Autophagy and toll-like receptors: a new link in cancer cells.

In addition to its clean-up function, autophagy is considered as an innate immunity mechanism due to its role in the removal of intracellular pathogens. Toll-like receptors (TLRs) are crucial components of innate immunity involved in the recognition of a diverse array of microbial products. Recent works demonstrated that different pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS) and single-strand RNA are able to induce autophagy via different TLRs in immune cells. In a recent report, we showed that bacterial CpG motifs, another PAMP, can induce autophagy in rodent and human tumor cell lines and that this process is TLR9-dependent. In addition, an increase in the number of autophagosomes can also be observed in vivo after the intratumoral injection of CpG motifs. These results extend the link between TLRs and autophagy to non-immune tumor cells and may be relevant for cancer treatment and more generally for gene therapy approaches in TLR9-positive tissues. In this addendum, we discuss the potential mechanisms and the consequences of the CpG-induced autophagy in tumor cells.