Promoter hypermethylation-related reduced somatostatin production promotes uncontrolled cell proliferation in colorectal cancer.
BACKGROUND
Somatostatin (SST) has anti-proliferative and pro-apoptotic effects. Our aims were to analyze and compare the SST expression during normal aging and colorectal carcinogenesis at mRNA and protein levels. Furthermore, we tested the methylation status of SST in biopsy samples, and the cell growth inhibitory effect of the SST analogue octreotide in human colorectal adenocarcinoma cell line.


METHODS
Colonic samples were collected from healthy children (n1 = 6), healthy adults (n2 = 41) and colorectal cancer patients (CRCs) (n3 = 34) for SST mRNA expression analysis, using HGU133 Plus2.0 microarrays. Results were validated both on original (n1 = 6; n2 = 6; n3 = 6) and independent samples ((n1 = 6; n2 = 6; n3 = 6) by real-time PCR. SST expressing cells were detected by immunohistochemistry on colonic biopsy samples (n1 = 14; n2 = 20; n3 = 23). The effect of octreotide on cell growth was tested on Caco-2 cell line. SST methylation percentage in biopsy samples (n1 = 5; n2 = 5; n3 = 9) was defined using methylation-sensitive restriction enzyme digestion.


RESULTS
In case of normal aging SST mRNA expression did not alter, but decreased in cancer (p < 0.05). The ratio of SST immunoreactive cells was significantly higher in children (0.70% ± 0.79%) compared to CRC (0% ± 0%) (p < 0.05). Octreotide significantly increased the proportion of apoptotic Caco-2 cells. SST showed significantly higher methylation level in tumor samples (30.2% ± 11.6%) compared to healthy young individuals (3.5% ± 1.9%) (p < 0.05).


CONCLUSIONS
In cancerous colonic mucosa the reduced SST production may contribute to the uncontrolled cell proliferation. Our observation that in colon cancer cells octreotide significantly enhanced cell death and attenuated cell proliferation suggests that SST may act as a regulator of epithelial cell kinetics. The inhibition of SST expression in CRC can be epigenetically regulated by promoter hypermethylation.
2nd Department of Internal Medicine, Semmelweis University, Budapest, Hungary.
Katalin
K
Leiszter
2nd Department of Internal Medicine, Semmelweis University, Budapest, Hungary.
Ferenc
F
Sipos
Molecular Medicine Research Unit, Hungarian Academy of Sciences, Budapest, Hungary.
Orsolya
O
Galamb
1st Department of Pathology and Experimental Cancer Research, Semmelweis University, Budapest, Hungary.
Tibor
T
Krenács
1st Department of Pediatrics, Semmelweis University, Budapest, Hungary.
Gábor
G
Veres
Molecular Medicine Research Unit, Hungarian Academy of Sciences, Budapest, Hungary.
Barna
B
Wichmann
Molecular Medicine Research Unit, Hungarian Academy of Sciences, Budapest, Hungary.
István
I
Fűri
2nd Department of Internal Medicine, Semmelweis University, Budapest, Hungary.
Alexandra
A
Kalmár
2nd Department of Internal Medicine, Semmelweis University, Budapest, Hungary.
Árpád V
ÁV
Patai
2nd Department of Internal Medicine, Semmelweis University, Budapest, Hungary.
Kinga
K
Tóth
Molecular Medicine Research Unit, Hungarian Academy of Sciences, Budapest, Hungary.
Gábor
G
Valcz
2nd Department of Internal Medicine, Semmelweis University, Budapest, Hungary; Molecular Medicine Research Unit, Hungarian Academy of Sciences, Budapest, Hungary.
Zsolt
Z
Tulassay
Molecular Medicine Research Unit, Hungarian Academy of Sciences, Budapest, Hungary.
Béla
B
Molnár
D000293:Adolescent; D000328:Adult; D000368:Aged; D018938:Caco-2 Cells; D016022:Case-Control Studies; D049109:Cell Proliferation; D002648:Child; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019175:DNA Methylation; D006801:Humans; D008875:Middle Aged; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013004:Somatostatin / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D013004:Somatostatin