Regulation of Hypoxic-Adenosinergic Signaling by Estrogen: Implications for Microvascular Injury

Loss of estrogen, as occurs with normal aging, leads to increased inflammation, pathologic angiogenesis, impaired mitochondrial function, and microvascular disease. While the influence of estrogens on purinergic pathways is largely unknown, extracellular adenosine, generated at high levels by CD39 and CD73, is known to be anti-inflammatory in the vasculature. To further define the cellular mechanisms necessary for vascular protection, we investigated how estrogen modulates hypoxic-adenosinergic vascular signaling responses and angiogenesis. Expression of estrogen receptors, purinergic mediators inclusive of adenosine, adenosine deaminase (ADA), and ATP were measured in human endothelial cells. Standard tube formation and wound healing assays were performed to assess angiogenesis in vitro. The impacts on purinergic responses in vivo were modeled using cardiac tissue from ovariectomized mice. CD39 and estrogen receptor alpha (ERα) levels were markedly increased in presence of estradiol (E2). Suppression of ERα resulted in decreased CD39 expression. Expression of ENT1 was decreased in an ER-dependent manner. Extracellular ATP and ADA activity levels decreased following E2 exposure while levels of adenosine increased. Phosphorylation of ERK1/2 increased following E2 treatment and was attenuated by blocking adenosine receptor (AR) and ER activity. Estradiol boosted angiogenesis, while inhibition of estrogen decreased tube formation in vitro. Expression of CD39 and phospho-ERK1/2 decreased in cardiac tissues from ovariectomized mice, whereas ENT1 expression increased with expected decreases in blood adenosine levels. Estradiol-induced upregulation of CD39 substantially increases adenosine availability, while augmenting vascular protective signaling responses. Control of CD39 by ERα follows on transcriptional regulation. These data suggest novel therapeutic avenues to explore in the amelioration of post-menopausal cardiovascular disease, by modulation of adenosinergic mechanisms.

Effects of the Level and Duration of Mobilization Therapy in the Surgical ICU on the Loss of the Ability to Live Independently: An International Prospective Cohort Study

OBJECTIVES

It is unclear whether early mobilization in the surgical ICU helps improve patients' functional recovery to a level that enables independent living. We assessed dose of mobilization (level + duration). We tested the research hypotheses that dose of mobilization predicts adverse discharge and that both duration of mobilization and maximum mobilization level predict adverse discharge.

DESIGN

International, prospective cohort study.

SETTING

Study conducted in five surgical ICUs at four different institutions.

PATIENTS

One hundred fifty patients who were functionally independent before admission (Barthel Index ≥ 70) and who were expected to stay in the ICU for greater than or equal to 72 hours.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Mobilization was quantified daily, and treatments from all healthcare providers were included. We developed and used the Mobilization Quantification Score that quantifies both level and duration of mobilization. We assessed the association between the dose of mobilization (level + duration; exposure) and adverse discharge disposition (loss of the ability to live independently; primary outcome). There was wide variability in the dose of mobilization across centers and patients, which could not be explained by patients' comorbidity or disease severity. Dose of mobilization was associated with reduced risk of adverse discharge (adjusted odds ratio, 0.21; 95%CI, 0.09-0.50; p < 0.001). Both level and duration explained variance of adverse discharge (adjusted odds ratio, 0.28; 95% CI, 0.12-0.65; p = 0.003; adjusted odds ratio, 0.14; 95% CI, 0.06-0.36; p < 0.001, respectively). Duration compared with the level of mobilization tended to explain more variance in adverse discharge (area under the curve duration 0.73; 95% CI, 0.64-0.82; area under the curve mobilization level 0.68; 95% CI, 0.58-0.77; p = 0.10).

CONCLUSIONS

We observed wide variability in dose of mobilization treatment applied, which could not be explained by patients' comorbidity or disease severity. High dose of mobilization is an independent predictor of patients' ability to live independently after discharge. Duration of mobilization sessions should be taken into account in future quality improvement and research projects.

