RESUMO
Huntington's disease (HD), a neurodegenerative disease characterized by progressive dementia, psychiatric problems, and chorea, is known to be caused by CAG repeat expansions in the HD gene HTT. However, the mechanism of this pathology is not fully understood. The translesion DNA polymerase θ (Polθ) carries a large insertion sequence in its catalytic domain, which has been shown to allow DNA loop-outs in the primer strand. As a result of high levels of oxidative DNA damage in neural cells and Polθ's subsequent involvement in base excision repair of oxidative DNA damage, we hypothesized that Polθ contributes to CAG repeat expansion while repairing oxidative damage within HTT. Here, we performed Polθ-catalyzed in vitro DNA synthesis using various CAGâ¢CTG repeat DNA substrates that are similar to base excision repair intermediates. We show that Polθ efficiently extends (CAG)nâ¢(CTG)n hairpin primers, resulting in hairpin retention and repeat expansion. Polθ also triggers repeat expansions to pass the threshold for HD when the DNA template contains 35 repeats upward. Strikingly, Polθ depleted of the catalytic insertion fails to induce repeat expansions regardless of primers and templates used, indicating that the insertion sequence is responsible for Polθ's error-causing activity. In addition, the level of chromatin-bound Polθ in HD cells is significantly higher than in non-HD cells and exactly correlates with the degree of CAG repeat expansion, implying Polθ's involvement in triplet repeat instability. Therefore, we have identified Polθ as a potent factor that promotes CAGâ¢CTG repeat expansions in HD and other neurodegenerative disorders.
Assuntos
Reparo do DNA , DNA Polimerase Dirigida por DNA/química , Doença de Huntington/enzimologia , Expansão das Repetições de Trinucleotídeos , Domínio Catalítico , Dano ao DNA , DNA Polimerase Dirigida por DNA/genética , DNA Polimerase Dirigida por DNA/metabolismo , Células HeLa , Humanos , Doença de Huntington/genética , DNA Polimerase tetaRESUMO
CTGâ¢CAG repeat expansions cause at least twelve inherited neurological diseases. Expansions require the presence, not the absence, of the mismatch repair protein MutSß (Msh2-Msh3 heterodimer). To evaluate properties of MutSß that drive expansions, previous studies have tested under-expression, ATPase function or polymorphic variants of Msh2 and Msh3, but in disparate experimental systems. Additionally, some variants destabilize MutSß, potentially masking the effects of biochemical alterations of the variations. Here, human Msh3 was mutated to selectively inactivate MutSß. Msh3-/- cells are severely defective for CTGâ¢CAG repeat expansions but show full activity on contractions. Msh3-/- cells provide a single, isogenic system to add back Msh3 and test key biochemical features of MutSß on expansions. Msh3 overexpression led to high expansion activity and elevated levels of MutSß complex, indicating that MutSß abundance drives expansions. An ATPase-defective Msh3 expressed at normal levels was as defective in expansions as Msh3-/- cells, indicating that Msh3 ATPase function is critical for expansions. Expression of two Msh3 polymorphic variants at normal levels showed no detectable change in expansions, suggesting these polymorphisms primarily affect Msh3 protein stability, not activity. In summary, CTGâ¢CAG expansions are limited by the abundance of MutSß and rely heavily on Msh3 ATPase function.
Assuntos
Trifosfato de Adenosina/metabolismo , Reparo de Erro de Pareamento de DNA , Proteína 3 Homóloga a MutS/fisiologia , Expansão das Repetições de Trinucleotídeos/fisiologia , Substituição de Aminoácidos , Astrócitos , Neoplasias Encefálicas , Sistemas CRISPR-Cas , Linhagem Celular , Neoplasias Colorretais , Dimerização , Técnicas de Inativação de Genes , Genes Reporter , Vetores Genéticos , Humanos , Hidrólise , Proteína 2 Homóloga a MutS/fisiologia , Proteína 3 Homóloga a MutS/deficiência , Proteína 3 Homóloga a MutS/genética , Mutação de Sentido Incorreto , Síndromes Neoplásicas Hereditárias , Mutação PuntualRESUMO
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to evolve, escape coronavirus disease 2019 therapeutics and vaccines, and jeopardize public health. To combat SARS-CoV-2 antigenic escape, we developed a rapid, high-throughput pipeline to discover monospecific VHH antibodies and iteratively develop VHH-Fc-VHH bispecifics capable of neutralizing emerging SARS-CoV-2 variants. By panning VHH single-domain phage libraries against ancestral or beta spike proteins, we discovered high-affinity VHH antibodies with unique target epitopes. Combining two VHHs into a tetravalent bispecific construct conferred broad neutralization activity against multiple variants and was more resistant to antigenic escape than the monospecific antibody alone. Following the rise of the Omicron variant, a VHH in the original bispecific construct was replaced with another VHH discovered against the Omicron BA.1 receptor binding domain; the resulting bispecific exhibited neutralization against both BA.1 and BA.5 sublineage variants. A heavy chain-only tetravalent VHH-Fc-VHH bispecific platform derived from humanized synthetic libraries held a myriad of unique advantages: (i) synthetic preconstructed libraries minimized risk of liabilities and maximized discovery speed, (ii) VHH scaffolds allowed for a modular "plug-and-play" format that could be rapidly iterated upon as variants of concern arose, (iii) natural dimerization of single VHH-Fc-VHH polypeptides allowed for straightforward bispecific production and purification methods, and (iv) multivalent approaches enhanced avidity boosting effects and neutralization potency, and conferred more robust resistance to antigenic escape than monovalent approaches against specific variants. This iterative platform of rapid VHH discovery combined with modular bispecific design holds promise for long-term viral control efforts.
