Abstract 4398: Liver is a major primary target for the Toll-like receptor-5 agonist CBLB502 providing radioprotective, antimicrobial and antitumor responses

We have previously shown that activation of Toll-like receptor 5 (TLR5) by bacterial flagellin and by pharmacologically optimized flagellin derivative CBLB502 protects mice and monkeys from lethal radiation injury to the hematopoietic and gastrointestinal systems. Here, we report that the liver is a major primary CBLB502 target organ in mice, with hepatocytes specifically showing rapid and strong NF-kB and STAT3 activation. Livers from CBLB502-treated mice showed up-regulation of numerous downstream genes encoding intracellular and secreted proteins with anti-apoptotic, anti-microbial and immunomodulatory activities. Unlike the TLR4 agonist LPS, the liver response to TLR5 agonists appears to be direct and does not involve high levels of proinflammatory cytokines. Thus, while LPS is toxic, TLR5 agonists have strong clinical potential. The importance of liver for CBLB502 radioprotective activity was confirmed by temporary occlusion of liver blood circulation which completely abrogated the protective effect of CBLB502 on hematopoietic precursor cells in irradiated mice. CBLB502 also protected liver tissue itself, increasing mouse resistance to lethal Salmonella tiphymurium liver infection and to hepatotoxic Fas agonistic antibodies. By testing CBLB502 in combination with radiation treatment of experimental mouse tumors in vivo, we demonstrated that its tissue protection properties are limited to normal tissues with no tumor protection detected in any of numerous mouse tumor models. Moreover, direct antitumor effects of CBLB502 treatment was observed in several tumor models. Comparison of the effect of CBLB502 on in vivo growth of isogenic pairs of tumor cell lines differing in their TLR5 status showed that the antitumor effect of the TLR5 agonist is TLR5 dependent and is associated with tumor infiltration by immunocytes, presumably attracted following activation of TLR5 signaling in the tumor cells. Remarkably, CBLB502 caused an immunotherapeutic effect in TLR5-negative tumors (CT26 colon adenocarcinoma and A20 lymphoma) growing as experimental liver metastases. Based on these results, we project clinical applications of CBLB502 as an anticancer immunotherapeutic drug against liver metastases independently on TLR5 status and TLR5-expressing tumors in other locations as well as supporting care drug to reduce adverse hepatotoxicity from radiation and chemotherapy.

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 4398. doi:1538-7445.AM2012-4398

Abstract A63: TLR5 agonist CBLB502 protects mice from Fas-mediated liver damage without protecting tumors

We have previously shown the strong radioprotective properties of the Toll-like receptor 5 (TLR5) agonist flagellin and its derivative CBLB502 in both mouse and non-human primate models (Burdelya et al., 2008, Science 320: 226–230). Because no protection has been observed in any in vitro cell model regardless of the TLR5 status of the cells, we hypothesized that the radioprotective effects of the TLR5 agonist are indirect and mediated by factors produced by primary cells responding to flagellin in the organism. Using a combination of tools, including NF-kB-responsive reporter mice and immunohistochemical determination of tissues responding to CBLB502 by NF-kB activation, we defined liver hepatocytes as the primary pharmacological targets of flagellin. Surgical exclusion of the liver from the blood circulation completely abolished radioprotection of the bone marrow hematopoietic progenitor cells by CBLB502 suggesting that the liver acts as a mediator of at least some of the effects of the TLR5 agonist. Since the induction of NF-kB is known to activate multiple pro-survival mechanisms, we further hypothesized that administration of the TLR5 agonist can result in liver resistance to otherwise toxic conditions. Mice treated with Fas agonistic antibodies were employed as a model of acute hepatotoxicity. Injection of CBLB502 showed a strong preventive effect against Fas-mediated injury rescuing all of the injected mice in contrast to complete lethality in the control groups. The ability of CBLB502 to protect the liver was also demonstrated via reduced levels of liver enzymes in the peripheral blood and caspase activation in liver extracts of mice treated with Fas agonistic antibodies. Using two syngeneic tumor models, colon adenocarcinoma CT26 and lymphoma A20, growing as liver metastases in mice, we found that CBLB502 injections not only prevented liver damage, but also suppressed tumor appearance and growth when injected with or without anti-Fas antibodies. Thus, TLR5 agonist has potential to become a new agent for liver protection and suppression of liver metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A63.

