Elk Activity Research Articles

Context-dependent effects of a reintroduced ungulate on soil properties are driven by soil texture, moisture, and herbivore activity.

Although there is considerable evidence that large mammalian herbivores influence ecosystem‐level processes, studies have reported such widely varying results that generalizations have remained elusive. Here, we use an 18‐year‐old exclosure experiment—stratified across a landscape heterogeneous with respect to soil texture, moisture and herbivore activity—to understand the variable effects of tule elk (Cervus canadensis nannodes), a native reintroduced herbivore, on soil properties along the coast of northern California. Elk significantly increased soil bulk density and created a compacted layer at shallow soil depth, while decreasing infiltration rate and pH. The effects of elk on bulk density, penetration resistance, and pH varied with soil type, being least pronounced in coarse, sandy loams, and greatest in loose sand. The effects of elk on nutrient availability varied along gradients of soil texture and moisture. In coarser soils, elk decreased ammonium availability, but increased it in finer soils. Elk also decreased soil moisture content, in part through their positive effect on bulk density, and this effect was most pronounced in coarser soils. Through decreasing soil moisture content, elk also decreased nitrate availability in coarser soils. At greater levels of elk activity (as measured by dung deposition), the elk effect on bulk density was amplified, and this had a corresponding negative effect on nitrate and phosphate availability. Our study has demonstrated that a better understanding of spatial variation in the effects of herbivores on ecosystems can emerge by evaluating their influences across gradients of soil texture, soil moisture, and herbivore activity. These data enabled us to evaluate several frameworks that have been developed to understand the variable effects of herbivores on ecosystems, which is a significant step in reconciling the many competing ideas put forth to explain the context‐dependent effects of large herbivores on grazed ecosystems.

Legacy effects of fire size and severity on forest regeneration, recruitment, and wildlife activity in aspen forests

Human activities and climate change are increasing the size and severity of wildfires globally, creating a need for research that links changes in fire regimes with community-level responses. The objective of this study was to understand how variability in fire regimes influences forest regeneration and recruitment patterns and wildlife activity at large temporal and spatial scales. Across 25 fires in five National Forests (Uinta-Wasatch-Cache NF, Ashley NF, Fishlake NF, Dixie NF, and Manti-La Sal NF) in the state of Utah, we examined aspen regeneration and recruitment levels, and wildlife and livestock fecal group counts along belt transects that spanned gradients of fire size and severity. Forest cover change was assessed by comparing pre-fire and post-fire satellite images. The fires dated from 1992 to 2002 and were at least 10years old when this study was conducted. Fire size and severity were positively related to aspen regeneration (density of saplings) and recruitment (saplings>2m in height). There was a significant fire size and severity interaction effect on aspen regeneration, such that the positive influence of fire size increased with greater fire severity (R2=0.40, P<0.001). Change in the extent of aspen cover was not correlated with fire size. Deer and cattle became more dispersed with increasing fire size and severity, but elk activity showed no difference. Deer preferred low severity burn patches in smaller fires, but appeared to avoid low severity patches as fires became larger. Our results suggest that fire size and severity are important ecological filters that can interact to affect forest development and the distribution and abundance of large herbivores. Effective management of forest systems in response to altered fire regimes will require an understanding of the legacy effects of fire size and severity at the landscape scale.

Ecology of the eastern population of the Siberian Crane Leucogeranus leucogeranus in the taiga section of its flyway: habitats, foraging, trophic links with Elk Alces alces, and threats

Stopovers along the flyway of the Siberian Crane in the taiga zone of northeastern Asia have not been previously described. In this study, we provide the first investigation of the stopovers of its eastern population in the taiga zone (2006-2011). Seven spring stopovers at bogs were investigated for 10-24 hr each. The birds spent 5-6 hr sleeping at night, while 54-74 % of their time was spent foraging outside the sleep time budget. Based on excreta samples, only 5/109 cranes successfully obtained adequate food during stopovers at typical bogs. Favorable foraging conditions were found at the rare shallow lakes or at Elk Alces alces salt licks where the foraging efficiency was 16 times greater than at bogs unaffected by ungulates. Elk activity led to areas of peat exposure in bogs where the availability of edible grass rhizomes and readily extractable sprouts were increased for the Siberian Crane. Investigations at three autumn stopovers at poor forage riverbeds lasted for 0.3-11.0 hr and were interrupted by boating activities, as were 22 other reported stopovers. Cranes allocated a high proportion of their time to foraging, which they commenced immediately after landing. However, the cranes failed to acquire any significant sustenance during the overwhelming majority of taiga stopovers. Our investigation showed that the eastern population was not specialized in foraging at typical taiga wetlands. Humans indirectly aggravated the naturally harsh migration conditions by overhunting Elk on the flyway and intensive boating activities during the most intense migration period.

