miRNA and cancer Flashcards
What enzyme was introduce into petunias that lead to the discovery of miRNAs
Charcone Synthase
What cuts pri-miRNA to pre-miRNA
The microprocess (DROSHA+DGCR8) Chops of the stem-loop
What cuts the pre-miRNA to miRNA
Dicer
Where do the majority of miRNA occur
40% occur in introns
Mainly occur in promoters
What are the methods of miRNA translation
1) Independent promoter
2) Intronic
3) Extronic
In intronic and extronic the miRNA volume produced is controlled by hte amount of RNA produced. The microprocessor excises the miRNA
What type of enzyme is DROSHA
RNAaseIII Enzyme
Describe the roles of Drosha and DGCR8
DGCR8 has two RNA-binding domain –> anchors the pri-miRNA before drosha cleavage
Drosha recognises the structure of pri-miRNA cleaves it 11 nucleotides from the ss-RNA:ds-RNA junction
Generates a pre-miRNA that is 65-70 nucleotides long
Describe the role of Dicer
Dicer has a blade and handle domain
PAZ bocket at the bottom of the handle binds the 3’ end of RNA and anchors it in
There are 2 nuclease domains in the blade which then cuts the dsDNA 22 nucleotides from the end leaving a 2 nucleotide overhand
What is the central component of the RISC
AGO2 part of the Argonaut family of proteins
How does the RISC work to cause mRNA cleavage/splicing
A paz domain in AGO2 binds the 3’ end of RNA. This guides the base pairs to target mRNA. the mmiRNA:MRNA binding proteins psoition the RNAase domain in the muddle of the guide RNA and cuts between the 10th and 11th nucletide
HOw does the RISC work to cause mRNA translation inhibiton
Interations between the miRNA and the 3’ UTR initiated by ‘seed residues’
Seed residues are typically 7 complimentary base pairs and binds between 2-8 bases of the miRNA –> can then mediate translation repression
What are the methods of translational repression once the miRNA is bound to RISC
1) Repression of initiation –> removal of cap, inhibit incorporation of 60S ribosomal subunit
2) Inhibit ribosomal elongation
3) May recuit RNA decapping and deadenylating enzymes
What regions to miRNAs like to bind to
AU-Rich regions
AREs are present in many mRNAs, particularly growth factors, cytokines and short lived mRNAs
What is DICER syndrome
Cuases predisposition to many cancers
E.g. cystic nephoroma
Mainly childhood cancers
What do mutations in DGCR8 produce
Di George Syndrome
Cardiac abnormalities Abnormal facies Thymic hypoplasia Cleft palate, cellular immune deficiency Hypoparathyroidism with hypoalcaemia 22 --> 22q11 deletion
What gene can drive the expression of mirR17-92 cluster
MYC
What cancers in miR17-92 often overexpressed in
B Cell lymphomas e.g. Burkitts
What deletions often occur in CLL
miR15 and miR16
What in frequently downregulated in lung cancer and neuroblastoma
let-7
What are the two types of miRNAs we can use for therapy and what is the difference between them
shRNA –> hairpn RNA which needs dicer cleavage
siRNA –> no need for DICER cleaveage however needs complete complimentarity to prevent offtarget effects
What ways can we influence miRNA expression
Upregulate using mimics
DOwn regulate using sponges
What are the 2 different methods of delivering RNA for therapeutic usage
Transfection (siRNA/mimics)
Transduction (shRNA/miRNA)
Example of miRNA used to treat liver cancer
AAV-mi-miR26
Targets cyclins D2 and E2 to cause cell cycle arrest and caused apoptosis in cancer cells
What other miRNA has been used to treat liver cancer and liver mets
MiR34 –> targers CDK4
