Basal Autophagy Induction Without AMP-Activated Protein Kinase Under Low Glucose Conditions

When ATP levels in a cell decrease, various homeostatic intracellular mechanisms initiate attempts to restore ATP levels. As a prominent energy sensor, AMP-activated protein kinase (AMPK) represents one molecular gauge that links energy levels to regulation of anabolic and catabolic processes to restore energy balance. Although pharmacological studies have suggested that an AMPK activator, AIC AR (5-aminoimidazole-4-carboxamide ribonucleoside) may link AMPK activation to autophagy, a process that can provide short-term energy within the cell, AICAR can have AMPK-independent effects. Therefore, using a genetic-based approach we investigated the role of AMPK in cellular energy balance. We demonstrate that genetically altered cells, mouse embryonic fibroblasts (MEFs), lacking functional AMPK, display altered energy balance under basal conditions and die prematurely under low glucose-serum starvation challenge. These AMPK mutant cells appear to be abnormally reliant on autophagy under low glucose basal conditions, and therefore cannot rely further on autophagy like wild-type cells during further energetic stress and instead undergo apoptosis. This data suggests that AMPK helps regulate basal energy levels under low glucose. Further, AMPK mutant cells show increased basal phosphorylation of p53 at serine 15, a residue phosphorylated under glucose deprivation. We propose that cells lacking AMPK function have altered p53 activity that may help sensitize these cells to apoptosis under energetic stress

AMPK Directly Inhibits NDPK Through a Phosphoserine Switch to Maintain Cellular Homeostasis

AMP-activated protein kinase (AMPK) is a key energy sensor that regulates metabolism to maintain cellular energy balance. AMPK activation has also been proposed to mimic benefits of caloric restriction and exercise. Therefore, identifying downstream AMPK targets could elucidate new mechanisms for maintaining cellular energy homeostasis. We identified the phosphotransferase nucleoside diphosphate kinase (NDPK), which maintains pools of nucleotides, as a direct AMPK target through the use of two-dimensional differential in-gel electrophoresis. Furthermore, we mapped the AMPK/NDPK phosphorylation site (serine 120) as a functionally potent enzymatic “off switch” both in vivo and in vitro. Because ATP is usually the most abundant cellular nucleotide, NDPK would normally consume ATP, whereas AMPK would inhibit NDPK to conserve energy. It is intriguing that serine 120 is mutated in advanced neuroblastoma, which suggests a mechanism by which NDPK in neuroblastoma can no longer be inhibited by AMPK-mediated phosphorylation. This novel placement of AMPK upstream and directly regulating NDPK activity has widespread implications for cellular energy/nucleotide balance, and we demonstrate in vivo that increased NDPK activity leads to susceptibility to energy deprivation–induced death

Basal autophagy induction without AMP-activated protein kinase under low glucose conditions

When ATP levels in a cell decrease, various homeostatic intracellular mechanisms initiate attempts to restore ATP levels. As a prominent energy sensor, AMP-activated protein kinase (AMPK) represents one molecular gauge that links energy levels to regulation of anabolic and catabolic processes to restore energy balance. Although pharmacological studies have suggested that an AMPK activator, AICAR (5-aminoimidazole-4-carboxamide ribonucleoside) may link AMPK activation to autophagy, a process that can provide short-term energy within the cell, AICAR can have AMPK-independent effects. Therefore, using a genetic-based approach we investigated the role of AMPK in cellular energy balance. We demonstrate that genetically altered cells, mouse embryonic fibroblasts (MEFs), lacking functional AMPK, display altered energy balance under basal conditions and die prematurely under low glucose-serum starvation challenge. These AMPK mutant cells appear to be abnormally reliant on autophagy under low glucose basal conditions, and therefore cannot rely further on autophagy like wild-type cells during further energetic stress and instead undergo apoptosis. This data suggests that AMPK helps regulate basal energy levels under low glucose. Further, AMPK mutant cells show increased basal phosphorylation of p53 at serine 15, a residue phosphorylated under glucose deprivation. We propose that cells lacking AMPK function have altered p53 activity that may help sensitize these cells to apoptosis under energetic stress

Parity-related molecular signatures and breast cancer subtypes by estrogen receptor status

Abstract Introduction Relationships of parity with breast cancer risk are complex. Parity is associated with decreased risk of postmenopausal hormone receptor–positive breast tumors, but may increase risk for basal-like breast cancers and early-onset tumors. Characterizing parity-related gene expression patterns in normal breast and breast tumor tissues may improve understanding of the biological mechanisms underlying this complex pattern of risk. Methods We developed a parity signature by analyzing microRNA microarray data from 130 reduction mammoplasty (RM) patients (54 nulliparous and 76 parous). This parity signature, together with published parity signatures, was evaluated in gene expression data from 150 paired tumors and adjacent benign breast tissues from the Polish Breast Cancer Study, both overall and by tumor estrogen receptor (ER) status. Results We identified 251 genes significantly upregulated by parity status in RM patients (parous versus nulliparous; false discovery rate = 0.008), including genes in immune, inflammation and wound response pathways. This parity signature was significantly enriched in normal and tumor tissues of parous breast cancer patients, specifically in ER-positive tumors. Conclusions Our data corroborate epidemiologic data, suggesting that the etiology and pathogenesis of breast cancers vary by ER status, which may have implications for developing prevention strategies for these tumors

