The Ras effector RASSF2 is a novel tumor-suppressor gene in human colorectal cancer.
OBJECTIVE
Activation of Ras signaling is a hallmark of colorectal cancer (CRC), but the roles of negative regulators of Ras are not fully understood. Our aim was to address that question by surveying genetic and epigenetic alterations of Ras-Ras effector genes in CRC cells.


METHODS
The expression and methylation status of 6 RASSF family genes were examined using RT-PCR and bisulfite PCR in CRC cell lines and in primary CRCs and colorectal adenomas. Colony formation assays and flow cytometry were used to assess the tumor suppressor activities of RASSF1 and RASSF2. Immunofluorescence microscopy was used to determine the effect of altered RASSF2 expression on cell morphology. Mutations of K- ras , BRAF, and p53 were identified using single-strand conformation analysis and direct sequencing.


RESULTS
Aberrant methylation and histone deacetylation of RASSF2 was associated with the gene's silencing in CRC. The activities of RASSF2, which were distinct from those of RASSF1, included induction of morphologic changes and apoptosis; moreover, its ability to prevent cell transformation suggests that RASSF2 acts as a tumor suppressor in CRC. Primary CRCs that showed K- ras /BRAF mutations also frequently showed RASSF2 methylation, and inactivation of RASSF2 enhanced K- ras -induced oncogenic transformation. RASSF2 methylation was also frequently identified in colorectal adenomas.


CONCLUSIONS
RASSF2 is a novel tumor suppressor gene that regulates Ras signaling and plays a pivotal role in the early stages of colorectal tumorigenesis.
Akino
Kimishige
K
First Department of Internal Medicine, Cancer Research Institute, Sapporo Medical University, Japan.
Toyota
Minoru
M
Suzuki
Hiromu
H
Mita
Hiroaki
H
Sasaki
Yasushi
Y
Ohe-Toyota
Mutsumi
M
Issa
Jean-Pierre J
JP
Hinoda
Yuji
Y
Imai
Kohzoh
K
Tokino
Takashi
T
D000107:Acetylation; D008841:Actin Cytoskeleton / Q000378:metabolism; D000236:Adenoma / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D011905:Genes, ras / Q000502:physiology; D006657:Histones / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000166:cytology; D008969:Molecular Sequence Data; D011506:Proteins / Q000235:genetics*; D051381:Rats; D015398:Signal Transduction / Q000235:genetics; D025521:Tumor Suppressor Proteins
D006657:Histones; D011506:Proteins; C425300:RASSF2 protein, human; D025521:Tumor Suppressor Proteins