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1.
MedEdPORTAL ; 17: 11197, 2021.
Article in English | MEDLINE | ID: mdl-34765724

ABSTRACT

INTRODUCTION: MedEdPORTAL is an open-access journal for health professions educators to publish their educational activities. The Educational Summary Report (ESR) is the manuscript that represents scholarly expression of those activities, aligned with Glassick's criteria for scholarship; however, prospective authors face challenges in writing ESRs, which can lead to rejection. METHODS: We developed a conference workshop to teach health professions educators how to write an ESR by reviewing a sample ESR in small groups. The workshop began with a didactic on best practices in crafting each section of an ESR. We then divided participants into small groups to review an assigned section of a sample ESR using a reviewer's checklist and completing a templated flip chart. Each small group then reported out in a large-group discussion. A conference evaluation was distributed online to solicit perceptions of the workshop's effectiveness. RESULTS: The 90-minute workshop was presented by separate teams of two facilitators at three national conferences. Approximately 35 participants attended the first workshop, and 50 attended the second and third workshops. Survey feedback from 19 respondents (38%) to the evaluation survey at the third workshop was representative of the previous two iterations and demonstrated that workshop content and materials were helpful. DISCUSSION: A workshop enabling educators to serve as group peer reviewers of a sample ESR for a MedEdPORTAL submission was well received. Associate editors, faculty mentors, and other experienced faculty development leaders can use these materials to support future authors in submitting to MedEdPORTAL while providing opportunities for national presentations.


Subject(s)
Education, Medical , Research Report , Fellowships and Scholarships , Humans , Prospective Studies , Publishing
2.
Med Sci Educ ; 30(1): 403-415, 2020 Mar.
Article in English | MEDLINE | ID: mdl-34457684

ABSTRACT

A shared secure biochemistry test bank (abeQbank) was developed by 61 members of the Association of Biochemistry Educators (ABE) who are from medical, pharmacy, and dental schools. The initial abeQbank contained 305 questions, which were almost all clinical vignettes, and were classified into 9 biochemistry megaThemes with subthemes as determined by ABE workshops 2009-2011. Three medical schools selected 163 board-style abeQbank questions approved by ABE and administered a proctored formative exam using ExamSoft to 97 second-year medical students prior to their USMLE or COMLEX 1 board exam followed by a review session in which students examined their answers and read the rationale for each question. The goals of this project were to (1) provide a resource to biochemistry educators; (2) evaluate the quality of these questions; and (3) ascertain students' relative knowledge in different biochemical concepts. Individual questions and 9 megaTheme groups performed similarly across schools, with the lowest and highest megaThemes ranging from 40 to 70% correct. Five questions were dropped due to miscoding, poor metrics, or questionable distractors requiring a rewrite. The results showed that the examination was strongly reliable with the average KR20 = 0.85, discrimination index and point-biserial > 0.2, and students scoring the examination 8 out of 10 in usefulness. This test bank represents the first attempt by an international biochemistry organization to create a standardized set of questions, with future expansion planned to help standardize the content of biochemistry topics in the curricula.

