Ligand-regulated transport of the Menkes copper P-type ATPase efflux pump from the Golgi apparatus to the plasma membrane: a novel mechanism of regulated trafficking.

Abstract

The Menkes P‐type ATPase (MNK), encoded by the Menkes gene (MNK; ATP7A), is a transmembrane copper‐translocating pump which is defective in the human disorder of copper metabolism, Menkes disease. Recent evidence that the MNK P‐type ATPase has a role in copper efflux has come from studies using copper‐resistant variants of cultured Chinese hamster ovary (CHO) cells. These variants have MNK gene amplification and consequently overexpress MNK, the extents of which correlate with the degree of elevated copper efflux. Here, we report on the localization of MNK in these copper‐resistant CHO cells when cultured in different levels of copper. Immunofluorescence studies demonstrated that MNK is predominantly localized to the Golgi apparatus of cells in basal medium. In elevated copper conditions there was a rapid trafficking of MNK from the Golgi to the plasma membrane. This shift in steady‐state distribution of MNK was reversible and not dependent on new protein synthesis. In media containing basal copper, MNK accumulated in cytoplasmic vesicles after treatment of cells with a variety of agents that inhibit endosomal recycling. We suggest that MNK continuously recycles between the Golgi and the plasma membrane and elevated copper shifts the steady‐state distribution from the Golgi to the plasma membrane. These data reveal a novel system of regulated protein trafficking which ultimately leads to the efflux of an essential yet potentially toxic ligand, where the ligand itself appears directly and specifically to stimulate the trafficking of its own transporter.

Delivering copper within plant cells

“…Within the vesicle, copper carriers bind the copper prior to fusion of the vesicle with the plasma membrane. In a third possi ble scenario, RANI could pump copper out of the cell directly if, like MNK, RANI is localized to the plasma membrane during periods when copper is accumulating in the cytoplasm [16). The unique carboxy-terminal helix of CCH may a)so have a senescence-specific role either in targeting or protein-protein interactions or in targeting CCH to a distinct intracellular location, but this remains to be determined.…”

Posttranslational regulation of copper transporters

“…Endogenous as well as overexpressed ATP7A and ATP7B were detected in the TGN in a wide variety of polarized and nonpolarized cell types under basal copper conditions, both in vitro and in vivo [9,11,12,14,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62]. In ATP7A, a putative TGN-targeting signal was identified within transmembrane helix 3 [54].…”

“…Barnes et al [68] demonstrated that copperinduced trafficking of endogenously expressed ATP7B in kidney-derived HEK293T cells, MDCK cells, Cos-7 cells, or primary kidney cells was perturbed, whereas copperdependent trafficking of ATP7A did take place in these same cell types. Reversible copper-dependent trafficking of ATP7A to the plasma membrane or post-Golgi vesicles in nonpolarized cells [11,[54][55][56][57][58] and specifically towards the basolateral membrane in polarized cells [59-62, 69, 70] was observed.…”

“…CTR1 is absolutely required for dietary copper absorption and is essential for cellular copper uptake [1][2][3][4][5][6][7]. Cellular copper export is equally important and is dependent on ATP7A and ATP7B [8][9][10][11][12]. In contrast to other organisms, hardly any transcriptional regulation of genes primarily involved in copper homeostasis exists in mammalian cells [13], and it is commonly accepted that regulation of copper homeostasis occurs predominantly by posttranslational mechanisms.…”

XIAP: Cell death regulation meets copper homeostasis

“…In the intestinal epithelium, ATP7A is required to mediate delivery of copper from the cell to the systemic circulation and thus it is essential for the systemic absorption of copper from the gastrointestinal tract [60]. In the presence of elevated copper levels, ATP7A translocates to the plasma membrane and pumps excess copper out of the cell [61]. Mutations of ATP7A result in Menkes disease, an X-linked disorder characterized by a lack of intestinal copper absorption.…”