Growth-suppressive function of phosphatidylethanolamine-binding protein in anaplastic thyroid cancer.

Background: A cDNA microarray analysis of anaplastic thyroid cancer cell lines (ACL) was recently performed and the down-regulation of phosphatidyl-ethanolamine-binding protein (PBP) [RAF kinase inhibitor protein (RKIP)] in ACL compared to normal thyroid tissues was identified. Materials and Methods: The expression levels of PBP in primary anaplastic and papillary thyroid cancer, thyroid cancer cell lines (anaplastic, papillary and follicular) and several normal human organs were examined. To examine the function of PBP, cell-growth assays were performed. Results: PBP expression was reduced in anaplastic thyroid cancers, compared to either normal thyroid tissues or differentiated thyroid cancers. PBP was expressed ubiquitously in normal human tissues. Exogenous PBP expression suppressed ACL growth, and suggested a tumor suppressive function of PBP in ACL. Conclusion: This is the first report demonstrating that PBP may be a tumor suppressor whose loss is associated with development of anaplastic thyroid cancer from differentiated thyroid cancer.