The complex interplay between cellular signaling and metabolism in eukaryotic cells just start to emerge. Coenzyme A (CoA) and its derivatives play a key role in cell metabolism and also participate in regulatory processes. CoA Synthase (CoASy) is a mitochondria-associated enzyme which mediates two final stages of de novo CoA biosynthesis. Here, we report that CoASy is involved in signaling events in the cell and forms a functional complex with p85 alpha PI3K in vivo. Importantly, observed interaction of endogenous CoASy and p85 alpha PI3K is regulated in a growth factor dependent manner. Surprisingly, both catalytic p110 alpha and regulatory p85 alpha subunits of PI3K were detected in mitochondrial fraction where mitochondria-localized p85aPI3K was found in complex with CoASy. Unexpectedly, significant changes of PI3K signaling pathway activity were observed in experiments with siRNA-mediated CoASy knockdown pointing on the role of CoA biosynthetic pathway in signal transduction. (c) 2009 Elsevier Inc. All rights reserved.