Frequent RASSF1A promoter hypermethylation and K-ras mutations in pancreatic carcinoma

Abstract

Recently, we have characterized the Ras association domain family 1A gene (RASSF1A) at the segment 3p21.3, which is frequently lost in variety of human cancers and epigenetically inactivated in many types of primary tumors, such as lung, breast, kidney, prostate and thyroid carcinomas. Here, we investigated the methylation status of the RASSF1A CpG island promoter in the pathogenesis of pancreatic cancer. RASSF1A hypermethylation was detected in 29 out of 45 (64%) primary adenocarcinomas, in 10 out of 12 (83%) endocrine tumors and in eight out of 18 (44%) pancreatitis samples. In seven out of eight pancreas cancer cell lines, RASSF1A was silenced and was retranscribed after treatment with 5-aza-2 0 -deoxycytidine. Additionally, we analysed the aberrant methylation frequency of cell cycle inhibitor p16INK4a and K-ras gene mutations in the pancreatic samples. p16 inactivation was detected in 43% of adenocarcinomas, in 17% of neuroendocrine tumors, in 18% of pancreatitis and in 63% of pancreas cancer cell lines. K-ras mutations were detected in 16 out of 45 (36%) primary adenocarcinomas. Pancreatic adenocarcinomas with K-ras mutation have significantly less RASSF1A methylation and vice versa (P ¼ 0.001, v 2 test). In conclusion, our data indicate that inactivation of the RASSF1A gene is a frequent event in pancreatic cancer and suggest an inverse correlation between RASSF1A silencing and K-ras activation.

Frequent hypermethylation of RASSF1A in early flat-type colorectal tumors

“…Only 5% (11 of 222) cases showed K-ras mutations and RASSF1A methylation (van Engeland et al, 2002). Similarly, an inverse correlation between RASSF1A silencing and K-ras activation is present in pancreatic cancer (Dammann et al, 2003a). Flat-type colorectal cancer has a low frequency of K-ras mutations, and we detected K-ras mutations in only seven of 48 (14.6%) cases, which is similar to previous reports Minamoto et al, 1994;Olschwang et al, 1998).…”

“…Methylation in nontumor portions has been detected in 4% of esophageal squamous mucosa in patients with squamous cell carcinoma (Kuroki et al, 2003). In all, 44% of chronic pancreatitis tissues possess RASSF1A methylation (Dammann et al, 2003a). In breast tissue, RASSF1A is frequently methylated in benign proliferative lesions and benign papilloma.…”

“…The RASSF1A isoform is epigenetically inactivated in carcinomas of lung (small-cell lung cancer 72-79%, non-small-cell lung cancer, 30-38%), breast (49-62%), kidney (56-91%), prostate (53-100%), thyroid (71%) and several other carcinomas (Dammann et al, 2003b). The frequency of methylation of RASSF1A is dependent on organs and the type of tumor (histopathologic type) even if it occurs in the same organ (subtypes of cancers in the lung , pancreas (Dammann et al, 2003a) and kidney (Morrissey et al, 2001)). In sporadic colorectal cancers, the frequency of methylation of the CpG island promoter region found in RASSF1A is relatively lower (12-45%) than for other solid tumors with low rates of K-ras mutations (Yoon et al, 2001;van Engeland et al, 2002;Wagner et al, 2002).…”

“…Furthermore, RASSF1A hypermethylation and K-ras activation are mutually exclusive events in the development of colorectal carcinomas (van Engeland et al, 2002). Similarly, an inverse relationship between RASSF1A hypermethylation and K-ras mutation has been reported in pancreatic cancer as well (Dammann et al, 2003a).…”

Inactivation of RASSF1A tumor suppressor gene by aberrant promoter hypermethylation in human pituitary adenomas

“…[6][7][8]10 Hypermethylation of CpG islands in the RASSF1A promoter and its associated gene silencing have been reported in a variety of tumors including endocrine tumors such as small cell lung cancer, thyroid carcinoma and pancreatic endocrine tumors. 12,20,34 In the current study, we demonstrate RASSF1A promoter hypermethylation in 38% of pituitary adenomas including all the major clinically functioning and hormonally inactive types. RASSF1A methylation was significantly associated with loss or reduction of mRNA expression in these pituitary adenomas.…”