RESUMO
New immune checkpoints are emerging in a bid to improve response rates to immunotherapeutic drugs. The adenosine A2A receptor (A2AR) has been proposed as a target for immunotherapeutic development due to its participation in immunosuppression of the tumor microenvironment. Blockade of A2AR could restore tumor immunity and, consequently, improve patient outcomes. Here, we describe the discovery of a potent, selective, and tumor-suppressing antibody antagonist of human A2AR (hA2AR) by phage display. We constructed and screened four single-chain variable fragment (scFv) libraries-two synthetic and two immunized-against hA2AR and antagonist-stabilized hA2AR. After biopanning and ELISA screening, scFv hits were reformatted to human IgG and triaged in a series of cellular binding and functional assays to identify a lead candidate. Lead candidate TB206-001 displayed nanomolar binding of hA2AR-overexpressing HEK293 cells; cross-reactivity with mouse and cynomolgus A2AR but not human A1, A2B, or A3 receptors; functional antagonism of hA2AR in hA2AR-overexpressing HEK293 cells and peripheral blood mononuclear cells (PBMCs); and tumor-suppressing activity in colon tumor-bearing HuCD34-NCG mice. Given its therapeutic properties, TB206-001 is a good candidate for incorporation into next-generation bispecific immunotherapeutics.
Assuntos
Antagonistas do Receptor A2 de Adenosina , Receptor A2A de Adenosina , Humanos , Animais , Receptor A2A de Adenosina/metabolismo , Receptor A2A de Adenosina/imunologia , Células HEK293 , Camundongos , Antagonistas do Receptor A2 de Adenosina/farmacologia , Antagonistas do Receptor A2 de Adenosina/uso terapêutico , Anticorpos de Cadeia Única/imunologia , Anticorpos de Cadeia Única/farmacologia , Macaca fascicularis , Biblioteca de PeptídeosRESUMO
Congenital hyperinsulinism (HI) is a genetic disorder in which pancreatic ß-cell insulin secretion is excessive and results in hypoglycemia that, without treatment, can cause brain damage or death. Most patients with loss-of-function mutations in ABCC8 and KCNJ11, the genes encoding the ß-cell ATP-sensitive potassium channel (KATP), are unresponsive to diazoxide, the only U.S. Food and Drug Administration-approved medical therapy and require pancreatectomy. The glucagon-like peptide 1 receptor (GLP-1R) antagonist exendin-(9-39) is an effective therapeutic agent that inhibits insulin secretion in both HI and acquired hyperinsulinism. Previously, we identified a highly potent antagonist antibody, TB-001-003, which was derived from our synthetic antibody libraries that were designed to target G protein-coupled receptors. Here, we designed a combinatorial variant antibody library to optimize the activity of TB-001-003 against GLP-1R and performed phage display on cells overexpressing GLP-1R. One antagonist, TB-222-023, is more potent than exendin-(9-39), also known as avexitide. TB-222-023 effectively decreased insulin secretion in primary isolated pancreatic islets from a mouse model of hyperinsulinism, Sur1-/- mice, and in islets from an infant with HI, and increased plasma glucose levels and decreased the insulin to glucose ratio in Sur1-/- mice. These findings demonstrate that targeting GLP-1R with an antibody antagonist is an effective and innovative strategy for treatment of hyperinsulinism. ARTICLE HIGHLIGHTS: Patients with the most common and severe form of diazoxide-unresponsive congenital hyperinsulinism (HI) require a pancreatectomy. Other second-line therapies are limited in their use because of severe side effects and short half-lives. Therefore, there is a critical need for better therapies. Studies with the glucagon-like peptide 1 receptor (GLP-1R) antagonist, avexitide (exendin-(9-39)), have demonstrated that GLP-1R antagonism is effective at lowering insulin secretion and increasing plasma glucose levels. We have optimized a GLP-1R antagonist antibody with more potent blocking of GLP-1R than avexitide. This antibody therapy is a potential novel and effective treatment for HI.
