1
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Zhang C, Yan Y, Zhou B, Wang Y, Tian X, Hao S, Ma P, Zheng L, Zhang Q, Hui L, Wang Y, Cao Z, Ma X. Identification of deep intronic variants of PAH in phenylketonuria using full-length gene sequencing. Orphanet J Rare Dis 2023; 18:128. [PMID: 37237386 PMCID: PMC10214626 DOI: 10.1186/s13023-023-02742-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Accepted: 05/18/2023] [Indexed: 05/28/2023] Open
Abstract
BACKGROUND Phenylketonuria (PKU) is an autosomal recessive congenital metabolic disorder caused by PAH variants. Previously, approximately 5% of PKU patients remained undiagnosed after Sanger sequencing and multiplex ligation-dependent probe amplification. To date, increasing numbers of pathogenic deep intronic variants have been reported in more than 100 disease-associated genes. METHODS In this study, we performed full-length sequencing of PAH to investigate the deep intronic variants in PAH of PKU patients without definite genetic diagnosis. RESULTS We identified five deep intronic variants (c.1199+502A>T, c.1065+241C>A, c.706+368T>C, c.706+531>C, and c.706+608A>C). Of these, the c.1199+502A>T variant was found at high frequency and may be a hotspot PAH variant in Chinese PKU. c.706+531T>C and c.706+608A>C are two novel variants that extend the deep intronic variant spectrum of PAH. CONCLUSION Deep intronic variant pathogenicity analysis can further improve the genetic diagnosis of PKU patients. In silico prediction and minigene analysis are powerful approaches for studying the functions and effects of deep intronic variants. Targeted sequencing after full-length gene amplification is an economical and effective tool for the detection of deep intron variation in genes with small fragments.
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Affiliation(s)
- Chuan Zhang
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
- National Research Institute for Health and Family Planning, National Human Genetic Resources Center, Beijing, China
- Graduate School of Peking, Union Medical College, Beijing, China
| | - Yousheng Yan
- Prenatal Diagnostic Center, Beijing Obstetrics and Gynecology Hospital, Capital Medical University; Beijing Maternal and Child Health Care Hospital, Beijing, China
| | - Bingbo Zhou
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Yupei Wang
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Xinyuan Tian
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Shengju Hao
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Panpan Ma
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Lei Zheng
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Qinghua Zhang
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Ling Hui
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Yan Wang
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Zongfu Cao
- National Research Institute for Health and Family Planning, National Human Genetic Resources Center, Beijing, China.
| | - Xu Ma
- National Research Institute for Health and Family Planning, National Human Genetic Resources Center, Beijing, China.
- Graduate School of Peking, Union Medical College, Beijing, China.
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2
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Matherly LH, Schneider M, Gangjee A, Hou Z. Biology and therapeutic applications of the proton-coupled folate transporter. Expert Opin Drug Metab Toxicol 2022; 18:695-706. [PMID: 36239195 PMCID: PMC9637735 DOI: 10.1080/17425255.2022.2136071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Accepted: 10/11/2022] [Indexed: 01/19/2023]
Abstract
INTRODUCTION The proton-coupled folate transporter (PCFT; SLC46A1) was discovered in 2006 as the principal mechanism by which folates are absorbed in the intestine and the causal basis for hereditary folate malabsorption (HFM). In 2011, it was found that PCFT is highly expressed in many tumors. This stimulated interest in using PCFT for cytotoxic drug targeting, taking advantage of the substantial levels of PCFT transport and acidic pH conditions commonly associated with tumors. AREAS COVERED We summarize the literature from 2006 to 2022 that explores the role of PCFT in the intestinal absorption of dietary folates and its role in HFM and as a transporter of folates and antifolates such as pemetrexed (Alimta) in relation to cancer. We provide the rationale for the discovery of a new generation of targeted pyrrolo[2,3-d]pyrimidine antifolates with selective PCFT transport and inhibitory activity toward de novo purine biosynthesis in solid tumors. We summarize the benefits of this approach to cancer therapy and exciting new developments in the structural biology of PCFT and its potential to foster refinement of active structures of PCFT-targeted anti-cancer drugs. EXPERT OPINION We summarize the promising future and potential challenges of implementing PCFT-targeted therapeutics for HFM and a variety of cancers.
