NAIP interacts with hippocalcin and protects neurons against calcium-induced cell death through caspase-3-dependent and -independent pathways

The neuronal calcium sensor family of Ca2+-binding proteins

Ca(2+) plays a central role in the function of neurons as the trigger for neurotransmitter release, and many aspects of neuronal activity, from rapid modulation to changes in gene expression, are controlled by Ca(2+). These actions of Ca(2+) must be mediated by Ca(2+)-binding proteins, including calmodulin, which is involved in Ca(2+) regulation, not only in neurons, but in most other cell types. A large number of other EF-hand-containing Ca(2+)-binding proteins are known. One family of these, the neuronal calcium sensor (NCS) proteins, has a restricted expression in retinal photoreceptors or neurons and neuroendocrine cells, suggesting that they have specialized roles in these cell types. Two members of the family (recoverin and guanylate cyclase-activating protein) have established roles in the regulation of phototransduction. Despite close sequence similarities, the NCS proteins have distinct neuronal distributions, suggesting that they have different functions. Recent work has begun to demonstrate the physiological roles of members of this protein family. These include roles in the modulation of neurotransmitter release, control of cyclic nucleotide metabolism, biosynthesis of polyphosphoinositides, regulation of gene expression and in the direct regulation of ion channels. In the present review we describe the known sequences and structures of the NCS proteins, information on their interactions with target proteins and current knowledge about their cellular and physiological functions.

Understanding IAP function and regulation: a view from Drosophila

Apoptosis is an active form of cell suicide that results in the orderly death and phagocytosis of cells during normal development and in the adult. Many death signals lead to the activation of members of a family of cysteine proteases known as caspases. These proteins act to transduce death signals from different cellular compartments and they cleave a number of cellular proteins, leading ultimately to many of the biochemical and morphological events associated with death. Many mechanisms act to inhibit cell death upstream of caspase activation. However, only one family of cellular proteins, the inhibitors of apoptosis (IAPs), has been identified that inhibit caspase activation and/or activity. The observations that IAP function is essential for cell survival in Drosophila, and that IAP expression is deregulated in many forms of cancer in humans, argue that IAPs are important cell death inhibitors and that deregulation of their function is likely to be important in human disease. Here we review IAP function, with particular reference to insights that study of the Drosophila IAPs has provided. We also discuss some directions for future study.