Assuntos
Hiperinsulinismo Congênito , Receptor do Peptídeo Semelhante ao Glucagon 1 , Hiperinsulinismo , Animais , Camundongos , Anticorpos/uso terapêutico , Glicemia , Hiperinsulinismo Congênito/tratamento farmacológico , Hiperinsulinismo Congênito/genética , Diazóxido/farmacologia , Peptídeo 1 Semelhante ao Glucagon , Receptor do Peptídeo Semelhante ao Glucagon 1/antagonistas & inibidores , Hiperinsulinismo/imunologia , Hiperinsulinismo/terapia , Mutação , Receptores de Sulfonilureias/genéticaRESUMO
How cancer cells cope with high levels of replication stress during rapid proliferation is currently unclear. Here, we show that macrophage migration inhibitory factor (MIF) is a 3' flap nuclease that translocates to the nucleus in S phase. Poly(ADP-ribose) polymerase 1 co-localizes with MIF to the DNA replication fork, where MIF nuclease activity is required to resolve replication stress and facilitates tumor growth. MIF loss in cancer cells leads to mutation frequency increases, cell cycle delays and DNA synthesis and cell growth inhibition, which can be rescued by restoring MIF, but not nuclease-deficient MIF mutant. MIF is significantly upregulated in breast tumors and correlates with poor overall survival in patients. We propose that MIF is a unique 3' nuclease, excises flaps at the immediate 3' end during DNA synthesis and favors cancer cells evading replication stress-induced threat for their growth.
Assuntos
Neoplasias da Mama/metabolismo , Replicação do DNA/fisiologia , Endonucleases Flap/metabolismo , Oxirredutases Intramoleculares/metabolismo , Fatores Inibidores da Migração de Macrófagos/metabolismo , Animais , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Linhagem Celular Tumoral , Proliferação de Células , DNA/química , DNA/metabolismo , Dano ao DNA , DNA Polimerase III/genética , DNA Polimerase III/metabolismo , Replicação do DNA/genética , Feminino , Endonucleases Flap/deficiência , Endonucleases Flap/genética , Técnicas de Inativação de Genes , Instabilidade Genômica , Células HCT116 , Humanos , Oxirredutases Intramoleculares/deficiência , Oxirredutases Intramoleculares/genética , Fatores Inibidores da Migração de Macrófagos/deficiência , Fatores Inibidores da Migração de Macrófagos/genética , Masculino , Camundongos , Camundongos Endogâmicos NOD , Camundongos SCID , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Conformação de Ácido Nucleico , Poli(ADP-Ribose) Polimerase-1/metabolismo , Fase S , Especificidade por SubstratoRESUMO
The fluorescence lifetimes of the estrogens, estrone, 17ß-estradiol and 17α-ethinylestradiol, were studied in various solvents. The fluorescence lifetimes of 17ß-estradiol and 17α-ethinylestradiol decreased from 4.7 to 0.9 ns as the solvent hydrogen bond accepting ability increased, in good agreement with other phenolic molecules. Estrone's two fluorescence bands had distinct lifetimes, with the 304 nm band having a lifetime shorter than 200 ps, reflecting efficient energy transfer to the carbonyl group, which had lifetimes ranging from 4.4 to 4.9 ns depending on the solvent. Solvent effects on the (1) ππ*, (1) πσ* and (1) nπ* states that are relevant to estrogen photophysics can adequately explain these trends. The solvent dependence on the excited states of these potent endocrine disruptors has significant implications for their photochemistry.
Assuntos
Disruptores Endócrinos/química , Estradiol/química , Estrona/química , Etinilestradiol/química , Solventes/química , Transferência de Energia , Fluorescência , Ligação de Hidrogênio , Fotólise , Espectrometria de FluorescênciaRESUMO
Absorption and emission yields for estrone and 17ß-estradiol were measured in a variety of room temperature solvents. Molar extinction coefficients were found to not vary as a function of solvent, while fluorescence yields were found to be significantly affected by the polarity and hydrogen-bond accepting ability of the solvent, with the yield for 17ß-estradiol being highest in nonpolar, hydrogen-bond donating solvents, and lowest in the nonpolar, hydrogen-bond accepting solvent ethyl acetate. Estrone's emission yield was found to be a factor of ten smaller than 17ß-estradiol's. Strong solvent and excitation wavelength dependences were found for the relative amounts of emission between estrone's two emission bands, with increased relative emission occurring in nonpolar aprotic solvents, and under higher excitation energies. These results are interpreted with the aid of vertical excitation energies from time-dependent density functional calculations using both explicit and implicit solvation models.