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Affiliation(s)
- Larry H. Matherly
- Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan 48201, United States
- Department of Oncology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States
- Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States
| | - Mathew Schneider
- Department of Oncology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States
| | - Aleem Gangjee
- Division of Medicinal Chemistry, Graduate School of Pharmaceutical Sciences, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
| | - Zhanjun Hou
- Molecular Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan 48201, United States
- Department of Oncology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States
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3
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Sakurai Y, Toriumi N, Sarashina T, Ishioka T, Nagata M, Kobayashi H, Azuma H. An infantile case of hereditary folate malabsorption with sudden development of pulmonary hemorrhage: a case report. J Med Case Rep 2022; 16:268. [PMID: 35773682 PMCID: PMC9245286 DOI: 10.1186/s13256-022-03448-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 05/06/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Hereditary folate malabsorption-a rare disorder caused by impairment of the folate transporter-can develop into severe folate deficiency manifesting as megaloblastic anemia and occasionally thrombocytopenia. Reportedly, megaloblastic anemia can manifest with hemorrhagic episodes, possibly due to ineffective platelet production and platelet dysfunction. However, life-threatening hemorrhage events in hereditary folate malabsorption have not been well investigated. CASE PRESENTATION A 3-month-old Japanese boy was transferred to our hospital due to thrombocytopenia and severe megaloblastic anemia. During a thorough examination of hematopoietic abnormalities, the patient suddenly went into cardiac arrest due to pulmonary hemorrhage. Although intravenous folate supplementation was started soon after the identification of folate deficiency, the patient died of circulatory defect and multiple organ failure. The cause of pulmonary hemorrhage, such as respiratory infection, could not be confirmed. Genetic investigation revealed a mutation in the SLC46A1 gene to be the cause of the hereditary folate malabsorption. CONCLUSION We report an infantile case of hereditary folate malabsorption that progressed to lethal pulmonary hemorrhage before folate deficiency was identified. Clinicians should consider that megaloblastic anemia could lead to severe bleeding without warning, and that nutrient supplementation should be initiated as soon as possible.
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Affiliation(s)
- Yukari Sakurai
- Department of Pediatrics, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan.
| | - Naohisa Toriumi
- Department of Pediatrics, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan
| | - Takeo Sarashina
- Department of Pediatrics, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan
| | - Toru Ishioka
- Department of Pediatrics, Wakkanai City Hospital, 4-11-6, Chuou, Wakkanai, Hokkaido, 097-8555, Japan
| | - Marino Nagata
- Division of Immunopathology, Department of Pathology, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan
| | - Hiroya Kobayashi
- Division of Immunopathology, Department of Pathology, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan
| | - Hiroshi Azuma
- Department of Pediatrics, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan
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4
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Mitsui-Sekinaka K, Sekinaka Y, Endo A, Imai K, Nonoyama S. The Primary Immunodeficiency Database in Japan. Front Immunol 2022; 12:805766. [PMID: 35082792 PMCID: PMC8786595 DOI: 10.3389/fimmu.2021.805766] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Accepted: 12/15/2021] [Indexed: 01/10/2023] Open
Abstract
The Primary Immunodeficiency Database in Japan (PIDJ) is a registry of primary immunodeficiency diseases (PIDs) that was established in 2007. The database is a joint research project with research groups associated with the Ministry of Health, Labor and Welfare; the RIKEN Research Center for Allergy and Immunology (RCAI); and the Kazusa DNA Research Institute (KDRI). The PIDJ contains patient details, including the age, sex, clinical and laboratory findings, types of infections, genetic analysis results, and treatments administered. In addition, web-based case consultation is also provided. The PIDJ serves as a database for patients with PIDs and as a patient consultation service connecting general physicians with PID specialists and specialized hospitals. Thus, the database contributes to investigations related to disease pathogenesis and the early diagnosis and treatment of patients with PIDs. In the 9 years since the launch of PIDJ, 4,481 patients have been enrolled, of whom 64% have been subjected to genetic analysis. In 2017, the Japanese Society for Immunodeficiency and Autoinflammatory Diseases (JSIAD) was established to advance the diagnosis, treatment, and research in the field of PIDs and autoinflammatory diseases (AIDs). JSIAD promotes the analysis of the pathogenesis of PIDs and AIDs, enabling improved patient care and networking via the expansion of the database and construction of a biobank obtained from the PIDJ. The PIDJ was upgraded to “PIDJ ver.2” in 2019 by JSIAD. Currently, PIDJ ver.2 is used as a platform for epidemiological studies, genetic analysis, and pathogenesis evaluation for PIDs and AIDs.