Cardiopulmonary Bypass Suppresses Forkhead Box O3 and Downstream Autophagy in the Diabetic Human Heart

BACKGROUND

Autophagy is an integral component of cellular homeostasis and metabolism. The exact mechanism of impaired autophagy in diabetes mellitus is unknown. Forkhead Box O3 (FOXO3α) is a key regulator of oxidative stress-related responses. We hypothesize FOXO3α is a direct upstream regulator of the autophagy pathway, and its upregulation is compromised in diabetic patients during stress of cardiopulmonary bypass (CPB).

METHODS

The study enrolled 32 diabetic and 33 nondiabetic patients undergoing a cardiac surgical procedure on CPB. Right atrial tissue and serum samples were collected before and after CPB per protocol. A set of key components were quantitatively assessed and compared by microarray, immunoblotting, and immunohistochemistry studies. Data were analyzed using paired or unpaired student test. A P of <.05 or less was considered significant.

RESULTS

Serum microarray showed FOXO3α was upregulated in the diabetic vs nondiabetic group after CPB (P = .033), autophagy-related 4B gene and Beclin 1 gene were greatly upregulated in the nondiabetic group (P = .028 and P = .002, respectively). On immunoblotting, there was upregulation of FOXO3α in the nondiabetic patients after CPB (P = .003). There were increased levels of Beclin-1, Bcl-2, and light chain 3B after CPB in the nondiabetic group only (P = .016, P = .005, P = .002, respectively). Sirtuin 1, Unc-51-like autophagy activating kinase 1 (ULK1), peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1α), and mammalian target of rapamycin (mTOR) were not significantly changed in the nondiabetic group after CPB.

CONCLUSIONS

Compared with nondiabetic patients, there was no significant upregulation of FOXO3α in diabetic patients, which could possibly explain the lack of upregulation of the autophagy process after CPB. FOXO3α could potentially serve as a therapeutic target to improve cellular homeostasis.

Abstract 4190: Ezrin plays a key role in the regulation of translation in metastatic osteosarcoma

Our previous studies have demonstrated the association between Ezrin and the metastatic biology of pediatric sarcomas including osteosarcoma (OS) and rhabdomyosarcoma. Mechanistic studies exploring this association have shown that Ezrin expression enhances the survival of metastatic cells upon their arrival to the secondary metastatic site. In order to better understand this role in metastasis, we undertook two non-candidate analyses of Ezrin function including a microarray subtraction of high and low Ezrin expressing cells and a proteomic approach to identify proteins that bind the N-terminus of Ezrin in tumor lysates. Functional analyses of these data led to a novel and unifying hypothesis that Ezrin contributes to the efficiency of metastasis through regulation of protein translation. In support of this hypothesis we found Ezrin to be part of a ribonucleoprotein complex and to bind with poly A binding protein 1 (PABA1; PABPC1). Using luciferase reporter-based assays, we have shown that OS cells expressing high levels of Ezrin are able to translate mRNAs containing a stem loop 5′ UTR structure, so called “weakly translated mRNAs,” more efficiently than low Ezrin OS cells. This finding suggests that Ezrin's contribution to the metastatic phenotype may be due in part to enhanced translation of specific mRNAs during metastasis that are normally expressed at low levels outside of the metastatic context. Ongoing studies will now assess the ability of Ezrin to enhance the expression of specific mRNAs in 3-dimensional contexts more relevant to cancer cell growth in vivo. We have developed stable high and low Ezrin osteosarcoma cell lines that express a GFP reporter with or without a complex 5′ UTR stem loop structure in the mRNA transcript and with and without protein destabilizing elements. Initial studies have shown that the addition of the 5′ UTR structure and destabilizing elements progressively limits GFP reporter expression. We plan to confirm that this reduction in expression is due to reduced translation and to assess whether 3-D culture conditions or the in vivo environment enhance expression of these tunable reporters of translation in an Ezrin-dependant manner. We expect these results to provide a novel mechanistic basis to consider how Ezrin may contribute to metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4190. doi:1538-7445.AM2012-4190

