This document summarizes the radiation-induced bystander effect and abscopal effect. It describes how radiation can cause biological effects in non-directly irradiated "bystander" cells through various mechanisms, including immune signaling, gene expression changes, and epigenetic modifications. It discusses how cytokines, MAPK genes, NF-κB, COX-2, and microRNAs can be involved in mediating the bystander response. The document also briefly explains how localized radiation therapy can sometimes reduce tumor growth at distant, non-irradiated sites through abscopal effects that may be mediated by immune-related or p53-dependent mechanisms.

2. Radiation-induced bystander effect
Presented by: masoud najafi

3. outline
• Introduction
• Mechanisms of radiation-induced bystander effect
• Abscopal effect
• Mechanisms of abscopal effect

4. Bystander effect
• The bystander effect refers to the induction of
biological effects in cells that are not directly
traversed by radiation
• bystander effect has been demonstrated for both
high- and low-LET radiations
• Bystander studies imply that the target for the
biological effects of radiation is larger than the cell

5. First time Low doses of α particles have been shown
to lead to the formation of sister chromatid
exchanges in 30–50% of the cell population despite
the fact that only 1% of the cells’ nuclei would have
been traversed by an α particle

7. Bystander effect
• Bystander effects lead to:
 reduced clonogenic survival
 increased sister chromatid exchange
 formation of micronuclei and apoptosis
 altered gene expression and levels of RNA transcripts
• These effects are very similar to direct effect of
radiation

8. mechanisms
The mechanisms of radiation-induced bystander
effect that have known so far include:
- immune system
- gene expression
- epigenetics modulators

9. Immune system
• cytokines, including IL-1, IL-2, IL-8, TGFß1 and TNFα
• TGFß1 and TNFα stimulates apoptosis pathway
• TGFß1 and TNFα produce NO and lead to elevated
stress oxidative
• IL-8 stimulate MAPKs activation and ROS
production
• IL-1 and IL-2 stimulate IL-8 production

10. Gene expression by stress oxidative
• Several genes can participate in bystander effect
include:
- Mitogen Activated Protein Kinases genes (MAPKs)
- cyclooxygenase-2 (COX-2)
- Nuclear factor of κB (NF-κB)

11. MAPKs genes
• MAPKs include ERK, P38, JNK and c-jun
• Activated forms of the proteins belonging to the
extracellular signal-regulated kinase (ERK) and
c-jun, N-terminal kinase (JNK) pathways have been
demonstrated in bystander cells
• Phosphorylated forms of p38 show significant
modulation in radiation-induced bystander cells
• The MAPKs activation leads to production of
enzymes such as iNOS and cyclooxygenase-2

12. MAPKs genes
• ERK is believed to respond predominantly to
mitogenic stimuli such as growth factors and
enhanced calcium ions
• JNK and p38 are thought to respond to physiological
stresses e.g. chemical exposure, oxidative stress and
radiation
• MAPKs has been shown to be activated in response
to DNA damage induced by exposure to chemicals
such as mitomycin C, bleomycin and ionizing
radiation

13. MAPK genes

14. Nuclear factor of κB
• Nuclear factor of κB (NF-κB) is a transcriptional
regulator that is made up of different protein dimers
• this transcription factor also regulates cell proliferation
and apoptosis
• NF-κB activation leads to production of enzymes such
as iNOS and cyclooxygenase-2, which enhance the
production of ROS, leading to additional DNA damage
• it is not surprising that NF-κB has been shown to be
constitutively activated in several types of cancer cell

15. NF-κ B contributes to the induction of four
classes of genes

16. cycloocigenase-2
• cyclooxygenase-2 (COX-2) signaling cascade which is
essential in mediating cellular inflammatory response
plays an essential role in the bystander process
• Microarray analyses of differentially expressed genes
among the bystander cells showed a 3-fold
overexpression of cyclooxygenase-2
• suppression of COX-2 activity in bystander cells
significantly reduced the bystander effect

18. Epigenetics
• Epigenetics is a system that turns our genes on and
off
• The process works by chemical tags, known as
epigenetic marks, attaching to DNA and telling a
cell to either use or ignore a particular gene
• offspring may inherit altered traits due to their
parents' past experiences

19. mechanism of epigenetic control
• DNA Methylation
• Histone modifications including
- acetylation
- methylation
- phosphorylation
- Ubiquitination
• miRNAs
• siRNAs
• piRNAs

20. DNA methylation
• DNA methylation is known to be associated with an
inactive chromatin state
• In mammals, three DNA methyltransferases
(DNMT1, DNMT3a and DNMT3b) are primarily
responsible for DNA methylation
• In mammals, the association of DNA methylation
with transcriptional repression is thought to be
mediated by the MBD (methyl CpG binding
domain)

21. miRNAome
• MicroRNAs are of a special interest, as they can
inhibit the translation of a variety of proteins
• After the association with the RISC complexes,
miRNAs bind to the 3’UTR of mRNAs and serve as
translational suppressors
• Regulatory miRNAs in association with the mRNA
machinery impact cellular differentiation,
proliferation and apoptosis

23. epigenetic changes in the exposed tissue
• DNA damaging agents including Ionizing Radiation
have been reported to affect DNA methylation
patterns
• IR exposure leads to profound dose-dependent and
sex- and tissue specific global DNA hypomethylation
• Radiation induce changes in histone methylation,
specifically the loss of histone H4 lysine
trimethylation

24. epigenetic changes in the bystander tissues
• DNA methylation is important for the maintenance
of the radiation-induced bystander effect in cultured
cells
• animal-based studies was shown to induce DNA
damage and modulate the epigenetic effectors in
distant bystander tissues
• localized cranial radiation exposure leads to the
decreased levels of global DNA methylation in spleen
tissue 7 months after irradiation

25. epigenetic changes in the bystander tissues
• Cranial irradiation lead to silencing of DNMT3a and
MeCP2 in the bystander spleen tissue
• The distant bystander effect leads down regulation of
DNMT3a and MeCP2
• Upregulation of the miR-29 family resulted in decreased
levels of its targets DNMT3a and MCL1, consequently
affecting DNA methylation and apoptosis
• irradiation significantly altered expression of miR-194, a
miRNA putatively targeting both DNA methyltransferase-
3a and MeCP2

26. miRNAs in bystander effect

27. Abscopal effect
• The Abscopal effect is the effect of radiation therapy
sometimes observed as response of tumor masses
remote from the site of irradiation
• Ionizing radiation can reduce tumor growth outside the
field of radiation
• Much of the observed physiological Abscopal effect has
been associated with splenic irradiation

28. That effect of radiation was related to diminishing of the
tumor´s immune suppression and enhanced infiltration of
activated T cells affecting the tumor

29. mechanisms
• In this model no significant abscopal effect was
found by radiation therapy combined with
immunization by radiation therapy combined with
immunization using IFN-gamma transfected tumor
cells
• This might indicate that factors other than
immunological are responsible for the radiation
induced abscopal effect
• Other study showed abscopal effect apparently
operates through p53 mediated mechanisms