4.
Med Sci Educ ; 30(2): 791-800, 2020 Jun.
Article in English | MEDLINE | ID: mdl-34457736

ABSTRACT

BACKGROUND: Integrating basic science into clinical teaching has been a struggle for medical schools. However, early exposure to clinical experience has been associated with an increased understanding of the importance of basic science, positive attitudes, and developing clinical skills faster. Furthermore, early clinical exposure can help students reconnect with what drove them into medicine in the first place, especially when they are starting to feel burned out by the volume of lecture material. As a result, increasing patient experience during the first year has become a goal of many medical schools. METHODS: At Rutgers Robert Wood Johnson Medical School, interprofessional case discussions (ICDs) begin with a lecture that explicitly integrates basic science with a disease, followed by a discussion with a patient, their family, the healthcare team, and first-year students. Our objective is to explore whether ICDs enhanced the learning experience of basic science. CONTEXT: ICD satisfaction was assessed using evaluations from two different courses (2013-2016). Responses were analyzed quantitatively using descriptive statistics and qualitatively using a grounded-theory-content analysis. Study 2: A follow-up measure with current third- and fourth-year students on long-term retention of basic science was analyzed using a Wilcoxon signed rank test. Relative rankings of three different case-based teaching modalities were assessed using chi-square. RESULTS: Students reported significantly higher satisfaction with ICDs (93%) for reinforcing concepts and integrating materials compared to Flipped Classrooms (66%) and Jigsaws (65%), x 2 = 120.9, p < .001. Student comments fit into five categories: enjoyment, learning/retention, the clinical usefulness of basic science, affirming passion to be in medicine, and others. The follow-up measure indicated significantly greater retention of the biochemical basis of diseases covered during ICDs. CONCLUSIONS: While other teaching modalities integrate basic science into a clinical context, ICDs go further by displaying interprofessional care and the manifestation of the disease on the patient and the lives of their family. As a result, ICDs lead to a positive learning environment in which students feel comfortable, have a sense of rapport with the patients and health care providers, and feel motivated to learn basic science.

5.
Acad Med ; 95(9S A Snapshot of Medical Student Education in the United States and Canada: Reports From 145 Schools): S339-S342, 2020 Sep.
Article in English | MEDLINE | ID: mdl-33626715
6.
Oncotarget ; 9(70): 33249-33257, 2018 Sep 07.
Article in English | MEDLINE | ID: mdl-30279956

ABSTRACT

E2F1-3a overexpression due to amplification or to mutation or loss of the retinoblastoma gene, induces genes involved in DNA synthesis and leads to abnormal cellular proliferation, tumor growth, and invasion. Therefore, inhibiting the overexpression of one or more of these activating E2Fs is a recognized target in cancer therapeutics. In previous studies we identified by phage display, a novel 7-mer peptide (PEP) that bound tightly to an immobilized consensus E2F1 promoter sequence, and when conjugated to penetratin to increase its uptake into cells, was cytotoxic to several malignant cell lines and human prostate and small cell lung cancer xenografts. Based on molecular simulation studies that showed that the D-Arg penetratin peptide (D-Arg PEP) secondary structure is more stable than the L-Arg PEP, the L-Arg in the peptide was substituted with D-Arg. In vitro studies confirmed that it was more stable than the L- form and was more cytotoxic as compared to the L-Arg PEP when tested against the human castrate resistant cell line, DU145 and the human lung cancer H196 cell line. When encapsulated in PEGylated liposomes, the D-Arg-PEP potently inhibited growth of the DU145 xenograft in mice. Our findings validate D- Arg PEP, an inhibitor of E2F1and 3a transcription, as an improved second generation drug candidate for targeted molecular therapy of cancers with elevated levels of activated E2F(s).

