Id1 Ablation Protects Hematopoietic Stem Cells from Stress-Induced Exhaustion and Aging

Defining mechanisms that maintain tissue stem cells during homeostasis, stress, and aging is important for improving tissue regeneration and repair and enhancing cancer therapies. Here, we show that Id1 is induced in hematopoietic stem cells (HSCs) by cytokines that promote HSC proliferation and differentiation, suggesting that it functions in stress hematopoiesis. Genetic ablation of Id1 increases HSC self-renewal in serial bone marrow transplantation (BMT) assays, correlating with decreases in HSC proliferation, mitochondrial biogenesis, and reactive oxygen species (ROS) production. Id1-/- HSCs have a quiescent molecular signature and harbor less DNA damage than control HSCs. Cytokines produced in the hematopoietic microenvironment after γ-irradiation induce Id1 expression. Id1-/- HSCs display a blunted proliferative response to such cytokines and other inducers of chronic proliferation including genotoxic and inflammatory stress and aging, protecting them from chronic stress and exhaustion. Thus, targeting Id1 may be therapeutically useful for improving HSC survival and function during BMT, chronic stress, and aging.

Abstract 104: Identification of the molecular components required for the protumorigenic effect of MSLN in pancreatic cancer

Mesothelin (MSLN) is a GPI-linked protein expressed in >90% of pancreatic adenocarcinomas (PDAC) but not in healthy pancreas nor in the parenchyma of other vital organs. Due to this differential expression, multiple antibody-based therapies are targeting MSLN. The physiologic role of MSLN is yet unknown. The MSLN gene encodes for a precursor protein which is cleaved to produce mature MSLN protein and soluble Megakaryocyte Potentiating Factor (MPF), both of which can be secreted or shed. Previous reports suggested that overexpression of MSLN precursor protein increases tumorigenicity and metastatic potential of PDAC. Here, we have used CRISPR-Cas9 gene editing to delete MSLN from the KLM-1 pancreatic cancer cell line (ΔMSLN) and have examined the growth of these cells compared to mock deleted cells (Mock). The ΔMSLN and Mock cells grew at the same rate both in cell culture and as subcutaneous tumors in nude mice, but ΔMSLN had significantly impaired growth when inoculated into the mouse intraperitoneal (IP) cavity as well as when injected orthotopically into the pancreas. Histological analysis (H&E, Ki67 and Trichrome) showed no significant gross differences between ΔMSLN and Mock IP tumors. RNA deep sequencing analysis comparing ΔMSLN and Mock cell lines showed strong upregulation of MUC-4 in KO cells. Restoration of WT MSLN expression in ΔMSLN cells restored IP growth, however, transduction of a Y318A point mutant could not. Point mutation of Y318 diminished ability of shed MSLN to interact with KLM-1 cells, presumably by impairing association with MUC-16, the only known binding partner of MSLN. To determine the role of mature MSLN and MPF in tumorigenicity, we expressed these proteins separately in ΔMSLN cells and found that neither could restore IP growth, although mature MSLN was appropriately expressed on the cell surface and MPF secreted. This suggests either that both proteins are required for tumorigenicity or that when synthesized individually they are incorrectly processed by the cell. To examine the role of MSLN in tumorigenesis, MSLN KO mouse were bred into the KPC genetically engineered mouse model of PDAC, which spontaneously develops autochthonous tumors. Unlike PDAC patients, KPC typically die from complications of their primary tumors. Loss of MSLN had no effect on the survival of these mice. Effect of MSLN loss on metastasis in this model is currently being evaluated. In summary, we have demonstrated that MSLN enhances the IP growth of PDAC and defined key regions of MSLN important for this activity.

Citation Format: Leela Rani Avula, Michael Rudloff, Danielle Arons, Salma El-Behaedi, Xianyu Zhang, Theresa Guerin, Serguei Kozlov, Christine Alewine. Identification of the molecular components required for the protumorigenic effect of MSLN in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 104.