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Affiliation(s)
| | - Yujin Sekinaka
- Department of Pediatrics, National Defense Medical College, Saitama, Japan
| | - Akifumi Endo
- Department of Pediatrics and Clinical Research Center, Tokyo Medical and Dental University, Tokyo, Japan
| | - Kohsuke Imai
- Department of Community Pediatrics, Perinatal and Maternal Medicine, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
| | - Shigeaki Nonoyama
- Department of Pediatrics, National Defense Medical College, Saitama, Japan
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5
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Keegan NP, Wilton SD, Fletcher S. Analysis of Pathogenic Pseudoexons Reveals Novel Mechanisms Driving Cryptic Splicing. Front Genet 2022; 12:806946. [PMID: 35140743 PMCID: PMC8819188 DOI: 10.3389/fgene.2021.806946] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 12/09/2021] [Indexed: 12/16/2022] Open
Abstract
Understanding pre-mRNA splicing is crucial to accurately diagnosing and treating genetic diseases. However, mutations that alter splicing can exert highly diverse effects. Of all the known types of splicing mutations, perhaps the rarest and most difficult to predict are those that activate pseudoexons, sometimes also called cryptic exons. Unlike other splicing mutations that either destroy or redirect existing splice events, pseudoexon mutations appear to create entirely new exons within introns. Since exon definition in vertebrates requires coordinated arrangements of numerous RNA motifs, one might expect that pseudoexons would only arise when rearrangements of intronic DNA create novel exons by chance. Surprisingly, although such mutations do occur, a far more common cause of pseudoexons is deep-intronic single nucleotide variants, raising the question of why these latent exon-like tracts near the mutation sites have not already been purged from the genome by the evolutionary advantage of more efficient splicing. Possible answers may lie in deep intronic splicing processes such as recursive splicing or poison exon splicing. Because these processes utilize intronic motifs that benignly engage with the spliceosome, the regions involved may be more susceptible to exonization than other intronic regions would be. We speculated that a comprehensive study of reported pseudoexons might detect alignments with known deep intronic splice sites and could also permit the characterisation of novel pseudoexon categories. In this report, we present and analyse a catalogue of over 400 published pseudoexon splice events. In addition to confirming prior observations of the most common pseudoexon mutation types, the size of this catalogue also enabled us to suggest new categories for some of the rarer types of pseudoexon mutation. By comparing our catalogue against published datasets of non-canonical splice events, we also found that 15.7% of pseudoexons exhibit some splicing activity at one or both of their splice sites in non-mutant cells. Importantly, this included seven examples of experimentally confirmed recursive splice sites, confirming for the first time a long-suspected link between these two splicing phenomena. These findings have the potential to improve the fidelity of genetic diagnostics and reveal new targets for splice-modulating therapies.
