A novel somatic mutation in ACD induces telomere lengthening and apoptosis resistance in leukemia cells.
BACKGROUND
The identification of oncogenic driver mutations has largely relied on the assumption that genes that exhibit more mutations than expected by chance are more likely to play an active role in tumorigenesis. Major cancer sequencing initiatives have therefore focused on recurrent mutations that are more likely to be drivers. However, in specific genetic contexts, low frequency mutations may also be capable of participating in oncogenic processes. Reliable strategies for identifying these rare or even patient-specific (private) mutations are needed in order to elucidate more personalized approaches to cancer diagnosis and treatment.


METHODS
Here we performed whole-exome sequencing on three cases of childhood pre-B acute lymphoblastic leukemia (cALL), representing three cytogenetically-defined subgroups (high hyperdiploid, t(12;21) translocation, and cytogenetically normal). We applied a data reduction strategy to identify both common and rare/private somatic events with high functional potential. Top-ranked candidate mutations were subsequently validated at high sequencing depth on an independent platform and in vitro expression assays were performed to evaluate the impact of identified mutations on cell growth and survival.


RESULTS
We identified 6 putatively damaging non-synonymous somatic mutations among the three cALL patients. Three of these mutations were well-characterized common cALL mutations involved in constitutive activation of the mitogen-activated protein kinase pathway (FLT3 p.D835Y, NRAS p.G13D, BRAF p.G466A). The remaining three patient-specific mutations (ACD p.G223V, DOT1L p.V114F, HCFC1 p.Y103H) were novel mutations previously undescribed in public cancer databases. Cytotoxicity assays demonstrated a protective effect of the ACD p.G223V mutation against apoptosis in leukemia cells. ACD plays a key role in protecting telomeres and recruiting telomerase. Using a telomere restriction fragment assay, we also showed that this novel mutation in ACD leads to increased telomere length in leukemia cells.


CONCLUSIONS
This study identified ACD as a novel gene involved in cALL and points to a functional role for ACD in enhancing leukemia cell survival. These results highlight the importance of rare/private somatic mutations in understanding cALL etiology, even within well-characterized molecular subgroups.
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. jf.spinella@gmail.com.
Jean-François
JF
Spinella
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. cassart.pauline@gmail.com.
Pauline
P
Cassart
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. nicolasgarnier3000@gmail.com.
Nicolas
N
Garnier
Lady Davis Institute Jewish General Hospital, Montreal, Qc, Canada. pmp.rousseau@gmail.com.
Philippe
P
Rousseau
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. claire.drullion@gmail.com.
Claire
C
Drullion
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. cricher.hsj@gmail.com.
Chantal
C
Richer
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. manon.ouimet@recherche-ste-justine.qc.ca.
Manon
M
Ouimet
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. vr.saillour@gmail.com.
Virginie
V
Saillour
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. jasmine.healy@umontreal.ca.
Jasmine
J
Healy
Lady Davis Institute Jewish General Hospital, Montreal, Qc, Canada. chantal.autexier@mcgill.ca.|Departments of Anatomy, Cell Biology and Medicine, McGill University, Montreal, Qc, Canada. chantal.autexier@mcgill.ca.
Chantal
C
Autexier
Division of Hematology-Oncology, Sainte-Justine UHC Research Center, 3175 Côte Ste-Catherine, H3T 1C5, Montréal, Québec, Canada. daniel.sinnett@umontreal.ca.|Department of Pediatrics, Faculty of Medicine, University of Montreal, Montreal, Qc, Canada. daniel.sinnett@umontreal.ca.
Daniel
D
Sinnett
D017209:Apoptosis / Q000235:genetics*; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis / Q000379:methods*; D059472:Exome / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D009154:Mutation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics* / Q000473:pathology; D000089804:Shelterin Complex; D059505:Telomere Homeostasis / Q000235:genetics*; D034501:Telomere-Binding Proteins / Q000235:genetics*
C495876:ACD protein, human; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins