miRNAs

biogenesis of miRNAs

transcribed by RNAPII from gDNA to produce pri-miRNAs that are cleaved by DROSHA
pre miRNA processed by dicer into miRNA duplex
mature miRNA incorporated in to RISC which mediates gene silencing via mRNA cleavage and degradation

mechanisms of miRNA dysregulation in cancer

amplification or deletion of TSG or OG miRNAs
transcriptional dysregulation by oncogenes
epigenetic silencing
defective biogenesis

LOH of TSG miRNA

B cell CLL loss of miRNA15a and 16 on Ch13

amplification of OG miRNA

miR17-92 cluster amplified in lung cancers

mechanisms that miRNAs drive cancer

sustaining proliferation
evading growth suppresses
resisting cell death
invasion and metastasis

miRNAs sustaining proliferation

miR17-92 cluster overexpression of E2F TFs in cooperation with myc
MiR-221 degrades p27 - G1-S entry

miRNAs resisting cell death

miR15a-16 loss leads to Bcl2 overexpression and apoptosis evasion in B-CLL
miR-21 upregulated in cancer - inhibits APAF1 and FasL to block apoptosis

miRNAs driving invasion and metastasis

miR200 suppresses EMT by targeting ZEB1/2 to suppress E-cadherin
miR-10b induced by TWIST promotes invasion and micrometastasis in BC

GCTs

arise from primordial germ cells during development

miRNA expression in GCTs

found miR371-373 upregulated in mGCTs
childhood data collected by microarray and adult data collected by PCR
shared seed region at position 2-7 that determines mRNA specificity

significance of miRNA cluster

mRNA targets degraded identified as functionally significant by sylamer algorithm
enrichment of seed complementarity region in mRNAs that had altered expression

use of miRNA over ctDNA

GCTs have decreased mutation burden - no ctDNA marker
miRNAs released in exc vesicles can be a biomarker

sensitivity and specificity of miRNA profiles

ROCA curve 0.88-0.96

problems with current biomarkers for GCTs

hCG and AFP
not universal
low signal in seminoma and EC
AFP present in benign tetroma

miR371 as a diagnostic biomarker

short half life - levels drop after tumour removal
can discern from histologically similar gliomas
can detect relapse early

functional significance of miRNAs

less invasive diagnostics
personalised prognostic miRNA signatures
targeted therapies
monitoring
early dichotomising of patients

neuroblastoma

mycN amplification leads to worse outcomes
5 miRNAs upregulated in mycN NB
miR-124 could be used to monitor progression and relapse
in therapy responders, miRNAs fall rapidly