Synergistic targeted inhibition of MEK and dual PI3K/mTOR diminishes viability and inhibits tumor growth of canine melanoma underscoring its utility as a preclinical model for human mucosal melanoma

Human mucosal melanoma (MM), an uncommon, aggressive and diverse subtype, shares characteristics with spontaneous MM in dogs. Although BRAF and N-RAS mutations are uncommon in MM in both species, the majority of human and canine MM evaluated exhibited RAS/ERK and/or PI3K/mTOR signaling pathway activation. Canine MM cell lines, with varying ERK and AKT/mTOR activation levels reflective of naturally occurring differences in dogs, were sensitive to the MEK inhibitor GSK1120212 and dual PI3K/mTOR inhibitor NVP-BEZ235. The two-drug combination synergistically decreased cell survival in association with caspase 3/7 activation, as well as altered expression of cell cycle regulatory proteins and Bcl-2 family proteins. In combination, the two drugs targeted their respective signaling pathways, potentiating reduction of pathway mediators p-ERK, p-AKT, p-S6, and 4E-BP1 in vitro, and in association with significantly inhibited solid tumor growth in MM xenografts in mice. These findings provide evidence of synergistic therapeutic efficacy when simultaneously targeting multiple mediators in melanoma with Ras/ERK and PI3K/mTOR pathway activation.

Abstract A17: p53 missense mutants R172H and R270H exhibit differential effects on tumorigenesis

p53 is a well-characterized transcription factor that is mutated in about 50% of human cancers. The majority of p53 genomic alterations are missense mutations which result in expression of p53 protein isoforms with deficient functionality. Such missense mutations cluster in several hotspots, with the most frequent alterations located at amino acids 175, 248 and 273 of human p53 (mouse amino acids 172, 245 and 270). p53 missense mutants disrupt the function of p53 tetramers, thereby behaving similarly to loss of p53. However, there is evidence that p53 missense mutants have additional tumor-promoting functions that differ from p53 deletions: p53 missense mutants can transform p53 null cells in vitro and in mouse models, and the p53 missense mutants induce a different tumor spectrum from that induced by p53 loss or other p53 missense mutants.

The information obtained from the engineered murine models featuring p53 missense mutations has greatly elucidated the role of p53 mutagenesis in cancer. However, the currently-available p53 models bear several drawbacks that make them sub-optimal for preclinical studies. These models contain a global p53 haploinsufficiency, potentially impacting the biology of tumor-modifying structures like stroma, the immune system, and the vasculature. Furthermore, activation of the p53 missense mutant alleles results in a transition from a single functional wild-type allele to a combination of a wild-type and a mutant allele. These features substantially deviate from those of observed in human tumorigenesis, where somatic p53 mutagenesis in cells undergoing transformation results in a transition from two wild-type alleles to a combination of a wild-type and a mutant alleles, while tumor-modifying structures retain an unaltered p53 biallelic configuration. Here we describe the molecular and phenotypic characterization of a new allelic series of conditional p53 missense mutant mouse lines in which Cre-mediated recombination converts p53 from a wild-type to a missense mutant (R172H, R270H or R270C) configuration.

To characterize the gradual molecular changes induced by expression of R172H and R270H mutants, we derived MEF lines harboring the alleles in a heterozygous conditional (p53-R172H fl/+ or p53-R270H fl/+) configuration. We observed that the wild-type p53 mRNA was lost but p53 protein abundance was increased after Cre-mediated activation of the mutant allele. Interestingly, we found that the R270H mutant allele provided a greater proliferative advantage, a distinct growth pattern and a greater ability to grow in vitro under starvation conditions than a similarly engineered R172H mutant allele. Consistent with published evidence, these observations suggest that the acquired functional changes are dissimilar between different p53 missense mutants. We further characterized the transcriptome profiles in MEF lines harboring R172H and R270H alleles and identified a number of unique and common transcriptional changes that could be causal for gain-of-function phenotypes and informative for uncovering additional mechanisms for carcinogenesis driven by p53 missense mutants.

