Cells may combat invading microbes by dumping their trash on them, according to Yale's Norma Andrews and colleagues, who explain how cells maintain their membranes under stress in today's issue of Cell.In muscles during exercise, or in skin as wounds are repaired, cells' membranes are placed under immense stress. Any tears in the cell membranes are repaired within ten to thirty seconds, before vital components of the cell can leak out and the cell disintegrates.
Although researchers knew that if there's no calcium outside cells they can't repair themselves, they didn't know how the calcium triggered membrane repair.
Now Andrews and her colleagues at Yale University's School of Medicine found proteins peculiar to lysosomes at the site of membrane repair. Lysosomes are the trash cans of cells, where damaging products of metabolism are stored before they can be broken down.
The Yale scientists also discovered that calcium ions from outside the cell trigger the fusion of lysosomes' membrane with the broken part of the cell membrane. The ions bind to a protein that spans the membrane of the lysosomes called Syt VII (synaptotagmin 7).
But why should the lysosomes be involved in repairing breaks?
One possibility is as a defense mechanism for the cell. Some incursions are caused by microbes that are trying to enter or destroy the cell. Dumping a load of noxious proteins on the invader could be a cell's equivalent of the medieval castle defense technique of pouring hot tar onto the enemy's heads.
[Contact: Norma Andrews]
27-Jul-2001