7.
Biomed Res Int ; 2018: 5051289, 2018.
Article in English | MEDLINE | ID: mdl-29850526

ABSTRACT

BACKGROUND: Cardiovascular disease (CVD) annually claims more lives and costs more dollars than any other disease globally amid widening health disparities, despite the known significant reductions in this burden by low cost dietary changes. The world's first medical school-based teaching kitchen therefore launched CHOP-Medical Students as the largest known multisite cohort study of hands-on cooking and nutrition education versus traditional curriculum for medical students. METHODS: This analysis provides a novel integration of artificial intelligence-based machine learning (ML) with causal inference statistics. 43 ML automated algorithms were tested, with the top performer compared to triply robust propensity score-adjusted multilevel mixed effects regression panel analysis of longitudinal data. Inverse-variance weighted fixed effects meta-analysis pooled the individual estimates for competencies. RESULTS: 3,248 unique medical trainees met study criteria from 20 medical schools nationally from August 1, 2012, to June 26, 2017, generating 4,026 completed validated surveys. ML analysis produced similar results to the causal inference statistics based on root mean squared error and accuracy. Hands-on cooking and nutrition education compared to traditional medical school curriculum significantly improved student competencies (OR 2.14, 95% CI 2.00-2.28, p < 0.001) and MedDiet adherence (OR 1.40, 95% CI 1.07-1.84, p = 0.015), while reducing trainees' soft drink consumption (OR 0.56, 95% CI 0.37-0.85, p = 0.007). Overall improved competencies were demonstrated from the initial study site through the scale-up of the intervention to 10 sites nationally (p < 0.001). DISCUSSION: This study provides the first machine learning-augmented causal inference analysis of a multisite cohort showing hands-on cooking and nutrition education for medical trainees improves their competencies counseling patients on nutrition, while improving students' own diets. This study suggests that the public health and medical sectors can unite population health management and precision medicine for a sustainable model of next-generation health systems providing effective, equitable, accessible care beginning with reversing the CVD epidemic.


Subject(s)
Cardiology/education , Cooking , Curriculum , Health Education , Machine Learning , Multilevel Analysis , Propensity Score , Students, Medical , Adult , Cohort Studies , Education, Medical , Female , Humans , Male , Nutritional Physiological Phenomena
9.
Clin Cancer Res ; 22(21): 5189-5195, 2016 Nov 01.
Article in English | MEDLINE | ID: mdl-27582489

ABSTRACT

NAD+ kinase (NADK) catalyzes the phosphorylation of nicotinamide adenine dinucleotide (NAD+) to nicotinamide adenine dinucleotide phosphate (NADP+) using ATP as the phosphate donor. NADP+ is then reduced to NADPH by dehydrogenases, in particular glucose-6-phosphate dehydrogenase and the malic enzymes. NADPH functions as an important cofactor in a variety of metabolic and biosynthetic pathways. The demand for NADPH is particularly high in proliferating cancer cells, where it acts as a cofactor for the synthesis of nucleotides, proteins, and fatty acids. Moreover, NADPH is essential for the neutralization of the dangerously high levels of reactive oxygen species (ROS) generated by increased metabolic activity. Given its key role in metabolism and regulation of ROS, it is not surprising that several recent studies, including in vitro and in vivo assays of tumor growth and querying of patient samples, have identified NADK as a potential therapeutic target for the treatment of cancer. In this review, we will discuss the experimental evidence justifying further exploration of NADK as a clinically relevant drug target and describe our studies with a lead compound, thionicotinamide, an NADK inhibitor prodrug. Clin Cancer Res; 22(21); 5189-95. ©2016 AACR.


Subject(s)
NAD/metabolism , Neoplasms/drug therapy , Neoplasms/metabolism , Animals , Humans , NADP/metabolism , Oxidation-Reduction/drug effects , Oxidative Stress/drug effects , Phosphotransferases (Alcohol Group Acceptor)/metabolism , Reactive Oxygen Species/metabolism
10.
Mol Pharmacol ; 88(4): 720-7, 2015 Oct.
Article in English | MEDLINE | ID: mdl-26219913

ABSTRACT

NAD(+) kinase (NADK) is the only known cytosolic enzyme that converts NAD(+) to NADP(+), which is subsequently reduced to NADPH. The demand for NADPH in cancer cells is elevated as reducing equivalents are required for the high levels of nucleotide, protein, and fatty acid synthesis found in proliferating cells as well as for neutralizing high levels of reactive oxygen species (ROS). We determined whether inhibition of NADK activity is a valid anticancer strategy alone and in combination with chemotherapeutic drugs known to induce ROS. In vitro and in vivo inhibition of NADK with either small-hairpin RNA or thionicotinamide inhibited proliferation. Thionicotinamide enhanced the ROS produced by several chemotherapeutic drugs and produced synergistic cell kill. NADK inhibitors alone or in combination with drugs that increase ROS-mediated stress may represent an efficacious antitumor combination and should be explored further.


