BaxΔ2 promotes apoptosis through caspase-8 activation in microsatellite-unstable colon cancer.
Loss of apoptotic Bax due to microsatellite mutation contributes to tumor development and chemoresistance. Recently, a Bax microsatellite mutation was uncovered in combination with a specific alternative splicing event that could generate a unique Bax isoform (BaxΔ2) in otherwise Bax-negative cells. Like the prototype Baxα, BaxΔ2 is a potent proapoptotic molecule. However, the proapoptotic mechanism and therapeutic implication of BaxΔ2 remain elusive. Here, the isolation and analysis of isogenic subcell lines are described that represent different Bax microsatellite statuses from colorectal cancer. Colon cancer cells harboring Bax microsatellite G7/G7 alleles are capable of producing low levels of endogenous BaxΔ2 transcripts and proteins. Interestingly, BaxΔ2-positive cells are selectively sensitive to a subgroup of chemotherapeutics compared with BaxΔ2-negative cells. Unlike other Bax isoforms, BaxΔ2 recruits caspase-8 into the proximity for activation, and the latter, in turn, activates caspase-3 and apoptosis independent of the mitochondrial pathway. These data suggest that the expression of BaxΔ2 may provide alternative apoptotic and chemotherapeutic advantages for Bax-negative tumors.


CONCLUSIONS
"Bax-negative" colorectal tumors expressing a Bax isoform are sensitive to selective chemotherapeutics.
Department of Biological and Chemical Sciences;
Honghong
H
Zhang
Department of Biological and Chemical Sciences;
Yuting
Y
Lin
Department of Biological and Chemical Sciences;
Adriana
A
Mañas
Department of Biological and Chemical Sciences;
Yu
Y
Zhao
Department of Pathology, Loyola University Medical Center, Maywood, Illinois.
Mitchell F
MF
Denning
Mumetel, LLC, University Technology Park, Illinois Institute of Technology, Chicago; and.
Li
L
Ma
Department of Biological and Chemical Sciences; xiang@iit.edu.
Jialing
J
Xiang
D017209:Apoptosis / Q000235:genetics*; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000096:biosynthesis / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D053842:Microsatellite Instability; D020033:Protein Isoforms / Q000096:biosynthesis* / Q000235:genetics; D051028:bcl-2-Associated X Protein / Q000096:biosynthesis* / Q000235:genetics
D020033:Protein Isoforms; D051028:bcl-2-Associated X Protein; D053148:Caspase 3; D053181:Caspase 8