[537] MLH1 Down-Regulation during the Neoplastic Progression of Follicular Cell Thyroid Neoplasms

O Turan, A Blanes, SJ Diaz-Cano. King's College Hospital, London, United Kingdom; University of Malaga School of Medicine, Malaga, Spain

Background: The contributions of mismatch repair proteins (MLH1 and MSH2) to topographic tumor heterogeneity and progression remain unknown in differentiated follicular cell thyroid neoplasms.
Design: We selected 15 hyperplastic nodules, 22 adenomas, 14 minimally-invasive carcinomas, 24 widely-invasive carcinomas, 15 papillary carcinomas and 13 anaplastic carcinomas (WHO criteria). Total RNA was extracted from normal and neoplastic tissues (peripheral and internal compartments) by hot acidic phenol, DNase I-treated, phenol extracted and cleaned (RNeasy columns). T7-(dT24) oligomer was used for priming the first-strand cDNA synthesis and the resultant cDNA was phenol/chloroform extracted, and used as template for cRNA synthesis (T7 MegaScript In Vitro Transcription Kit). The cRNA was fragmented, Cy3- and Cy5-labeled, and hybridized to the human GeneChip U133A Array noncompetitively. Cross-validated gene expression analyses were performed (expression factor2, significance0.01), and variables studied regarding the histological diagnosis and MLH1/MSH2 expression.
Results: MLH1 and MSH2 expression was homogeneous in peripheral and internal compartments, with a significant inter-lesional variability for MLH1 in peripheral and internal compartments across the spectrum of follicular thyroid lesions. Additionally, expression of MLH1 in internal compartments is greater than the periphery. MLH1 was greatest between FTHN and FTA, declining with neoplastic progression. MSH2 shows no statistically significant topographical heterogeneity within follicular thyroid lesions and there is also no variance across the spectrum. MLH1/MSH2 expression was positively correlated with SWI/SNF related, matrix associated, actin dependent regulator of chromatin member 1, Nuclear fragile X mental retardation protein, Cell division cycle 2-like 5, RecQ protein-like (DNA helicase), and protein expressed in non-metastatic cells 4, and negative correlated with Heterogeneous nuclear ribonucleoproteins L, D-like and R, Excision repair cross-complementing rodent repair deficiency, BCL2-associated transcription factor 1, Forkhead box O1, Interleukin 1 receptor, type II, and Laminin, alpha 3.
Conclusions: MLH1 expression is homogeneously down-regulated during the neoplastic progression of follicular cell thyroid neoplasms. MLH1 down-regulation contributes to impaired genetic repair (mismatch and excision repair), abnormal chromatin (heterogeneous nuclear ribonucleoproteins, SWI/SNF, DNA helicase) and stromal interaction (laminin).
Category: Endocrine

Tuesday, March 10, 2009 1:00 PM

Poster Session IV # 89, Tuesday Afternoon