Abstract
Gigaxonin, the protein product of the Giant axonal neuropathy (GAN) gene, is a E3 ubiquitin ligase involved in neural cell and fibroblast intermediate filament processing. We have previously ...shown that Gigaxonin interacts with p16 in cisplatin-mediated ubiquitination of NF-κB. We analyzed cervical and head and neck cancer cell lines and primary tumors and have found exon 8 c.1293C>T single nucleotide polymorphism (SNP) to occur in both HPV positive and negative tumor cells lines and primary tumors. The prevalence of this SNP in the tumor samples was double that of the normal population (47.25% vs. 22%) and there was no relationship to HPV status. Cell lines containing the SNP showed higher expression of gigaxonin, and an inverse relationship to in vitro tumor cell line growth and cisplatin sensitivity. There was a direct relationship between the expression of gigaxonin and e-cadherin and inverse relationship to the expression of twist, snail and n-cadherin. CRISPR-Cas9 mediated conversion of T to C allele in gigaxonin overexpressing cervical cancer cell line ME 180 resulted in decreased gigaxonin expression accompanied by increased expression of twist, and snail and increased in vitro cell growth. Re-expression of gigaxonin in the CRISPR-Cas9 clone with a plasmid gigaxonin cDNA construct resulted in decreased expression of twist pointing to gigaxonin mediated downregulation of the EMT marker. We therefore hypothesize that GAN, associated with the neurodegenerative disease, is also a human tumor cell growth suppressor gene.
Citation Format: Mysore S. Veena, Daniel Sanghoon Shin, Chan Jeong, Jenna R. Chatoff, Natarajan Venkatesan, Saroj K. Basak, David Gray, Sharon P. Wilczynski, Sharon P. Wilczynski, Steven J. Gray, Donald B. Kohn, Marilene B. Wang, Eri S. Srivatsan. Inverse relationship between Giant Axonal Neuropathy gene expression and EMT in human tumors abstract. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5986.
Metabolic obstacles of the tumor microenvironment remain a challenge to T-cell-mediated cancer immunotherapies. To better understand the interplay of immune checkpoint signaling and immune ...metabolism, this study developed and used an optimized metabolite extraction protocol for non-adherent primary human T-cells, to broadly profile in vitro metabolic changes effected by PD-1 signaling by mass spectrometry-based metabolomics and isotopomer analysis. Inhibitory signaling reduced aerobic glycolysis and glutaminolysis. A general scarcity across the panel of metabolites measured supported widespread metabolic regulation by PD-1. Glucose carbon fate analysis supported tricarboxylic acid cycle reliance on pyruvate carboxylation, catabolic-state fluxes into acetyl-CoA and succinyl-CoA, and a block in de novo nucleoside phosphate synthesis that was accompanied by reduced mTORC1 signaling. Nonetheless, exogenous administration of nucleosides was not sufficient to ameliorate proliferation of T-cells in the context of multiple metabolic insufficiencies due to PD-L1 treatment. Carbon fate analysis did not support the use of primarily glucose-derived carbons to fuel fatty acid beta oxidation, in contrast to reports on T-memory cells. These findings add to our understanding of metabolic dysregulation by PD-1 signaling and inform the effort to rationally develop metabolic interventions coupled with immune-checkpoint blockade for increased treatment efficacy.
The proton-coupled folate transporter (PCFT-SLC46A1) mediates intestinal folate absorption and folate transport across the choroid plexus, processes defective in hereditary folate malabsorption ...(HFM). This paper characterizes the functional defect, and the roles of two mutated PCFT residues, associated with HFM (G338R and A335D). The A335D-PCFT and other mutations at this residue result in an unstable protein; when expression of a mutant protein was preserved, function was always retained. The G338R and other charged mutants resulted in an unstable protein; substitutions with small neutral and polar amino acids preserved protein but with impaired function. Pemetrexed and methotrexate (MTX) influx kinetics mediated by the G338C mutant PCFT revealed marked (15- to 20-fold) decreases in K(t) and V(max) compared with wild-type PCFT. In contrast, there was only a small (∼2-fold) decrease in the MTX influx K(i) and an increase (∼3-fold) in the pemetrexed influx K(i) for the G338C-PCFT mutant. Neither a decrease in pH to 4.5, nor an increase to 7.4, restored function of the G338C mutant relative to wild-type PCFT excluding a role for this residue in proton binding or proton coupling. Homology modeling localized the A335 and G338 residues embedded in the 9th transmembrane, consistent with the inaccessibility of the A335C and G338C proteins to MTS reagents. Hence, the loss of intrinsic G338C-PCFT function was due solely to impaired oscillation of the carrier between its conformational states. The data illustrate how alterations in carrier cycling can impact influx K(t) without comparable alterations in substrate binding to the carrier.
