Promoter methylation correlates with reduced Smad4 expression in advanced prostate cancer.
BACKGROUND
Transforming growth factor-beta (TGF-beta) is a potent growth inhibitor in a wide range of cell types. A transducer of TGF-beta signaling known as Mothers against decapentaplegic homologue 4 (Smad4) is a known tumor suppressor found on chromosome 18q21.1 and is typically inactivated by deletion or mutation in pancreatic and colorectal cancers. The purpose of the article is to investigate Smad4 expression, gene copy number and methylation status in advanced cases of prostate cancer.


METHODS
We have employed Methylation Specific PCR (MSP) to identify methylation sites within the Smad4 promoter and combined this with quantitative real-time PCR to look for correlates between methylation status and Smad4 expression and to examine androgen receptor (AR) expression. Bacterial artificial chromosome-comparative genomic hybridization (BAC-CGH) has been used to look for genomic amplifications and deletions which may also contribute to expression changes.


RESULTS
We fail to find evidence of genomic deletions or amplifications affecting the Smad4 locus on chromosome 18 but show a correlation between promoter methylation and the loss of Smad4 expression in the same material. We confirm that the AR locus on the X chromosome is amplified in 30% of the advanced clinical samples and that this correlates with increased transcript levels as previously reported by other groups.


CONCLUSIONS
This indicates that epigenetic changes affect the expression of the Smad4 protein in prostate cancer and points to methylation of the promoter as a novel marker of and contributor to the disease warranting further study.
Aitchison
Alan A
AA
Department of Oncology, Hutchison/MRC Research Centre, CRUK Uro-Oncology Group, University of Cambridge, Cambridge, United Kingdom.
Veerakumarasivam
Abhi
A
Vias
Maria
M
Kumar
Rajeev
R
Hamdy
Freddie C
FC
Neal
David E
DE
Mills
Ian G
IG
D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D022202:Chromosomes, Artificial, Bacterial; D041321:Chromosomes, Human, X; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000032:analysis; D006801:Humans; D008297:Male; D009364:Neoplasm Recurrence, Local; D009693:Nucleic Acid Hybridization; D009841:Oligonucleotides; D011401:Promoter Regions, Genetic; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051901:Smad4 Protein / Q000235:genetics* / Q000378:metabolism
D014408:Biomarkers, Tumor; D004273:DNA, Neoplasm; D009841:Oligonucleotides; C497796:SMAD4 protein, human; D051901:Smad4 Protein