Discovering New Regulators Of The Immune System

In an attempt to find new regulators of the immune system, a team of researchers at Rigel Pharmaceuticals, Inc. have created a successful method for discovering molecules that are involved in signalling pathways. As published this week in the Journal of Biology, the team conducted a functional genome-wide screen and discovered novel modulators of T-cell receptor signalling that could aid in the development of drugs that target the immune response.

T cells are an integral part of the immune response. Helper T cells encourage antibody-producing B cells to replicate and secrete antibodies, and play a role in the inflammatory response. Cytotoxic T cells identify and kill cells that have been infected with viruses. As all these functions are initiated by T-cell receptors, each response must be determined by the particular set of downstream signalling components that are activated. Until now, identifying novel components of these pathways has been slow. As the article notes, the researchers believe that this study demonstrates, “a successful approach for discovering and validating, in a functionally relevant context, important immune regulators on a genome-wide scale.”

The research team, led by Dr. Charlene Liao, as part of a collaboration with Novartis, used retroviruses to carry into cells lymphoid genes that regulate T-cell receptor signalling when expressed. Normally, a cell surface marker called CD69 is up regulated when T-cell receptors are activated. However, the researchers selected cells that, when given a new gene to express, failed to up regulate this protein. They then checked that this repression was caused by the introduced gene and was not a side effect of the procedure. After three rounds of selection, 33 individual genes were cloned. Some of these were already known to play a role in the immune response, some already had unrelated functions assigned to them, and others were completely novel.

The Rigel team carried out additional experiments on three of the genes that were identified in the screen to verify their functional relevance. These experiments confirmed that the genes EDG1, PAK2, and the previously unidentified TRAC-1 were normally expressed in the lymphoid system and that truncated versions of the proteins they produce could repress T-cell receptor signalling in T-cells.

The authors write: “This approach provides a tool for functional cloning of regulators in numerous signal transduction pathways. […] Importantly, the outlined strategy, which requires no prior sequence information of the players involved, does not bias the search to previously known signalling molecules, molecules flagged by DNA-array technologies or signalling molecules discovered in other contexts.”