Abstract
A subset of colorectal carcinomas (CRC) with high microsatellite instability (MSI-high) have been shown to respond to immune checkpoint blockade, while the much more common microsatellite ...stable (MSS) CRC do not usually respond to these immunotherapies. Most MSI-high tumors grow progressively despite a high mutational load, suggesting that the cancer may have developed means to escape from immune recognition, which is termed immunoediting. This immunoediting process includes three phases: an initial phase of nascent cancer cell elimination due to high immunogenicity, then a period of equilibrium with the immune response, finally leading to escape of the cancer cells that have developed genetic or epigenetic mechanisms allowing them to grow progressively in an immunocompetent host. It is likely that MSI-high cancers would go through similar processes to eventually escape from immune recognition. To better understand the differential immunoediting in MSI-high and MSS CRC, we combined tumor exome data from 592 cases from The Cancer Genome Atlas (TCGA) with previously published tumor exome data from 619 cases from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study to yield an unprecedented sample of 1,211 CRC molecularly characterized cases. The large number of samples, including a very large number of MSI-high cases (N = 179), gives us the power to identify the prevalence of the mechanisms of resistance discussed and thereby prioritize downstream efforts. We utilized the MutSigCV algorithm to identify significantly mutated genes in MSS and MSI-high tumors in the TCGA cohort (496 MSS and 75 MSI-high cases), and the NHS/HPFS cohorts (438 MSS and 104 MSI-high cases). We identified a total of 62 significantly mutated genes, of which 9 were identified in MSS tumors only, 40 in MSI-high tumors only, and 13 in both. Twenty-seven of the 53 significantly mutated genes in MSI-high were novel, likely resulting from a large increase in the number of MSI-high tumors relative to previous studies. We identified 13 significantly mutated genes with a documented role in the immune system, specifically in MSI-high tumors, a subtype shown previously to have a high level of T-cell infiltration; ZFP36L2 and B2M were significantly mutated in both MSS and MSI-high. B2M, HLA-A, and HLA-B are significantly mutated antigen presenting genes that were previously reported to be recurrently mutated in MSI-high. Eleven of the significantly mutated immune-related genes had roles in modulating diverse hematopoietic cell types and effects beyond antigen presentation; those genes include XYLT2, a dendritic cell trafficking gene; ZBTB20, a Toll-like receptor mediating immune response; RNF128, a regulator of IL2 and IL4 mediated T-cell maturation; KLF3, a gene involved in B-cell development; ZFP36L2, a gene involved in thymocyte development; CASP8, a gene involved in innate immunity; and CD58, a gene involved in the activation of both T lymphocytes and NK cells. Together, these mutations indicate positive selection for immune escape through other mechanisms beyond mutations in antigen-presenting machinery.
Citation Format: Catherine Grasso, Marios Giannakis, Daniel Wells, David Wheeler, Eve Shinbrot, Syed Zaidi, Jeroen Huyghe, Milan Geybels, Stephen Salipante, Gabriel Abril-Rodriguez, Helena Escuin-Ordinas, Cristina Puig-Saus, Daniel Sanghoon Shin, Shuji Ogino, Antoni Ribas, Ulrike Peters. Immunoediting in untreated mismatch repair deficient colorectal cancer abstract. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B011.
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Background: We tested the biological significance of the loss of function (LOF) mutations in JAK1 or JAK2 within the IFN-receptor-pathway and in beta-2-microglobulin (B2M), which ...had been found in patient biopsies with resistance to anti-PD-1 therapy. Methods: We used CRISPR/Cas9 genome editing to generate JAK1, JAK2 and B2M knockout (KO) sublines of HLA-A*02:01 MART-1 or NY-ESO-1 positive human melanoma cell lines, tested using in-vitro T cell co-culture systems and in a syngeneic mouse model (MC38) to analyze the in-vivo antitumor activity with anti-PD1 therapy. Results: The JAK2-KO cell line was insensitive to IFN-gamma induced signaling and growth arrest (p < 0.001 compared with IFN-alpha or beta), while the JAK1-KO cell line was insensitive to all three IFNs. Baseline MHC class I expression after JAK1-KO was unaffected (baseline-MFI 1230 JAK1-KO vs 1570 parental, p = 0.66), but the magnitude of change was lower upon IFN-gamma exposure compared to the parental (MFI change with IFN-gamma, 26% decrease for JAK1-KO vs 50% increase for parental). There was no difference in in-vitro cytotoxicity by NY-ESO-1-TCR transgenic T-cells against JAK1-KO-NY-ESO-1+ melanoma cells compared to the parental (78% vs 82% cytotoxicity at 10:1 E:T ratio, p NS). However, B2M-KO was resistant to killing by MART-1 specific T-cells (2% vs 96% cytotoxicity at 10:1 E:T ratio, p < 0.0001). On the other hand, in the MC38 model the significant antitumor activity of anti-PD-1 against the wild type cells was lost in both JAK2-KO and B2M-KO. The percentage of CD8+ T cells has a trend of increase with anti-PD1 compared to untreated in the MC38 wild type (p = 0.1 d12), and a trend of decrease in MC38 B2M-KO (p = 0.2 d12), but no change in JAK2-KO tumors (p = 0.7 d12). Conclusions: JAK1/2 LOF mutations result in insensitivity to IFN induced antitumor effects, but does not impair T cell recognition and cytotoxicity, while B2M LOF results in lack of antigen presentation to T cells and loss of antitumor activity. However both lead to in-vivo resistance to anti-PD-1 therapy, suggesting they do so by independent mechanisms.
