Genomic analysis of stress response genes

Acute molecular response of mouse hindlimb muscles to chronic stimulation

Stimulation of the mouse hindlimb via the sciatic nerve was performed for a 4-h period to investigate acute muscle gene activation in a model of muscle phenotype conversion. Initial force production (1.6 +/- 0.1 g/g body wt) declined 45% within 10 min and was maintained for the remainder of the experiment. Force returned to initial levels upon study completion. An immediate-early growth response was present in the extensor digitorum longus (EDL) muscle (FOS, JUN, activating transcription factor 3, and musculoaponeurotic fibrosarcoma oncogene) with a similar but attenuated pattern in the soleus muscle. Transcript profiles showed decreased fast fiber-specific mRNA (myosin heavy chains 2A and 2B, fast troponins T(3) and I, alpha-tropomyosin, muscle creatine kinase, and parvalbumin) and increased slow transcripts (myosin heavy chain-1beta/slow, troponin C slow, and tropomyosin 3y) in the EDL versus soleus muscles. Histological analysis of the EDL revealed glycogen depletion without inflammatory cell infiltration in stimulated versus control muscles, whereas ultrastructural analysis showed no evidence of myofiber damage after stimulation. Multiple fiber type-specific transcription factors (tea domain family member 1, nuclear factor of activated T cells 1, peroxisome proliferator-activated receptor-gamma coactivator-1alpha and -beta, circadian locomotor output cycles kaput, and hypoxia-inducible factor-1alpha) increased in the EDL along with transcription factors characteristic of embryogenesis (Kruppel-like factor 4; SRY box containing 17; transcription factor 15; PBX/knotted 1 homeobox 1; and embryonic lethal, abnormal vision). No established in vivo satellite cell markers or genes activated in our parallel experiments of satellite cell proliferation in vitro (cyclins A(2), B(2), C, and E(1) and MyoD) were differentially increased in the stimulated muscles. These results indicated that the molecular onset of fast to slow phenotype conversion occurred in the EDL within 4 h of stimulation without injury or satellite cell recruitment. This conversion was associated with the expression of phenotype-specific transcription factors from resident fiber myonuclei, including the activation of nascent developmental transcriptional programs.

A novel WD-40 repeat protein WDR26 suppresses H2O2-induced cell death in neural cells

WD-40 repeat proteins play important roles in a variety of cellular functions, such as cell growth, proliferation, apoptosis and intracellular signal transduction. We previously identified a novel member of this family, WDR26. To examine the biological function of WDR26, we used hWDR26 plasmids and antisense phosphorothioate oligodeoxynucleotides (asODNs) against WDR26 to examine its role in response to oxidative stress in human SH-SY5Y neuroblastoma cells. Our results showed that H2O2 at 0.5mM substantially induced cell death and significantly up-regulated the WDR26 expression, and WDR26 over-expression in turn strongly suppressed H2O2-induced cell death. Moreover, asODNs markedly inhibited the de novo biosynthesis of WDR26, which contributed to enhanced cell death induced by H2O2. Finally, we found that WDR26 over-expression also down-regulated the transcriptional activity of AP-1 during H2O2-induced SH-SY5Y cell death. Taken together, these results indicated that WDR26 was up-regulated by oxidative stress and played a key role in H2O2-induced SH-SY5Y cell death, which may be mediated by the down-regulation of AP-1 transcriptional activity.

Induction of KLF4 in response to heat stress

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor with diverse regulatory functions in cell growth, proliferation, differentiation, and embryogenesis. However, little is known about the response of KLF4 to heat stress. In this study, Western blot and reverse transcriptase-polymerase chain reaction were performed to determine the changes in KLF4 expression in response to heat stress. The results showed that heat stress up-regulated KLF4 messenger RNA and protein levels in a time-dependent manner in vivo and in 4 cell lines. Moreover, a study with heat shock transcription factor 1 (Hsf1) gene knockout mice indicated that the induction of KLF4 in response to heat stress was mediated by Hsf1. This process occurred rapidly, indicating that KLF4 is an immediate early response gene of heat stress. Next, the roles of KLF4 under heat stress conditions were analyzed for cells overexpressing or deficient in KLF4. The results showed overexpression of KLF4 increased the death rate of C2C12 cells, whereas KLF4 deficiency decreased the injury of C2C12 cells from heat stress conditions, suggesting that KLF4 might play an important role in cell injury induced by heat stress. KLF4 might be an immediate early response gene and could play an important role in cell injury induced by heat stress.

Dynamic metabolic adjustments and genome plasticity are implicated in the heat shock response of the extremely thermoacidophilic archaeon Sulfolobus solfataricus

Approximately one-third of the open reading frames encoded in the Sulfolobus solfataricus genome were differentially expressed within 5 min following an 80 to 90 degrees C temperature shift at pH 4.0. This included many toxin-antitoxin loci and insertion elements, implicating a connection between genome plasticity and metabolic regulation in the early stages of stress response.

Gene expression responses to DNA damage are altered in human aging and in Werner Syndrome

The accumulation of DNA damage and mutations is considered a major cause of cancer and aging. While it is known that DNA damage can affect changes in gene expression, transcriptional regulation after DNA damage is poorly understood. We characterized the expression of 6912 genes in human primary fibroblasts after exposure to three different kinds of cellular stress that introduces DNA damage: 4-nitroquinoline-1-oxide (4NQO), gamma-irradiation, or UV-irradiation. Each type of stress elicited damage specific gene expression changes of up to 10-fold. A total of 85 genes had similar changes in expression of 3-40-fold after all three kinds of stress. We examined transcription in cells from young and old individuals and from patients with Werner syndrome (WS), a segmental progeroid condition with a high incidence of cancer, and found various age-associated transcriptional changes depending upon the type of cellular stress. Compared to young individuals, both WS and old individuals had similarly aberrant transcriptional responses to gamma- and UV-irradiation, suggesting a role for Werner protein in stress-induced gene expression. Our results suggest that aberrant DNA damage-induced gene regulation may contribute to the aging process and the premature aging in WS.

Microscopical heat stress investigations under application of quantum dots

Heat stress responses are analyzed in cancer cells by applying different microscopy techniques for targeting various fluorescently labeled or native structures. Thermotreatments are performed at 40, 45, 50, and 56 degrees C, respectively, for 30 min each, while controls were kept at 37 degrees C. Actin cytoskeletons labeled with Alexa Fluor 488-conjugated phalloidin are imaged by wide-field fluorescence microscopy (WFFM). Structural plasma membrane stabilities are labeled with fluorescent quantum dots and analyzed by laser scanning microscopy (LSM). High-resolution atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to study morphological features and surface structures. Fluorescence images reveal F-actin to be a comparatively thermolabile cell component showing distinctive alteration after heat treatment at 40 degrees C. Destabilization of actin cytoskeletons proceed with increasing stress temperatures. Active reorganization of plasma membranes coincidental to heat-induced shrinkage and rounding of cell shapes, and loosening of monolayered tissue are observed after treatment at 45 or 50 degrees C. Active stress response is inhibited by stress at 56 degrees C, because actin cytoskeletons as well as plasma membranes are destroyed, resulting in necrotic cell phenotypes. Comparing data measured with the same microscopic technique and comparing the different datasets with each other reveal that heat stress response in MX1 cells results from the overlap of different heat-induced subcellular defects.