Objective     To determine the effects of metallothioneins (MTs) induced by hypoxia on epithelial-mesenchymal transition (EMT) in human papillary thyroid carcinoma NPA cells.     Methods     NPA cells were divided into 3 groups

normoxia (21% O

2

)

hypoxia (5% O

2

) and hypoxia with MTs-siRNA. The expression levels of MTs

E-cadherin and Vimentin in the 3 groups of NPA cells were analyzed by Western

blotting and RT-PCR. The invasion and metastasis potential of these groups were detected by Transwell/Matrigel assay.     Results     Hypoxia treatment led to inducible expression of MTs

down-regulated of E-cadherin and up-regulated Vimentin at the same time

which were marker molecules of EMT in NPA cells. Meanwhile

invasive cell population of hypoxia group was increased to 40.3±5.1 from 15.6±2.8 of normoxia group (P0.01). Migrating cell population was increased to 48.7±7.6 from 25.1±5.6 of normoxia group (P0.01). However

the inducible expression of MTs was effectively inhibited by transfection of MTs-siRNA vector in NPA cells

followed by increased expression of E-cadherin and decreased expression of Vimentin. Moreover

invasive and migrating cell population of the hypoxia group with MTs-siRNA were only increased to 25.7±4.2 and 35.5±5.4(P0.05).     Conclusion     The expression of MTs induced by hypoxia can promote EMT in human papillary thyroid carcinoma. siRNA targeting MTs can partially inhibit EMT promoted by hypoxia.