Comethylation of p16 and MGMT genes in colorectal carcinoma: correlation with clinicopathological features and prognostic value.
OBJECTIVE
To investigate the significance of p16 and O(6)-methylguanine-DNA methyltransferase (MGMT) genes promoter hypermethylation and K-ras mutations on colorectal tumorigenesis and progression.


METHODS
p16 and MGMT methylation status was examined on 47 tumor samples, and K-ras mutational status was examined on 85 tumor samples. For methylation analysis, a methylation specific PCR (MS-PCR) method was used.


RESULTS
p16 and MGMT promoter methylation was found in 51% (24/47) and 43% (20/47) of CRCs, respectively, and the K-ras mutation was found in 44% (37/85) of CRCs. Comethylation of p16 and MGMT genes was significantly associated with lower aggressiveness of the disease within a two-year period of observation. Only 27% of patients with simultaneous p16 and MGMT methylation showed the detectable occurrence of metastasis and/or death, compared to 67% of patients without double methylation or with no methylation (3/11 vs 22/33, P < 0.05, chi(2)-test). In addition, p16 and MGMT comethylation showed a trend toward an association with longer survival in patients with CRCs (35.5 +/- 6.0 mo vs 23.1 +/- 3.2 mo, P = 0.072, Log-rank test). Progression of the disease within a two-year period was observed in 66% of patients carrying the K-ras mutation, compared to only 19% of patients with wild type K-ras (29/44 vs 7/37, P < 0.001, chi(2)-test). The presence of the K-ras mutation significantly correlated to shortened overall survival (20.0 +/- 1.9 mo vs 37.0 +/- 1.8 mo, P < 0.001, Log-rank test). The comethylation of p16 and MGMT genes was significantly associated with lower aggressiveness of the disease even when K-ras mutations were included in the analysis as an independent variable.


CONCLUSIONS
Our data suggest that comethylation of promoters of p16 and MGMT genes could have a prognostic value in patients with CRC. Specifically, concurrent methylation of both genes correlates with better prognosis.
Krtolica
Koviljka
K
Laboratory for Radiobiology and Molecular Genetics, Institute of Nuclear Sciences Vinca, P. O. BOX 522, Belgrade, Serbia. krtolica@vin.bg.ac.yu
Krajnovic
Milena
M
Usaj-Knezevic
Slavica
S
Babic
Dragan
D
Jovanovic
Dusan
D
Dimitrijevic
Bogomir
B
D000328:Adult; D000367:Age Factors; D000368:Aged; D015820:Cadherins / Q000378:metabolism; D002277:Carcinoma / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D049109:Cell Proliferation; D003106:Colon / Q000473:pathology; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics*; D045643:DNA Repair Enzymes / Q000235:genetics*; D005260:Female; D019942:Genes, p16; D011905:Genes, ras; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D007150:Immunohistochemistry; D007797:Laminin / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D012007:Rectum / Q000473:pathology; D016019:Survival Analysis; D025521:Tumor Suppressor Proteins / Q000235:genetics*
C497483:CD44 protein, human; D015820:Cadherins; D018960:Hyaluronan Receptors; D007797:Laminin; D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes