Elevated osteopontin levels in metastatic melanoma correlate with epigenetic silencing of breast cancer metastasis suppressor 1.
OBJECTIVE
Breast cancer metastasis suppressor 1 (BRMS1) has been shown to functionally reduce the metastatic potential of melanoma. We also previously reported that BRMS1 negatively regulates the expression of the oncoprotein osteopontin (OPN). This study was carried out to assess the clinical relevance of BRMS1 and OPN in melanoma.


METHODS
Epigenetic regulation of BRMS1 was assessed by treating clinically derived melanoma cell lines with the demethylating agent 5-aza-2'-deoxycytidine (DAC) and the histone deacetylase inhibitor trichostatin A (TSA), followed by sodium bisulfite modification and methylation-specific PCR. Assessments of BRMS1 and OPN levels were performed using immunoblotting, quantitative real-time RT-PCR or reporter assays. RNA silencing was employed to abrogate the expression of OPN in melanoma-derived cell lines. The in vivo relevance of our findings was determined with experiments using athymic nude mice.


RESULTS
The reduced expression of BRMS1 in surgically excised melanoma specimens correlated with increased OPN expression during the progression from primary to metastatic melanoma. Treatment with DAC and TSA elevated BRMS1 levels, but caused an inconsistent change in OPN gene expression. Abrogating the expression of OPN in BRMS1-deficient metastatic melanoma-derived cell lines retarded the growth of melanoma tumor xenografts in athymic nude mice.


CONCLUSIONS
While treatment with DAC and TSA may not be a universally applicable treatment alternative in melanoma, silencing the expression of OPN in metastatic melanomas that have lost expression of BRMS1 is a potential option for therapeutic intervention.
Metge
Brandon J
BJ
Mitchell Cancer Institute, University of South Alabama, 1660 Springhill Avenue, Mobile, AL 36604, USA.
Liu
Suhu
S
Riker
Adam I
AI
Fodstad
Oystein
O
Samant
Rajeev S
RS
Shevde
Lalita A
LA
D000818:Animals; D045744:Cell Line, Tumor; D018899:CpG Islands / Q000235:genetics; D004195:Disease Models, Animal; D015536:Down-Regulation; D044127:Epigenesis, Genetic; D020869:Gene Expression Profiling; D020868:Gene Silencing; D008545:Melanoma / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D053495:Osteopontin / Q000096:biosynthesis / Q000235:genetics*; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics*; D012878:Skin Neoplasms / Q000235:genetics* / Q000378:metabolism
C544679:BRMS1 protein, mouse; D012097:Repressor Proteins; D053495:Osteopontin