Loss-of-function mutations in the proton-coupled folate transporter (PCFT, SLC46A1) result in the autosomal recessive disorder, hereditary folate malabsorption (HFM). Identification and ...characterization of HFM mutations provide a wealth of information on the structure-function relationship of this transporter. In the current study, PCR-based random mutagenesis was employed to generate unbiased loss-of-function mutations of PCFT, simulating the spectrum of alterations that might occur in the human disorder. A total of 26 mutations were generated and 4 were identical to HFM mutations. Eleven were base deletion or insertion mutations that led to a frameshift and, along with similar HFM mutations, are predominantly localized to two narrow regions of the pcft gene at the 5′-end. Base substitution mutations identified in the current study and HFM patients were largely distributed across the pcft gene. Elimination of the ATG initiation codon by a one-base substitution (G > A) did not result in a complete lack of translation at the same codon consistent with rare non-ATG translation initiation. Among six missense mutants evaluated, three mutant PCFTs were not detected at the plasma membrane, one mutation resulted in decreased binding to folate substrate, and one had a reduced rate of conformational change associated with substrate translocation. The remaining PCFT mutant had defects in both processes. These results broaden understanding of the regions of the pcft gene prone to base insertion and deletion and inform further approaches to the analysis of the structure-function of PCFT.
Hereditary folate malabsorption (HFM) is an autosomal recessive disorder, recently shown to be due to loss-of-function mutations of the proton-coupled folate transporter (PCFT-SLC46A1), resulting in ...systemic and central nervous system folate deficiency. Data is emerging on the spectrum of PCFT mutations associated with this disorder. In this report, novel mutations are described in three subjects with HFM: A335D/N68Kfs (c.1004C>A/c.204-205delCC), compound heterozygous mutations, and two homozygous PCFT mutations, G338R (c.1012G>C) and E9Gfs (c.17-18insC). Functional assessment of A335D and G338R PCFT mutants transfected into folate transporter-deficient HeLa R1-11 cells indicated a complete loss of transport activity. There were neurological deficiencies in two of the families reported; in particular, late-onset seizures. The importance of early diagnosis and treatment to achieve physiological cerebrospinal fluid folate levels is emphasized.
The proton-coupled transporter (PCFT) mediates intestinal folate absorption and folate transport from blood across the choroid plexus. The membrane topology of PCFT has been defined using the ...substituted cysteine accessibility method; an intramolecular disulfide bond between the Cys 66 and 298 residues, in the first and fourth extracellular loops, respectively, is present but not essential for function. The current report describes Lys 422 mutations (K422C, K422E) that have no effect on transport activity when introduced into wild-type PCFT but result in a marked loss of activity when introduced into a Cys-less PCFT which is otherwise near-fully functional. The loss of activity of both mutant PCFTs was shown to be due to impaired protein stability and expression. Additional studies were conducted with the K422C mutation in Cys-less PCFT. The impact of re-introduction of one, two, three or five, Cys residues was assessed. While there were some differences in the impact of the different Cys residues re-introduced, restoration was attributed more to a cumulative effect rather than the specific role of individual Cys residues. Preservation of the Cys66–Cys298 intramolecular disulfide bond was not required for stability of the K422C protein. These observations are relevant to studies with Cys-less transporters utilized for the characterization of proteins with the substituted cysteine accessibility method and indicate that functional defects detected in a Cys-less protein, when the tertiary structure of the molecule is stressed, are not necessarily relevant to the wild-type protein.
► The highly conserved Lys 422 is fully replaceable in wild-type PCFT. ► K422C and K422E mutants are inactive in the functional Cys-less PCFT. ► The K422C in Cys-less PCFT loses activity due to decreased protein expression. ► Additions of Cys residues cumulatively restore K422C PCFT expression and activity.
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