Autophagy contributes to the pathogenesis of
cancer, whereas
toll-like receptors (TLRs) also play an important role in
cancer development and immune escape. However, little is known about the potential interaction between TLR signaling and autophagy in
cancer cells. Here we show that autophagy induced by TLR4 or TLR3 activation enhances various
cytokine productions through promoting
TRAF6 (
TNF receptor-associated factor 6, E3
ubiquitin protein ligase) ubiquitination and thus facilitates migration and invasion of
lung cancer cells. Stimulation of TLR4 and TLR3 with
lipopolysaccharide (LPS) and
polyinosinic-polycytidylic acid [
poly(I:C)] respectively triggered autophagy in
lung cancer cells. This was mediated by the adaptor
protein,
toll-like receptor adaptor molecule 1 (TICAM1/TRIF), and was required for TLR4- and TLR3-induced increases in the production of
IL6, CCL2/MCP-1 [
chemokine (C-C motif) ligand 2], CCL20/MIP-3α [
chemokine (C-C motif)
ligand 20], VEGFA (
vascular endothelial growth factor A), and MMP2 [matrix
metallopeptidase 2 (
gelatinase A,
72 kDa gelatinase,
72 kDa type IV collagenase)]. These
cytokines appeared to be necessary for enhanced migration and invasion of
lung cancer cells upon TLR activation. Remarkably, inhibition of autophagy by chemical or genetic approaches blocked TLR4- or TLR3-induced Lys63 (K63)-linked ubiquitination of
TRAF6 that was essential for activation of MAPK and NFKB (nuclear factor of kappa light
polypeptide gene enhancer in B-cells) pathways, both of which were involved in the increased production of the
cytokines. Collectively, these results identify induction of autophagy by TLR4 and TLR3 as an important mechanism that drives
lung cancer progression, and indicate that inhibition of autophagy may be a useful strategy in the treatment of
lung cancer.