Vegetation Responses to Supplemental Winter Feeding of Elk in Western Wyoming

ABSTRACT. To compensate for losses in overwintering habitat, elk are fed hay in winter at approximately 37 locations throughout the western United States. These winter feeding programs concentrate elk activity, and there is concern that such concentrations could degrade plant communities. Except for one study focused exclusively on aspen (Populus tremuloides), ours is the first to quantify vegetation responses to supplemental winter feeding of elk. The western Wyoming feedground we studied was established in winter 1981–1982, and supplemental feeding occurred every winter through 2006. Transects were arranged in a before-after control-impact (BACI) design, and vegetation data were gathered in the midsummers of 1981 and 2006. Over the study period, the feedground became invaded by smooth brome (Bromus inermis), a nonnative grass constituent of hay fed to the elk. The smooth brome invasion was attended by declines in native forb cover and the apparent extirpation of shrubs from the feedground. The smooth br...

Utilizing Ras Signaling Pathway to Direct Selective Replication of Herpes Simplex Virus-1

Re-engineering the tropism of viruses is an attractive translational strategy for targeting cancer cells. The Ras signal transduction pathway is a central hub for a variety of pro-oncogenic events with a fundamental role in normal and neoplastic physiology. In this work we were interested in linking Ras activation to HSV-1 replication in a direct manner in order to generate a novel oncolytic herpes virus which can target cancer cells. To establish such link, we developed a mutant HSV-1 in which the expression of ICP4 (infected cell protein-4, a viral protein necessary for replication) is controlled by activation of ELK, a transcription factor down-stream of the Ras pathway and mainly activated by ERK (extracellular signal-regulated kinase, an important Ras effector pathway). This mutant HSV-1 was named as Signal-Smart 1 (SS1). A series of prostate cells were infected with the SS1 virus. Cells with elevated levels of ELK activation were preferentially infected by the SS1 virus, as demonstrated by increased levels of viral progeny, herpetic glycoprotein C and overall SS1 viral protein production. Upon exposure to SS1, the proliferation, invasiveness and colony formation capabilities of prostate cancer cells with increased ELK activation were significantly decreased (p<0.05), while the rate of apoptosis/necrosis in these cells was increased. Additionally, high Ras signaling cells infected with SS1 showed a prominent arrest in the G1 phase of the cell cycle as compared to cells exposed to parental HSV-1. The results of this study reveal the potential for re-modeling the host-herpes interaction to specifically interfere with the life of cancer cells with increased Ras signaling. SS1 also serves as a “prototype” for development of a family of signal-smart viruses which can target cancer cells on the basis of their signaling portfolio.

Development of a Sightability Model for Low‐Density Elk Populations in Ontario, Canada

ABSTRACT The status of recolonizing elk (Cervus elaphus) populations in Ontario, Canada, is unclear and there is a need for effective population survey methods that can be applied locally. We sought to develop a sightability model that could account for both low densities of elk and dense forest cover in elk‐release areas in Ontario. We corrected winter aerial survey counts for sightability based on radiocollared animals known to be within observable distance of the aircraft. The multivariate model with the highest Akaike's Information Criterion corrected for sample size weight (wi = 0.427) revealed that elk group size, elk activity, dominant tree type, percent canopy cover, and percent conifer cover were significant predictors of elk sightability. The group‐size effect indicated that odds of sighting an elk increased by 1.353 (95% CI = 0.874‐3.689) for every additional elk. Standing elk were 5.033 (95% CI = 0.936‐15.541) times more likely to be observed than were resting elk, and those located in conifer cover were 0.013 (95% CI = 0.001‐0.278) times less likely to be sighted than elk in deciduous cover. Furthermore, elk located in &gt;50% canopy cover and &gt;50% conifer cover were 0.041 (95% CI = 0.003‐0.619) times and 0.484 (95% CI = 0.024‐9.721) times less likely to be sighted than elk in more open habitat, respectively. During model validation, observers detected 79% (113/143) of known elk in any given area, and population and sightability model predictions (±90% CI) overlapped with the population estimate, implying that our predictive model was robust. Unsurprisingly, large groups of elk in open habitat increased model precision, which highlights difficulties of counting Ontario elk in their northern range. We conclude that our model provided increased reliability for estimating elk numbers in Ontario compared to existing methods, and that the estimator may be useful in other areas where elk density is low and sightability is poor due to dense forest cover.