Neural potential of a stem cell population in the hair follicle

The bulge region of the hair follicle serves as a repository for epithelial stem cells that can regenerate the follicle in each hair growth cycle and contribute to epidermis regeneration upon injury. Here we describe a population of multipotential stem cells in the hair follicle bulge region; these cells can be identified by fluorescence in transgenic nestin-GFP mice. The morphological features of these cells suggest that they maintain close associations with each other and with the surrounding niche. Upon explantation, these cells can give rise to neurosphere-like structures in vitro. When these cells are permitted to differentiate, they produce several cell types, including cells with neuronal, astrocytic, oligodendrocytic, smooth muscle, adipocytic, and other phenotypes. Furthermore, upon implantation into the developing nervous system of chick, these cells generate neuronal cells in vivo. We used transcriptional profiling to assess the relationship between these cells and embryonic and postnatal neural stem cells and to compare them with other stem cell populations of the bulge. Our results show that nestin-expressing cells in the bulge region of the hair follicle have stem cell-like properties, are multipotent, and can effectively generate cells of neural lineage in vitro and in vivo.

Identification of a Wnt/Dvl/beta-Catenin --> Pitx2 pathway mediating cell-type-specific proliferation during development

Understanding the cell type-specific molecular mechanisms by which distinct signaling pathways combinatorially control proliferation during organogenesis is a central issue in development and disease. Here, we report that the bicoid-related transcription factor Pitx2 is rapidly induced by the Wnt/Dvl/beta-catenin pathway and is required for effective cell-type-specific proliferation by directly activating specific growth-regulating genes. Regulated exchange of HDAC1/beta-catenin converts Pitx2 from repressor to activator, analogous to control of TCF/LEF1. Pitx2 then serves as a competence factor required for the temporally ordered and growth factor-dependent recruitment of a series of specific coactivator complexes that prove necessary for Cyclin D2 gene induction. The molecular strategy underlying interactions between the Wnt and growth factor-dependent signaling pathways in cardiac outflow tract and pituitary proliferation is likely to be prototypic of cell-specific proliferation strategies in other tissues.

Tbx19, a tissue-selective regulator of POMC gene expression

Pituitary cell types arise in a temporally and spatially specific fashion, in response to combinatorial actions of transcription factors induced by transient signaling gradients. The critical transcriptional determinants of the two pituitary cell types that express the pro-opiomelanocortin (POMC) gene, the anterior lobe corticotropes, producing adrenocorticotropin, and the intermediate lobe melanotropes, producing melanocyte-stimulating hormone (MSH alpha), have remained unknown. Here, we report that a member of the T-box gene family, Tbx19, which is expressed only in the rostral ventral diencephalon and pituitary gland, commencing on e11.5, marks pituitary cells that will subsequently express the POMC gene and is capable of altering progression of ventral cell types and inducing adrenocorticotropin in rostral tip cells. It is suggested that Tbx19, depending on the presence of synergizing transcription factors, can activate POMC gene expression and repress the alpha glycoprotein subunit and thyroid-stimulating hormone beta promoters.