We used the newly-derived p53 mutant alleles to establish improved autochthonous and orthotopic pancreatic cancer models suitable for preclinical efficacy studies and we are currently developing lung cancer, ovarian cancer, and medullary thyroid carcinoma models.

Citation Format: Tomas Vilimas, Keith Collins, Theresa Guerin, Roackie Awasthi, Lionel Feigenbaum, Guillermina Lozano, Terry Van Dyke, Serguei Kozlov. p53 missense mutants R172H and R270H exhibit differential effects on tumorigenesis. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A17.

Vitamin D receptor-mediated stromal reprogramming suppresses pancreatitis and enhances pancreatic cancer therapy

The poor clinical outcome in pancreatic ductal adenocarcinoma (PDA) is attributed to intrinsic chemoresistance and a growth-permissive tumor microenvironment. Conversion of quiescent to activated pancreatic stellate cells (PSCs) drives the severe stromal reaction that characterizes PDA. Here, we reveal that the vitamin D receptor (VDR) is expressed in stroma from human pancreatic tumors and that treatment with the VDR ligand calcipotriol markedly reduced markers of inflammation and fibrosis in pancreatitis and human tumor stroma. We show that VDR acts as a master transcriptional regulator of PSCs to reprise the quiescent state, resulting in induced stromal remodeling, increased intratumoral gemcitabine, reduced tumor volume, and a 57% increase in survival compared to chemotherapy alone. This work describes a molecular strategy through which transcriptional reprogramming of tumor stroma enables chemotherapeutic response and suggests vitamin D priming as an adjunct in PDA therapy. PAPERFLICK:

Selective inhibition of the T cell p38 alternative activation pathway and pancreatic cancer (TUM3P.1046)

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive neoplasm with a five year survival rate of ~5%, that is characterized by a marked fibro-inflammatory microenvironment, the presence of which can promote cancer induction and growth. Therefore, selective manipulation of local cytokines is an attractive if unrealized therapeutic approach. T cells possess a unique mechanism for activation of p38 MAPK downstream of T cell receptor (TCR) engagement in which it is phosphorylated on Tyr-323 (pY323), which is required for pro-inflammatory cytokine production. Analysis of 192 human pancreatic carcinomas revealed that having a high percentage of infiltrating pY323+ T cells was accompanied by large numbers of TNFa and IL-17-producing CD4+ TIL and very aggressive disease. Cancer progression was inhibited in two different murine pancreatic tumors models by genetic ablation of the alternative p38 activation pathway. Strikingly, a plasma membrane-permeable peptide derived from Gadd45α, the naturally-occurring inhibitor of p38 pY323+, reduced infiltrating CD4+ T cell production of TNFa, IL-17A, IL-10, and induction of secondary cytokines, slowed the growth of implanted tumor cells and inhibited progression of spontaneous K-ras-driven adenocarcinoma. Thus, TCR-mediated alternative p38 activation in tumor-infiltrating CD4+ T cells, which promotes the production of pro-tumorigenic inflammatory factors, can be targeted for therapeutic benefit.

The LINC complex is essential for hearing

Hereditary hearing loss is the most common sensory deficit. We determined that progressive high-frequency hearing loss in 2 families of Iraqi Jewish ancestry was due to homozygosity for the protein truncating mutation SYNE4 c.228delAT. SYNE4, a gene not previously associated with hearing loss, encodes nesprin-4 (NESP4), an outer nuclear membrane (ONM) protein expressed in the hair cells of the inner ear. The truncated NESP4 encoded by the families' mutation did not localize to the ONM. NESP4 and SUN domain-containing protein 1 (SUN1), which localizes to the inner nuclear membrane (INM), are part of the linker of nucleoskeleton and cytoskeleton (LINC) complex in the nuclear envelope. Mice lacking either Nesp4 or Sun1 were evaluated for hair cell defects and hearing loss. In both Nesp4-/- and Sun1-/- mice, OHCs formed normally, but degenerated as hearing matured, leading to progressive hearing loss. The nuclei of OHCs from mutant mice failed to maintain their basal localization, potentially affecting cell motility and hence the response to sound. These results demonstrate that the LINC complex is essential for viability and normal morphology of OHCs and suggest that the position of the nucleus in sensory epithelial cells is critical for maintenance of normal hearing.

