COINCIDENT EXPRESSION OF MENKES GENE WITH COPPER EFFLUX IN HUMAN PLACENTAL CELLS

BeWo cells, a human choriocarcinoma cell line, have a high-affinity sy stem for transporting copper ions into the cell (K-m, = 0.21 mu M) but are sluggish in releasing copper back into the medium from preloaded cells. The slow efflux rate has recently been shown to correlate with a failure of BeWo cells to express the Menkes transcript [Y. Qian, E. Tiffany-Castiglioni, and E. D. Harris. Am. J. Physiol. 271 (Cell Physi ol. 40). In press]. We have now determined that only when BeWo cells w ere grown on plastic surfaces such as petri dishes or flasks did they display negligible release and enhanced retention of Cu-67. Reverse tr anscriptase-polymerase chain reaction with the use of primers selectiv e for the Menkes gene failed to show any evidence of a Menkes transcri pt in cells cultured on plastic surfaces. In contrast, cells grown on porous filters previously shown to allow apical and basolateral surfac es to develop did display the transcript and showed significant copper release with normal retention. Release of copper from filter-grown ce lls was blocked with p-chloromercuribenzoate, thus confirming sulfhydr yl group involvement. Absorption of the Cu-67, either as a free ion or bound to ceruloplasmin, was unaffected by the different culture condi tions. The data link the Menkes gene product with the ability of cells to release copper ions. They also suggest that the expression of the Menkes gene may be regulated by the development-of polarized cell memb ranes.