Adaptor SKAP-55 Binds p21ras Activating Exchange Factor RasGRP1 and Negatively Regulates the p21ras-ERK Pathway in T-Cells

While the adaptor SKAP-55 mediates LFA-1 adhesion on T-cells, it is not known whether the adaptor regulates other aspects of signaling. SKAP-55 could potentially act as a node to coordinate the modulation of adhesion with downstream signaling. In this regard, the GTPase p21ras and the extracellular signal-regulated kinase (ERK) pathway play central roles in T-cell function. In this study, we report that SKAP-55 has opposing effects on adhesion and the activation of the p21ras -ERK pathway in T-cells. SKAP-55 deficient primary T-cells showed a defect in LFA-1 adhesion concurrent with the hyper-activation of the ERK pathway relative to wild-type cells. RNAi knock down (KD) of SKAP-55 in T-cell lines also showed an increase in p21ras activation, while over-expression of SKAP-55 inhibited activation of ERK and its transcriptional target ELK. Three observations implicated the p21ras activating exchange factor RasGRP1 in the process. Firstly, SKAP-55 bound to RasGRP1 via its C-terminus, while secondly, the loss of binding abrogated SKAP-55 inhibition of ERK and ELK activation. Thirdly, SKAP-55−/− primary T-cells showed an increased presence of RasGRP1 in the trans-Golgi network (TGN) following TCR activation, the site where p21ras becomes activated. Our findings indicate that SKAP-55 has a dual role in regulating p21ras-ERK pathway via RasGRP1, as a possible mechanism to restrict activation during T-cell adhesion.

Elk Use of Wallows and Potential Chronic Wasting Disease Transmission

Deposition of prions into the environment by infected animals may contribute to transmission and spread of chronic wasting disease (CWD) among free-ranging cervids, and identification of such environmental sources may provide an avenue for managing CWD. We evaluated the role that wallow use by elk (Cervus elaphus) may play in CWD transmission by monitoring wallows with animal-activated cameras throughout their period of use. We monitored 39 wallows from 5 August 2005 to 14 October 2005. Elk visited 20 sites; we recorded 22 events when only male elk wallowed and 374 additional events when male and female elk had naso-oral contact with wallow contents. Because wallows are foci of male elk activity, behaviors at wallows could potentially contribute to the maintenance and transmission of CWD. Our findings, however, suggest that because wallows are only used an average of one or two times a season they may not be important in CWD transmission. The data also suggest that mineral licks could be more important in CWD transmission because they were used more frequently and by three species that contract CWD.

Activity and Movements of Reintroduced Elk in Southeastern Kentucky

We assessed daily and seasonal activity and movements of reintroduced elk in eastern Kentucky from March 1999 to November 2000. Elk activity was determined by monitoring radio-transmitter pulse rate changes, and movements were calculated using hourly ground locations. A total of 1469 activity bouts and 1441 locations were collected on 38 and 32 radio-collared elk, respectively. Elk exhibited a tri-modal activity pattern with peaks near dawn, dusk, and midnight. Activity did not differ between seasons, although it was influenced by gender and time of day. Peak movements corresponded with peaks in activity at dawn and dusk, and increased from spring to winter. Elk were more gregarious and visible during the fall and winter, which increased their susceptibility to human disturbance and caused longer movements.

