Comparative transcriptomics reveals circadian and pluripotency networks as two pillars of longevity regulation

Mammals differ more than 100-fold in maximum lifespan. Here, we conducted comparative transcriptomics on 26 species with diverse lifespans. We identified thousands of genes with expression levels negatively or positively correlated with a species' maximum lifespan (Neg- or Pos-MLS genes). Neg-MLS genes are primarily involved in energy metabolism and inflammation. Pos-MLS genes show enrichment in DNA repair, microtubule organization, and RNA transport. Expression of Neg- and Pos-MLS genes is modulated by interventions, including mTOR and PI3K inhibition. Regulatory networks analysis showed that Neg-MLS genes are under circadian regulation possibly to avoid persistent high expression, whereas Pos-MLS genes are targets of master pluripotency regulators OCT4 and NANOG and are upregulated during somatic cell reprogramming. Pos-MLS genes are highly expressed during embryogenesis but significantly downregulated after birth. This work provides targets for anti-aging interventions by defining pathways correlating with longevity across mammals and uncovering circadian and pluripotency networks as central regulators of longevity.

Cytokine driven effector functions of CD8 cells: application to protease-activated cytokine therapy for cancer

Cytokines are potent immune mediators and play a crucial role in the differentiation and activation of effector CD8 T cells which are critical in anti-tumor responses. Here we tested the ability of IL-2, IL-12, and IL-18 to drive expression of gamma interferon (IFNg) in the absence of intentional antigen stimulation. We show in vitro that spleen cells from both BALB/c and C57BL/6 mice produced large amounts of IFNg and downstream mediators in response to these cytokines individually or synergistically in combination. Moreover, CD8 cells purified from Colon38 tumors can be similarly activated, demonstrating that they are not permanently inactivated or exhausted. These data illustrate innate-like function of CD8 cells, including those in the tumor microenvironment (TME). To address concerns of severe toxicities that can accompany systemic delivery of cytokines, we designed protease-activated cytokine fusion proteins (FPs) which exploit the overexpression of proteases in tumors to release active cytokine in the TME. Using gene transfection techniques, we show that an IL-2FP with a matrix metalloproteinase 2, 9 cleavage sequence can be activated in the TME and reduce tumor growth. In contrast, a FP with a scrambled non-cleavable sequence does not reduce tumor growth, illustrating the specificity of cleavage of the FP in vivo. Additionally, we demonstrate that systemic expression of the IL-2FP elicits little systemic toxicity in striking contrast to the delivery of free IL-2. Collectively, these data support the development of cytokine fusions proteins as a new class of therapeutics to promote anti-tumor effectors with limited detrimental cytokine side effects.

The Adhesion G-Protein-Coupled Receptor, GPR56/ADGRG1, Inhibits Cell-Extracellular Matrix Signaling to Prevent Metastatic Melanoma Growth

Metastatic growth is considered a rate-limiting step in cancer progression, and upregulation of extracellular matrix (ECM) deposition and cell-ECM signaling are major drivers of this process. Mechanisms to reverse ECM upregulation in cancer could potentially facilitate its prevention and treatment but they are poorly understood. We previously reported that the adhesion G-protein-coupled receptor GPR56/ADGRG1 is downregulated in melanoma metastases. Its re-expression inhibited melanoma growth and metastasis and reduced the deposition of fibronectin, a major ECM component. We hypothesize that its effect on fibronectin deposition contributes to its inhibitory role on metastatic growth. To test this, we investigated the function of GPR56 on cell-fibronectin adhesion and its relationship with metastatic growth in melanoma. Our results reveal that GPR56 inhibits melanoma metastatic growth by impeding the expansion of micrometastases to macrometastases. Meanwhile, we present evidence that GPR56 inhibits fibronectin deposition and its downstream signaling, such as phosphorylation of focal adhesion kinase (FAK), during this process. Administration of the FAK inhibitor Y15 perturbed the proliferation of melanoma metastases, supporting a causative link between the cell adhesion defect induced by GPR56 and its inhibition of metastatic growth. Taken together, our results suggest that GPR56 in melanoma metastases inhibits ECM accumulation and adhesion, which contributes to its negative effects on metastatic growth.

