The goals of this research are, first to develop a widely applicable assay for measuring the activation of calcium- dependent proteases ("calpains", EC 3.4.22.17), and second, to determine whether alterations in calcium homeostasis, either influx through the plasma membrane or release of intracellular calcium stores regulate autoproteolytic activation of these proteases. The results of these studies will provide the basis for subsequent investigations to identify physiological substrates, which may include talin, filamin, fodrin and protein kinase C, and the consequences of proteolytic modification on the functions of these proteins. An increase in intracellular calcium is one important type of cellular response to certain external signals. Mechanisms by which a generalized increase in intracellular calcium is translated into specific, local effects on different cellular functions are currently being sought and studied by many laboratories. One such mechanism which has only begun to be appreciated is the activation by calcium of specific protease enzymes. This mechanism is potentially of great importance, but the absence of an assay for calcium-dependent proteases in cells has prevented elucidation of the details of their regulation and identification of their physiological substrates. Thus, the contributions of these enzymes to localized, calcium-dependent processes such as secretion, membrane fusion, and other cellular functions have remained obscure. The results of this research promise to provide a new dimension of insight into the mechanisms of cellular signalling involving calcium.