Adaptive hypersensitivity to estrogen: Mechanisms and clinical relevance to aromatase inhibitor therapy in breast cancer treatment

Breast tumors in women can adapt to endocrine deprivation therapy by developing hypersensitivity to estradiol. For this reason, aromatase inhibitors can be effective in women relapsing after treatment with tamoxifen or following oophorectomy. To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided in vitro and in vivo evidence that long-term estradiol deprivation (LTED) causes “adaptive hypersensitivity”. The primary mechanisms responsible involve up-regulation of ERα as well as the MAP kinase, PI-3 kinase, and mTOR growth factor pathways. ERα is 4–10-fold up-regulated and co-opts a classical growth factor pathway using Shc, Grb2, and Sos. This induces rapid non-genomic effects which are enhanced in LTED cells. Estradiol binds to cell membrane associated ERα, physically associates with the adaptor protein Shc, and induces its phosphorylation. In turn, Shc binds Grb2 and Sos which result in the rapid activation of MAP kinase. These non-genomic effects of estradiol produce biologic effects as evidenced by Elk activation and by morphologic changes in cell membranes. Additional effects include activation of PI-3 kinase and mTOR pathways through estradiol induced binding of ERα to the IGF-1 and EGF receptors. Further proof of the non-genomic effects of estradiol involved use of “designer” cells which selectively express ERα in nucleus, cytosol, and cell membrane. We have used a new downstream inhibitor of these pathways, farnesyl-thio-salicylic acid (FTS), to block proliferation in hypersensitive cells as a model for a potentially effective strategy for treatment of patients.

Effects of EGF-R on Signal Transduction and Anti-Apoptotic Cascades in Hematopoietic Cells: EGF-R Activates Multiple Signal Transduction Cascades Which Result in the Prevention of Apoptosis in the Absence of Autocrine Cytokines.

v-ErbB is an oncogene related to the Epidermal Growth Factor Receptor (EGF-R) that was initially discovered in the genome of avian erythoblastosis virus. v-ErbB will abrogate the requirement of erythroid progenitor cells for erythropoietin and stem cell factor and block terminal differentiation. EGF-R overexpression has been observed in many pathological situations and there is a truncated form of EGF-R referred to as EGFvIII which resembles v-ErbB in biological properties. EGF-R expression is often constitutive and may occur in the presence of expression of other oncogenes or in the absence of certain tumor suppressor genes. To circumvent these problems, we subcloned v-ErbB into a vector which contained the estrogen receptor hormone binding domain which renders the v-ErbB protein dependent upon the addition of beta-estradiol for activity. v-ErbB:ER conditionally abrogated the cytokine dependence of human (TF-1) and murine (FL5.12 and FDC-P1) hematopoietic cells efficiently. This construct allowed examination of the signal transduction and anti-apoptotic pathways activated by v-ErbB:ER in hematopoietic cells. By determining which signal transduction pathways were activated in response to either v-ErbB:ER or IL-3 in the presence and absence of inhibitors, we could ascertain that v-ErbB:ER expression activated the Jak/STAT, Raf/MEK/ERK, PI3K/Akt/mTOR/p70S6K and JNK pathways. Thus v-ErbB:ER activated a broad spectrum of signal transduction pathways some of which were linked to the prevention of apoptosis. Apoptosis was measured by annexin V/PI binding and activation of caspases 3, 8 & 9. Treatment of v-ErbB:ER cells with the EGF-R inhibitor AG1478 efficiently induced apoptosis in these cells at 100 to 1000 fold lower concentrations than MEK, PI3K/mTOR or JNK inhibitors, and activation of all these signal transduction pathways was inhibited with the EGFR inhibitor. Induction of apoptosis by the EGF-R inhibitor was only observed when the cells were grown in response to v-ErbB:ER activation demonstrating specificity. In contrast, other inhibitors suppressed kinase activation and induced some apoptosis when the cells were grown in response to v-ErbB:ER or IL-3. When the cells were treated with MEK, PI3K/mTOR or JNK inhibitors, only the kinases specific for those pathways were inhibited. When MEK and PI3K/mTOR inhibitors were added a synergistic apoptotic response was observed. In contrast, combinations of Jak or JNK and either MEK or PI3K/mTOR inhibitors did not result in a synergistic apoptotic response. Thus the Raf/MEK/ERK and PI3K/Akt/mTOR/p70S6K pathways are the most important pathways in preventing apoptosis in these cells. FL5.12 cells conditionally transformed to grow in response to activated Raf and Akt, (FL/Akt:ER+Raf-1:AR) were also isolated. Activation of STAT5 by either Raf or Akt did not occur in these cells, but did occur upon IL-3 treatment. Furthermore, Elk activation occurred in response to Raf activation but not IL-3 stimulation in the cells which grew in response to Raf and Akt. v-ErbB:ER is more effective in its ability to abrogate cytokine dependence of hematopoietic cells than Raf or Akt, and it induces multiple signal transduction pathways, only some of which are required for growth and the prevention of apoptosis in tissue culture systems.