Temporal molecular and biological assessment of an erlotinib-resistant lung adenocarcinoma model reveals markers of tumor progression and treatment response

Patients with lung cancer with activating mutations in the EGF receptor (EGFR) kinase, who are treated long-term with tyrosine kinase inhibitors (TKI), often develop secondary mutations in EGFR associated with resistance. Mice engineered to develop lung adenocarcinomas driven by the human EGFR T790M resistance mutation are similarly resistant to the EGFR TKI erlotinib. By tumor volume endpoint analysis, these mouse tumors respond to BIBW 2992 (an irreversible EGFR/HER2 TKI) and rapamycin combination therapy. To correlate EGFR-driven changes in the lung with response to drug treatment, we conducted an integrative analysis of global transcriptome and metabolite profiling compared with quantitative imaging and histopathology at several time points during tumor progression and treatment. Responses to single-drug treatments were temporary, whereas combination therapy elicited a sustained response. During tumor development, metabolomic signatures indicated a shift to high anabolic activity and suppression of antitumor programs with 11 metabolites consistently present in both lung tissue and blood. Combination drug treatment reversed many of the molecular changes found in tumored lung. Data integration linking cancer signaling networks with metabolic activity identified key pathways such as glutamine and glutathione metabolism that signified response to single or dual treatments. Results from combination drug treatment suggest that metabolic transcriptional control through C-MYC and SREBP, as well as ELK1, NRF1, and NRF2, depends on both EGFR and mTORC1 signaling. Our findings establish the importance of kinetic therapeutic studies in preclinical assessment and provide in vivo evidence that TKI-mediated antiproliferative effects also manifest in specific metabolic regulation.

Behavioral and molecular exploration of the AR-CMT2A mouse model Lmna (R298C/R298C)

In 2002, we identified LMNA as the first gene responsible for an autosomal recessive axonal form of Charcot-Marie-Tooth disease, AR-CMT2A. All patients were found to be homozygous for the same mutation in the LMNA gene, p.Arg298Cys. In order to investigate the physiopathological mechanisms underlying AR-CMT2A, we have generated a knock-in mouse model for the Lmna p.Arg298Cys mutation. We have explored these mice through an exhaustive series of behavioral tests and histopathological analyses, but were not able to find any peripheral nerve phenotype, even at 18 months of age. Interestingly at the molecular level, however, we detect a downregulation of the Lmna gene in all tissues tested from the homozygous knock-in mouse Lmna (R298C/R298C) (skeletal muscle, heart, peripheral nerve, spinal cord and cerebral trunk). Importantly, we further reveal a significant upregulation of Pmp22, specifically in the sciatic nerves of Lmna (R298C/R298C) mice. These results indicate that, despite the absence of a perceptible phenotype, abnormalities exist in the peripheral nerves of Lmna (R298C/R298C) mice that are absent from other tissues. Although the mechanisms leading to deregulation of Pmp22 in Lmna (R298C/R298C) mice are still unclear, our results support a relation between Lmna and Pmp22 and constitute a first step toward understanding AR-CMT2A physiopathology.

Functional coupling between the extracellular matrix and nuclear lamina by Wnt signaling in progeria

The segmental premature aging disease Hutchinson-Gilford Progeria (HGPS) is caused by a truncated and farnesylated form of Lamin A. In a mouse model for HGPS, a similar Lamin A variant causes the proliferative arrest and death of postnatal, but not embryonic, fibroblasts. Arrest is due to an inability to produce a functional extracellular matrix (ECM), because growth on normal ECM rescues proliferation. The defects are associated with inhibition of canonical Wnt signaling, due to reduced nuclear localization and transcriptional activity of Lef1, but not Tcf4, in both mouse and human progeric cells. Defective Wnt signaling, affecting ECM synthesis, may be critical to the etiology of HGPS because mice exhibit skeletal defects and apoptosis in major blood vessels proximal to the heart. These results establish a functional link between the nuclear envelope/lamina and the cell surface/ECM and may provide insights into the role of Wnt signaling and the ECM in aging.

