Overexpression of the cholesterol-binding protein MLN64 induces liver damage in the mouse

Abstract

INTRODUCTIONMLN64 (metastatic lymph node 64) cDNA was originally discovered as a highly expressed and amplified gene in certain breast, gastric, and esophageal cancers [1][2][3] . Although MLN64 could play a causative role in tumorigenesis, its amplification probably reflects the close genomic proximity (within 36 kb) to the oncogene c-erb-B2 (her-2/ neu), which is invariantly coamplified [3,4] . The N-terminal of MLN64, the so-called MENTAL domain, includes four transmembrane helices, whereas the C-terminal domain contains the StAR-related lipid transfer domain (START) [5,6] . The latter domain is present in proteins involved in diverse cell functions [6,7] and exhibits 37% identity with StAR [5,6] . There is a family of proteins with There is a family of proteins with homolog y to StAR, each containing the 200-210-aa START domain, in which MLN64 is known as StarD3 [5,6] . Like StAR, the isolated MLN64 START domain binds [5] and transfers [8] cholesterol in vitro to the mitochondria and stimulates steroidogenesis when cotransfected with the cytochrome P450scc [8,9] . However, full-length MLN64 is less active in steroidogenic assays since its transmembrane domain localizes it to late endosomes with the START domain facing the cytosol [8,10] . For this reason, the role of MLN64 in steroidogenesis is still unclear, but it has been suggested that proteolysis could release the START domain to allow delivery of cholesterol to mitochondria [8] . METHODS: Recom�inant�adenovirus�mediated MLN64 gene transfer was used to overe�press MLN64 in the livers of C57BL/� mice. We measured the effects of MLN64 overe�pression on hepatic cholesterol content, �ile flow, �iliary lipid secretion and apoptosis markers.For in vitro studies cultured CH� cells with transient MLN64 overe�pression were utilized and apoptosis �y TUNEL assa� was measured. RESULTS:Livers from Ad.MLN64�infected mice e�hi�ited early onset of liver damage and apoptosis. This response correlated with increases in liver cholesterol content and �iliary �ile acid concentration, and impaired �ile flow. We investigated whether liver MLN64 e�pression could �e modulated in a murine model of he�atic injur�. We found increased he�atic MLN�� mRN� and �rotein levels in mice with chenodeo�ycholic acid�induced liver damage. In addition, cultured CH� cells with transient MLN64 overe�pression showed increased apoptosis. CONCLUSION:In summary, hepatic MLN64 over� e�pression induced damage and apoptosis in murine

Cellular Adaptation to Anthrax Lethal Toxin-Induced Mitochondrial Cholesterol Enrichment, Hyperpolarization, and Reactive Oxygen Species Generation through Downregulating MLN64 in Macrophages

“…Although it is not clear how MLN64 trafficking or expression is regulated under pathogenic conditions, the involvement of MLN64 and mitochondrial cholesterol load in cell death has been demonstrated. For example, overexpression of MLN64 caused cell death in hepatocytes and CHO cells (60), and mitochondrial cholesterol load sensitizes cells to amyloid ␤ peptide-and tumor necrosis factor-induced cell death (9,41). In line with these studies, we first showed that MLN64 trafficking to mitochondria was enhanced by LeTx (Fig.…”

STARTing to understand MLN64 function in cholesterol transport

“…The fi ndings by Charman et al ( 11 ) complement our previous report that adenovirus-mediated overexpression of MLN64 induces an increase in hepatic free cholesterol that is associated with apoptosis and liver damage ( 15 ). Based on the fi ndings of Charman et al ( 11 ), we hypothesize that the liver damage observed in MLN64-overexpressing mice is mediated, at least in part, by an increase in mitochondrial cholesterol transport.…”

“…For instance, hepatocytes from leptin-defi cient ob / ob mice or rats with diet-induced mitochondrial cholesterol accumulation exhibited reduced mitochondrial membrane fl uidity and glutathione levels that correlated with increased sensitivity to TNF α -dependent cell death ( 13 ). In this connection, we have previously shown increased MLN64 mRNA and protein levels in a murine model of liver damage induced by bile acids ( 15 ), suggesting that MLN64-mediated cholesterol transport to mitochondria may underlie bile acid-induced cytotoxicity. In addition, mitochondrial dysfunction is commonly associated with increased generation of reactive oxygen species, induction of apoptosis, infl ammation, and fi brosis, depending upon the tissue ( 22 -25 ).…”

HDAC8-Mediated Epigenetic Reprogramming Plays a Key Role in Resistance to Anthrax Lethal Toxin–Induced Pyroptosis in Macrophages

“…Therefore, it will be interesting to examine whether edema toxin potentiates LeTx-induced cytotoxic and pathophysiologic effects (51, 52) through inhibiting HDAC8 and inducing the mitochondrial death genes. Enhanced expression of the mitochondrial death genes BNIP3, BNIP3L, and MLN64 can cause cytotoxicity and is involved in hypoxia-induced cardiovascular pathology (53)(54)(55)(56), which is also observed in anthrax animal models (57,58).…”