Native Chromatin Immunoprecipitation Using Murine Brain Tumor Neurospheres

Summary

Epigenetic mechanisms are frequently altered in glioma. Chromatin immunoprecipitation could be used to study the consequences of genetic alterations in glioma that result from changes in histone modifications which regulate chromatin structure and gene transcription. This protocol describes native chromatin immunoprecipitation on murine brain tumor neurospheres.

Abstract

Epigenetic modifications may be involved in the development and progression of glioma. Changes in methylation and acetylation of promoters and regulatory regions of oncogenes and tumor suppressors can lead to changes in gene expression and play an important role in the pathogenesis of brain tumors. Native chromatin immunoprecipitation (ChIP) is a popular technique that allows the detection of modifications or other proteins tightly bound to DNA. In contrast to cross-linked ChIP, in native ChIP, cells are not treated with formaldehyde to covalently link protein to DNA. This is advantageous because sometimes crosslinking may fix proteins that only transiently interact with DNA and do not have functional significance in gene regulation. In addition, antibodies are generally raised against unfixed peptides. Therefore, antibody specificity is increased in native ChIP. However, it is important to keep in mind that native ChIP is only applicable to study histones or other proteins that bind tightly to DNA. This protocol describes the native chromatin immunoprecipitation on murine brain tumor neurospheres.

Introduction

Epigenetic events are frequent in gliomas and likely play an important role in tumor pathogenesis. Indeed, in pediatric high-grade glioma, mutations in genes encoding histone variants H3.3 and H3.1 occur frequently¹. The mutations affect histone modifications and have major epigenetic consequences^2,3. In the adolescent to adult spectrum, recurrent mutations in isocitrate dehydrogenase gene 1/2 (IDH1/2), a mutation that inhibits α-KG dependent histone and DNA de-methylasaes, and genetic alterations in other chromatin regulators such as ATRX and DAXX occur⁴. T....

Protocol

All methods described here have been approved by the Institutional Animal Care and Use Committee (IACUC) of the University of Michigan.

1. Generation of brain tumor NS and culturing conditions.

1. Prepare Neural Stem Cell Medium (NSC) with Dulbecco's Modified Eagle Medium/F12B27 supplement (1x), N2 supplement (1x), and an antimicrobial reagent. Supplement NSC medium on the day of use with human recombinant endothelial growth factor (EGF) and basic-fibroblast growth factor (FGF) at a final concentration of 20 ng/mL each.
2. Induce the brain tumor in mouse using the Sleeping Beauty transposon system in which plasmids encod....

Results

A schematic representation of tumor NS generated from a brain tumor where brain tumor cells are Katushka positive is presented in Figure 1. Figure 2 is a schematic representation of the entire ChIP technique. Figure 3 shows the representative results of chromatin from brain tumor NS digested with MNase for 12 min, yielding a majority of mono, di-, and tri- nucleosomes. Following ChIP, a qPCR may be p.......

Discussion

The protocol presented here will enable the user to perform native ChIP on NS derived from genetically engineered brain tumors. In contrast to cross-linking ChIP, this protocol is limited for the study of proteins that associate tightly with DNA⁶. The number of cells used can be modified as necessary and the protocol can be scaled up. We used 1 X 10⁶ cells per IP, however, native ChIP may also be performed with as little as 4 x 10⁴ cells⁵. In this prot.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Agilent 2100 Bioanalyzer	Agilent	G2946-90004	bioanalyzer
AccuSpin Micro 17R, refrigerated	Fisher Scientific	13-100-676
C57BL/6	Taconic	B6-f	C57BL/6 mouse
Calcium Chloride	Aldrich	22350-6	buffer reagent
D-Luciferin, Potassium Salt	Goldbio	LuckK-1g
DiaMag1.5 magnetic rack	Diagenode	B04000003	for magnetic bead washes
DiaMag Rotator EU	Diagenode	B05000001	rotator
DMEM/F-12	Gibco	11330-057	NSC component
Dynabeads Protein A	Thermo Fisher Scientific	10001D	protein A magnetic beads
Dynabeads Protein G	Thermo Fisher Scientific	10003D	protein G magnetic beads
EGF	PeproTech	AF-100-15	prepare 20 μg/mL stock in 0.1% BSA and aliquot.
Ethylenediaminetetraacetic acid (EDTA)	Sigma	E-4884	buffer reagent
ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid) (EGTA)	Sigma	E-4378	buffer reagent
Fast SYBR Green Master Mix	Applied Biosystems	4385612	qPCR reagent
Fetal Bovine Serum	Gibco	10437028	for freezing cells
FGF	PeproTech	100-18b	Prepare 20 μg/mL stock in 0.1% BSA and aliquot.
Forceps	Fine Science Tools	11008-13	for dissection of tumor
Glycerol, MB Grade	EMD- Millipore	356352
H3K4me3	Abcam	Ab8580
H3K27me3	Millipore	07-449
HBSS	Gibco	14175-103	balanced salt solution
Fluriso	VETone	501017	inhalation anesthetic
Ivis Spectrum	Perkin-Elmer	124262	in vivo optical imaging system
Hyqtase	HyClon	SV3003001	cell detachment media
Lithium Chloride	Sigma	L8895	buffer reagent
Low binding microtubes	Corning Costar	CLS3207	low protein binding microcentrifuge tube
Microcentrifuge tube	Fisher	21-402-903	regular microcentrifuge tube
Micrococcal Nuclease	Thermo Fisher Scientific, Affymetrix	70196Y	each batch may differ; purchase sufficient amount for experiments and aliquot.
N2	Gibco	17502-048	NSC component
Normal Rabbit IgG	Millipore	12-372
Normocin	Invivogen	NOL-36-063	anti-microbial agent, use at 0.1 mg/mL.
NP-40 (Igepal CA-630)	Sigma	18896-50ML	buffer reagent
Kimble Kontes Pellet Pestle	Fisher Scientific	K749515-0000
Protease Inhibitor Cocktail	Sigma-Aldrich	P8340	aliquot and store at -20 °C.
Protinase K	Sigma-Aldrich	P2308	make 10 mg/mL stock in water; aliquot and store at -20 °C.
QIAquick PCR Purification Kit	Qiagen	28104	DNA purification kit
Scalpel	Fine Science Tools	10007-16	for dissection of tumor
Sodium Chloride	VWR	0241-5KG	buffer reagent
Sodium Deoxycholate	Sigma-Aldrich	D670-25G	buffer reagent
Sodium Dodecyl sulfate (SDS)	Sigma	L-4390	buffer reagent
Tris Base	Thermo Fisher Scientific	Bp152-1	buffer reagent
Triton X-100	Thermo Fisher Scientific	BP 151-500	polyethylene glycol octylphenyl ether
Standard Mini Centrifuge	Fisherbrand	12-006-901	standard mini centrifuge
SZX16 microscope	Olympus	SZX16	flourescent dissecting microscope
ViiA 7 Real-Time PCR System with Fast 96-Well Block	Applied Biosystems	4453535
Nanodrop One	Thermo-Fisher Scientific	ND-ONEC-W