Parathyroid hormone (PTH) inhibits proximal tubular brush border membrane Na؉ /P i cotransport activity; this decrease in the transport activity was found to be associated with a decrease in type II Na ؉ /P i cotransporter protein content in rat brush border membranes. In the present study we investigated the PTH-dependent regulation of the type II Na ؉ /P i cotransporter in opossum kidney cells, a previously established model to study cellular mechanisms involved in the regulation of proximal tubular Na ؉ /P i cotransport. We transfected opossum kidney cells with a cDNA coding for NaP i -2 (rat renal type II Na ؉ /P i cotransporter). This allowed the study of PTH-dependent regulation of the transfected NaP i -2 and of the corresponding intrinsic cotransporter (NaP i -4). The results show (i) that the intrinsic and the transfected cotransporters are functionally (transport) and morphologically (immunofluorescence) localized at the apical membrane, (ii) that the intrinsic as well as the transfected Na ؉ /P i cotransport activities are inhibited by PTH, (iii) that PTH leads to a retrieval of both cotransporters from the apical membrane, (iv) that both cotransporters are rapidly degraded in response to PTH, and (v) that the reappearance/recovery of type II Na ؉ /P i cotransporter protein and function from PTH inhibition requires de novo protein synthesis. These results document that PTH leads to a removal of type II Na ؉ /P i cotransporters from the apical membrane and to their subsequent degradation. Renal proximal tubular P i reabsorption is acutely regulated by parathyroid hormone (PTH).1 This effect involves inhibition of the brush border membrane sodium-dependent P i transport and is characterized by a decrease in the maximal transport rate (V max ) (1, 2). Two different renal Na ϩ /P i cotransporters have been cloned, classified either as type I Na ϩ /P i cotransporter or as type II Na ϩ /P i cotransporter (3-14). Both are localized at the brush border membrane in proximal tubules. Recent data documented that physiologically and pathophysiologically altered brush border membrane Na ϩ /P i cotransport involves altered brush border expression of the type II Na ϩ /P i cotransporter (15)(16)(17).In the present study we investigated the PTH-mediated regulation of the type II Na ϩ /P i cotransporter in opossum cells (OK cells); these cells have recently been shown to contain such a cotransporter (NaP i -4; Ref. 8). The validity of the opossum kidney cell model to study proximal tubular Na ϩ /P i cotransport and its regulation has been established (18 -23). With respect to PTH-dependent control of Na ϩ /P i cotransport activity, we have reported that the recovery from the PTH-mediated inhibition of Na ϩ /P i cotransport in OK cells is dependent on de novo protein synthesis. This latter observation led to the hypothesis that PTH might lead to the retrieval and degradation of the transporter (27).The aims of the present study were 2-fold: (i) to study cellular/molecular mechanisms involved in PTH-dependent control of ...

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Nitrogen-bisphosphonates (n-BP), such as zoledronate, are the main class of drugs used for the prevention of osteoporotic fractures and the management of cancer-associated bone disease. However, long-term or high-dose use has been associated with certain adverse drug effects, such as osteonecrosis of the jaw and the loss of peripheral of blood Vγ9Vδ2 T cells, which appear to be linked to drug-induced immune dysfunction. In this report we show that neutrophils present in human peripheral blood readily take up zoledronate, and this phenomenon is associated with the potent immune suppression of human peripheral blood Vγ9Vδ2 T cells. Furthermore, we found this zoledronate-mediated inhibition by neutrophils could be overcome to fully reconstitute Vγ9Vδ2 T cell proliferation by concomitantly targeting neutrophil-derived hydrogen peroxide, serine proteases, and arginase I activity. These findings will enable the development of targeted strategies to mitigate some of the adverse effects of n-BP treatment on immune homeostasis and to improve the success of immunotherapy trials based on harnessing the anticancer potential of peripheral blood γδ T cells in the context of n-BP treatment.

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