The findings, published in the Proceedings of the National Academy of Sciences, describe how myeloid differentiation factor (MyD88), a protein that plays a major role in mediating host defense response against invading pathogens, is tightly regulated to prevent uncontrolled inflammation.

MyD88 interacts with receptors known as Toll-like receptors that detect invading pathogens, but until now it has remained unknown how MYD88-mediated signaling was controlled.

In this study, the researchers used nontypeable Haemophilus influenzae (NTHi), a bacterium that is the leading cause of chronic obstructive pulmonary disease (COPD) and ear infections, to induce inflammatory response in mice and human epithelial cells.

Their results demonstrate for the first time that NTHi induces lysine 63 (K63)-linked polyubiquitination, a process that is critical for MyD88 to transduce Toll-like receptor signaling, of MyD88 in human epithelial cells and the mice.

The study also found for the first time that CYLD directly interacts with and deubiquitinates or deactivates bacteria-induced K63-linked polyubiquitination of MyD88 at lysine 231 in mice and human epithelial cells.

When pathogens invade the body, this triggers the cell signaling pathway, and small proteins called ubiquitin proteins are added to MyD88 to activate it. To deactivate MyD88, ubiquitin proteins need to be removed, an inactivation process called deubiquitination.

http://www.eurekalert.org/pub_releases/2015-12/gsu-btc122815.php