Effects of EGF-R on Transcription Factor Activation in Hematopoietic Cells: EGF-R Activates Multiple Transcription Factors Which Induce Proliferation in the Absence of Autocrine Cytokines.

v-ErbB is an oncogene related to the Epidermal Growth Factor Receptor (EGF-R) that was initially discovered in the genome of avian erythoblastosis virus. v-ErbB will abrogate the requirement of erythroid progenitor cells for erythropoietin and stem cell factor and block terminal differentiation. EGF-R overexpression has been observed in many pathological situations and the EGF-R gene is amplified in certain tumors. Moreover, there is a truncated form of EGF-R referred to as EGFvIII which resembles v-ErbB in biological properties. One problem frequently encountered in studying the effects of EGF-R overexpression in many tumors is that EGF-R expression is often constitutive and in the presence of increased expression of other oncogenes or in the absence of certain tumor suppressor genes. To circumvent these problems, we subcloned v-ErbB into a vector which contained the estrogen receptor hormone binding domain which renders the v-ErbB protein dependent upon the addition of beta-estradiol or 4 OH tamoxifen for activity. The v-ErbB:ER oncogene will conditionally abrogate the cytokine dependence of human (TF-1) and murine (FL5.12 and FDC-P1) hematopoietic cells efficiently. This construct has allowed us to examine the transcription factors pathways activated by v-ErbB:ER in hematopoietic cells which are required for proliferation in the absence of previously required cytokines. By determining which signal transduction pathways were activated in response to either v-ErbB:ER activation or IL-3 addition in the presence and absence of specific small molecular weight membrane permeable kinase inhibitors, we could ascertain that v-ErbB:ER expression activated the STAT5, Elk, CREB, Jun, and Forkhead (Foxo) family of transcription factors in FL/v-ErbB:ER cells. The activation of these transcription factors was blocked by the respective kinase inhibitors. Thus v-ErbB:ER activated a broad spectrum of transcription factors. Treatment of v-ErbB:ER cells with the EGF-R inhibitor AG1478 very efficiently induced apoptosis in these cells at 100 to 1000 fold lower concentrations than MEK, PI3K or JNK inhibitors and activation of all these transcription factor inhibitors was inhibited. In contrast, when the cells were treated with MEK, PI3K or JNK inhibitors, only the transcription factors specific for the individual pathways were inhibited. FL5.12 cells conditionally transformed to grow in response to activated Raf and Akt, (FL/Akt:ER+Raf-1:AR) were also isolated. Activation of STAT5 by either Raf or Akt did not occur in FL/Akt:ER+Raf-1:AR cells, but did occur when the cells were treated with IL-3. Furthermore, Elk activation occurred in response to Raf activation but not IL-3 stimulation in the FL/Akt:ER+Raf-1:AR cells which grew in response to Raf and Akt. Thus oncogenes such as v-ErbB:ER, which are more effective in their ability to transform hematopoietic cells than oncogenes such as Raf and Akt, can induce multiple transcription factors, only some of which are required for growth in tissue culture systems.

Erythropoietin regulation of Raf-1 and MEK: evidence for a Ras-independent mechanism

AbstractStimulation of the erythropoietin (EPO) receptor triggers a cascade of signaling events. We reported that EPO upregulates c-myc expression through 2 pathways in BaF3-EpoR cells—a phosphatidylinositol 3-kinase (PI3K) pathway operating on transcriptional initiation and a Raf-1–mitogen-activated protein kinase (MAPK) pathway affecting elongation. We now show that EPO induces phosphorylation of Raf-1 at serine 338 and within the carboxy-terminal domain, resulting in an electrophoretic mobility change (hyperphosphorylation). Importantly, MEK 1 inhibitor PD98059 blocked only the hyperphosphorylation of Raf-1 but not the phosphorylation at serine 338. This inhibition of Raf-1 hyperphosphorylation resulted in increased kinase activity of Raf-1 and increased phosphorylation of MEK, suggesting that the hyperphosphorylation of Raf-1 inhibits its MEK kinase activity. Deletion of the first 184 amino acids of Raf-1, which are involved in its interaction with Ras, had no effect on EPO-induced phosphorylation. Introducing the dominant-negative N17Ras or GAP had no effect on EPO-induced kinase activity of Raf-1 and ELK activation. N17Ras failed to inhibit ELK activation in another cell line—Rauscher murine erythroleukemia— which expresses the EPO receptor endogenously and differentiates in response to the hormone. These results indicate the presence of a Ras-independent mechanism for Raf-1 and MEK activation in these cells.