Subject(s)
Antineoplastic Agents/administration & dosage , Cytosol/metabolism , NADP/antagonists & inhibitors , Niacinamide/analogs & derivatives , Oxidative Stress/physiology , Animals , Cytosol/drug effects , Drug Synergism , Humans , Male , Mice , Mice, Inbred NOD , Mice, SCID , NADP/metabolism , Niacinamide/administration & dosage , Oxidative Stress/drug effects , Tumor Cells, Cultured , Xenograft Model Antitumor Assays/methods
11.
Biochem Mol Biol Educ ; 42(3): 259-69, 2014.
Article in English | MEDLINE | ID: mdl-24599571

ABSTRACT

The rationale for this mandatory, guided online e-journal exercise is to foster the ability of students to independently read medical and scientific literature in a critical manner and to integrate journal reading with their basic science knowledge. After a lecture on oxidative phosphorylation, students were assigned to read an article on brown adipose tissue published in New England Journal of Medicine and were guided to analyze the article by answering online questions. After two iterations, student surveys about the project, its key pedagogical features, and ways to improve it suggest that the students perceived these exercises as active learning, which is clinically relevant and built on their course material. Furthermore, students agreed that the e-journal project was useful for learning how to read an article, for reviewing the material learned in class, and for promoting evidence-based medicine. This online e-journal exercise models some aspects students will experience as future physicians, where it is essential to keep up with literature and extract relevant information on a tight physician's schedule. This study demonstrated the usefulness of guided e-journal exercises as a simple effective active teaching tool for preclinical medical students, which can also be used for prehealth undergraduate programs.


Subject(s)
Adipose Tissue, Brown/metabolism , Clinical Clerkship , Online Systems , Oxidative Phosphorylation
12.
Oncotarget ; 5(4): 901-7, 2014 Feb 28.
Article in English | MEDLINE | ID: mdl-24658650

ABSTRACT

E2F-1, a key transcription factor necessary for cell growth, DNA repair and differentiation, is an attractive target for development of useful anticancer drugs in tumors that are E2F "oncogene addicted". A peptide, isolated from phage clones, based on its binding to an E2F-1 consensus sequence, was cytotoxic against a wide range of cancer cell lines. The peptide was coupled to penetratin (PEP) and tested against prostate cancer cell lines, and a fresh sample from a patient with metastatic cancer. As the PEP was found to be relatively unstable in serum, it was encapsulated in PEGylated liposomes for in vivo studies. The peptide was cytotoxic against prostate cell lines and a fresh sample from a patient with metastatic prostate cancer. Treatment of mice bearing the human Du-145 human prostate tumor with the PEP encapsulated in PEGylated liposomes (PL-PEP) caused tumor regression without significant toxicity. The liposome encapsulated PEP has promise as an antitumor agent, alone or in combination with inhibitors of DNA synthesis.


Subject(s)
E2F1 Transcription Factor/antagonists & inhibitors , Peptides/pharmacology , Prostatic Neoplasms, Castration-Resistant/drug therapy , Animals , Apoptosis/drug effects , Cell Line, Tumor , Cell Proliferation/drug effects , Cell Survival/drug effects , E2F1 Transcription Factor/metabolism , Humans , Male , Mice , Mice, Nude , Prostatic Neoplasms, Castration-Resistant/metabolism , Prostatic Neoplasms, Castration-Resistant/pathology , Random Allocation , Signal Transduction , Xenograft Model Antitumor Assays
13.
Biochem Mol Biol Educ ; 41(6): 384-7, 2013.
Article in English | MEDLINE | ID: mdl-24214182