Structure of the lamin A/C R482W mutant responsible for dominant familial partial lipodystrophy (FPLD)

Proteins of the A-type lamin family, which consists of two members, lamin A and lamin C, are the major components of a thin proteinaceous filamentous meshwork, the lamina, that underlies the inner nuclear membrane. A-type lamins have recently become the focus of extensive functional studies as a consequence of the linking of at least eight congenital diseases to mutations in the lamin A/C gene (LMNA). This spectrum of pathologies, which mostly manifest themselves as dominant traits, includes muscle dystrophies, dilated cardiomyopathies, the premature aging syndrome Hutchinson-Guilford progeria and familial partial lipodystrophy (FPLD). The crystal structure of the lamin A/C mutant R482W, a variant that causes FPLD, has been determined at 1.5 A resolution. A completely novel aggregation state of the C-terminal globular domain and the position of the mutated amino-acid residue suggest means by which the mutation may affect lamin A/C-protein and protein-DNA interactions.

Loss of nucleoplasmic LAP2alpha-lamin A complexes causes erythroid and epidermal progenitor hyperproliferation

Lamina-associated polypeptide (LAP) 2alpha is a chromatin-associated protein that binds A-type lamins. Mutations in both LAP2alpha and A-type lamins are linked to human diseases called laminopathies, but the molecular mechanisms are poorly understood. The A-type lamin-LAP2alpha complex interacts with and regulates retinoblastoma protein (pRb), but the significance of this interaction in vivo is unknown. Here we address the function of the A-type lamin-LAP2alpha complex with the use of LAP2alpha-deficient mice. We show that LAP2alpha loss causes relocalization of nucleoplasmic A-type lamins to the nuclear envelope and impairs pRb function. This causes inefficient cell-cycle arrest in dense fibroblast cultures and hyperproliferation of epidermal and erythroid progenitor cells in vivo, leading to tissue hyperplasia. Our results support a disease-relevant model in which LAP2alpha defines A-type lamin localization in the nucleoplasm, which in turn affects pRb-mediated regulation of progenitor cell proliferation and differentiation in highly regenerative tissues.

[Forms of LonB protease from Archaeoglobus fulgidus devoid of the transmembrane domain: the contribution of the quaternary structure to the regulation of enzyme proteolytic activity]

Deletion of the transmembrane domain (TM-domain) of Archaeoglobus flggidus LonB protease (AfLon) was shown to result in uncontrollable activation of the enzyme proteolytic site and in vivo autolysis yielding a stable and functionally inactive fragment consisting of both alpha-helical and proteolytic domains (alphaP). The deltaTM-AfLonTM-S590A enzyme form, obtained by site-directed mutagenesis of the catalytic Ser residue, is capable of recombination with the alphaP fragment. The mixed oligomers were shown to be proteolytically active, which indicates a crucial role of subunit interactions in the activation of the AfLon proteolytic site. The thermophilic nature of AfLon protease was found to be due to the special features of the enzyme activity regulation, the structure of ATPase domain, and the quaternary structure.

Mouse models of the laminopathies

The A and B type lamins are nuclear intermediate filament proteins that comprise the bulk of the nuclear lamina, a thin proteinaceous structure underlying the inner nuclear membrane. The A type lamins are encoded by the lamin A gene (LMNA). Mutations in this gene have been linked to at least nine diseases, including the progeroid diseases Hutchinson-Gilford progeria and atypical Werner's syndromes, striated muscle diseases including muscular dystrophies and dilated cardiomyopathies, lipodystrophies affecting adipose tissue deposition, diseases affecting skeletal development, and a peripheral neuropathy. To understand how different diseases arise from different mutations in the same gene, mouse lines carrying some of the same mutations found in the human diseases have been established. We, and others have generated mice with different mutations that result in progeria, muscular dystrophy, and dilated cardiomyopathy. To further our understanding of the functions of the lamins, we also created mice lacking lamin B1, as well as mice expressing only one of the A type lamins. These mouse lines are providing insights into the functions of the lamina and how changes to the lamina affect the mechanical integrity of the nucleus as well as signaling pathways that, when disrupted, may contribute to the disease.