Abstract C32: The function of GPR56 in metastasis formation of melanoma

Disseminated cancer cells often persist in tissues for a long period before being manifested as clinically detectable metastases. This metastasis dormancy imposes a main threat for cancer patients, especially after their first line of cancer treatment. Little is known as to how this dormancy is maintained and what triggers its awakening, but tumor microenvironment is thought to play a decisive role. We discovered that a member of newly described family of adhesion G protein-coupled receptors (GPCRs), GPR56, inhibits metastasis formation of melanoma cell lines and sequesters them at a dormant state in lung. GPR56 binds to TG2, a component in extracellular matrix (ECM) that could also function as a cross linking enzyme. It is significantly up-regulated in human melanoma metastases relative to the primary tumors and its expression promotes metastasis formation of melanoma cells in the experimental metastasis model. The down-regulation of TG2 by GPR56 may abolish the pro-metastasis function of TG2 in melanoma cells via destabilizing ECM and contribute to their sequestration at the dormant state. Furthermore, RNAseq analyses suggest that GPR56 may regulate the expression of factors involved in cellular homeostasis. It is thus possible that GPR56 maintains metastasis dormancy in melanoma by down-regulating TG2 in ECM and perturbing cellular homeostasis.

Citation Format: Nancy Corson, Liquan Yang, Lei Xu. The function of GPR56 in metastasis formation of melanoma. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr C32.

Abstract A36: Function of GPR56 in metastasis dormancy of melanoma

Dormancy imposes significant challenges for cancer diagnosis and prognosis. We use pairs of metastatic melanoma cell lines that have different abilities to form metastases to investigate the molecular mechanisms of metastatic dormancy. We found that a novel receptor, GPR56, was down-regulated in highly metastatic melanoma cells compared with the poorly metastatic parental line. Re-expression of GPR56 in five different melanoma cell lines resulted in inhibition of metastasis formation in mouse lung. RNAseq analyses revealed that GPR56 might regulate the expression of genes involved in cellular homeostasis. Furthermore, our preliminary data show that GPR56 internalizes and degrades its ligand, TG2 from cell surface. TG2 is an ECM protein and functions to stabilize ECM and facilitate its signaling. The loss of TG2 resulting from GPR56 expression would disrupt ECM deposition and signaling in melanomas, ultimately leading to disturbance of cellular homeostasis of melanoma cells and their growth arrest. Taken together, we propose a model in which the novel receptor GPR56 sequesters metastatic melanomas at dormant states by down-regulating TG2 from cell surface and modulating cellular homeostasis.

Citation Format: Nancy Corson, Michelle Warren, Lei Xu. Function of GPR56 in metastasis dormancy of melanoma. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A36.

Abstract LB-144: GPR56 internalizes and degrades TG2 in melanoma

Excessive accumulation of extracellular matrix (ECM) is a hallmark of tumor microenvironment and plays active roles during tumor progression. How this process is regulated and whether it is reversible for cancer treatment are outstanding questions. Our earlier study showed that an adhesion G protein-coupled receptor (GPCR), GPR56, inhibits melanoma growth and metastasis and binds to tissue transglutaminase (TG2), a major cross-linking enzyme in ECM. To understand the function of TG2 in GPR56-mediated melanoma inhibition, we generated immunodeficient Tg2-/- mice and performed xenograft transplantation studies in these mice. Our results revealed an antagonistic relationship between GPR56 and TG2 during melanoma growth: whereas TG2 promotes melanoma growth, GPR56 antagonizes this effect via receptor-mediated internalization and degradation. Furthermore, the down-regulation of TG2 by GPR56 is associated with a reduction in the levels of fibronectin and focal adhesion kinase (FAK), suggesting that the fibronectin-mediated cell adhesion is compromised upon GPR56 expression in melanoma. Taken together, our findings provide genetic evidence for the function of TG2 in GPR56-mediated melanoma inhibition. The uncovered antagonistic relationship between GPR56 and TG2 proposes a mechanism by which ECM accumulation/crosslinking may be reversed, and thus might be exploited for cancer control and treatment.