ABSTRACT

For successful delivery of basic science topics for health-professional students, it is critical to reduce apprehension and illustrate relevance to clinical settings and everyday life. At the beginning of the Biochemistry course for Physician Assistants, a team-based assignment was designed to develop an understanding of the mechanism of action, effectiveness, and toxicity of five common over the counter (OTC) drugs and dietary supplements, and place these familiar medicines in a political and historical context. The objectives of this exercise were to stimulate interest in biochemistry; to provide basic information on enzymes and enzyme inhibitors related to these drugs to be expanded upon later in the course; and to encourage active and interactive learning. Teams of five students were formed, and each student was given an information sheet on aspirin, alpha-galactosidase, orlistat, dextromethorphan, or simvastatin, a low dose statin, which was previously available without prescription at pharmacies in the UK. After each member of the team acquired information on one OTC drug/dietary supplement by reading an assigned information sheet, the team was asked to go through a series of questions, and then submit answers to a quiz as a group. A high rate of success on the quiz, an overwhelmingly positive response on formal course evaluations, and enthusiastic exchanges during class suggested this team-based session accomplished its goals.


Subject(s)
Biochemistry/education , Nonprescription Drugs/chemistry , Physician Assistants/education , Teaching/methods , Aspirin/administration & dosage , Aspirin/adverse effects , Aspirin/chemistry , Dextromethorphan/administration & dosage , Dextromethorphan/adverse effects , Dextromethorphan/chemistry , Dietary Supplements , Humans , Lactones/administration & dosage , Lactones/adverse effects , Lactones/chemistry , Nonprescription Drugs/administration & dosage , Nonprescription Drugs/adverse effects , Orlistat , Problem-Based Learning/methods , Reproducibility of Results , Simvastatin/administration & dosage , Simvastatin/adverse effects , Simvastatin/chemistry , Students , Surveys and Questionnaires , alpha-Galactosidase/administration & dosage , alpha-Galactosidase/adverse effects , alpha-Galactosidase/chemistry
14.
Cancer Biol Ther ; 14(8): 742-51, 2013 Aug.
Article in English | MEDLINE | ID: mdl-23792570

ABSTRACT

E2F-1, a key transcription factor necessary for cell growth, DNA repair, and differentiation, is an attractive target for development of anticancer drugs in tumors that are E2F "oncogene addicted". We identified a peptide isolated from phage clones that bound tightly to the E2F-1 promoter consensus sequence. The peptide was coupled to penetratin to enhance cellular uptake. Modeling of the penetratin-peptide (PEP) binding to the DNA E2F-1 promoter demonstrated favorable interactions that also involved the participation of most of the penetratin sequence. The penetratin-peptide (PEP) demonstrated potent in vitro cytotoxic effects against a range of cancer cell lines, particularly against Burkitt lymphoma cells and small cell lung cancer (SCLC) cells. Further studies in the H-69 SCLC cell line showed that the PEP inhibited transcription of E2F-1 and also several important E2F-regulated enzymes involved in DNA synthesis, namely, thymidylate synthase, thymidine kinase, and ribonucleotide reductase. As the PEP was found to be relatively unstable in serum, it was encapsulated in PEGylated liposomes for in vivo studies. Treatment of mice bearing the human small cell lung carcinoma H-69 with the PEP encapsulated in PEGylated liposomes (PL-PEP) caused tumor regression without significant toxicity. The liposome encapsulated PEP has promise as an antitumor agent, alone or in combination with inhibitors of DNA synthesis.