Loss of emerin at the nuclear envelope disrupts the Rb1/E2F and MyoD pathways during muscle regeneration

Emery-Dreifuss muscular dystrophy (EDMD1) is caused by mutations in either the X-linked gene emerin (EMD) or the autosomal lamin A/C (LMNA) gene. Here, we describe the derivation of mice lacking emerin in an attempt to derive a mouse model for EDMD1. Although mice lacking emerin show no overt pathology, muscle regeneration in these mice revealed defects. A bioinformatic array analysis of regenerating Emd null muscle revealed abnormalities in cell-cycle parameters and delayed myogenic differentiation, which were associated with perturbations to transcriptional pathways regulated by the retinoblastoma (Rb1) and MyoD genes. Temporal activation of MyoD transcriptional targets was significantly delayed, whereas targets of the Rb1/E2F transcriptional repressor complex remained inappropriately active. The inappropriate modulation of Rb1/MyoD transcriptional targets was associated with up-regulation of Rb1, MyoD and their co-activators/repressors transcripts, suggesting a compensatory effort to overcome a molecular block to differentiation at the myoblast/myotube transition during regeneration. This compensation appeared to be effective for MyoD transcriptional targets, although was less effective for Rb1 targets. Analysis of Rb1 phosphorylation states showed prolonged hyper-phosphorylation at key developmental stages in Emd null myogenic cells, both in vivo and in vitro. We also analyzed the same pathways in Lmna null muscle, which shows extensive dystrophy. Surprisingly, Lmna null muscle did not show the same perturbations to Rb- and MyoD-dependent pathways. We did observe increased transcriptional expression of Lap2alpha and delayed expression of Rb1, which may regulate alternative transcriptional pathways in the Lmna null myoblasts. We suggest that the dominant LMNA mutations seen in many clinically disparate laminopathies may similarly alter Rb function, with regard to either the timing of exit from the cell cycle or terminal differentiation programs or both.

Atomic-resolution crystal structure of the proteolytic domain of Archaeoglobus fulgidus lon reveals the conformational variability in the active sites of lon proteases

The atomic-resolution crystal structure of the proteolytic domain (P-domain, residues 415-621) of Archaeoglobus fulgidus B-type Lon protease (wtAfLonB) and the structures of several mutants have revealed significant differences in the conformation of the active-site residues when compared to other known Lon P-domains, despite the conservation of the overall fold. The catalytic Ser509 is facing the solvent and is distant from Lys552, the other member of the catalytic dyad. Instead, the adjacent Asp508 forms an ion pair with the catalytic lysine residue. Glu506, an analog of the putative third catalytic residue from a related Methanococcus jannaschii LonB, also faces the solvent and does not interact with the catalytic dyad. We have established that full-length wtAfLonB is proteolytically active in an ATP-dependent manner. The loss of enzymatic activity of the S509A mutant confirms the functional significance of this residue, while retention of considerable level of activity by the D508A and E506A mutants rules out their critical involvement in catalysis. In contrast to the full-length enzymes, all individually purified P-domains (wild-type and mutants) were inactive, and the mutations had no influence on the active-site structure. These findings raise the possibility that, although isolated proteolytic domains of both AfLonB and E.coli LonA are able to assemble into expected functional hexamers, the presence of the other domains, as well as substrate binding, may be needed to stabilize the productive conformation of their active sites. Thus, the observed conformational variability may reflect the differences in the stability of active-site structures for the proteolytic counterparts of single-chain Lon versus independently folded proteolytic subunits of two-chain AAA+ proteases.