Functional analysis of a genetic defect of copper transport (Menkes disease) in different cell lines

Abstract

To define the function of the Cu-transporting ATPase in Menkes disease, Menkes and normal fibroblasts were incubated with 67Cu before and after brief exposure to -SH reagents, p-chloromercuribenzoate (PCMB) and dithiothreitol (DTT). Accumulation and retention were compared among these cells, BeWo cells, and rat C6 glioma cells similarly treated. The Michaelis constant for influx of 67Cu into normal and Menkes fibroblasts was practically the same (0.21 +/- 0.07 vs. 0.24 +/- 0.06 microM). The PCMB treatment stimulated 67Cu accumulation in C6 cells, inhibited accumulation in normal and Menkes fibroblasts, and did not affect BeWo cells. DTT stimulated 67Cu uptake in all cells but BeWo cells. DTT treatment after PCMB further enhanced 67Cu accumulation in normal fibroblasts and C6 cells but had no enhancing effect on Menkes fibroblasts or BeWo cells. Menkes fibroblasts and BeWo cells released 67Cu at rates considerably slower than normal fibroblasts (0.06 and 0.09 vs. 0.22%/min, respectively). The PCMB blocked 67Cu release from normal fibroblasts but did not affect Menkes fibroblasts or BeWo cells. Reverse transcription-polymerase chain reaction analysis of total RNA from BeWo cells failed to show a predicted 943-base pair fragment representing a partial transcript of the Menkes factor. The fragment was present in extracts from normal fibroblasts. We conclude that the mechanism underlying Cu homeostasis varies among different cell types. As exemplified by BeWo and Menkes cells, failure to efflux Cu ions may be linked with the failure to express a functional Cu-transporting ATPase, namely, the Menkes protein.