Relationship of Mammographic Density and Gene Expression: Analysis of Normal Breast Tissue Surrounding Breast Cancer

Previous studies of breast tissue gene expression have demonstrated that the extratumoral microenvironment has substantial variability across individuals, some of which can be attributed to epidemiologic factors. To evaluate how mammographic density (MD) and breast tissue composition relate to extratumoral microenvironment gene expression, we used data on 121 breast cancer patients from the population-based Polish Women's Breast Cancer Study

Parity-related molecular signatures and breast cancer subtypes by estrogen receptor status

INTRODUCTION: Relationships of parity with breast cancer risk are complex. Parity is associated with decreased risk of postmenopausal hormone receptor–positive breast tumors, but may increase risk for basal-like breast cancers and early-onset tumors. Characterizing parity-related gene expression patterns in normal breast and breast tumor tissues may improve understanding of the biological mechanisms underlying this complex pattern of risk. METHODS: We developed a parity signature by analyzing microRNA microarray data from 130 reduction mammoplasty (RM) patients (54 nulliparous and 76 parous). This parity signature, together with published parity signatures, was evaluated in gene expression data from 150 paired tumors and adjacent benign breast tissues from the Polish Breast Cancer Study, both overall and by tumor estrogen receptor (ER) status. RESULTS: We identified 251 genes significantly upregulated by parity status in RM patients (parous versus nulliparous; false discovery rate = 0.008), including genes in immune, inflammation and wound response pathways. This parity signature was significantly enriched in normal and tumor tissues of parous breast cancer patients, specifically in ER-positive tumors. CONCLUSIONS: Our data corroborate epidemiologic data, suggesting that the etiology and pathogenesis of breast cancers vary by ER status, which may have implications for developing prevention strategies for these tumors

Boletín diario del Instituto Central Meteorológico: Año XIII Número 162 - 1905 Junio 11

The metabolic regulator AMP-activated protein kinase (AMPK) maintains cellular homeostasis through regulation of proteins involved in energy-producing and-consuming pathways. Although AMPK phosphorylation targets include cytoplasmic and nuclear proteins, the precise mechanisms that regulate AMPK localization, and thus its access to these substrates, are unclear. We identify highly conserved carboxy-terminal hydrophobic amino acids that function as a leptomycin B–sensitive, CRM1-dependent nuclear export sequence (NES) in the AMPK catalytic subunit (AMPK). When this sequence is modified AMPK shows increased nuclear localization via a Ran-dependent import pathway. Cytoplas-mic localization can be restored by substituting well-defined snurportin-1 or protein kinase A inhibitor (PKIA) CRM1-binding NESs into AMPK. We demonstrate a functional requirement in vivo for the AMPK carboxy-terminal NES, as transgenic Drosophila expressing AMPK lacking this NES fail to rescue lethality of AMPK null mutant flies and show decreased activation loop phosphorylation under heat-shock stress. Sequestered to the nucleus, this truncated protein shows highly reduced phosphorylation at the key Thr172 activation residue, suggesting that AMPK activation predom-inantly occurs in the cytoplasm under unstressed conditions. Thus, modulation of CRM1-mediated export of AMPK via its C-terminal NES provides an additional mechanism for cells to use in the regulation of AMPK activity and localization

Relationship of Mammographic Density and Gene Expression: Analysis of Normal Breast Tissue Surrounding Breast Cancer

PURPOSE: Previous studies of breast tissue gene expression have demonstrated that the extratumoral microenvironment has substantial variability across individuals, some of which can be attributed to epidemiologic factors. To evaluate how mammographic density (MD) and breast tissue composition relate to extratumoral microenvironment gene expression, we used data on 121 breast cancer patients from the population-based Polish Women's Breast Cancer Study. DESIGN: Breast cancer cases were classified based on a previously reported, biologically-defined extratumoral gene expression signature with two subtypes: an Active subtype, which is associated with high expression of genes related to fibrosis and wound response, and an Inactive subtype, which has high expression of cellular adhesion genes. MD of the contralateral breast was assessed using pre-treatment mammograms and a quantitative, reliable computer-assisted thresholding method. Breast tissue composition was evaluated based on digital image analysis of tissue sections. RESULTS: The Inactive extratumoral subtype was associated with significantly higher percentage mammographic density (PD) and dense area (DA) in univariate analysis (PD: p=0.001; DA: p=0.049) and in multivariable analyses adjusted for age and body mass index (PD: p=0.004; DA: p=0.049). Inactive/higher MD tissue was characterized by a significantly higher percentage of stroma and a significantly lower percentage of adipose tissue, with no significant change in epithelial content. Analysis of published gene expression signatures suggested that Inactive/higher MD tissue expressed increased estrogen response and decreased TGF-β signaling. CONCLUSIONS: By linking novel molecular phenotypes with MD, our results indicate that MD reflects broad transcriptional changes, including changes in both epithelia- and stroma-derived signaling