Monosomy of chromosome 10 associated with dysregulation of epidermal growth factor signaling in glioblastomas.
BACKGROUND
Glioblastomas--uniformly fatal brain tumors--often have both monosomy of chromosome 10 and gains of the epidermal growth factor receptor (EGFR) gene locus on chromosome 7, an association for which the mechanism is poorly understood.


OBJECTIVE
To assess whether coselection of EGFR gains on 7p12 and monosomy 10 in glioblastomas promotes tumorigenic epidermal growth factor (EGF) signaling through loss of the annexin A7 (ANXA7) gene on 10q21.1-q21.2 and whether ANXA7 acts as a tumor suppressor gene by regulating EGFR in glioblastomas.


METHODS
Multidimensional analysis of gene, coding sequence, promoter methylation, messenger RNA (mRNA) transcript, protein data for ANXA7 (and EGFR), and clinical patient data profiles of 543 high-grade gliomas from US medical centers and The Cancer Genome Atlas pilot project (made public 2006-2008; and unpublished, tumors collected 2001-2008). Functional analyses using LN229 and U87 glioblastoma cells.


METHODS
Associations among ANXA7 gene dosage, coding sequence, promoter methylation, mRNA transcript, and protein expression. Effect of ANXA7 haploinsufficiency on EGFR signaling and patient survival. Joint effects of loss of ANXA7 and gain of EGFR expression on tumorigenesis.


RESULTS
Heterozygous ANXA7 gene deletion is associated with significant loss of ANXA7 mRNA transcript expression (P = 1 x 10(-15); linear regression) and a reduction (mean [SEM]) of 91.5% (2.3%) of ANXA7 protein expression compared with ANXA7 wild-type glioblastomas (P = .004; unpaired t test). ANXA7 loss of function stabilizes the EGFR protein (72%-744% increase in EGFR protein abundance) and augments EGFR transforming signaling in glioblastoma cells. ANXA7 haploinsufficiency doubles tumorigenic potential of glioblastoma cells, and combined ANXA7 knockdown and EGFR overexpression promotes tumorigenicity synergistically. The heterozygous loss of ANXA7 in approximately 75% of glioblastomas in the The Cancer Genome Atlas plus infrequency of ANXA7 mutation (approximately 6% of tumors) indicates its role as a haploinsufficiency gene. ANXA7 mRNA transcript expression, dichotomized at the median, associates with patient survival in 191 glioblastomas (log-rank P = .008; hazard ratio [HR], 0.667; 95% confidence interval [CI], 0.493-0.902; 46.9 vs 74.8 deaths/100 person-years for high vs low ANXA7 mRNA expression) and with a separate group of 180 high-grade gliomas (log-rank P = .00003; HR, 0.476; 95% CI, 0.333-0.680; 21.8 vs 50.0 deaths/100 person-years for high vs low ANXA7 mRNA expression). Deletion of the ANXA7 gene associates with poor patient survival in 189 glioblastomas (log-rank P = .042; HR, 0.686; 95% CI, 0.476-0.989; 54.0 vs 80.1 deaths/100 person-years for wild-type ANXA7 vs ANXA7 deletion).


CONCLUSIONS
Haploinsufficiency of the tumor suppressor ANXA7 due to monosomy of chromosome 10 provides a clinically relevant mechanism to augment EGFR signaling in glioblastomas beyond that resulting from amplification of the EGFR gene.
Yadav
Ajay K
AK
Department of Neurological Surgery, Northwestern Brain Tumor Institute, Lurie Center for Cancer Genetics Research, Northwestern University Feinberg School of Medicine, Chicago, IL 60611-3015, USA.
Renfrow
Jaclyn J
JJ
Scholtens
Denise M
DM
Xie
Hehuang
H
Duran
George E
GE
Bredel
Claudia
C
Vogel
Hannes
H
Chandler
James P
JP
Chakravarti
Arnab
A
Robe
Pierre A
PA
Das
Sunit
S
Scheck
Adrienne C
AC
Kessler
John A
JA
Soares
Marcelo B
MB
Sikic
Branimir I
BI
Harsh
Griffith R
GR
Bredel
Markus
M
D017310:Annexin A7 / Q000235:genetics* / Q000378:metabolism; D001932:Brain Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000401:mortality; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D002879:Chromosomes, Human, Pair 10 / Q000235:genetics*; D002897:Chromosomes, Human, Pair 7; D004815:Epidermal Growth Factor / Q000378:metabolism; D044127:Epigenesis, Genetic; D066246:ErbB Receptors / Q000235:genetics* / Q000378:metabolism; D005260:Female; D017353:Gene Deletion; D018628:Gene Dosage; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D016147:Genes, Tumor Suppressor; D005909:Glioblastoma / Q000235:genetics* / Q000378:metabolism / Q000401:mortality; D006801:Humans; D019656:Loss of Heterozygosity; D008297:Male; D008875:Middle Aged; D009006:Monosomy; D009154:Mutation; D051059:PTEN Phosphohydrolase / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D015398:Signal Transduction; D016019:Survival Analysis
D017310:Annexin A7; D012333:RNA, Messenger; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human