Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases: Workshop Proceedings

The Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases workshop was a 1.5-day scientific conference at the National Institutes of Health (Bethesda, MD) that engaged clinical and basic science investigators interested in diseases of the pancreas. This report provides a summary of the proceedings from the workshop. The goals of the workshop were to forge connections and identify gaps in knowledge that could guide future research directions. Presentations were segregated into six major theme areas, including 1) pancreas anatomy and physiology, 2) diabetes in the setting of exocrine disease, 3) metabolic influences on the exocrine pancreas, 4) genetic drivers of pancreatic diseases, 5) tools for integrated pancreatic analysis, and 6) implications of exocrine-endocrine cross talk. For each theme, multiple presentations were followed by panel discussions on specific topics relevant to each area of research; these are summarized here. Significantly, the discussions resulted in the identification of research gaps and opportunities for the field to address. In general, it was concluded that as a pancreas research community, we must more thoughtfully integrate our current knowledge of normal physiology as well as the disease mechanisms that underlie endocrine and exocrine disorders so that there is a better understanding of the interplay between these compartments.

Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases: Workshop Proceedings

ABSTRACT

The "Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases" Workshop was a 1.5-day scientific conference at the National Institutes of Health (Bethesda, MD) that engaged clinical and basic science investigators interested in diseases of the pancreas. This report summarizes the workshop proceedings. The goal of the workshop was to forge connections and identify gaps in knowledge that could guide future research directions. Presentations were segregated into 6 major themes, including (a) Pancreas Anatomy and Physiology; (b) Diabetes in the Setting of Exocrine Disease; (c) Metabolic Influences on the Exocrine Pancreas; (d) Genetic Drivers of Pancreatic Diseases; (e) Tools for Integrated Pancreatic Analysis; and (f) Implications of Exocrine-Endocrine Crosstalk. For each theme, there were multiple presentations followed by panel discussions on specific topics relevant to each area of research; these are summarized herein. Significantly, the discussions resulted in the identification of research gaps and opportunities for the field to address. In general, it was concluded that as a pancreas research community, we must more thoughtfully integrate our current knowledge of the normal physiology as well as the disease mechanisms that underlie endocrine and exocrine disorders so that there is a better understanding of the interplay between these compartments.

768 Systemic delivery of a tumor-targeted TLR9 agonist conjugate transforms the tumor immune landscape and induces tumor regression in mice

Background

Tumor-localized delivery of Toll-like receptor (TLR) agonists is a promising strategy to promote immune activation within the tumor microenvironment (TME) to overcome tumor immunosuppression and induce anti-tumor immune responses. To enable localization to multiple tumor sites following systemic administration, we developed a fully-synthetic tumor-targeting TLR9 agonist and demonstrate its potential to transform the tumor immune microenvironment for effective tumor regression in mice.

Methods

An engineered synthetic peptide (PIP) that binds to multiple integrin receptors overexpressed in many solid tumors was chemically conjugated to a synthetic CpG oligonucleotide (TLR9 agonist), thereby generating a tumor-targeting immune-stimulant referred to as PIP-CpG. To facilitate clinical translation, PIP-CpG is cross-reactive between mouse, non-human primate, and human. Therapeutic studies were conducted in immune-competent mice bearing breast or pancreatic tumors to evaluate the efficacy of intravenously (IV)-injected PIP-CpG compared to IV-injected unmodified CpG or vehicle (PBS). We then performed mechanistic studies to evaluate the immune response elicited by PIP-CpG therapy.

Results

Intravenous dosing of PIP-CpG led to tumor regression and prolonged survival, and in some cases cures, relative to vehicle or unmodified CpG therapy in both murine breast (4T1) and pancreatic cancer (KPC-G2) models. This tumor regression was dependent on T cells as T cell depletion resulted in loss of therapeutic response. To study the effect of systemic therapy on the cellular landscape in the TME, we analyzed 4T1 breast tumors by flow cytometry. We found that vehicle and CpG IV-dosed mice had immunosuppressive TMEs comprised mostly of myeloid-derived suppressor cells (MDSCs; 43–68% of live cells) with minimal infiltrating T cells and B cells (5–16% of live cells). In contrast, the TME of PIP-CpG treated mice was transformed into a lymphocyte-rich “hot” tumor phenotype with massive infiltration by T cells and B cells (92–95% of live cells) and plummeting levels of MDSCs (down to ~1%). In addition, tumor-specific effector CD8+ T cells were generated in response to PIP-CpG therapy, but not CpG dosed IV, indicating that PIP-CpG therapy transforms the TME and elicits a T cell-mediated tumor-specific immune response. Furthermore, PIP-CpG was effective for treating MMTV-PyMT transgenic mice, which spontaneously develop multiple breast tumors. Murine toxicity studies indicated that effects of PIP-CpG were similar to CpG dosed IV or intratumorally, which have been well-tolerated in human clinical trials.