Citation Format: Liquan Yang, Scott Friedland, Nancy Corson, Lei Xu. GPR56 internalizes and degrades TG2 in melanoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-144. doi:10.1158/1538-7445.AM2014-LB-144

ERBB3 is required for metastasis formation of melanoma cells

Melanoma is curable when it is at an early phase but is lethal once it becomes metastatic. The recent development of BRAF(V600E) inhibitors (BIs) showed great promise in treating metastatic melanoma, but resistance developed quickly in the treated patients, and these inhibitors are not effective on melanomas that express wild-type BRAF. Alternative therapeutic strategies for metastatic melanoma are urgently needed. Here we report that ERBB3, a member of the epidermal growth factor receptor family, is required for the formation of lung metastasis from both the BI-sensitive melanoma cell line, MA-2, and the BI-resistant melanoma cell line, 451Lu-R. Further analyses revealed that ERBB3 does not affect the initial seeding of melanoma cells in lung but is required for their further development into overt metastases, indicating that ERBB3 might be essential for the survival of melanoma cells after they reach the lung. Consistent with this, the ERBB3 ligand, NRG1, is highly expressed in mouse lungs and induces ERBB3-depdnent phosphorylation of AKT in both MA-2 and 451Lu-R cells in vitro. These findings suggest that ERBB3 may serve as a target for treating metastatic melanomas that are resistant to BIs. In support of this, administration of the pan-ERBB inhibitor, canertinib, significantly suppresses the metastasis formation of BI-resistant melanoma cell lines.

GPR56 inhibits melanoma growth by internalizing and degrading its ligand TG2

Excessive accumulation of extracellular matrix (ECM) is a hallmark of tumor microenvironment and plays active roles during tumor progression. How this process is regulated and whether it is reversible for cancer treatment are outstanding questions. The adhesion G protein-coupled receptor GPR56 inhibits melanoma growth and binds to tissue transglutaminase (TG2), a major crosslinking enzyme in ECM. To understand the function of TG2 in GPR56-mediated melanoma inhibition, we performed xenograft studies in immunodeficient Tg2(-/-) mice. Our results revealed an antagonistic relationship between GPR56 and TG2 in melanoma, although TG2 and its crosslinking activity promote melanoma growth, GPR56 antagonizes this effect by internalizing and degrading it. The negative regulation of TG2 by GPR56 associates with the decreased deposition of a major ECM protein, fibronectin, and impaired accumulation of focal adhesion kinase, indicating that the GPR56-TG2 interaction regulates ECM deposition and cell-ECM adhesion. Taken together, our findings establish the roles of TG2 in GPR56-mediated melanoma inhibition. The uncovered antagonistic relationship between GPR56 and TG2 proposes a mechanism by which ECM accumulation/crosslinking in tumors may be reversed, and thus could have therapeutic potential for cancer control and treatment.

Extraction and quantification of carbon nanotubes in biological matrices with application to rat lung tissue

Extraction of carbon nanotubes (CNTs) from biological matrices such as rat lung tissue is integral to developing a quantification method for evaluating the environmental and human health exposure and toxicity of CNTs. The ability of various chemical treatment methods, including Solvable (2.5% sodium hydroxide/surfactant mixture), ammonium hydroxide, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, hydrogen peroxide, and proteinase K, to extract CNTs from rat lung tissue was evaluated. CNTs were quantified using programmed thermal analysis (PTA). Two CNTs were used to represent the lower (500 °C) and upper (800 °C) PTA limit of CNT thermal stability. The recovery efficiency of each of the eight chemical reagents evaluated was found to depend on the ability to (1) minimize oxidation of CNTs, (2) remove interfering background carbon from the rat lung tissue, and (3) separate the solid-phase CNTs from the liquid-phase dissolved tissue via centrifugation. A two-step extraction method using Solvable and proteinase K emerged as the optimal approach, enabling a recovery of 98 ± 15% of a 2.9 ± 0.19 μg CNT loading that was spiked into whole rat lungs. Due to its high yield and applicability to low organ burdens of nanomaterials, this extraction method is particularly well suited for in vivo studies to quantify clearance rates and retained CNTs in lungs and other organs.

