ATP Binding Cassette Transporters in Human Health and Disease

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ATP Binding Cassette Transporters in Human Health
and Disease
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Previous Years Comments

• too much biochemistry
• not enough clinical relevance
• not enough content!

3
This Years Vital Statistics

• Adverse Drug Reactions, 76
• Neurobiology of Pain, 28
• The Host's View on Bacterial Infections, 9
• Ion Channels Disease, 4
• Human ATP Binding Cassette Transporter in Health
  and Disease, 1

4
Course Overview

• 2 Lectures (weeks 1,2)
• E1 9.30-11 a.m. All to attend.
• 2 small group sessions (week 3,4)
• Sparrow Suite (C99) 9.30-11.00.
• 1 Presentations (week 5)
• E1. 9-12.00 All to attend.

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Course Assessment

• Presentation 30
• Unless clear that one person in a pair has over
  or under-performed (or contributed) you will get
  the same mark as your partner
• 1.5 hour paper 70
• Part A single, general question compulsory.
  50 of the module.
• Part B choice of 1 from 4, more focussed
  question. 20 of the module.

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NLE

• Both lectures
• Project titles reminder
• Helpful websites
• All project presentations when they are complete.
  They will be part of the body of material I will
  expect you to know
• Sample examination paper and guideline answers

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Presentation Groups

• Two per group
• ca. 12 topics to select from. First come first
  served! Group members and the proposed project to
  me asap.
• Two tutorial session drop in.
• Identify papers to read and interpret data

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Presentation Format

• 12 or 13 minutes plus 2 or 3 minutes questions
  from the audience
• PowerPoint ONLY
• MUST include a final slide of fully referenced
  sources of information. Failure to do so will
  incur a 10 penalty.
• Talks must reach me by e-mail by 5pm Friday
  October 27th on CD preferably.
• I will make the presentation into a handout
• Assessed 30 of the module mark.

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Presentations FAQs

• What are the objectives?
• Can you narrow the scope down and make sure we
  cover the right things?
• Can we get handouts?
• Can you fill in the gaps if peoples
  presentations leave them?
• Will we be expected to know what other people
  present?

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Presentation Titles - I

• Can gene therapy work to cure cystic fibrosis?
• Define GT, examples of CF trials and results,
  problems and successes. Dont need a treatise on
  CF please!
• The relationship between genotype and phenotype
  in ABCA4/ABCR associated retinal disease
• Physiological background, genetic information,
  protein functional information
• P-glycoprotein Is it really associated with
  increased drug resistance in solid tumours?
• Weigh up the evidence for this based upon papers
  and review articles.

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Presentation Titles - II

• ABCA1, reverse cholesterol transport and
  hypercholesterolaemia
• Define role of A1, implication in disease, likely
  substrates, location etc.
• ABCB4 and bile secretion in human health and
  disease
• Role of ABCB4 in bile secretion. Failure of
  B4-mediated bile secretion in disease(s) of your
  choice
• The role of the TAP protein in the immune
  response
• What is the function of TAP, what is unusual
  about its sub-cellular location, structure, what
  proteins does it interact with etc?

12
Presentation Titles - III

• How do K-channel openers work as anti-diabetic
  therapies?
• Organisation of the SUR/KATP complex, binding of
  diazoxides etc.
• The cancer stem cell hypothesis are multidrug
  pumps inherent to tumour formation and survival?
• Define the cancer stem cell hypothesis and the
  role ABC transporters are proposed to play?
• Is ABCG2 involved in stem cell stress survival?
• Define stem cells and stress they may be under.
  Describe evidence for role of ABCG2

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Presentation Titles - IV

• Lorenzos Oil fails ALD patients. What next?
• What is adrenoleukodystrophy, what ABC
  transporter misfunction occurs, what was
  Lorenzos Oil and what is the current treatment
  hopes
• Double whammy. Is there a common switch to avoid
  anti-cancer drugs?
• cytochrome P450s and P-glycoprotein are both
  transcriptionally activated by the same
  chemicals.
• Dont eat your greens if youve got
  sitosterolemia!
• What ABC transporter is involved in
  sitosterolemia, prevalence of disease, function
  of the G5/G8 complex. What data currently
  supports this?

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Starting points

• Special issue in FEBS Letters on ABC transporters
  www.febsletters.com
• ABC protein book http//aleph.nottingham.ac.uk/ALE
  PH
• ABC transporter on-line book
• http//www.ncbi.nlm.nih.gov/

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Learning Goals, Lectures 12

• Understand principles of membrane transport
• Recognize diversity in ABC transporters
• Understand structural aspects
• Understand proposed catalytic and transport cycle
  of best-studied ABC protein.