Conclusions

Tumor-directed systemic delivery of a TLR9 agonist transforms the TME via activated B and T cells and is promising for further development in patients with solid tumors.

Ethics Approval

All mouse experiments were performed in accordance with protocols approved by the Stanford Administrative Panel on Laboratory Animal Care.

Tissue-specific telomere shortening and degenerative changes in a patient with TINF2 mutation and dyskeratosis congenita

Dyskeratosis congenita is a disease of impaired tissue maintenance downstream of telomere dysfunction. Characteristically, patients present with the clinical triad of nail dystrophy, oral leukoplakia, and skin pigmentation defects, but the disease involves degenerative changes in multiple organs. Mutations in telomere-binding proteins such as TINF2 (TRF1-interacting nuclear factor 2) or in telomerase, the enzyme that counteracts age related telomere shortening, are causative in dyskeratosis congenita. We present a patient who presented with severe hypoxemia at age 13. The patient had a history of myelodysplastic syndrome treated with bone marrow transplant at the age of 5. At age 18 she was hospitalized for an acute pneumonia progressing to respiratory failure, developed renal failure and ultimately, she and her family opted to withdraw support as she was not a candidate for a lung transplant. Sequencing of the patient's TINF2 locus revealed a heterozygous mutation (c.844C > T, Arg282Cys) which has previously been reported in a subset of dyskeratosis congenita patients. Tissue sections from multiple organs showed degenerative changes including disorganized bone remodeling, diffuse alveolar damage and small vessel proliferation in the lung, and hyperkeratosis with hyperpigmentation of the skin. Autopsy samples revealed a bimodal distribution of telomere length, with telomeres from donor hematopoietic tissues being an age-appropriate length and those from patient tissues showing pathogenic shortening, with the shortest telomeres in lung, liver, and kidney. We report for the first time a survey of degenerative changes and telomere lengths in multiple organs in a patient with dyskeratosis congenita.

Dual SMAD Signaling Inhibition Enables Long-Term Expansion of Diverse Epithelial Basal Cells

Functional modeling of many adult epithelia is limited by the difficulty in maintaining relevant stem cell populations in culture. Here, we show that dual inhibition of SMAD signaling pathways enables robust expansion of primary epithelial basal cell populations. We find that TGFβ/BMP/SMAD pathway signaling is strongly activated in luminal and suprabasal cells of several epithelia, but suppressed in p63+ basal cells. In airway epithelium, SMAD signaling promotes differentiation, and its inhibition leads to stem cell hyperplasia. Using dual SMAD signaling inhibition in a feeder-free culture system, we have been able to expand airway basal stem cells from multiple species. Expanded cells can produce functional airway epithelium physiologically responsive to clinically relevant drugs, such as CFTR modulators. This approach is effective for the clonal expansion of single human cells and for basal cell populations from epithelial tissues from all three germ layers and therefore may be broadly applicable for modeling of epithelia.

Stem cell aging and aberrant differentiation within the niche

Stem cells age, but the underlying mechanisms remain unclear. In a recent issue of Cell, Inomata and colleagues (2009) show that DNA damage, a prime suspect in stem cell aging, causes graying and loss of melanocyte stem cells by inducing premature differentiation, without inducing apoptosis or senescence.

YY1 and c-Myc associate in vivo in a manner that depends on c-Myc levels

The c-Myc oncoprotein has previously been shown to associate with transcription regulator YY1 and to inhibit its activity. We show herein that endogenous c-Myc and YY1 associate in vivo and that changes in c-Myc levels, which accompany mitogenic stimulation or differentiation of cultured cells, affect the ratio of free to c-Myc-associated YY1. We have also investigated the mechanism by which association with c-Myc inhibits YY1's ability to regulate transcription. c-Myc does not block binding of YY1 to DNA. However, protein association studies suggest that c-Myc interferes with the ability of YY1 to contact basal transcription proteins TATA-binding protein and TFIIB.