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Affiliation(s)
- Niall P. Keegan
- Centre for Molecular Medicine and Innovative Therapeutics, Health Futures Institute, Murdoch University, Perth, WA, Australia
- Centre for Neuromuscular and Neurological Disorders, Perron Institute for Neurological and Translational Science, The University of Western Australia, Perth, WA, Australia
- *Correspondence: Niall P. Keegan,
| | - Steve D. Wilton
- Centre for Molecular Medicine and Innovative Therapeutics, Health Futures Institute, Murdoch University, Perth, WA, Australia
- Centre for Neuromuscular and Neurological Disorders, Perron Institute for Neurological and Translational Science, The University of Western Australia, Perth, WA, Australia
| | - Sue Fletcher
- Centre for Molecular Medicine and Innovative Therapeutics, Health Futures Institute, Murdoch University, Perth, WA, Australia
- Centre for Neuromuscular and Neurological Disorders, Perron Institute for Neurological and Translational Science, The University of Western Australia, Perth, WA, Australia
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6
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Hou Z, Gangjee A, Matherly LH. The evolving biology of the proton‐coupled folate transporter: New insights into regulation, structure, and mechanism. FASEB J 2022; 36:e22164. [PMID: 35061292 PMCID: PMC8978580 DOI: 10.1096/fj.202101704r] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 12/15/2021] [Accepted: 01/03/2022] [Indexed: 01/19/2023]
Abstract
The human proton‐coupled folate transporter (PCFT; SLC46A1) or hPCFT was identified in 2006 as the principal folate transporter involved in the intestinal absorption of dietary folates. A rare autosomal recessive hereditary folate malabsorption syndrome is attributable to human SLC46A1 variants. The recognition that hPCFT was highly expressed in many tumors stimulated substantial interest in its potential for cytotoxic drug targeting, taking advantage of its high‐level transport activity under acidic pH conditions that characterize many tumors and its modest expression in most normal tissues. To better understand the basis for variations in hPCFT levels between tissues including human tumors, studies have examined the transcriptional regulation of hPCFT including the roles of CpG hypermethylation and critical transcription factors and cis elements. Additional focus involved identifying key structural and functional determinants of hPCFT transport that, combined with homology models based on structural homologies to the bacterial transporters GlpT and LacY, have enabled new structural and mechanistic insights. Recently, cryo‐electron microscopy structures of chicken PCFT in a substrate‐free state and in complex with the antifolate pemetrexed were reported, providing further structural insights into determinants of (anti)folate recognition and the mechanism of pH‐regulated (anti)folate transport by PCFT. Like many major facilitator proteins, hPCFT exists as a homo‐oligomer, and evidence suggests that homo‐oligomerization of hPCFT monomeric proteins may be important for its intracellular trafficking and/or transport function. Better understanding of the structure, function and regulation of hPCFT should facilitate the rational development of new therapeutic strategies for conditions associated with folate deficiency, as well as cancer.
