Protein kinase A-mediated CREB phosphorylation is an oxidant-induced survival pathway in alveolar type II cells.

Oxidant stress plays a role in the pathogenesis of pulmonary diseases, including fibrotic lung disease and cancer. We previously found that hydrogen peroxide (H2O2) initiates an increase in Ca2+/cAMP-response element binding protein (CREB) phosphorylation in C10 alveolar type II cells that requires activation of extracellular regulated kinases 1/2 (ERK1/2). Here, we investigated the role of crosstalk between protein kinase A (PKA) and epidermal growth factor receptor (EGFR) in oxidant-induced signaling to ERK1/2 and CREB in C10 cells. Application of H2O2 increased nuclear accumulation of PKA, and inhibition of PKA with H89 reduced oxidant-mediated phosphorylation of both CREB and ERK1/2. Single cell measurements of cAMP and redox status, using a FRET-based biosensor and a redox-sensitive GFP, respectively, indicated that H2O2 increases production of cAMP that correlates with redox state. Inhibition of EGFR activity decreased both H2O2-induced CREB phosphorylation and translocation of PKA to the nucleus, suggesting that crosstalk between PKA and EGFR underlies the oxidant-induced CREB response. Furthermore, knockdown of CREB expression using siRNA led to a decrease in bcl-2 and an increase in oxidant-induced apoptosis. Together these data reveal a novel role for crosstalk between PKA, ERK1/2 and CREB that mediates cell survival during oxidant stress.

A hot spot for RAD51C interactions revealed by a peptide that sensitizes cells to cisplatin.

DNA repair via the homologous recombination pathway requires the recombinase RAD51 and, in vertabrates, five RAD51 paralogs. The paralogs form two complexes in solution, a XRCC3/RAD51C heterodimer and a RAD51B/RAD51C/RAD51D/XRCC2 heterotetramer. Mutation of any one of the five paralog genes prevents subnuclear assembly of recombinase at damaged sites and renders cells 30-100 fold sensitive to DNA cross-linking drugs. Phage display was used to isolate peptides that bind the paralog XRCC3. Sequences of binding peptides showed similarity to residues 14-25 of RAD51C protein. Point mutations in this region of RAD51C altered its interaction with both XRCC3 and RAD51B in a two-hybrid system. A synthetic peptide composed of residues 14-25 of RAD51C fused to a membrane transduction sequence [protein transduction domain 4 (PTD4)], inhibited subnuclear assembly of RAD51 recombinase, and sensitized Chinese hamster ovary cells to cisplatin when added to growth medium. These results suggest that residues 14-25 of RAD51C contribute to a "hot spot" used in both XRCC3-RAD51C and RAD51B-RAD51C interactions. Peptide-based inhibition of homologous recombination may prove useful for improving the efficacy of existing cancer therapies.