title: Epigenetic silencing of RASSF1A deregulates cytoskeleton and promotes malignant behavior of adrenocortical carcinoma.
abstract: BACKGROUND
  Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with high mutational heterogeneity and a generally poor clinical outcome. Despite implicated roles of deregulated TP53, IGF-2 and Wnt signaling pathways, a clear genetic association or unique mutational link to the disease is still missing. Recent studies suggest a crucial role for epigenetic modifications in the genesis and/or progression of ACC. This study specifically evaluates the potential role of epigenetic silencing of RASSF1A, the most commonly silenced tumor suppressor gene, in adrenocortical malignancy.
  
  
  RESULTS
  Using adrenocortical tumor and normal tissue specimens, we show a significant reduction in expression of RASSF1A mRNA and protein in ACC. Methylation-sensitive and -dependent restriction enzyme based PCR assays revealed significant DNA hypermethylation of the RASSF1A promoter, suggesting an epigenetic mechanism for RASSF1A silencing in ACC. Conversely, the RASSF1A promoter methylation profile in benign adrenocortical adenomas (ACAs) was found to be very similar to that found in normal adrenal cortex. Enforced expression of ectopic RASSF1A in the SW-13 ACC cell line reduced the overall malignant behavior of the cells, which included impairment of invasion through the basement membrane, cell motility, and solitary cell survival and growth. On the other hand, expression of RASSF1A/A133S, a loss-of-function mutant form of RASSF1A, failed to elicit similar malignancy-suppressing responses in ACC cells. Moreover, association of RASSF1A with the cytoskeleton in RASSF1A-expressing ACC cells and normal adrenal cortex suggests a role for RASSF1A in modulating microtubule dynamics in the adrenal cortex, and thereby potentially blocking malignant progression.
  
  
  CONCLUSIONS
  Downregulation of RASSF1A via promoter hypermethylation may play a role in the malignant progression of adrenocortical carcinoma possibly by abrogating differentiation-promoting RASSF1A- microtubule interactions.
authors.affiliation: Department of Surgery, Yale Endocrine Neoplasia Laboratory, Yale University School of Medicine, New Haven, CT 06520, USA.
authors.forename: Reju
authors.initials: R
authors.lastname: Korah
authors.forename: James M
authors.initials: JM
authors.lastname: Healy
authors.forename: John W
authors.initials: JW
authors.lastname: Kunstman
authors.forename: Annabelle L
authors.initials: AL
authors.lastname: Fonseca
authors.forename: Amir H
authors.initials: AH
authors.lastname: Ameri
authors.forename: Manju L
authors.initials: ML
authors.lastname: Prasad
authors.forename: Tobias
authors.initials: T
authors.lastname: Carling
mesh_terms: D000306:Adrenal Cortex Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018268:Adrenocortical Carcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000328:Adult; D045744:Cell Line, Tumor; D018899:CpG Islands; D003599:Cytoskeleton / Q000378:metabolism*; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D008297:Male; D008870:Microtubules / Q000378:metabolism; D008875:Middle Aged; D009367:Neoplasm Staging; D010641:Phenotype; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: C411762:RASSF1 protein, human; D025521:Tumor Suppressor Proteins
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