Subject(s)
Carrier Proteins/metabolism , E2F1 Transcription Factor/metabolism , Lung Neoplasms/drug therapy , Peptide Fragments/pharmacology , Small Cell Lung Carcinoma/drug therapy , Amino Acid Sequence , Animals , Apoptosis/drug effects , Carrier Proteins/chemistry , Carrier Proteins/genetics , Cell-Penetrating Peptides , Down-Regulation , Drug Screening Assays, Antitumor , E2F1 Transcription Factor/biosynthesis , E2F1 Transcription Factor/chemistry , E2F1 Transcription Factor/genetics , Female , Humans , Lung Neoplasms/genetics , Lung Neoplasms/metabolism , Lung Neoplasms/pathology , Mice , Models, Molecular , Molecular Sequence Data , Molecular Targeted Therapy , Peptide Fragments/chemistry , Peptide Fragments/pharmacokinetics , Promoter Regions, Genetic , RNA, Messenger/genetics , RNA, Messenger/metabolism , Random Allocation , Small Cell Lung Carcinoma/genetics , Small Cell Lung Carcinoma/metabolism , Small Cell Lung Carcinoma/pathology , Xenograft Model Antitumor Assays
15.
Mol Pharmacol ; 83(2): 339-53, 2013 Feb.
Article in English | MEDLINE | ID: mdl-23197646

ABSTRACT

Dihydrofolate reductase (DHFR), because of its essential role in DNA synthesis, has been targeted for the treatment of a wide variety of human diseases, including cancer, autoimmune diseases, and infectious diseases. Methotrexate (MTX), a tight binding inhibitor of DHFR, is one of the most widely used drugs in cancer treatment and is especially effective in the treatment of acute lymphocytic leukemia, non-Hodgkin's lymphoma, and osteosarcoma. Limitations to its use in cancer include natural resistance and acquired resistance due to decreased cellular uptake and decreased retention due to impaired polyglutamylate formation and toxicity at higher doses. Here, we describe a novel mechanism to induce DHFR degradation through cofactor depletion in neoplastic cells by inhibition of NAD kinase, the only enzyme responsible for generating NADP, which is rapidly converted to NADPH by dehydrogenases/reductases. We identified an inhibitor of NAD kinase, thionicotinamide adenine dinucleotide phosphate (NADPS), which led to accelerated degradation of DHFR and to inhibition of cancer cell growth. Of importance, combination treatment of NADPS with MTX displayed significant synergy in a metastatic colon cancer cell line and was effective in a MTX-transport resistant leukemic cell line. We suggest that NAD kinase is a valid target for further inhibitor development for cancer treatment.


Subject(s)
NADP/analogs & derivatives , Niacinamide/analogs & derivatives , Niacinamide/pharmacology , Phosphotransferases (Alcohol Group Acceptor)/antagonists & inhibitors , Phosphotransferases (Alcohol Group Acceptor)/metabolism , Tetrahydrofolate Dehydrogenase/metabolism , Biological Transport/drug effects , Biological Transport/genetics , Cell Line, Tumor , Half-Life , Humans , Methotrexate/pharmacology , NADP/metabolism , NADP/pharmacology , Proteolysis/drug effects , Transcription, Genetic/drug effects , Transcription, Genetic/genetics , Up-Regulation/drug effects , Up-Regulation/genetics
16.
Cancer Biol Ther ; 13(13): 1290-8, 2012 Nov.
Article in English | MEDLINE | ID: mdl-22954684

ABSTRACT

Dihydrofolate reductase (DHFR) is an essential enzyme involved in de novo purine and thymidine biosynthesis. For several decades, selective inhibition of DHFR has proven to be a potent therapeutic approach in the treatment of various cancers including acute lymphoblastic leukemia, non-Hodgkin's lymphoma, osteogenic sarcoma, carcinoma of the breast, and head and neck cancer. Therapeutic success with DHFR inhibitor methotrexate (MTX) has been compromised in the clinic, which limits the success of MTX treatment by both acquired and intrinsic resistance mechanisms. We report that benzamide riboside (BR), via anabolism to benzamide adenine dinucleotide (BAD) known to potently inhibit inosine monophosphate dehydrogenase (IMPDH), also inhibits cell growth through a mechanism involving downregulation of DHFR protein. Evidence to support this second site of action of BR includes the finding that CCRF-CEM/R human T-cell lymphoblasic leukemia cells, resistant to MTX as a consequence of gene amplification and overexpression of DHFR, are more resistant to BR than are parental cells. Studies of the mechanism by which BR lowers DHFR showed that BR, through its metabolite BAD, reduced NADP and NADPH cellular levels by inhibiting nicotinamide adenine dinucleotide kinase (NADK). As consequence of the lack of NADPH, DHFR was shown to be destabilized. We suggest that, inhibition of NADK is a new approach to downregulate DHFR and to inhibit cell growth.


