Lecture 16: Regulation of Metabolism & Transport

transcriptional regulation

gene transcription

post-transcriptional regulation

mRNA processing, mRNA stabilization, translation & protein modification, enzyme stabilization

mechanisms of regulation

increased or decrease protein stability and synthesis

constitutive androstane receptor (CAR)

phenobarbital (antiepileptic) is the agonist

pregnane X receptor (PXR)

rifampin (antituberculosis) is the agonist

peroxisome proliferated activated receptor (PPAR)

thiazolidinediones (antidiabetic) is the agonist

HSP90/AIP

AhR chaperone complex

aryl hydrocarbon nuclear translocator (ARNT)

heterodimerize with AhR

omeprazole

increase CYP metabolism of chemical carcinogens

TCDD (dioxin)

contaminant of Agent Orange, a defoliant mixture sprayed over land during Vietnam War

chloracne, birth defects, cancers

AhR ligand toxicites

protein phosphatase (PP)

CAR is dephosphorylated by ___

CaM kinase

CAR translocates to nucleus where it is phosphorylated by ___

phenobarbital response elements (PBREMs) or direct repeat (DR4) response elements

CAR heterodimerizes with RXR and then binds to ___

phenobarbital

primary activator of CAR signaling

CYP2B6, CYP2C9

phase I enzyme targets in CAR

GSTs, SULTs, UGTs

phase II enzyme targets in CAR

direct repeat (DR3) and everted repeat (ER6) response elements

PCR translocates to the nucleus and heterodimerizes with RCR and binds to ___

corticosteroids (dexamethasone), St. John’s wort, rifampicin

primary activator of PXR signaling

CYP2A4, CYP2B6

phase I enzyme targets in PXR signaling

SULTs, UGTs

phase II enzyme targets in PXR signaling

17 alpha - ethinylestradiol

St. John’s wort decreases __ t ½ from 24 h to 12 h

lipid metabolism

PPAR-alpha focus

gemfibrozil

example of PPAR - alpha fibrate drugs

proliferation and liver carcinogenesis

PPAR-alpha causes peroxisome __ in rodents

mixed lipid/glucose metabolism

PPAR-beta/delta focus

glucose metabolism

PPAR-gamma focus

rosiglitazone

examples of PPAR-gamma glitazone drug

direct repeat (DR1) and peroxisome proliferator response elements (PPRE)

PPARs translocate to nucleus and heterodimerize with RXR and bind to __

prostaglandins, fatty acids for PPAR beta/delta

endogenous activators of PPAR signaling

CYP4A11 isoforms

phase I target of PPAR signaling

Keap1

Nrf2 is sequestered in the cytosol by __ and broken down by the proteasome

disulfide bond formation

activation by drugs (dimethyl fumarate), electrophiles, or oxidants causes __ formation in Keap1 and release of Nrf2

small Maf proteins

Nrf2 translocated to the nucleus, binds to ___ and electrophile response elements (EpREs)

NQO1, CES

phase I target genes of Nrf2 signaling

GST, UGT

phase II target genes of Nrf2 signaling

MRPs

transport target gene of Nrf2 signaling

epigenetics

study of changes in gene expression by mechanisms that do not involve changes in the DNA sequence

CpG dinucleotide area

addition/removal of a methyl group to the cytosine pyrimidine ring at the 5 position in a ___

silencing

methylation/demethylation is critical for long-term __

heterochromatin

methylation/demethylation is critical for formation of __

closed DNA conformation

transcriptional repression

open DNA conformation

transcriptional activation

lysine

in transcriptional activation, acetylation neutralizes the basic charge of __ residue and weakens interaction between DNA-histone

DNA hypomethylation, histone acetylation

increased MDR1 expression

non-coding RNAs

regulatory RNA molecules that are not translated into proteins

microRNAs (miRs)

• about 22 nucleotides in length

• base-pair with complementary sequences in 3’ untranslated region (UTR) of targeted mRNA molecules

• interaction leads to decreased translational efficiency or promotes destabilization and degradation of mRNAs

long non-coding RNAs (IncRNAs)

• >200 nucleotides in length

• regulate cell cycle, pluripotency, cell differentiation and development

RNA polymerase II

miRNA coding sequences are transcribed by __ to pri-miRNA's in the nucleus

drosha-DGCR8 endonuclease

pri-miRNAs are further processed by ___ complex to pre-miRNAs

exportin 5

__ transports pre-miRNAs into cytoplasm

Dicer-TRBP

in cytoplasm, pre-miRNAs further processed by the __ complex to double-stranded miRNAs

helicase

miRNA duplexes are subsequently unwound by a ___

argonaute 2 (AGO2)-containing miRISCs

single-stranded mature miRNAs are loaded into __

translational repression, mRNA degradation

by pairing MREs within 3’UTRs of target mRNAs, miRNAs mediate __ and → lower levels of protein expression

clotrimazole - CYP3A4, ethanol - CYP2E1, isosafrole (fragrance) - CYP1A2

ADME proteins that can be induced without changing mRNA levels

chronic liver disease

induction of CYP2E1 by ethanol can cause reactive oxygen species that contribute to ___

protein kinase C

mechanism for protein stabilization

NAPQI production

stabilization of CYP2E1 by chronic ethanol consumption increases __

saline or endotoxin

reduce CYP-mediated metabolism

decreased hepatic blood flow

acute liver failure absorption

variable decrease in protein binding

acute liver failure distribution

impairment of phase II enzymes —> decrease metabolism —> longer half life

acute liver failure metabolism

impaired biliary excretion/renal failure due to accumulation of toxic metabolites

acute liver failure elimination

reduced first-pass metabolism → increased systemic drug exposure

chronic liver failure absorption

decrease albumin → increased free drug → increase volume of distribution

chronic liver failure distribution

decrease enzyme activity (mainly phase I) → decrease hepatocyte function

chronic liver failure metabolism

impaired renal and biliary excretion

chronic liver failure elimination

steatohepatitis

decreased CYP1A2, CYP2C19, CYP2E1

obestiy

increased CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, decreased CYP3A4

increase or decrease enzyme production

transcription factor function

controls if gene is ON or OFF

epigenetics functioon

decrease protein production

microRNA

change how long enzymes last

protein stability

reduces enzyme activity

disease (inflammation, liver)