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Affiliation(s)
- Zhanjun Hou
- Molecular Therapeutics Program Barbara Ann Karmanos Cancer Institute Detroit Michigan USA
- Department of Oncology Wayne State University School of Medicine Detroit Michigan USA
| | - Aleem Gangjee
- Division of Medicinal Chemistry Graduate School of Pharmaceutical Sciences Duquesne University Pittsburgh Pennsylvania USA
| | - Larry H. Matherly
- Molecular Therapeutics Program Barbara Ann Karmanos Cancer Institute Detroit Michigan USA
- Department of Oncology Wayne State University School of Medicine Detroit Michigan USA
- Department of Pharmacology Wayne State University School of Medicine Detroit Michigan USA
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7
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Kobayashi R, Kishimoto K, Sano H, Hori D, Kobayashi K. Long follow-up of hereditary folate malabsorption using intravenous folinate. Pediatr Int 2022; 64:e14667. [PMID: 34529878 DOI: 10.1111/ped.14667] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 02/05/2021] [Accepted: 02/16/2021] [Indexed: 11/28/2022]
Affiliation(s)
- Ryoji Kobayashi
- Department of Hematology/Oncology for Children and Adolescents, Sapporo Hokuyu Hospital, Shiroishiku, Sapporo, Japan
| | - Kenji Kishimoto
- Department of Hematology/Oncology for Children and Adolescents, Sapporo Hokuyu Hospital, Shiroishiku, Sapporo, Japan
| | - Hirozumi Sano
- Department of Hematology/Oncology for Children and Adolescents, Sapporo Hokuyu Hospital, Shiroishiku, Sapporo, Japan
| | - Daiki Hori
- Department of Hematology/Oncology for Children and Adolescents, Sapporo Hokuyu Hospital, Shiroishiku, Sapporo, Japan
| | - Kunihiko Kobayashi
- Department of Hematology/Oncology for Children and Adolescents, Sapporo Hokuyu Hospital, Shiroishiku, Sapporo, Japan
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8
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Jin X, Yan Y, Zhang C, Tai Y, An L, Yu X, Zhang L, Hao S, Cao X, Yin C, Ma X. Identification of novel deep intronic PAH gene variants in patients diagnosed with phenylketonuria. Hum Mutat 2021; 43:56-66. [PMID: 34747549 DOI: 10.1002/humu.24292] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 10/21/2021] [Accepted: 10/28/2021] [Indexed: 12/17/2022]
Abstract
Phenylketonuria (PKU) is caused by phenylalanine hydroxylase (PAH) gene variants. Previously, 94.21% of variants were identified using Sanger sequencing and multiplex ligation-dependent probe amplification. To investigate the remaining variants, we performed whole-genome sequencing for four patients with PKU and unknown genotypes to identify deep intronic or structural variants. We identified three novel heterozygous variants (c.706+368T>C, c.1065+241C>A, and c.1199+502A>T) in a deep PAH gene intron. We detected a c.1199+502A>T variant in 60% (6/10) of PKU patients with genetically undetermined PKU. In silico predictions indicated that the three deep variants may impact splice site selection and result in the inclusion of a pseudo-exon. A c.1199+502A>T PAH minigene and reverse transcription PCR (RT-PCR) on blood RNA from a PKU patient with biallelic variants c.1199+502A>T and c.1199G>A confirmed that the c.1199+502A>T variant may strengthen the predicted branch point and leads to the inclusion of a 25-nt pseudo-exon in the PAH mRNA. Reverse transcription polymerase chain reaction (RT-PCR) on the minigene revealed that c.706+368T>C may create an SRSF2 (SC35) binding site via a 313-nt pseudo-exon, whereas c.1065+241C>A may produce an 81-nt pseudo-exon that strengthens the predicted SRSF1 (SF2/ASF) binding site. These results augment current knowledge of PAH genotypes and show that deep intronic analysis of PAH can genetically diagnose PKU.