Subject(s)
Nucleosides/pharmacology , Precursor Cell Lymphoblastic Leukemia-Lymphoma/drug therapy , Tetrahydrofolate Dehydrogenase/genetics , Tetrahydrofolate Dehydrogenase/metabolism , Adenine Nucleotides/genetics , Adenine Nucleotides/metabolism , Benzamides/metabolism , Cell Line, Tumor , Down-Regulation/drug effects , Drug Resistance, Neoplasm , Humans , IMP Dehydrogenase/antagonists & inhibitors , IMP Dehydrogenase/genetics , IMP Dehydrogenase/metabolism , Methotrexate/pharmacology , Molecular Targeted Therapy , NADP/genetics , NADP/metabolism , Phosphotransferases (Alcohol Group Acceptor)/antagonists & inhibitors , Phosphotransferases (Alcohol Group Acceptor)/genetics , Phosphotransferases (Alcohol Group Acceptor)/metabolism , Precursor Cell Lymphoblastic Leukemia-Lymphoma/genetics , Precursor Cell Lymphoblastic Leukemia-Lymphoma/metabolism
17.
Mol Pharmacol ; 76(4): 723-33, 2009 Oct.
Article in English | MEDLINE | ID: mdl-19570950

ABSTRACT

We have observed that rodent cell lines (mouse, hamster) contain approximately 10 times the levels of dihydrofolate reductase as human cell lines, yet the sensitivity to methotrexate (ED(50)), the folate antagonist that targets this enzyme, is similar. Our previous studies showed that dihydrofolate reductase protein levels increased after methotrexate exposure, and we proposed that this increase was due to the relief of feedback inhibition of translation as a consequence of methotrexate binding to dihydrofolate reductase. In the current report, we show that unlike what was observed in human cells, dihydrofolate reductase (DHFR) levels do not increase in hamster cells after methotrexate exposure. We provide evidence to show that although there are differences in the putative mRNA structure between hamster and human mRNA in the dihydrofolate reductase binding region previously identified, "hamsterization" of this region in human dihydrofolate reductase mRNA did not change the level of the enzyme or its induction by methotrexate. Further experiments showed that human dihydrofolate reductase is a promiscuous enzyme and that it is the difference between the hamster and human dihydrofolate reductase protein, rather than the DHFR mRNA, that determines the response to methotrexate exposure. We also present evidence to suggest that the translational up-regulation of dihydrofolate reductase by methotrexate in tumor cells is an adaptive mechanism that decreases sensitivity to this drug.


Subject(s)
Gene Expression Regulation, Enzymologic , Protein Biosynthesis , Tetrahydrofolate Dehydrogenase/genetics , Amino Acid Sequence , Animals , Base Sequence , Blotting, Western , CHO Cells , Cricetinae , Cricetulus , DNA Primers , Humans , Molecular Sequence Data , Mutagenesis, Site-Directed , Nucleic Acid Conformation , RNA, Messenger/chemistry , RNA, Messenger/genetics , Sequence Homology, Amino Acid , Species Specificity , Tetrahydrofolate Dehydrogenase/chemistry
18.
Vitam Horm ; 79: 267-92, 2008.
Article in English | MEDLINE | ID: mdl-18804698

