Zinc-␣2-glycoprotein (ZAG), a 43-kDa protein, is overexpressed in certain human malignant tumors and acts as a lipid-mobilizing factor to stimulate lipolysis in adipocytes leading to cachexia in mice implanted with ZAG-producing tumors. Because white adipose tissue (WAT) is an endocrine organ secreting a wide range of protein factors, including those involved in lipid metabolism, we have investigated whether ZAG is produced locally by adipocytes. ZAG mRNA was detected by RT-PCR in the mouse WAT depots examined (epididymal, perirenal, s.c., and mammary gland) and in interscapular brown fat. In WAT, ZAG gene expression was evident in mature adipocytes and in stromal-vascular cells. Using a ZAG Ab, ZAG protein was located in WAT by Western blotting and immunohistochemistry. Mice bearing the MAC16-tumor displayed substantial losses of body weight and fat mass, which was accompanied by major increases in ZAG mRNA and protein levels in WAT and brown fat. ZAG mRNA was detected in 3T3-L1 cells, before and after the induction of differentiation, with the level increasing progressively after differentiation with a peak at days 8 -10. Both dexamethasone and a ␤3 agonist, BRL 37344, increased ZAG mRNA levels in 3T3-L1 adipocytes. ZAG gene expression and protein were also detected in human adipose tissue (visceral and s.c.). It is suggested that ZAG is a new adipose tissue protein factor, which may be involved in the modulation of lipolysis in adipocytes. Overexpression in WAT of tumor-bearing mice suggests a local role for adipocyte-derived ZAG in the substantial reduction of adiposity of cancer cachexia.

Malignant transformation of primary cells requires at least two distinct and characteristic alterations in cellular behaviour. The first, cellular immortality, can be induced by chemical carcinogens or by cloned oncogenes such as polyoma large T (ref. 4), adenovirus early region 1A (E1A) or the oncogene from avian (MC29) myelocytomatosis virus, v-myc. Cells whose in vitro life-span has been extended by these procedures can be fully transformed by transfection with oncogenes belonging to a different complementation group, including genes of the ras family, adenovirus E1b and polyoma virus middle T (refs 4, 5). The unstable cellular phosphoprotein p53 is frequently present at elevated levels in transformed cells and is stabilized by the formation of complexes with simian virus 40 (SV40) large T or adenovirus E1b 57K protein. Although several reports have associated p53 with cell proliferation, its role remains obscure. We have cloned complementary DNA sequences encoding murine p53 and report here that transfection of p53 expression constructs into cells of finite lifespan in vitro results in cellular immortality and susceptibility to transformation by a ras oncogene.

The expression profile of a series of adipokine genes linked to inflammation has been examined by quantitative PCR during the differentiation of human preadipocytes to adipocytes in primary culture, together with the integrated effects of TNF-α on the expression of these adipokines in the differentiated adipocytes. Expression of the genes encoding adiponectin, leptin, and haptoglobin was highly differentiation dependent, the mRNA being undetectable predifferentiation with the level peaking 9–15 days postdifferentiation. Although angiotensinogen (AGT) and monocyte chemoattractant protein-1 (MCP-1) were both expressed before differentiation, the mRNA level increased markedly on differentiation. The expression of nerve growth factor (NGF) and plasminogen activator inhibitor-1 (PAI-1) fell after differentiation, whereas that of TNF-α and IL-6 changed little. Measurement of adiponectin, leptin, MCP-1, and NGF in the medium by ELISA showed that the protein secretion pattern paralleled cellular mRNA levels. Treatment of differentiated human adipocytes with TNF-α (5 or 100 ng/ml for 24 h) significantly decreased the level of adiponectin, AGT, and haptoglobin mRNA (by 2- to 4-fold), whereas that of leptin and PAI-1 was unchanged. In contrast, TNF-α induced substantial increases in IL-6, TNF-α, metallothionein, MCP-1, and NGF mRNAs, the largest increase being with MCP-1 (14.5-fold). MCP-1 and NGF secretion increased 8- to 10-fold with TNF-α, whereas leptin and adiponectin did not change. These results demonstrate that there are major quantitative changes in adipokine gene expression during differentiation of human adipocytes and that TNF-α has a pleiotropic effect on inflammation-related adipokine production, the synthesis of MCP-1 and NGF being highly induced by the cytokine.