GPR91 deficiency exacerbates allergic contact dermatitis while reducing arthritic disease in mice

Background

Succinate, in addition to its role as an intermediary of the citric acid cycle, acts as an alarmin, initiating and propagating danger signals resulting from tissue injury or inflammatory stimuli. The contribution of this immune sensing pathway to the development of allergic and inflammatory responses is unknown.

Methods

Ear thickness of wild‐type (wt) and Sucnr1‐deficient (Sucnr1^−/−) mice, sensitized and challenged with oxazolone, was used as a criterion to assess the relevance of SUCNR1/GPR91 expression mediating allergic contact dermatitis (ACD). Results obtained in this system were contrasted with data generated using passive cutaneous anaphylaxis, ovalbumin‐induced asthma and arthritis models.

Results

We found augmented ACD reactions in Sucnr1^−/− mice. This observation correlated with increased mast cell activation in vitro and in vivo. However, exacerbated mast cell activation in Sucnr1^−/− mice did not contribute to the enhancement of asthma or arthritis and seemed to be due to alterations during mast cell development as augmented mast cell responses could be recapitulated in wt mast cells differentiated in the absence of succinate.

Conclusions

A deficiency in succinate sensing during mast cell development confers these cells with a hyperactive phenotype. Such a phenomenon does not translate into exacerbation of asthma or mast cell‐dependent arthritis. On the contrary, the fact that Sucnr1^−/− mice developed reduced arthritic disease, using two different in vivo models, indicates that GPR91 antagonists may have therapeutic potential for the treatment of allergic and autoimmune diseases.

Biological Evidence for Dual Antiangiogenic – Antiaromatase Activity of the VEGF-R Inhibitor PTK787/ZK222584

Background: Targeting the Vascular Endothelial Growth Factor (VEGF) and Estrogen Receptor (ER) signaling pathways concomitantly may provide enhanced therapeutic benefit in ER positive breast cancer. We have previously shown the VEGFR tyrosine kinase inhibitor, PTK787/ZK222584 (PTK/ZK) is a competitive aromatase inhibitor in vitro (Banerjee et al Cancer Res 2009 69: 4716-4723). Here we investigated whether (1) PTK/ZK shows both anti-angiogenic and aromatase inhibitory properties in in vivo models of ER positive breast cancer and (2) the combination of PTK/ZK and letrozole (LET) is superior to letrozole alone.Methods: Human breast cancer cell lines were engineered to express aromatase. Both MCF7 AROM1 (ER+HER2-) and BT474 AROM3 (ER+, HER2+) cells were grown as subcutaneous xenografts with androstenedione support in ovariectomized, nude mice. Mice bearing MCF7 AROM1 or BT474 AROM3 tumors were randomised to receive daily, by oral gavage, concentrations of vehicle, PTK/ZK (25, 50, or 100mg/kg), letrozole (1 mg/kg) or PTK/ZK (50mg/kg) in combination with letrozole (1 mg/kg) for 28 days. Mice were injected with FITC-lectin prior to sacrifice at weekly intervals. Tumor sections were stained for Ki67, apoptosis (TUNEL), CD31 and PgR. Mice bearing BT474 AROM3 xenografts were also treated twice daily with either vehicle or 50 mg/kg PTK/ZK for 3 days and uteri were then weighed and TFF1 and mRNA expression determined.Results: In MCF7 AROM1 xenografts, the daily growth rate was significantly reduced in all treatment groups compared to vehicle (p<0.05). Whilst letrozole caused tumor regression and PTK/ZK at 50 mg/kg and 100 mg/kg stabilized tumor volumes, there was no significant differences between the tumor volumes observed in the 50 mg/kg PTK/ZK and letrozole groups (p=0.14) or letrozole and combination group (p=0.14). The cell turnover index (CTI), a composite measurement of both proliferation and apoptosis significantly decreased (>50%) after 1 week with all treatments (p<0.05) except for 25 mg/kg PTK/ZK compared to the vehicle group The addition of PTK/ZK to letrozole did not lower the CTI further compared to letrozole alone. The vessel density was significantly reduced in the PTK/ZK (50 mg/kg and 100mg/kg) and combination groups compared to the vehicle group from as early as day 7 (p<0.05). However, in the letrozole group, there was no significant reduction in the vessel number until day 28 (p<0.05). PTK/ZK also significantly decreased the growth rate and vessel number compared to the vehicle (p<0.05) in BT474 AROM3 xenografts. PTK/ZK decreased PgR protein expression (p<0.01), TFF1 expression (p=0.002) and uterine weight (p=0.02) suggesting that PTK/ZK decreases E2 signaling in vivo.Conclusions: The VEGF-R inhibitor PTK/ZK showed effects on E2-dependent gene expression consistent with aromatase inhibition as well as anti-angiogenesis in xenograft models of breast cancer. Letrozole alone showed highly effective antitumor activity and the combination of PTK/ZK with letrozole was not superior. Nonetheless these results provide further support for a potential therapeutic approach of dual inhibition of VEGF and E2 signaling using a single agent.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5139.

