Tumorigenic 3T3 cells maintain an alkaline intracellular pH under physiological conditions.

Abstract

One of the earliest events in the response of mammalian cells to mitogens is activation of Na+/H+ exchange, which increases intracellular pH (pH"') in the absence of HCO5 or at external pH values below 7.2. The proliferative response can be blocked by preventing the pHI' increase; yet, the proliferative response cannot be stimulated by artificially raising p11' with weak bases or high medium pH. These observations support the hypothesis that optimal pHin is a necessary, but not sufficient, component of the proliferativeresponse sequence. This hypothesis has recently been challenged by the observation that transfection of NIH 3T3 cells with yeast H+-ATPase renders them tumorigenic. Although previous measurements indicated that these transfected cells maintain a higher pH" in the absence of HCO-, whether H+-ATPase transfection raised the pH1" under physiologically relevant conditions was not known. The current report shows that these transfected cells do maintain a higher pH"' than control cells in the presence of HCO-, supporting the possibility that elevated pH" is a proliferative trigger in situ. We also show that these cells are serum-independent for growth and that they glycolyze much more rapidly than phenotypically normal cells.All mammalian cells maintain a higher intracellular pH (pHin) than predicted from Nernst equilibrium (1). Maintenance of this pH gradient can be mediated by three transport systems: Na+/H+ exchange, HCO-transport, and plasma membrane H+-ATPase. Most, if not all, cells contain Na+/H+ exchange and HCO-transport activities, whereas plasma membrane H+-ATPase activity is generally observed only in specialized epithelia, such as bladder, intestine, and kidney (2). Interplay between these two (and sometimes three) systems buffers the pHin against changes in the extracellular pH (pHex) and can mediate changes in pHin during certain physiological responses.One of the earliest events in the response of mammalian cells to mitogens is activation of Na+/H+ exchange (3, 4). In the absence of HCO-or at low pHex, this increases pHin (5, 6). Although it was earlier thought that elevated pHmn might be a second messenger in the proliferative response (7,8) tTo whom reprint requests should be addressed. 7414The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

The chemistry, physiology and pathology of pH in cancer

“…The pH sensors involved in cancer disease progression have proved to be more challenging to identify, possibly because of difficulties in distinguishing bona fide pH sensors from the plethora of proteins that bind H þ ions [2]. Cells sensing an alkaline pH i have been shown to proliferate [61], enter the cell cycle [62,63], differentiate [64], migrate [65,66], reduce apoptosis [67] and clastogenesis [68], and undergo malignant transformation [69,70]-events that are critical in cancer formation and metastasis. Considering the complexity of these processes, the observed pH i sensitivity may involve a number of H þ -binding molecular switches.…”

Why are epididymal tumours so rare?

“…149 Proton export by the tumour cells raises their intracellular pH, which is an effective proliferative trigger. 150 Atypical responses to hypoxia in the epididymis VHL, a protein component of the VBC complex, is encoded by a cancer suppressor gene, since its mutation in patients with von Hippel-Lindau (VHL) disease is responsible for a certain group of tumours found at various sites including the epididymis. 4 The multifocal epithelial tumourlets in the epididymis associated with VHL disease are confined to the efferent ducts, 146,148 which comprise much of the head of the human epididymis 151 (Figure 1b).…”

Abnormal Acidification of Melanoma Cells Induces Tyrosinase Retention in the Early Secretory Pathway

“…V-ATPases have been implicated in neutralizing cytosolic pH by pumping protons away from the cytoplasm to the outside milieu as well as into acidic organelles such as the Golgi, endosomes, and lysosomes (25,40,41). Therefore, we tested the effect of the Na ϩ /K ϩ and proton ionophore monensin known to reversibly raise the pH of endocytic vesicles (22,42) and the high affinity V-ATPase inhibitors concanamycin A and bafilomycin A1 (43) on tyrosinase maturation and activity.…”