Proliferative potential in nasopharyngeal carcinoma: correlations with metallothionein expression and tissue zinc levels

Metallothionein (MT) is a cysteine-rich protein with pleiotropic functions and a high binding affinity for heavy metals, The present study was designe d to examine the relationship between MT expression and tissue zinc levels in conjunction with cell proliferation in nasopharyngeal cancer (NPC), Prol iferative activity in NPC was quantified by Ki67 immunolabelling and MT exp ression was determined by immunohistochemistry. Total zinc and subcellular zinc fractions were analysed by flame atomic absorption spectrometry, MT im munostaining was observed in the nuclei of NPC cells, with the percentage M T immunopositivity ranging from 3.0 to 59.7%. Thirteen tumours displayed we ak MT staining and the remaining 11 showed moderate to strong immunostainin g, There was a significant positive correlation between MT and Ki67 positiv ity (P = 0.0127). Tissue zinc levels were higher in NPC as compared with be nign nasopharyngeal tissues (4.800 +/- 0.4610 versus 2.889 +/- 0.4045 mug/g dry wt tissue, respectively; P 0.0122), Nuclear zinc levels in NPC were si gnificantly higher than levels in membrane and cytosolic fractions (mean zi nc levels 1.4840 +/- 0.1489, 0.6286 +/- 0.0789 and 0.3014 +/- 0.0250 mug/mg protein, respectively), A linear relationship was also observed between nu clear zinc levels and MT immunostaining (P = 0.0024) as well as with Ki67 i mmunopositivity (P = 0.0123), Our results show that MT and zinc are correla ted with proliferative activity in NPC, providing further insights into the biology of this enigmatic and aggressive tumour.