Stimulation of NADH oxidase activity from rat liver plasma membranes by growth factors and hormones is decreased or absent with hepatoma plasma membranes

Abstract

Plasma membranes of rat liver isolated by aqueous two-phase partition exhibited basal levels of NADH oxidase activity that were increased approx. 2-fold by addition of hormones and growth factors to which liver cells were known to respond. In contrast, hepatoma plasma membranes demonstrated an intrinsically increased level of NADH oxidase, which was not stimulated further by addition of growth factors. The results suggest that the NADH oxidase of the hepatoma plasma membrane is no longer correctly coupled to hormone and growth-factor receptors. This biochemical defect may parallel the loss of growth control that is characteristic of neoplastic transformation in hepatocarcinogenesis and other transformation systems. INTRODUCTIONAn NADH oxidase activity (transfer of electrons from NADH to oxygen) of plasma membranes purified from rat liver was described that was stimulated by the growth factor transferrin [1]. The stimulated activity was not inhibited by cyanide and was not seen in plasma membranes prepared from hyperplastic nodules from livers of animals given the hepatocarcinogen 2-acetylaminofluorene, nor was it due to reduction of iron associated with diferric transferrin [1]. In the present study, these findings were extended to a comparison of the effects of several growth factors and hormones to which liver cells are known to respond for both liver plasma membranes and plasma membranes prepared from rat hepatomas carried in syngeneic recipients. The findings show that the cyanide-resistant NADH oxidase was stimulated by several other growth factors in addition to diferric transferrin. Additionally, the ability of the growth factors and hormones to stimulate the NADH oxidase activity was lost in the plasma membranes of hepatomas. The latter exhibited intrinsically higher levels of activity, comparable with the hormonestimulated activity levels for liver plasma membranes. The findings point to a fundamental alteration of the hepatoma plasma membrane involving regulation of the activity of the NADH oxidase, which may be important to the unregulated growth that is characteristic of hepatomas in situ.

Cancer Site-Specific Isoforms of ENOX2 (tNOX), A Cancer-Specific Cell Surface Oxidase

“…Their association with the cancer cell surface helps explain the well-known uncontrolled growth of cancer cells. In contrast to the ENOX1 proteins which are activated by growth factors, the cancer-associated ENOX2 proteins are unresponsive to growth factors and constitutively activated [6]. A defining characteristic of the cancer-associated ENOX2 proteins is their ability to be inhibited by drugs such as adriamycin and cis-platinum which normally bind to DNA but also occupy quinonebinding pockets on proteins such as ENOX2 [7].…”

Inhibition by brefeldin A of NADH oxidation activity of rat liver Golgi apparatus accelerated by GDP

“…The NADH oxidase of rat liver plasma membranes does respond to guanine nucleotides, GTP-7-S, mastoparan and aluminum fluoride [36]. The activity is growth factorand hormone-responsive with plasma membranes of rat liver [37], but is constitutively activated and no longer growth factor-and hormone-responsive in plasma membranes from rat hepatomas [38]. Alteration of a guanine nucleotide exchange activity similar to that involved with ARF and accessory protein binding to Golgi apparatus membranes [17,18] could help to explain how GDP and brefeldin A interact to inhibit Golgi apparatus NADH oxidase activity.…”

The changes of prooxidant and antioxidant enzyme activities in bovine leukemia virus‐transformed cells Their influence on quinone cytotoxicity

“…NAD(P)H oxidase activities were insensitive to rotenone (2 PM) or azide (1 mM). They could be evidently attributed to O;'-generating NAD(P)H oxidases of the plasma membrane [13,22,23], since according to the used method of lysate preparation, the latter should include a fibroblast membrane fraction as well [22,23]. Besides, the reduction of cytochrome c is inhibited by 40% by adding superoxide dismutase (30 ,ug .…”

“…Some data show that the activities of certain 0;' and H,O, generating enzymes, e.g. plasma membrane NADH oxidase [13] or the peroxisomal fatty acid /?-oxidation enzyme system [ 141 are higher in transformed cells. The increased activities of these or similar redox enzymes, catalyzing the redox cycling of quinonones by complex changes of enzyme activity, which complicate the discrimination between the mechanisms of toxicity of anthracyclines or the evaluation of their contribution.…”