The atfl ÷ gene of Schizosaccharomyces pombe encodes a bZIP transcription factor with strong homology to the mammalian factor ATF-2. ATF-2 is regulated through phosphorylation in mammalian cells by the stress-activated mitogen-activated protein (MAP) kinases SAPK/JNK and p38. We show here that the fission yeast Atfl factor is also regulated by a stress-activated kinase, Styl. The Styl kinase is stimulated by a variety of different stress conditions including osmotic and oxidative stress and heat shock. Deletion of the atfl + gene results in many, but not all, of the phenotypes associated with loss of Styl, including sensitivity to environmental stress and inability to undergo sexual conjugation. Furthermore, we identify a number of target genes that are induced rapidly in a manner dependent upon both the Styl kinase and the Atfl transcription factor. These genes include gpdl +, which is important for the response of cells to osmotic stress, the catalase gene ~ important for cells to combat oxidative stress, and pyp2 +, which encodes a tyrosine-specific MAP kinase phosphatase. Induction of Pyp2 by Atfl is direct in that it does not require de novo protein synthesis and results in a negative feedback loop that serves to control signaling through the Styl/Wisl pathway. We show that Atfl associates stably and is phosphorylated by the Styl kinase in vitro. Taken together, these results indicate that the interaction between Atfl and Styl is direct. These findings highlight a remarkable level of conservation in transcriptional control by stress-activated MAP kinase pathways between fission yeast and mammalian cells.

The fission yeast Styl MAP kinase is required for cell cycle control, initiation of sexual differentiation, and protection against cellular stress. Like the mammalian JNK/SAPK and p38/CSBP1 MAP kinases, Styl is activated by a range of environmental insults including osmotic stress, hydrogen peroxide, menadione, heat shock, and the protein synthesis inhibitor anisomycin. We have identified an upstream regulator that mediates activation of the Styl MAP kinase by multiple environmental stresses as the product of the mitotic catastrophe suppressor, mcs4. Mcs4 is structurally and functionally homologous to the budding yeast SSK1 response regulator, suggesting that the eukaryotic stress-activated MAP kinase pathway is controlled by a conserved two-component system. Mcs4 acts upstream of Wakl, a homolog of the SSK2 and SSK22 MEK kinases, which transmits the stress signal to the Wisl MEK. We show that the Wisl MEK is controlled by an additional pathway that is independent of both Mcs4 and the Wakl MEK kinase. Furthermore, we demonstrate that Mcs4 is required for the correct timing of mitotic initiation by mechanisms both dependent and independent on Styl, indicating that Mcs4 coordinately controls cell cycle progression with the cellular response to environmental stress.

Resveratrol functions as an agonist for estrogen receptor (ER)-mediated transcription. However, other researchers have reported that resveratrol decreases proliferation of breast cancer cells that are either ER-positive or ER-negative, which suggests that the interaction of resveratrol with the ER may not fully explain its inhibitory effect on proliferation. Similar to those effects associated with caloric restriction (CR), resveratrol has multiple beneficial activities, such as increased life span and delay in the onset of diseases associated with aging. One key enzyme thought to be activated during CR is the AMP-activated kinase (AMPK), a sensor of cellular energy levels. The suppression of nonessential energy expenditure by activated AMPK along with the CR mimetic and antiproliferative properties of resveratrol has led us to hypothesize that resveratrol activity might have an important role in the activation of AMPK. Here, we show that resveratrol activated AMPK in both ER-positive and ER-negative breast cancer cells. Once activated, AMPK inhibited 4E-BP1 signaling and mRNA translation via mammalian target of rapamycin (mTOR). Moreover, we also found that AMPK activity mediated by resveratrol in cancer cells was due to inducing the expression of Sirtuin type 1 (SIRT1) via elevation in the cellular NAD(+)/NADH in ER-positive cells. To our knowledge, we demonstrate here for the first time that resveratrol induces the expression of SIRT1 protein in human cancer cells. These observations raise the possibility that SIRT1 functions as a novel upstream regulator for AMPK signaling and may additionally modulate tumor cell proliferation. Targeting SIRT1/AMPK signaling by resveratrol may have potential therapeutic implications for cancer and age-related diseases.

The fission yeast Sty1 mitogen-activated protein (MAP) kinase (MAPK) and its activator the Wis1 MAP kinase kinase (MAPKK) are required for cell cycle control, initiation of sexual differentiation, and protection against cellular stress. Like the mammalian JNK/ SAPK and p38/CSBP1 MAPKs, Sty1 is activated by a range of environmental insults including osmotic stress, hydrogen peroxide, UV light, menadione, heat shock, and the protein synthesis inhibitor anisomycin. We have recently identified two upstream regulators of the Wis1 MAPKK, namely the Wak1 MAPKKK and the Mcs4 response regulator. Cells lacking Mcs4 or Wak1, however, are able to proliferate under stressful conditions and undergo sexual differentiation, suggesting that additional pathway(s) control the Wis1 MAPKK. We now show that this additional signal information is provided, at least in part, by the Win1 mitotic regulator. We show that Wak1 and Win1 coordinately control activation of Sty1 in response to multiple environmental stresses, but that Wak1 and Win1 perform distinct roles in the control of Sty1 under poor nutritional conditions. Our results suggest that the stress-activated Sty1 MAPK integrates information from multiple signaling pathways.

In the present study, we successively extracted the pu-erh raw tea with methanol (PR-1), chloroform (PR-2), ethyl acetate (PR-3), n-butanol (PR-4), and water (PR-5). Among these extracts, PR-3 extract contained ingredients with the most effective hypolipidemic potential and was further purified by column chromatography. Moreover, chronic administration of PR-3 provoked a significant reduction in levels of serum triglyceride and low-density lipoprotein (LDL) in rats. Our study demonstrated that fraction 5 from the PR-3 extract (PR-3-5s) showed a hypolipidemic effect in human hepatoma HepG2 cells. PR-3-5s decreased the expression of fatty acid synthase (FASN) and inhibited the activity of acetyl-coenzyme A carboxylase (ACC) by stimulating AMP-activated protein kinase (AMPK) through the LKB1 pathway. Moreover, PR-3-5s blocked the progression of the cell cycle at the G1 phase by inducing p53 expression and in turn upregulating p21 expression.