The cell wall sensors Mtl1, Wsc1, and Mid2 are required for stress-induced nuclear to cytoplasmic translocation of cyclin C and programmed cell death in yeast.

Mtl1 is a member of a cell wall sensor family that monitors cell wall integrity in budding yeast. In response to cell wall stress, Mtl1 activates the cell wall integrity (CWI) MAP kinase pathway which transmits this signal to the nucleus to effect changes in gene expression. One target of the CWI MAP kinase is cyclin C, a negative regulator of stress response genes. CWI activation results in cyclin C relocalization from the nucleus to the cytoplasm where it stimulates programmed cell death (PCD) before it is destroyed. This report demonstrates that under low oxidative stress conditions, a combination of membrane sensors, Mtl1 and either Wsc1 or Mid2, are required jointly to transmit the oxidative stress signal to initiate cyclin C destruction. However, when exposed to elevated oxidative stress, additional pathways independent of these three sensor proteins are activated to destroy cyclin C. In addition, N-glycosylation is important for Mtl1 function as mutating the receptor residue (Asn42) or an enzyme required for synthesis of N-acetylglucosamine (Gfa1) reduces sensor activity. Finally, combining gfa1-1 with the cyclin C null allele induces a severe synthetic growth defect. This surprising result reveals a previously unknown genetic interaction between cyclin C and plasma membrane integrity.

Identification of a family of cAMP response element-binding protein coactivators by genome-scale functional analysis in mammalian cells.

This report describes an unbiased method for systematically determining gene function in mammalian cells. A total of 20,704 predicted human full-length cDNAs were tested for induction of the IL-8 promoter. A number of genes, including those for cytokines, receptors, adapters, kinases, and transcription factors, were identified that induced the IL-8 promoter through known regulatory sites. Proteins that acted through a cooperative interaction between an AP-1 and an unrecognized cAMP response element (CRE)-like site were also identified. A protein, termed transducer of regulated cAMP response element-binding protein (CREB) (TORC1), was identified that activated expression through the variant CRE and consensus CRE sites. TORC1 potently induced known CREB1 target genes, bound CREB1, and activated expression through a potent transcription activation domain. A functional Drosophila TORC gene was also identified. Thus, TORCs represent a family of highly conserved CREB coactivators that may control the potency and specificity of CRE-mediated responses.