Dear Editor,

IRAS was discovered only recently1 and is a highly unique protein with little structural similarity to known proteins listed in sequence databases. Nischarin was cloned as the mouse homologue of IRAS.2 The amino-acid sequence of Nischarin is about 80% homologous with IRAS, with a main difference being that Nischarin lacks the N-terminal 244 amino acids of IRAS. 1,2 Nischarin was reported2 to interact with the cytoplasmic tail of the integrin α5subunit of the fibronectin receptor, and to inhibit cell migration and lamellipodia formation in transfected 3T3 cells. The human protein IRAS (hIRAS) was also found to interact with insulin receptor substrates (IRS) in HEK 293 cells and to enhance IRS4-dependent insulin activation of extracellularly regulated kinase, ERK1/2.3 Herein, we report a new cellular role for IRAS, which is to allow PC12 cells to experience markedly less caspase-3 enzyme activity induced by apoptotic stimuli such as serum deprivation, thapsigargin, or staurosporine treatment. This decrease in apoptotic effector enzyme activity was accompanied by a decrease in the proportion of apoptotic cells presumably due to an increase in the delay to initiate apoptosis.

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