Free calcium ions (Ca²⁺) play an essential signaling role in biological systems, where they regulate cellular processes ranging from fertilization to programmed cell death. Ca²⁺ signaling involves a specific ?toolkit? of proteins that act as transporters, buffers and sensors of Ca²⁺ and work in concert to generate, integrate and process the Ca²⁺ signal. Inappropriate Ca²⁺ signaling and Ca²⁺ dyshomeostasis are involved in a multitude of clinical disorders including heart disease, Alzheimer's disease and stroke. Ca²⁺ also plays a major role in cell growth, differentiation and motility; disturbances in these processes underlie cell transformation and the progression of cancer.

Ca²⁺ signaling is tightly controlled in a spatially and temporally defined manner that involves specific "Ca²⁺ microdomains." We are interested in the biochemical, molecular, and cellular basis for localized Ca²⁺ signaling, the mechanism of Ca²⁺ transport across the membrane, and the role that these processes play in normal and pathological cell function.

One of our long-term goals is to better understand the structure, regulation, and physiological role of the plasma membrane Ca²⁺ pumps (PMCAs). These transporters represent a primary high-affinity Ca²⁺ efflux system in eukaryotes. We hypothesize that different PMCA isoforms are targeted to specific membrane domains where they participate in local Ca²⁺ signaling. We are using recombinant protein expression, site-directed mutagenesis, functional assays, and confocal fluorescence microscopy to study the specific properties and targeting of different PMCAs. Biochemical and genetic methods are being used to icharacterize novel protein-protein interactions of the pumps. Such interactions may be important for "cross-talk" between the pumps and other membrane transporters and signaling molecules.

Much excitement in the field stems from recent findings showing that mutations in a specific PMCA isoform (PMCA2) lead to deafness and imbalance in mice. It now appears likely that some forms of congenital hearing impairment and age-related hearing loss in humans may also involve this PMCA. Accordingly, we are studying the functional properties, mechanism of membrane localization and protein interactions of the PMCA2 in the sensory hair cells of the inner ear.

A second major project of our laboratory is concerned with an intriguing Ca²⁺ sensor protein named calmodulin-like protein (CLP). In humans, CLP is specifically and abundantly expressed in epithelial cells of the breast, skin and prostate but is absent or downregulated in cancers derived from these tissues. Protein biochemical and cell biological studies are being performed to obtain insights into the normal function of CLP in epithelial cells, and the cellular processes affected by the loss of CLP in cancer cells. We recently demonstrated that CLP acts as a "light chain" for a novel unconventional myosin, myosin-10. This myosin appears to be involved in cellular motility and the integration of extracellular matrix-cell membrane signals. The effect of CLP on the regulation of this myosin and its impact on cell shape, cell division and differentiation are areas of current research interest.