ERK activation by mechanical strain is regulated by the small G proteins rac-1 and rhoA.

Physical forces play an important role in regulating cell functions. We applied mechanical strain to human fibroblasts by magnetic attraction of superparamagnetic arginine-glycine-aspartic acid (RGD)-coated beads. We confirmed that the MAP kinases Erk and p38 are activated by mechanical strain, and went further by demonstrating the activation of Elk-1 by mechanical strain, mainly through a MEK-Erk pathway. Transfection of a dominant negative form of the G protein rac-1 (rac T17N), and inhibition of PI3K, an effector of rac-1, efficiently prevented Elk-1 activation by mechanical forces. Transfection with C3 transferase, known to inhibit rhoA, and inhibition of rock (a downstream effector of rhoA), gave similar results. However, contrary to the active form of rhoA (rho G14V), transfection of the active form of rac-1 (rac G12V) induced Elk activation and mimicked the effects of mechanical strain. These results point out that the two small G proteins rhoA and rac-1 participate in cell sensitivity to mechanical strain and lead to the modulation of the Erk pathway.

Adaptive hypersensitivity to estrogen: mechanism for superiority of aromatase inhibitors over selective estrogen receptor modulators for breast cancer treatment and prevention.

Clinical observations suggest that human breast tumors can adapt to endocrine therapy by developing hypersensitivity to estradiol (E(2)). To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided in vitro and in vivo evidence that long-term E(2) deprivation (LTED) causes "adaptive hypersensitivity". The enhanced responses to E(2) do not involve mechanisms acting at the level of transcription of estrogen-regulated genes. We found no evidence of hypersensitivity when examining the effects of E(2) on regulation of c-myc, pS2, progesterone receptor, several estrogen receptor (ER) reporter genes, or c-myb in hypersensitive cells. Estrogen deprivation of breast cells long-term does up-regulate both the MAP kinase and phosphatidyl-inositol 3-kinase pathways. As a potential explanation for up-regulation of these signaling pathways, we found that ERalpha is 4- to 10-fold up-regulated and co-opts a classic growth factor pathway using Shc, Grb-2 and Sos. This induces rapid non-genomic effects which are enhanced in LTED cells. E(2) binds to cell membrane-associated ERalpha, physically associates with the adapter protein SHC, and induces its phosphorylation. In turn, Shc binds Grb-2 and Sos, which results in the rapid activation of MAP kinase. These non-genomic effects of E(2) produce biological effects as evidenced by Elk activation and by morphological changes in cell membranes. Further proof of the non-genomic effects of E(2) involved use of cells which selectively expressed ERalpha in the nucleus, cytosol and cell membrane. We created these COS-1 "designer cells" by transfecting ERalpha lacking a nuclear localization signal and containing a membrane localizing signal. The concept of "adaptive hypersensitivity" and the mechanisms responsible for this phenomenon have important clinical implications. Adaptive hypersensitivity would explain the superiority of aromatase inhibitors over the selective ER modulators (SERMs) for treatment of breast cancer. The development of highly potent third-generation aromatase inhibitors allows reduction of breast tissue E2 to very low levels and circumvents the enhanced sensitivity of these cells to the proliferative effects of E(2). Clinical trials in the adjuvant, neoadjuvant and advanced disease settings demonstrate the greater clinical efficacy of the aromatase inhibitors over the SERMs. More recent observations indicate that the aromatase inhibitors are superior for the prevention of breast cancer as well. These observations may be explained by the hypothesis that estrogens induce breast cancer both by stimulating cell proliferation and by their metabolism to genotoxic products. The SERMs block ER-mediated proliferation only, whereas the aromatase inhibitors exert dual effects on proliferation and genotoxic metabolite formation.

