Reactive oxygen species (ROS) promote tumor cell proliferation and survival by directly modulating growthregulatory molecules and key transcription factors. The signal transducer and activator of transcription 3 (STAT3) is constitutively active in a variety of tumor cell types, where the effect of ROS on the Janus kinase/ STAT pathway has been examined. We report here that STAT3 is directly sensitive to intracellular oxidants. Oxidation of conserved cysteines by peroxide decreased STAT3 binding to consensus serum-inducible elements (SIE) in vitro and in vivo and diminished interleukin (IL)-6-mediated reporter expression. Inhibitory effects produced by cysteine oxidation in STAT3 were negated in redox-insensitive STAT3 mutants. In contrast, ROS had no effect on IL-6-induced STAT3 recruitment to the c-myc P2 promoter. Expression of a redoxinsensitive STAT3 in breast carcinoma cells accelerated their proliferation while reducing resistance to oxidative stress. Our results implicate STAT3 in coupling intracellular redox homeostasis to cell proliferation and survival. Cancer Res; 70(20); 8222-32. ©2010 AACR.

Many eukaryotic genes are acutely regulated by extra-cellular signals. The c-fos serum response element (SRE) mediates transcriptional activation in response to mitogens through serum response factor (SRF)-dependent recruitment of Elk-1, a mitogen-activated protein kinase (MAPK)-responsive transcription factor. How subsequent events at SRE promoters stimulate initiation of transcription has yet to be fully resolved. Here we show that extra-cellular signal-regulated kinase (ERK) and mitogen and stress-activated kinase (MSK) are recruited to SRE promoter complexes in vitro and in vivo. Their recruitment in vitro correlates with Elk-1 binding and for ERK the D domain/KIM of Elk-1 is specifically involved. In vivo, recruitment of ERK and MSK is stimulated by mitogens, correlates with histone H3 phosphorylation and is impaired by Elk-1 knockdown. Immunocytochemistry and confocal microscopy reveal that ERK appears to associate to some extent with initiating rather than elongating RNA polymerase II. Taken together, our data add to the body of evidence implying that ERK and related MAPKs may fulfil a generic role at the promoters of acutely regulated genes.

The ETS (E26) protein Elk-1 serves as a paradigm for mitogen-responsive transcription factors. It is multiply phosphorylated by mitogen-activated protein kinases (MAPKs), which it recruits into pre-initiation complexes on target gene promoters. However, events preparatory to Elk-1 phosphorylation are less well understood. Here, we identify two novel, functional elements in Elk-1 that determine its stability and nuclear accumulation. One element corresponds to a dimerization interface in the ETS domain and the second is a cryptic degron adjacent to the serum response factor (SRF)-interaction domain that marks dimerization-defective Elk-1 for rapid degradation by the ubiquitin–proteasome system. Dimerization appears to be crucial for Elk-1 stability only in the cytoplasm, as latent Elk-1 accumulates in the nucleus and interacts dynamically with DNA as a monomer. These findings define a novel role for the ETS domain of Elk-1 and demonstrate that nuclear accumulation of Elk-1 involves conformational flexibility prior to its phosphorylation by MAPKs.

In carbonate aquifers, dissolved organic carbon from the surface drives heterotrophic metabolism, generating CO 2 in the subsurface. Although this has been a proposed mechanism for enhanced dissolution at the water table, respiration rates and their controlling factors have not been widely evaluated. This study investigates the composition and concentration of dissolved organic carbon (DOC) reaching the water table from different recharge pathways on a subtropical carbonate island using a combination of DOC concentration measurements, fluorescence and absorption characterisation. In addition, direct measurements of the microbial response to the differing water types were made. Interactions of rainfall with the vegetation, via throughfall and stemflow, increase the concentration of DOC. The highest DOC concentrations are associated with stemflow, overland recharge and dissolution hole waters which interact with bark lignin and exhibit strong terrestrial-derived characteristics. The groundwater samples exhibit the lowest concentrations of DOC and are comprised of refractory humic-like organic matter. The heterotrophic response seems to be controlled by the concentration of DOC in the sample. The terrestrially sourced humic-like matter in the stemflow and dissolution hole samples was highly labile, thus increasing the amount of biologically produced CO 2 to drive dissolution. Based on the calculated respiration rates, microbial activity could enhance carbonate dissolution, increasing porosity generation by a maximum of 1 % kyr -1 at the top of the freshwater lens.

Supplementary Methods, Figures 1-9 from Modulation of Gene Expression and Tumor Cell Growth by Redox Modification of STAT3

Supplementary Methods, Figures 1-9 from Modulation of Gene Expression and Tumor Cell Growth by Redox Modification of STAT3