Ig/EBP (C/EBP gamma) is a transdominant negative inhibitor of C/EBP family transcriptional activators

Analysis of cDNA and genomic clones shows that the murine Ig/EBP (C/EBP gamma) gene encodes a small protein with a predicted molecular weight of 16.4 kDa which contains C/EBP family basic and leucine zipper domains but lacks the transcriptional activation domains present in C/EBP (C/EBP alpha) and NF-IL6 (C/EBP beta). In transfection assays Ig/EBP is neither an activator nor a repressor of transcription; however, Ig/EBP inhibits the transcriptional ability of NF-IL6 (C/EBP beta) and C/EBP (C/EBP alpha), acting as a transdominant negative regulator. Thus Ig/EBP resembles LIP, another negative regulator of the C/EBP family, in both structure and transcriptional activity. Of the three known C/EBP family inhibitors, Ig/EBP, LIP and CHOP-10, only Ig/EBP is ubiquitously expressed. Therefore, Ig/EBP may act as a general buffer for C/EBP activators in many cell types.

Polyamines alter sequence-specific DNA-protein interactions

The polyamines are abundant biogenic cations implicated in many biological processes. Despite a plethora of evidence on polyamine-induced DNA conformational changes, no thorough study of their effects on the activities of sequence-specific DNA binding proteins has been performed. We describe the in vitro effects of polyamines on the activities of purified, representative DNA-binding proteins, and on complex protein mixtures. Polyamines at physiological concentrations enhance the binding of several proteins to DNA (e.g. USF, TFE3, Ig/EBP, NF-IL6, YY1 and ICP-4, a herpes simplex virus gene regulator), but inhibit others (e.g. Oct-1). The degree of enhancement correlates with cationic charge; divalent putrescine is ineffective whereas tetravalent spermine is more potent than trivalent spermidine. Polyamine effects on USF and ICP-4 result from increased rate of complex formation rather than a decreased rate of dissociation. DNAse I footprint analysis indicated that polyamines do not alter DNA-protein contacts. Polyamines also facilitate formation of complexes involving binding of more than one protein on a DNA fragment.

Inhibition of transcriptional regulator Yin-Yang-1 by association with c-Myc

Yin-Yang-1 (YY1) regulates the transcription of many genes, including the oncogenes c-fos and c-myc. Depending on the context, YY1 acts as a transcriptional repressor, a transcriptional activator, or a transcriptional initiator. The yeast two-hybrid system was used to screen a human complementary DNA (cDNA) library for proteins that associate with YY1, and a c-myc cDNA was isolated. Affinity chromatography confirmed that YY1 associates with c-Myc but not with Max. In cotransfections, c-Myc inhibits both the repressor and the activator functions of YY1, which suggests that one way c-Myc acts is by modulating the activity of YY1.

mTFE3, an X-linked transcriptional activator containing basic helix-loop-helix and zipper domains, utilizes the zipper to stabilize both DNA binding and multimerization

Southwestern (DNA-protein) screening of a murine L-cell cDNA library by using a probe for the microE3 site in the immunoglobulin heavy-chain enhancer yielded a clone, mTFE3, which is a member of the subset of basic helix-loop-helix (BHLH) proteins that also contain a leucine zipper (ZIP). Since the individual contribution of these domains is not well understood for proteins which contain them both, mutational analyses were performed to assess the functional roles of the HLH and ZIP regions for DNA binding and multimerization. The HLH region is stringently required for DNA binding but not for multimerization. The ZIP region is not stringently required for binding or multimerization, but stabilizes both multimer formation and DNA binding. A high degree of conservation at both the amino acid and nucleotide levels between the human transcription factor TFE3 and mTFE3 suggests that mTFE3 is the murine homolog of human TFE3. By using fluorescent in situ hybridization, mTFE3 was mapped to mouse chromosome X in band A2, which is just below the centromere. We show that in addition to the immunoglobulin heavy-chain microE3 site, mTFE3 binds to transcriptional elements important for lymphoid-specific, muscle-specific, and ubiquitously expressed genes. Binding of mTFE3 to DNA induces DNA bending.

On-line information systems in perspective

The rationale supporting the desirability of on-line information systems and the arguments underlying their development are discussed. A major argument in favor of on-line retrieval has been the assumption that the opportunity to negotiate search problems through on-line access to the data base has the inherent effect of improved system performance. The extent to which on-line retrieval has fulfilled this and other expectations is considered along with trends relating to the operational characteristics of existing systems.