Negative Regulation of ERK and Elk by Protein Kinase B Modulates c-fos Transcription

In this study, we have identified novel regulatory steps involved in the cross-talk between protein kinase B (PKB) and MAPK signaling pathways. We found that PKB down-regulates the Ras-Raf-MEK-ERK pathway by reducing the activity of ERK, which leads to inactivation of the transcription factor Elk1. In addition, PKB is able to reduce protein levels of Elk1. Both events lead to suppression of serum response element (SRE)-dependent transcription and a consequent decrease in the transcription of SRE-containing genes, such as c-fos. Because activation of the Ras/MAPK cascade is reported to increase c-fos transcription before apoptosis, our results are consistent with a specific role for PKB in promoting cell survival. Decrease in c-Fos protein levels in glioblastoma cells with constitutively active PKB provides further support for our observations. Therefore, our findings delineate a novel mechanism regulating immediate-early transcription, which may be involved in the initial steps in PKB-induced oncogenic transformation.

Nuclear Factor-κB Activation by the CXC Chemokine Melanoma Growth-stimulatory Activity/Growth-regulated Protein Involves the MEKK1/p38 Mitogen-activated Protein Kinase Pathway

Melanoma growth stimulatory activity/growth-regulated protein (MGSA/GRO), a CXC chemokine, plays an important role in inflammation, wound healing, growth regulation, angiogenesis, and tumorigenesis. Constitutive expression of MGSA/GROalpha in melanoma tumors is associated with constitutive nuclear factor (NF)-kappaB activity. We show here that either exogenous addition or continuous expression of MGSA/GROalpha in immortalized melanocytes enhances NF-kappaB activation, as well as mitogen-activated protein (MAP) kinase kinase kinase (MEKK) 1, MAP kinase kinase (MEK) 3/6, and p38 MAP kinase activation. Expression of dominant negative M-Ras (S27N), dominant negative MEKK1 (K432M), or specific chemical inhibitors for p38 MAP kinase (SB202190 and SB203580) block MGSA/GROalpha-induced NF-kappaB transactivation, demonstrating that Ras, MEKK1, and p38 are involved in the signal pathways of MGSA/GROalpha activation of NF-kappaB. Expression of dominant active Ras or dominant active MEKK1 alone can also stimulate NF-kappaB activation. The expression of dominant negative MEKK1 inhibits the Ras-induced NF-kappaB activation, suggesting that MEKK1 is a downstream target of Ras. Moreover, MGSA/GROalpha induction of NF-kappaB is independent of the MEK1/ERK cascade, because MGSA/GROalpha failed to increase ERK and ELK activation, and specific chemical inhibitors for MEK1 (PD98059) had no effect on MGSA/GROalpha-enhanced NF-kappaB activation. These data demonstrate that NF-kappaB activation is required for MGSA/GROalpha-induced melanocyte transformation through a Ras/MEKK1/p38 cascade in melanocytes.

Collagen-homology domain 1 deletion mutant of Shc suppresses transformation mediated by neu through a MAPK-independent pathway.

Shc proteins are implicated in coupling receptor tyrosine kinase to the mitogen-activated protein kinase (MAPK) pathway by recruiting Grb2/SOS to the plasma membrane. To better understand the role of Shc in the oncogenesis by point-mutation activated neu (p185*), we transfected a Shc mutant (ShcdeltaCHI), which lacks the Grb2 binding site Y317 by deletion of collagen-homology domain 1, into p185*-transformed NIH3T3 cells. The cellular transformation phenotypes were found to be largely suppressed by expression of ShcdeltaCH1. Although ShcdeltaCH1 still retained another Grb2 binding site (Y239/240), we did not detect its physical association with Grb2. We also found that ShcdeltaCH1 could associate with p185*; however, this association did not interfere with the endogenous Shc-p185* interaction or the Shc-Grb2 interaction. In addition, p185*-mediated MAPK and Elk activation likewise were not inhibited by ShcdeltaCH1 expression. Taken together, these data demonstrate that ShcdeltaCH1 suppresses the transformation induced by activated neu through a MAPK-independent pathway, indicating that Shc may be involved in other signal pathway(s) critical for cellular transformation in addition to the MAPK pathway.