Hedgehog signaling is required for pituitary gland development

Pituitary gland development serves as an excellent model system in which to study the emergence of distinct cell types from a common primordium in mammalian organogenesis. We have investigated the role of the morphogen Sonic hedgehog (SHH) in outgrowth and differentiation of the pituitary gland using loss- and gain-of-function studies in transgenic mice. Shh is expressed throughout the ventral diencephalon and the oral ectoderm, but its expression is subsequently absent from the nascent Rathke's pouch as soon as it becomes morphologically visible, creating a Shh boundary within the oral epithelium. We used oral ectoderm/Rathke's pouch-specific 5′ regulatory sequences (Pitx1(HS)) from the bicoid related pituitary homeobox gene (Pitx1) to target overexpression of the Hedgehog inhibitor Hip (Huntingtin interacting protein) to block Hedgehog signaling, finding that SHH is required for proliferation of the pituitary gland. In addition, we provide evidence that Hedgehog signaling, acting at the Shh boundary within the oral ectoderm, may exert a role in differentiation of ventral cell types (gonadotropes and thyrotropes) by inducing Bmp2 expression in Rathke's pouch, which subsequently regulates expression of ventral transcription factors, particularly Gata2. Furthermore, our data suggest that Hedgehog signaling, together with FGF8/10 signaling, synergizes to regulate expression of the LIM homeobox gene Lhx3, which has been proved to be essential for initial pituitary gland formation. Thus, SHH appears to exert effects on both proliferation and cell-type determination in pituitary gland development.

Regulation of somatic growth by the p160 coactivator p/CIP

A family of p160 coactivators was initially identified based on ligand-dependent interactions with nuclear receptors and thought to function, in part, by recruiting CREB-binding protein/p300 to several classes of transcription factors. One of the p160 factors, p/CIP/AIB1, often amplified and overexpressed in breast cancer, also exhibits particularly strong interaction with CREB-binding protein/p300. In this manuscript, we report that p/CIP, which exhibits regulated transfer from cytoplasm to nucleus, is required for normal somatic growth from embryonic day 13.5 through maturity. Our data suggest that a short stature phenotype of p/CIP gene-deleted mice reflect both altered regulation of insulin-like growth factor-1 (IGF-1) gene expression in specific tissues and a cell-autonomous defect of response to IGF-1, including ineffective transcriptional activities by several classes of regulated transcription factors under specific conditions. The actions of p/CIP are therefore required for full expression of a subset of genes critical for regulating physiological patterns of somatic growth in mammals.

POU domain factors of the Brn-3 class recognize functional DNA elements which are distinctive, symmetrical, and highly conserved in evolution

To better understand the diversity of function within the POU domain class of transcriptional regulators, we have determined the optimal DNA recognition site of several proteins of the POU-IV (Brn-3) subclass by random oligonucleotide selection. The consensus recognition element derived in this study, ATAATTAAT, is clearly distinct from octamer sites described for the POU factor Oct-1. The optimal POU-IV site determined here also binds Brn-3.0 with significantly higher affinity than consensus recognition sites previously proposed for this POU subclass. The binding affinity of Brn-3.0 on its optimal site, several variants of this site, and several naturally occurring POU recognition elements is highly correlated with the activation of reporter gene expression by Brn-3.0 in transfection assays. The preferred DNA recognition site of Brn-3.0 resembles strongly the optimal sites of another mammalian POU-IV class protein, Brn-3.2, and of the Caenorhabditis elegans Brn-3.0 homolog Unc-86, demonstrating that the site-specific DNA recognition properties of these factors are highly conserved between widely divergent species.

Adhesion of mouse hepatocytes to type I collagen: role of supramolecular forms and effect of proteolytic degradation

Mouse hepatocytes were found to adhere much stronger to intact native type I collagen than to native, telopeptide-devoid collagen. Removal of telopeptides (by pepsin treatment) caused disintegration of supramolecular collagen aggregates. Similar differences in hepatocyte adhesion were observed between oligomeric and monomeric collagens separated from intact native preparations. It was concluded that the more active cell binding to intact collagen is due to a higher binding affinity of hepatocytes to supramolecular (oligomeric) forms of type I collagen. Heat denturation did not affect cell adhesion to intact collagen but restored adhesion to telopeptide-devoid substrates. Cell adhesion to denatured collagen was RGD-dependent whereas adhesion to native substrates proved RGD-independent. These data provide the first evidence of the role of supramolecular arrangement and the effect of proteolytic degradation of type I collagen on its adhesive behavior.