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Outcome measures of your presentations

• Understand details behind the ABC transporter in
  question.
• i.e. must go way beyond what I tell you in the
  next couple of hours.
• Knowing the evidence that supports the proteins
  function or role in disease
• Conveying that information to your colleagues

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Basic Principles of Transport

• The lipid membrane has a barrier function
• Most substances do NOT diffuse across membranes
• Vectorial (i.e. directional) transport occurs

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Types of Membrane Transport Proteins

• Facilitative transporters
• promote transport down a concentration gradient
• Primary active transporters
• Use the energy of ATP hydrolysis to power
  transport
• Secondary active transporters
• Use a downhill gradient of substance X to power
  the uphill transport of substance Y.

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The ABC of ABC Transport

• ATP
• Binding
• Cassette
• Bind and hydrolyse ATP
• Coupled to the transport of substances across
  cellular membranes.

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ABC Transporters why I should sit up and take
notice
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Why you should have put this module down as
first choice
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ABC TransportersDiverse Functions in Humans
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what do they look like?shared modular design
(NBD-TMD)2
Drug efflux P-glycoprotein (P-gp)
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Core Domains

• Two nucleotide binding domains
• bind and hydrolyse ATP
• Two transmembrane domains
• bind and form a substrate translocation pathway
• multiple transmembrane a-helices

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ABC Transporter Families in Man

• Seven sub-families (A-G)
• ABCA, ABCB, ABCC, you get the idea
• 601 amino acids up to gt 2500 amino acids
• Two families comprised of proteins with no known
  role in transport
• All characterized transporters are exporters

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Export? Are we arms dealers now?
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ABCA Sub-familyLipids, cholesterol and
homeostatic disorders

• Two additional extracellular domains
• ABCA1 role in regulation of high density
  lipoprotein (HDL)
• ABCA4 transporter of lipid-conjugated retinal
  derivatives in the eye?
• ABCA7 role in cellular lipid homeostasis

presentation 4
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ABCA4 and its location

• Rod and cone cell specific transporter.
• Disks arise from the plasma membrane in rods.
  Cone cell structure similar but the disks may be
  contiguous with plasma membrane
• Disks shed at a rate of 00s per day.

presentation 2
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ABCA4 and its function
Rod Cytoplasm
Disk Lumen
hv
This would be import..into the cytoplasm.
Slightly heretical
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ABCB Sub-family

• P-glycoprotein (ABCB1)
• drug detoxification
• cancer cell drug resistance
• MDR3 (ABCB4)
• PC transporter in bile
• cholestasis
• Tap1/2 (ABCB2, B3)
• 2 half-transporters involved in peptide
  presentation
• related ABCB family members in parasitic organisms

presentation 11
presentation 5
presentation 6
Tap1
Tap2
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P-glycoprotein and Drug Transport
cytoplasm
cancer cell
presentation 3
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TAP1/2 and Antigen Processing
presentation 6
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ABCC Extra Domains and Unusual Functions

• MRP1 (ABCC1)
• drug resistance in cancer
• CFTR (ABCC7)
• ATP-gated chloride channel
• defective in cystic fibrosis
• SUR (ABCC8 C9)
• ATP-regulated potassium channel
• defective insulin secretion

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Cystic fibrosis and an epithelial chloride channel

• CFTR role in maintaining epithelial integrity
• ABC transporter, but actually an ion channel.
• Commonest defect leads to improper targeting of
  protein.

presentation 1
35
Sulphonylurea receptor and insulin secretion
presentation 7
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ABCD and long-chain fatty acid oxidation

• ALDP (ABCD1)
• half-transporter
• peroxisomal fatty acid transporter
• associates with
• PMP70 (ABCD3)
• similar to ALDP
• Implicated in adrenoleukodystrophy

presentation 10
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ABCG

• ABCG2 (BCRP)
• drug resistance in cancer stem cells?
• stem cell stress tolerance
• ABCG5 / G8
• sterol transport
• implicated in sitosterolaemia

presentation 8
presentation 9
G8
G5
presentation 12
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ABCG5 and ABCG8

• Function as a heterodimer
• Export plant sterols into the bile?
• Prevent plant sterols from accumulating in plasma?

bile
plant sterols
G5
G8
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Summary

• Dozen or so ABC transporters in humans with
  considerable clinical relevance.
• Time to learn more!