Glucose sensing via the protein kinase A pathway in Schizosaccharomyces pombe

Abstract

The fission yeast Schizosaccharomyces pombe primarily detects glucose via a cAMP-signalling pathway. Components of this pathway include the Git3 G-protein-coupled receptor and a heterotrimeric G-protein, from which the Gpa2 Galpha subunit activates adenylate cyclase (Git2/Cyr1). Three additional proteins, Git1, Git7 and Git10 are required to generate a cAMP response even in a strain expressing an activated form of Gpa2, which is capable of bypassing the loss of the GPCR and Gbetagamma dimer. Therefore, Git1, Git7 and Git10 either act in a G-protein-independent manner or are required to stabilize or assemble a functional signalling complex. Although prior data suggested that the Cgs2 cAMP phosphodiesterase (PDE) does not regulate the cAMP response, we now have evidence that along with adenylate cyclase regulation, PDE activation is important for limiting the response to glucose. Finally, regulation of protein kinase A activation appears to involve both traditional post-translational regulation of the function of the components of the cAMP pathway and glucose-dependent transcriptional regulation of some of these cAMP pathway genes.