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Affiliation(s)
- Xiaohua Jin
- National Research Institute for Family Planning, Beijing, China.,National Human Genetic Resources Center, Beijing, China
| | - Yousheng Yan
- Prenatal Diagnostic Center, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, China
| | - Chuan Zhang
- National Research Institute for Family Planning, Beijing, China.,National Human Genetic Resources Center, Beijing, China.,Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Ya Tai
- Department of Obstetrics and Gynecology, Peking University International Hospital, Beijing, China
| | - Lisha An
- National Research Institute for Family Planning, Beijing, China.,National Human Genetic Resources Center, Beijing, China
| | - Xinyou Yu
- Department of Prenatal Diagnosis Center, General Hospital of Ningxia Medical University, Yinchuan, China
| | - Linlin Zhang
- Clinical Lab, The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Shengju Hao
- Gansu Province Medical Genetics Center, Gansu Provincial Maternity and Child-Care Hospital, Lanzhou, China
| | - Xiaofang Cao
- National Research Institute for Family Planning, Beijing, China.,National Human Genetic Resources Center, Beijing, China
| | - Chenghong Yin
- Prenatal Diagnostic Center, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, China
| | - Xu Ma
- National Research Institute for Family Planning, Beijing, China.,National Human Genetic Resources Center, Beijing, China
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9
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Zhan HQ, Najmi M, Lin K, Aluri S, Fiser A, Goldman ID, Zhao R. A proton-coupled folate transporter mutation causing hereditary folate malabsorption locks the protein in an inward-open conformation. J Biol Chem 2020; 295:15650-15661. [PMID: 32893190 DOI: 10.1074/jbc.ra120.014757] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Revised: 08/26/2020] [Indexed: 11/06/2022] Open
Abstract
The proton-coupled folate transporter (PCFT, SLC46A1) is required for folate intestinal absorption and transport across the choroid plexus. Recent work has identified a F392V mutation causing hereditary folate malabsorption. However, the residue properties responsible for this loss of function remains unknown. Using site-directed mutagenesis, we observed complete loss of function with charged (Lys, Asp, and Glu) and polar (Thr, Ser, and Gln) Phe-392 substitutions and minimal function with some neutral substitutions; however, F392M retained full function. Using the substituted-cysteine accessibility method (with N-biotinyl aminoethyl methanethiosulfonate labeling), Phe-392 mutations causing loss of function, although preserving membrane expression and trafficking, also resulted in loss of accessibility of the substituted cysteine in P314C-PCFT located within the aqueous translocation pathway. F392V function and accessibility of the P314C cysteine were restored by insertion of a G305L (suppressor) mutation. A S196L mutation localized in proximity to Gly-305 by homology modeling was inactive. However, when inserted into the inactive F392V scaffold, function was restored (mutually compensatory mutations), as was accessibility of the P314C cysteine residue. Reduced function, documented with F392H PCFT, was due to a 15-fold decrease in methotrexate influx V max, accompanied by a decreased influx Kt (4.5-fold) and Ki (3-fold). The data indicate that Phe-392 is required for rapid oscillation of the carrier among its conformational states and suggest that this is achieved by dampening affinity of the protein for its folate substrates. F392V and other inactivating Phe-392 PCFT mutations lock the protein in its inward-open conformation. Reach (length) and hydrophobicity of Phe-392 appear to be features required for full activity.
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Affiliation(s)
- He-Qin Zhan
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Pathology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Mitra Najmi
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Kai Lin
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA; Air Force Medical Center, People's Liberation Army, Beijing, China
| | - Srinivas Aluri
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Andras Fiser
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, USA
| | - I David Goldman
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA.
| | - Rongbao Zhao
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA
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10
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Miyashita N, Kurosawa H, Yamashita Y, Miki Y, Ishida T. Pulmonary hypertension related to hereditary folate malabsorption in an infant. Pediatr Int 2020; 62:1119-1120. [PMID: 32893915 DOI: 10.1111/ped.14266] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 03/21/2020] [Accepted: 04/15/2020] [Indexed: 11/27/2022]
Affiliation(s)
- Norihisa Miyashita
- Division of Pediatric Critical Care Medicine, Hyogo Prefectural Kobe Children's Hospital, Kobe, Hyogo, Japan
| | - Hiroshi Kurosawa
- Division of Pediatric Critical Care Medicine, Hyogo Prefectural Kobe Children's Hospital, Kobe, Hyogo, Japan
| | - Yuriko Yamashita
- Division of Pediatric Critical Care Medicine, Hyogo Prefectural Kobe Children's Hospital, Kobe, Hyogo, Japan
| | - Yasunobu Miki
- Division of Cardiology, Hyogo Prefectural Kobe Children's Hospital, Kobe, Hyogo, Japan
| | - Toshiaki Ishida
- Division of Hematology and Oncology, Hyogo Prefectural Kobe Children's Hospital, Kobe, Hyogo, Japan
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