Abstract 210: GPR56 regulates the turnover of tissue transglutaminase and tumor growth in melanoma

Biochemical and biophysical properties of extracellular matrix (ECM) regulate multiple aspects of cancer cell behavior during tumor progression. The mechanisms of these regulations are not well defined. We previously reported that an atypical G protein-coupled receptor (GPCR), GPR56, inhibited melanoma growth and metastasis and its N-terminus binds to tissue transglutaminase, TG2, a major cross-linking enzyme in ECM. We thus postulated that GPR56 might suppress melanoma progression by influencing ECM properties through its interaction with TG2. To test this, we examined the effects of GPR56 on melanoma growth in the presence or absence of TG2, using the immunodeficient Tg2+/+ or Tg2−/− mice. Our results showed that the crosslinking enzyme, TG2, promoted melanoma growth, but this tumor-promoting effect was antagonized by GPR56. The mechanisms of this antagonism were revealed through a series of immunohistochemical and biochemical analyses. In GPR56-expressing cells, the extracellular TG2 was internalized by GPR56 and subsequently degraded in a lysome-dependent manner, resulting in a down-regulation of TG2 in ECM. This down-regulation of TG2 by GPR56 led to changes in the deposition of TG2 and other matrix proteins in melanomas and a reduction in melanoma growth. Taken together, we present evidence that a surface receptor on melanoma cells, GPR56, regulates the turnover of the crosslinking enzyme, TG2, in the tumor microenvironment, leading to changes in ECM deposition and melanoma progression.

Citation Format: Liquan Yang, Sonali Mohanty, Nancy Corson, Lei Xu. GPR56 regulates the turnover of tissue transglutaminase and tumor growth in melanoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 210. doi:10.1158/1538-7445.AM2013-210

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Assessing the relevance of in vitro studies in nanotoxicology by examining correlations between in vitro and in vivo data

There is an urgent need for in vitro screening assays to evaluate nanoparticle (NP) toxicity. However, the relevance of in vitro assays is still disputable. We administered doses of TiO(2) NPs of different sizes to alveolar epithelial cells in vitro and the same NPs by intratracheal instillation in rats in vivo to examine the correlation between in vitro and in vivo responses. The correlations were based on toxicity rankings of NPs after adopting NP surface area as dose metric, and response per unit surface area as response metric. Sizes of the anatase TiO(2) NPs ranged from 3 to 100 nm. A cell-free assay for measuring reactive oxygen species (ROS) was used, and lactate dehydrogenase (LDH) release, and protein oxidation induction were the in vitro cellular assays using a rat lung Type I epithelial cell line (R3/1) following 24 h incubation. The in vivo endpoint was number of PMNs in bronchoalveolar lavage fluid (BALF) after exposure of rats to the NPs via intratracheal instillation. Slope analyses of the dose response curves shows that the in vivo and in vitro responses were well correlated. We conclude that using the approach of steepest slope analysis offers a superior method to correlate in vitro with in vivo results of NP toxicity and for ranking their toxic potency.

Validation of an LDH assay for assessing nanoparticle toxicity

Studies showed that certain cytotoxicity assays were not suitable for assessing nanoparticle (NP) toxicity. We evaluated a lactate dehydrogenase (LDH) assay for assessing copper (Cu-40, 40nm), silver (Ag-35, 35nm; Ag-40, 40nm), and titanium dioxide (TiO(2)-25, 25nm) NPs by examining their potential to inactivate LDH and interference with β-nicotinamide adenine dinucleotide (NADH), a substrate for the assay. We also performed a dissolution assay for some of the NPs. We found that the copper NPs, because of their high dissolution rate, could interfere with the LDH assay by inactivating LDH. Ag-35 could also inactivate LDH probably because of the carbon matrix used to cage the particles during synthesis. TiO(2)-25 NPs were found to adsorb LDH molecules. In conclusion, NP interference with the LDH assay depends on the type of NPs and the suitability of the assay for assessing NP toxicity should be examined case by case.

A comparative dose-related response of several key pro- and antiinflammatory mediators in the lungs of rats, mice, and hamsters after subchronic inhalation of carbon black

OBJECTIVE

The objective of this study was to investigate mechanisms underlying species specificity in particle-induced lung inflammation.

