Date of Award
1993
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
The metal-binding protein metallothionein (MT) confers resistance to the toxic effects of metals. A role in metal homeostasis and protection against toxic free radicals has been suggested, but no physiological function has been established. The ability of human monocytes to be activated by lipopolysaccharide (LPS) provided a model to investigate the effect of zinc on both cellular activation ({dollar}\rm H\sb2O\sb2{dollar} production, indicating the respiratory burst) and MT expression. In freshly-isolated primary human monocytes and a human monocytic cell line (THP-1), LPS induced activation and MT expression: LPS did not induce MT expression in human melanoma cells. Co-treatment of THP-1 cells with zinc plus LPS decreased MT mRNA and protein levels, and inhibited the respiratory burst. Freshly-isolated primary human monocytes responded similarly to zinc plus LPS treatment. We concluded that THP-1 cells were a good model for studying the role of metallothioneins in monocyte function.;The effects of LPS treatment on monocyte function are complex. To determine whether MT was directly involved in aspects of monocyte function, and whether increases in MT as a result of LPS treatment facilitated monocyte activation, the basal level of MT in THP-1 cells was decreased by transient transfection of an antisense MT expression vector. THP-1 cells expressed antisense MT RNA; levels of MT protein were 30% lower than in cells transfected with the control vector. Down-regulation of MT was correlated with enhanced invasiveness, adherence, and basal production of {dollar}\rm H\sb2O\sb2{dollar}, in the absence of activating stimuli. LPS treatment increased antisense MT RNA accumulation by 2-fold and depressed the level of MT protein a further 6-fold. Adherence and the respiratory burst were diminished in antisense-expressing THP-1 cells activated with LPS, but invasive ability was unaffected. These data indicated that the increased MT levels in activated monocytes were associated with response to LPS. Augmentation of constitutive adherence, invasion and production of {dollar}\rm H\sb2O\sb2{dollar} by specifically decreasing the levels of MT suggests that this protein plays a fundamental role in normal monocyte function. This work supports the hypothesis that metallothionein mediates homeostatic processes in addition to detoxification of heavy metals.
Recommended Citation
Leibbrandt, Martha E., "A Role For Metallothionein In Human Monocytes" (1993). Digitized Theses. 2392.
https://ir.lib.uwo.ca/digitizedtheses/2392