Vol. 13, Issue 9, 3344-3354, September 2002

Purification and Identification of Secernin, a Novel Cytosolic Protein that Regulates Exocytosis in Mast Cells

Gemma Way,^* Nicholas Morrice, Carl Smythe, and Antony J. O'Sullivan^*

 ^*Department of Biological and Biomedical Sciences, University of Durham, Durham, DH1 3LE, United Kingdom; and  Division of Cell Signalling, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland

After permeabilization with the pore-forming toxin streptolysin-O mast cells can be triggered to secrete by addition of both calcium and a GTP analogue. If stimulation is delayed after permeabilization, there is a progressive decrease in the extent of secretion upon stimulation, eventually leading to a complete loss of the secretory response. This loss of secretory response can be retarded by the addition of cytosol from other secretory tissues, demonstrating that the response is dependent on a number of cytosolic proteins. We have used this as the basis of a bioassay to purify Secernin 1, a novel 50-kDa cytosolic protein that appears to be involved in the regulation of exocytosis from peritoneal mast cells. Secernin 1 increases both the extent of secretion and increases the sensitivity of mast cells to stimulation with calcium.