Dr. Hogan says the discovery took the research team by surprise. "We knew septins existed in the cellular plasma (surface) membrane, but we didn't know they had anything to do with calcium signaling," he says. Septins are known to build scaffolding to provide structural support during cell division.
This finding builds on Dr. Rao and Dr. Hogan's groundbreaking discovery in 2006 showing that the protein ORAI1 forms the pore of the calcium channel. The channel's entryway had been one of the most sought after mysteries in biomedical science because it is the gateway to T cell functioning and, consequently, to better understanding how the body uses these cells to fight disease.
To the research team's surprise, the septins were forming a ring around the calcium channel. "We aren't sure why, but we theorize that the septins are rearranging the cellular membrane's structure to "corral" the key proteins STIM and ORAI1, and maybe other factors needed for the calcium channel to operate," says Dr. Hogan.
Dr. Sharma adds that, "essentially we believe the septins are choreographing the interaction of these two proteins that are important in instigating the immune response." Without the septins' involvement, T cell activation does not occur.
In the study, the researchers devised a simple visual readout of activity in a main pathway responsible for activation of T cells the same pathway that is targeted by the immunosuppressive drug cyclosporin A that is used clinically and looked for impairment of the activity when individual genes were, in effect, deleted. After sorting through the roughly 20,000 human genes, they turned up 887 gene "hits," says Dr. Hogan.
With further experiments, they should
|Contact: Bonnie Ward|
La Jolla Institute for Allergy and Immunology