Dysregulation of ezrin phosphorylation prevents metastasis and alters cellular metabolism in osteosarcoma

Ezrin links the plasma membrane to the actin cytoskeleton where it plays a pivotal role in the metastatic progression of several human cancers; however, the precise mechanistic basis for its role remains unknown. Here, we define transitions between active (phosphorylated open) and inactive (dephosphorylated closed) forms of Ezrin that occur during metastatic progression in osteosarcoma. In our evaluation of these conformations we expressed C-terminal mutant forms of Ezrin that are open (phosphomimetic T567D) or closed (phosphodeficient T567A) and compared their biologic characteristics to full-length wild-type Ezrin in osteosarcoma cells. Unexpectedly, cells expressing open, active Ezrin could form neither primary orthotopic tumors nor lung metastases. In contrast, cells expressing closed, inactive Ezrin were also deficient in metastasis but were unaffected in their capacity for primary tumor growth. By imaging single metastatic cells in the lung, we found that cells expressing either open or closed Ezrin displayed increased levels of apoptosis early after their arrival in the lung. Gene expression analysis suggested dysregulation of genes that are functionally linked to carbohydrate and amino acid metabolism. In particular, cells expressing closed, inactive Ezrin exhibited reduced lactate production and basal or ATP-dependent oxygen consumption. Collectively, our results suggest that dynamic regulation of Ezrin phosphorylation at amino acid T567 that controls structural transitions of this protein plays a pivotal role in tumor progression and metastasis, possibly in part by altering cellular metabolism.

Abstract 3092: FBW7 targets hypoxia inducible factor-1α (HIF-1α) for proteasomal degradation during hypoxia

Hypoxia Inducible Factor-1α (HIF-1α) mediates expression of genes associated with endothelial cell-mediated angiogenesis and is associated with poor outcomes in a variety of cancers. In normoxia, HIF-1α is ubiquitinated and degraded through interactions with the E3 ubiqutin ligase, von Hippel-Lindau (vHL); however, little is known about the negative regulation of HIF-1α in hypoxia. FBW7, an E3 ubiquitin ligase, has been shown to interact with several transcription factors including those phosphorylated by glycogen synthase kinase 3β (GSK3β). The current study tested the hypothesis that phosphorylation of HIF-1α by GSK3β increases the FBW7-mediated ubiquitination and degradation of HIF-1α, thereby resulting in suppression of the hypoxia-mediated angiogenic response in SKOV-3 ovarian cancer cells. HIF-1α protein and VEGF transcript levels in hypoxia were increased when GSK3β activity was inhibited and were reduced by expression of constitutively active GSK3β (GSK3S9A). Additionally, expression of GSK3S9A increased HIF-1α ubiquitination. Conditioned media from SKOV-3 cells expressing shRNA against GSK3β (shGSK3) had an enhanced effect on endothelial tube formation in a Matrigel matrix, suggesting that GSK3β exerts an inhibitory effect on hypoxia-mediated angiogenesis. Overexpression of the β and γ isoforms of FBW7 decreased HIF-1α stabilization, and HIF-1α interacts with FBW7 by co-immunoprecipitation. Furthermore, knockdown of FBW7 using siRNA resulted in increased HIF-1α levels in hypoxia. These data suggest a new mechanism for negative regulation of HIF-1α during hypoxia that utilizes phosphorylation by GSK3β and interaction with FBW7 leading to ubiquitination and proteasomal degradation. Results of this study better define the signaling pathways necessary for HIF-1α-mediated signaling and may identify new targets that mediate angiogenesis in disease.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3092. doi:10.1158/1538-7445.AM2011-3092