PHOSPHORYLATION OF CALPAINS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The long-term goal of this research is to learn how activity of the ubiquitous calpains, ¿- and m-calpain, is regulated in living cells. The calpains are Ca2+-dependent proteases found in every vertebrate cell. Disruption of the gene encoding the 28-kDa subunit common to ¿- and m-calpain is embryonically lethal. Inappropriate calpain degradation is implicated in many tissue pathologies ranging from loss of muscle mass in the muscular dystrophies, to crystallin degradation and cataract formation, to Alzheimer?s disease, to tissue damage in ischemic areas near a blocked blood vessel (stroke or myocardial infarction), to traumatic spinal cord injury, etc. Calpain activity in these pathologies is triggered by elevated, intracellular [Ca2+]; however, Ca2+ requirement of the calpains in in vitro assays is 3-50 ¿M (¿-calpain) or 300-500 ¿M (m-calpain), much higher than intracellular free [Ca2+] is, even near ischemic areas. Cells, therefore, have a mechanism to reduce the [Ca2+] required for calpain activity. This mechanism evidently is altered in a way that activates the calpains during ischemic events. The same mechanism must regulate calpain activity during normal cell function. We have found that both ¿- and m-calpain are phosphorylated at multiple sites. The objective of our current research project is to identify the phosphorylated sites on both ¿- and m-calpain and determine their effect on regulation of calpain activity.