium that causes 
contagious tuberculosis (TB). Recently, Mtb-secreted proteins have been 
considered virulence factors and candidates for drugs and vaccines. Among these 
proteins, 6-kDa early secreted antigenic target (ESAT-6) is known to be able to 
induce component of matrix metalloproteinase-9 (MMP-9) in epithelial cells, 
leading to recruitment of macrophages. However, detailed function of ESAT-6 
during macrophage recruitment to inflammatory sites remains unknown. Thus, the 
objective of the present study was to elucidate such function of EAST-6 and 
mechanism(s) involved. In the present study, we have found that recombinant 
ESAT-6 purified in the form of ESAT-6 double-connected structure (2E6D) could 
inhibit lipopolysaccharide (LPS)-induced potential of cell migration and 
inflammation in murine macrophage cells. Interestingly, 2E6D suppressed 
LPS-induced MMP-9 expression at both protein and mRNA levels as well as its 
enzyme activity. Levels of cyclooxygenase-2 (COX-2) and inducible nitric oxide 
synthase (iNOS) enzymes as known upregulators of MMP-9 were significantly 
decreased when 2E6D has been treated. In addition, nitric oxide (NO) as a second 
messenger was also significantly decreased by treatment with the purified 2E6D. 
Furthermore, 2E6D inhibited LPS-induced phosphorylation of IκB and translocation 
of NF-κB. Moreover, 2E6D suppressed phosphorylation of MAPK signaling proteins. 
Taken together, these results suggest that ESAT-6 can suppress LPS-induced MMP-9 
and inflammation by downregulating COX-2, iNOS, and NO through NF-κB and MAPK 
signaling.