Beta1-class integrins regulate the development of laminae and folia in the cerebral and cerebellar cortex

Mice that lack all beta1-class integrins in neurons and glia die prematurely after birth with severe brain malformations. Cortical hemispheres and cerebellar folia fuse, and cortical laminae are perturbed. These defects result from disorganization of the cortical marginal zone, where beta1-class integrins regulate glial endfeet anchorage, meningeal basement membrane remodeling, and formation of the Cajal-Retzius cell layer. Surprisingly, beta1-class integrins are not essential for neuron-glia interactions and neuronal migration during corticogenesis. The phenotype of the beta1-deficient mice resembles pathological changes observed in human cortical dysplasias, suggesting that defective integrin-mediated signal transduction contributes to the development of some of these diseases.

Mechanisms that regulate mechanosensory hair cell differentiation

Hair cells of the vertebrate inner ear are mechanosensors that detect sound, gravity and acceleration. They have a specialized cytoskeleton optimized for the transmission of mechanical force. Hair cell defects are a major cause of deafness. The cloning of disease genes and studies of model organisms have provided insights into the mechanisms that regulate the differentiation of hair cells and their cytoskeleton. The studies have also provided new insights into the function of receptors such as integrins and protocadherins, and cytoplasmic proteins such as Rho-type GTPases and unconventional myosins, in organizing the actin cytoskeleton.

Regulation of epidermal homeostasis through P2Y2 receptors

1. Previous studies have indicated a role for extracellular ATP in the regulation of epidermal homeostasis. Here we have investigated the expression of P2Y2 receptors by human keratinocytes, the cells which comprise the epidermis. 2. Reverse transcriptase-polymerase chain reaction (RT - PCR) revealed expression of mRNA for the G-protein-coupled, P2Y2 receptor in primary cultured human keratinocytes. 3. In situ hybridization studies of skin sections revealed that P2Y2 receptor transcripts were expressed in the native tissue. These studies demonstrated a striking pattern of localization of P2Y2 receptor transcripts to the basal layer of the epidermis, the site of cell proliferation. 4. Increases in intracellular free Ca2+ concentration ([Ca2+]i) in keratinocytes stimulated with ATP or UTP demonstrated the presence of functional P2Y receptors. 5. In proliferation studies based on the incorporation of bromodeoxyuridine (BrdU), ATP, UTP and ATPgammaS were found to stimulate the proliferation of keratinocytes. 6. Using a real-time firefly luciferase and luciferin assay we have shown that under static conditions cultured human keratinocytes release ATP. 7. These findings indicate that P2Y2 receptors play a major role in epidermal homeostasis, and may provide novel targets for therapy of proliferative disorders of the epidermis, including psoriasis.

P2Y2 receptors are expressed by human osteoclasts of giant cell tumor but do not mediate ATP-induced bone resorption

Extracellular nucleotides acting through P2 receptors elicit a range of responses in many cell types. Previously, we have cloned the G-protein coupled P2Y2 receptor from a human osteoclastoma complementary deoxyribonucleic acid (cDNA) library and demonstrated its expression by reverse transcription linked (RT)-PCR and Southern analysis in a number of skeletal tissues, including a purified population of giant cells. In this study we have localized the expression of P2Y2 receptor transcripts to osteoclasts of giant cell tumor of bone by in situ hybridization. In osteoblasts and other cell types, the P2Y2 receptor is coupled to Ins(1,4,5)P3-mediated Ca2+ release from intracellular stores. In this study, the P2Y2 receptor agonists adenosine triphosphate (ATP) and uridine triphosphate (UTP) did not increase cytosolic free calcium concentration ([Ca2+]i) in giant cells isolated from osteoclastoma, while the G-protein coupled calcium sensing receptor agonist, Ni2+, elevated [Ca2+]i in the same cells. These data indicate that P2Y2 receptor transcripts expressed by giant cells are not presented at the surface of cells as functional receptors, or alternatively, functional receptors are coupled to an effector other than [Ca2+]i. ATPgammaS (10 micromol/L), but not UTP (10 micromol/L), significantly stimulated resorption by an enriched giant cell population. These results indicate that ATP-induced effects on resorption, following direct osteoclastic activation, are mediated by a P2 receptor other than the P2Y2 subtype. Nucleotides, released locally in the bone microenvironment in response to acute trauma or transient physical stress, will interact with a complement of P2 receptors expressed by both osteoclasts and osteoblasts to influence the remodeling process.

Localization of cathepsin K in human osteoclasts by in situ hybridization and immunohistochemistry

We have recently cloned cathepsin K from a human bone cDNA library. Since cathepsins are proposed to be involved in the degradation of mineralized bone matrix, we have investigated, by in situ hybridization and immunocytochemistry, the expression of the cathepsin K mRNA transcripts and protein in sections of bone and giant cell tumor to determine which cells express this enzyme. Within all tissues studied, cathepsin K was highly expressed in osteoclasts. Furthermore, the expression of cathepsin K mRNA in giant cell tumor tissue appeared to be confined to the periphery of the osteoclast indicating a compartmentalization of the mRNA. Immunohistochemistry confirmed the specific localization of cathepsin K to the osteoclast. In actively resorbing osteoclasts, the immunostaining was localized at the ruffled border, whereas in osteoclasts in sections of giant cell tumor, staining was observed in lysosomal vacuoles, which in some cases were seen to fuse with the cell membrane. Other cells within the bone, such as osteoblasts and osteocytes, did not express either the cathepsin K transcript or protein. However, there were very low levels of cathepsin K detected in a population of mononuclear cells, possibly representing osteoclast progenitor cells, within the marrow/stromal layer. The specific localization of cathepsin K within osteoclasts would therefore indicate the potential role of this enzyme in the bone resorptive process.