BAX and caspase-5 frameshift mutations and spontaneous apoptosis in colorectal cancer with microsatellite instability.
OBJECTIVE
Hereditary nonpolyposis colorectal cancer (HNPCC) and a subset of sporadic colorectal cancers are characterized by microsatellite instability (MSI) and inactivating frameshift mutations of target genes. Inactivation of BAX, caspase-5 ( cas-5), and other genes coding for pro-apoptotic proteins might contribute to tumor progression by enhancing escape from apoptosis. The aim of this study was to further characterize the role of BAX and cas-5 inactivation for spontaneous apoptosis.


METHODS
Twenty-five colorectal cancers with MSI were analyzed for frameshift mutations in the BAX (G)8 and cas-5 (A)10 tract by fluorescence PCR, cloning, and sequencing. The rate of spontaneous apoptosis was examined by in situ DNA nick end-labeling. The results were compared with 25 stage-matched microsatellite stable (MSS) colorectal cancers.


RESULTS
In colorectal cancer with MSI frameshift mutations in BAX and cas-5 were present in 16 of 25 (64%) and in 12 of 25 (48%) tumors, respectively, whereas neither mutant BAX nor cas-5 alleles were detected in all stage-matched sporadic MSS colorectal cancer. Tumors with MSI showed a higher apoptotic rate than MSS tumors (2.5+/-1.0 vs. 2.1+/-0.7; p <0.05), whereas the presence of BAX or cas-5 frameshift mutations had only minor influence on this finding (2.4+/-1.1% and 2.5+/-0.9%, respectively).


CONCLUSIONS
Mismatch-repair deficiency itself is associated with increased spontaneous apoptosis, not further accelerated by either inactivating BAX or cas-5 frameshift mutations.
Trojan
Joerg
J
2nd Department of Medicine and Senckenberg Center of Pathology, Johann Wolfgang Goethe University Medical Center, Theodor-Stern-Kai 7, 60590 Frankfurt a.M., Germany. trojan@em.uni-frankfurt.de.
Brieger
Angela
A
Raedle
Jochen
J
Weber
Nicole
N
Kriener
Susanne
S
Kronenberger
Bernd
B
Caspary
Wolfgang F
WF
Zeuzem
Stefan
S
D000368:Aged; D017209:Apoptosis / Q000235:genetics*; D020169:Caspases / Q000235:genetics* / Q000494:pharmacology*; D015179:Colorectal Neoplasms / Q000235:genetics*; D004252:DNA Mutational Analysis; D004260:DNA Repair; D004273:DNA, Neoplasm; D018450:Disease Progression; D005260:Female; D016368:Frameshift Mutation; D006801:Humans; D020287:In Situ Nick-End Labeling; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D004273:DNA, Neoplasm; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; C099217:CASP5 protein, human; D020169:Caspases