METHODS

Rats, mice, and hamsters exposed to air, 1, 7, or 50 mg/m3 of carbon black for 13 weeks were killed at 1 day, 3 months, and 11 months after exposure. Bronchoalveolar lavage was performed and characterized for cell number, cell type, reactive oxygen and nitrogen species, and cytokine levels. Ex vivo mutational analysis of inflammatory cells was evaluated by coincubating with lung epithelial cells. Lung tissue was evaluated for gene expression of various antiinflammatory mediators.

RESULTS

There was a dose- and time-related effect with all the parameters. Rats demonstrated greater propensity for generating a proinflammatory response, whereas mice and hamsters demonstrated an increased antiinflammatory response.

CONCLUSIONS

These differences in pro- and antiinflammatory responses may contribute to the apparent species differences in inflammation and tumorigenesis.

The rat ear vein model for investigating in vivo thrombogenicity of ultrafine particles (UFP)

Recent studies in rodents indicate that intravenous or intratracheal administration of ultrafine particles (UFP) increases thrombogenesis in a surgically exposed peripheral vein after photodynamic excitation of intravenously injected rose bengal (RB). We sought to adapt the invasive peripheral vein RB model to a noninvasive monitoring of ear veins under an inverted microscope. Animals received one of the following: an intraperitoneal, intravenous bolus, or intravenously infused dose of RB. An ear vein was illuminated by a green laser, and formation of a thrombus was captured with a digital camera. Only continuous intravenous infusion produced a steady-state RB plasma level and reproducible thrombus responses in different ear veins of the same rat. This system was then used to study the thrombogenic effects of iv-administered positively or negatively charged 60-nm ultrafine polystyrene particles (PSP). Significant dose-dependent enhancement of thrombus formation was found, as indicated by decreased laser illumination time to 33% of baseline values at 0.5 mg/kg. Negatively charged PSP of the same size failed to affect thrombus formation. We also studied the thrombogenic effect of PSP without the use of RB. The findings were the same as with RB, although the illumination time had to be increased. When 0.5 mg/kg was instilled intratracheally, the laser illumination time to form a thrombus was decreased to 42% of the baseline value, suggesting translocation of UFP into the bloodstream. These results are consistent with previous findings using the invasive model, and they validate the use of this non-invasive ear vein model to evaluate thrombogenic effects of UFP deposition in the respiratory tract.

Pulmonary effects induced by ultrafine PTFE particles

PTFE (polytetrafluoroethylene) fumes consisting of large numbers of ultrafine (uf) particles and low concentrations of gas-phase compounds can cause severe acute lung injury. Our studies were designed to test three hypotheses: (i) uf PTFE fume particles are causally involved in the induction of acute lung injury, (ii) uf PTFE elicit greater pulmonary effects than larger sized PTFE accumulation mode particles, and (iii) preexposure to the uf PTFE fume particles will induce tolerance. We used uf Teflon (PTFE) fumes (count median particle size approximately 16 nm) generated by heating PTFE in a tube furnace to 486 degrees C to evaluate principles of ultrafine particle toxicity. Teflon fumes at ultrafine particle concentrations of 50 microg/m(3) were extremely toxic to rats when inhaled for only 15 min. We found that when generated in argon, the ultrafine Teflon particles alone are not toxic at these exposure conditions; neither were Teflon fume gas-phase constituents when generated in air. Only the combination of both phases when generated in air caused high toxicity, suggesting either the existence of radicals on the surface or a carrier mechanism of the ultrafine particles for adsorbed gas compounds. Aging of the fresh Teflon fumes for 3.5 min led to a predicted coagulation to >100 nm particles which no longer caused toxicity in exposed animals. This result is consistent with a greater toxicity of ultrafine particles compared to accumulation mode particles, although changes in particle surface chemistry during the aging process may have contributed to the diminished toxicity. Furthermore, the pulmonary toxicity of the ultrafine Teflon fumes could be prevented by adapting the animals with short 5-min exposures on 3 days prior to a 15-min exposure. Messages encoding antioxidants and chemokines were increased substantially in nonadapted animals, yet were unaltered in adapted animals. This study shows the importance of preexposure history for the susceptibility to acute ultrafine particle effects.