A CpG island hypermethylation profile of primary colorectal carcinomas and colon cancer cell lines.
BACKGROUND
Tumor cell lines are commonly used as experimental tools in cancer research, but their relevance for the in vivo situation is debated. In a series of 11 microsatellite stable (MSS) and 9 microsatellite unstable (MSI) colon cancer cell lines and primary colon carcinomas (25 MSS and 28 MSI) with known ploidy stem line and APC, KRAS, and TP53 mutation status, we analyzed the promoter methylation of the following genes: hMLH1, MGMT, p16INK4a (CDKN2A alpha-transcript), p14ARF (CDKN2A beta-transcript), APC, and E-cadherin (CDH1). We compared the DNA methylation profiles of the cell lines with those of the primary tumors. Finally, we examined if the epigenetic changes were associated with known genetic markers and/or clinicopathological variables.


RESULTS
The cell lines and primary tumors generally showed similar overall distribution and frequencies of gene methylation. Among the cell lines, 15%, 50%, 75%, 65%, 20% and 15% showed promoter methylation for hMLH1, MGMT, p16INK4a, p14ARF, APC, and E-cadherin, respectively, whereas 21%, 40%, 32%, 38%, 32%, and 40% of the primary tumors were methylated for the same genes. hMLH1 and p14ARF were significantly more often methylated in MSI than in MSS primary tumors, whereas the remaining four genes showed similar methylation frequencies in the two groups. Methylation of p14ARF, which indirectly inactivates TP53, was seen more frequently in tumors with normal TP53 than in mutated samples, but the difference was not statistically significant. Methylation of p14ARF and p16INK4a was often present in the same primary tumors, but association to diploidy, MSI, right-sided location and female gender was only significant for p14ARF. E-cadherin was methylated in 14/34 tumors with altered APC further stimulating WNT signaling.


CONCLUSIONS
The present study shows that colon cancer cell lines are in general relevant in vitro models, comparable with the in vivo situation, as the cell lines display many of the same molecular alterations as do the primary carcinomas. The combined pattern of epigenetic and genetic aberrations in the primary carcinomas reveals associations between them as well as to clinicopathological variables, and may aid in the future molecular assisted classification of clinically distinct stages.
Department of Genetics, Institute for Cancer Research, The Norwegian Radium Hospital, 0310 Oslo, Norway. guroli@ulrik.uio.no
Guro E
GE
Lind
Lin
L
Thorstensen
Tone
T
Løvig
Gunn I
GI
Meling
Richard
R
Hamelin
Torleiv O
TO
Rognum
Manel
M
Esteller
Ragnhild A
RA
Lothe
D048868:Adaptor Proteins, Signal Transducing; D015820:Cadherins / Q000235:genetics; D002352:Carrier Proteins; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D018899:CpG Islands; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D019175:DNA Methylation; D005260:Female; D017491:Genes, APC; D006801:Humans; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics; D009687:Nuclear Proteins; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics; D011401:Promoter Regions, Genetic; D012737:Sex Factors; D025803:Tumor Suppressor Protein p14ARF / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D015820:Cadherins; D002352:Carrier Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D025803:Tumor Suppressor Protein p14ARF; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000070957:MutL Protein Homolog 1