ABSTRACT

Dihydrofolate reductase (DHFR) enzyme catalyzes tetrahydrofolate regeneration by reduction of dihydrofolate using NADPH as a cofactor. Tetrahydrofolate and its one carbon adducts are required for de novo synthesis of purines and thymidylate, as well as glycine, methionine and serine. DHFR inhibition causes disruption of purine and thymidylate biosynthesis and DNA replication, leading to cell death. Therefore, DHFR has been an attractive target for chemotherapy of many diseases including cancer. Over the following years, in order to develop better antifolates, a detailed understanding of DHFR at every level has been undertaken such as structure-functional analysis, mechanisms of action, transcriptional and translation regulation of DHFR using a wide range of technologies. Because of this wealth of information created, DHFR has been used extensively as a model system for enzyme catalysis, investigating the relations between structure in-silico structure-based drug design, transcription from TATA-less promoters, regulation of transcription through the cell cycle, and translational autoregulation. In this review, the current understanding of human DHFR in terms of structure, function and regulation is summarized.


Subject(s)
Folic Acid Antagonists/pharmacology , Gene Expression Regulation, Enzymologic/drug effects , Tetrahydrofolate Dehydrogenase/metabolism , Folic Acid Antagonists/chemistry , Humans , Molecular Structure , Protein Conformation , Tetrahydrofolate Dehydrogenase/chemistry , Tetrahydrofolate Dehydrogenase/genetics
19.
J Biol Chem ; 280(24): 22721-31, 2005 Jun 17.
Article in English | MEDLINE | ID: mdl-15817466

ABSTRACT

Human dihydrofolate reductase (DHFR) protein levels rapidly increase upon exposure to methotrexate, a potent inhibitor of this enzyme. A model to explain this increase proposes that DHFR inhibits its own translation by binding to its cognate mRNA and that methotrexate disrupts the DHFR protein-mRNA complex allowing its translation to resume. In the present study, Chinese hamster ovary cells lacking DHFR were transfected with wild type and mutants of human DHFR to identify amino acids that are essential for increases in DHFR in response to methotrexate. Glu-30, Leu-22, and Ser-118 were involved in the up-regulation of DHFR protein levels by methotrexate and certain other antifolates. Cells transfected with E30A, L22R, and S118A mutants that did not respond to methotrexate up-regulation had higher basal levels of DHFR, consistent with the model, i.e. lack of feedback regulation of these enzymes. Although cells containing the S118A mutant enzyme had higher levels of DHFR and had catalytic activity similar to that of wild type DHFR, they had the same sensitivity to the cytotoxicity of methotrexate, as were cells with wild type DHFR. This finding provides evidence that the adaptive up-regulation of DHFR by methotrexate contributes to the decreased sensitivity to this drug. Based on these observations, a new model is proposed whereby DHFR exists in two conformations, one bound to DHFR mRNA and the other bound to NADPH. The mutants that are not up-regulated by methotrexate are unable to bind their cognate mRNA.


Subject(s)
Gene Expression Regulation, Enzymologic , Tetrahydrofolate Dehydrogenase/biosynthesis , Up-Regulation , Amino Acids/chemistry , Animals , Binding Sites , Blotting, Western , CHO Cells , Catalysis , Cell Survival , Cloning, Molecular , Cricetinae , Cysteine/chemistry , DNA Primers/chemistry , Folic Acid Antagonists/pharmacology , Glutamic Acid/chemistry , Glutathione Transferase/metabolism , Green Fluorescent Proteins/chemistry , Humans , Inhibitory Concentration 50 , Kinetics , Leucine/chemistry , Methotrexate/pharmacology , Microscopy, Fluorescence , Models, Biological , Mutagenesis, Site-Directed , Mutation , NADP/chemistry , Protein Biosynthesis , RNA, Messenger/metabolism , Recombinant Fusion Proteins/chemistry , Reverse Transcriptase Polymerase Chain Reaction , Serine/chemistry , Spectrophotometry , Tetrahydrofolate Dehydrogenase/chemistry , Time Factors , Transcription, Genetic , Transfection
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