Implications of methylation patterns of cancer genes in salivary gland tumors.
OBJECTIVE
We investigated the methylation status and protein expression of four tumor suppressor genes to determine their role in salivary gland tumorigenesis.


METHODS
We performed methylation-specific PCR and protein analyses of 29 normal salivary glands, 23 benign, and 79 malignant salivary gland neoplasms to determine the pattern and potential diagnostic and/or biological role of the RASSF1, RARbeta2, DAPK, and MGMT tumor suppressor gene methylation in these tumors.


RESULTS
No methylation was detected in the normal tissues. Methylation occurred in 9 of 23 (39.1%) benign tumors; 3 (25.0%) pleomorphic adenomas and 6 (66.7%) Warthin's tumors at the MGMT, DAPK, or RASSF1 genes. Methylation occurred in 33 of 79 (41.8%) malignant tumors; 8 (30.8%) adenoid cystic carcinomas, 6 (33.3%) mucoepidermoid carcinomas, 6 (42.9%) acinic cell carcinomas, and 13 (62.0%) salivary duct carcinomas. RASSF1 and RARbeta2 represented 75.8% of methylation events occurring most frequently in salivary duct and acinic cell carcinomas. Overall, we found no significant correlation between protein expression and methylation status of individual genes, but observed low or absent protein expression in several methylated tumors. Significant correlations were found between methylation and aggressive malignant phenotypes (P = 0.0004) and age (P = 0.05).


CONCLUSIONS
(a) Benign and malignant salivary tumors differed in the frequency and pattern of gene methylation; (b) high-grade carcinomas were significantly methylated compared with low-grade phenotypes; (c) RASSF1 and RARbeta2 were highly methylated in malignant tumors and can be targeted for therapy; and (d) methylation pattern may serve as a diagnostic and biological marker in assessing these tumors.
Williams
Michelle D
MD
Department of Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030-4009, USA.
Chakravarti
Nitin
N
Kies
Merrill S
MS
Maruya
Shin-ichiro
S
Myers
Jeffrey N
JN
Haviland
Joie C
JC
Weber
Randal S
RS
Lotan
Reuben
R
El-Naggar
Adel K
AK
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002277:Carcinoma / Q000378:metabolism*; D018267:Carcinoma, Acinar Cell / Q000378:metabolism; D003528:Carcinoma, Adenoid Cystic / Q000378:metabolism; D018277:Carcinoma, Mucoepidermoid / Q000378:metabolism; D002648:Child; D019175:DNA Methylation; D015254:DNA Modification Methylases; D045643:DNA Repair Enzymes; D064550:Death-Associated Protein Kinases; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D052138:Genes, Neoplasm; D006801:Humans; D008297:Male; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D012468:Salivary Gland Neoplasms / Q000235:genetics* / Q000378:metabolism*; D025803:Tumor Suppressor Protein p14ARF / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D009363:Neoplasm Proteins; C411762:RASSF1 protein, human; D018168:Receptors, Retinoic Acid; D025803:Tumor Suppressor Protein p14ARF; D025521:Tumor Suppressor Proteins; C082925:retinoic acid receptor beta; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D064550:Death-Associated Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D045643:DNA Repair Enzymes