We found previously that overexpression of an F-box protein ␤TrCP1 and the structurally related ␤TrCP2 augments ubiquitination of phosphorylated IB␣ (pIB␣) induced by tumor necrosis factor-␣ (TNF-␣), but the relationship of the two homologous ␤TrCP proteins remains unknown. Herein we reveal that deletion mutants of ␤TrCP1 and ␤TrCP2 lacking the F-box domain suppressed ubiquitination and destruction of pIB␣ as well as transcriptional activation of NF-B. The ectopically expressed ␤TrCP1 and ␤TrCP2 formed both homodimer and heterodimer complexes without displaying the trimer complex. Dimerization of ␤TrCP1 and/or ␤TrCP2 takes place at their conserved NH 2 -terminal regions, termed a "D-domain" (for dimerization domain), located upstream of the F-box domain. The D-domain was necessary and sufficient for the dimer formation. Intriguingly, the ␤TrCP homodimer, but not the heterodimer, was selectively recruited to pIB␣ induced by TNF-␣. These results indicate that not only ␤TrCP1 but also ␤TrCP2 participates in the ubiquitination-dependent destruction of IB␣ by forming SCF ␤TrCP1-␤TrCP1 and SCF ␤TrCP2-␤TrCP2 ubiquitin-ligase complexes.

Lipoprotein lipase (LPL) is a key enzyme in the hydrolysis of TG-rich lipoproteins. To elucidate the physiological roles of LPL in lipid and lipoprotein metabolism, we generated transgenic rabbits expressing human LPL. In postheparinized plasma of transgenic rabbits, the human LPL protein levels were about 650 ng/ml, and LPL enzymatic activity was found at levels up to 4-fold greater than that in nontransgenic littermates. Increased LPL activity in transgenic rabbits was associated with as much as an 80% decrease in plasma triglycerides and a 59% decrease in high density lipoprotein-cholesterol. Analysis of the lipoprotein density fractions revealed that increased expression of the LPL transgene resulted in a remarkable reduction in the level of very low density lipoproteins as well as in the level of intermediate density lipoproteins. In addition, LDL cholesterol levels in transgenic rabbits were significantly increased. When transgenic rabbits were fed a cholesterol-rich diet, the development of hypercholesterolemia and aortic atherosclerosis was dramatically suppressed in transgenic rabbits. These results demonstrate that systemically increased LPL activity functions in the metabolism of all classes of lipoproteins, thereby playing a crucial role in plasma triglyceride hydrolysis and lipoprotein conversion, and that overexpression of LPL protects against diet-induced hypercholesterolemia and atherosclerosis. Lipoprotein lipase (LPL)1 plays a crucial role in lipid metabolism and transport by catalyzing the hydrolysis of triglyceriderich (TG-rich) lipoproteins such as chylomicrons and very low density lipoproteins (VLDL). Through the hydrolysis of TG in these particles, LPL converts these lipoproteins to denser lipoproteins such as chylomicron remnants, intermediate density lipoprotein (IDL), and low density lipoproteins (LDL) (1-3). This process generates free fatty acids (FFA), which are taken up and used for metabolic energy or stored as TG after reesterification and also results in the generation of surface remnants, which give rise to high density lipoproteins (HDL). It has been suggested that LPL influences not only plasma TG levels but also plasma HDL levels (4).LPL is mainly produced by mesenchymal cells such as adipose and muscle cells and then transported to the luminal surface of the vascular endothelium, where it is bound to heparan sulfate proteoglycans (HSPG). Small amounts of LPL are also present in other types of tissues, including the adrenals, brain, lung, and spleen (5). Furthermore, LPL is also expressed by macrophages and smooth muscle cells in atherosclerotic lesions (6, 7), suggesting that LPL modulates vascular functions and may be involved in atherogenesis. Elucidation of the precise roles of LPL in atherosclerosis has been compounded by the fact that LPL has multiple functions in lipoprotein metabolism through its catalytic properties and acts as a ligand for the LDL receptor-related protein (8) or a bridge between lipoproteins and HSPG (9). In humans, it has been found that familial L...

Increased proteolytic activity of matrix metalloproteinases (MMPs) may promote articular destruction such as occurs in rheumatoid arthritis and osteoarthritis. Recently, we reported that synovial tissue and fluid obtained from patients with rheumatoid arthritis contained higher activity of macrophage elastase (MMP-12). To examine the hypothesis that MMP-12 may potentially enhance the progression of arthritis, we investigated the effects of overexpression of MMP-12 on inflammatory arthritis in transgenic rabbits that express the human MMP-12 transgene in the macrophage lineage. Inflammatory arthritis was produced by articular injection of carrageenan solution and the degree of inflammatory arthritis in transgenic rabbits was compared with that in control rabbits. We found that overexpression of MMP-12 in transgenic rabbits significantly enhanced the arthritic lesions, resulting in severe synovial thickening, pannus formation, and prominent macrophage infiltration at an early stage and a marked destruction of articular cartilage associated with loss of proteoglycan at a later stage. These results demonstrate that excessive MMP-12 expression exacerbates articular connective tissue and cartilage degradation and thus plays a critical role in the development of

1 The aim of this study was to evaluate the potency of YM-53601 ((E)-2-[2-¯uoro-2-(quinuclidin-3-ylidene) ethoxy]-9H-carbazole monohydrochloride), a new inhibitor of squalene synthase, in reducing both plasma cholesterol and triglyceride levels, compared with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor and ®brates, respectively. 2 YM-53601 equally inhibited squalene synthase activities in hepatic microsomes prepared from several animal species and also suppressed cholesterol biosynthesis in rats (ED 50 , 32 mg kg 71 ). 3 In guinea-pigs, YM-53601 and pravastatin reduced plasma nonHDL-C (=total cholesterol ± high density lipoprotein cholesterol) by 47% (P50.001) and 33% (P50.001), respectively (100 mg kg 71 , daily for 14 days). In rhesus monkeys, YM-53601 decreased plasma nonHDL-C by 37% (50 mg kg 71, twice daily for 21 days, P50.01), whereas the HMG-CoA reductase inhibitor, pravastatin, failed to do (25 mg kg 71 , twice daily for 28 days). 4 YM-53601 caused plasma triglyceride reduction in hamsters fed a normal diet (81% decrease at 50 mg kg 71 , daily for 5 days, P50.001). In hamsters fed a high-fat diet, the ability of YM-53601 to lower triglyceride (by 73%, P50.001) was superior to that of feno®brate (by 53%, P50.001), the most potent ®brate (dosage of each drug: 100 mg kg 71, daily for 7 days). 5 This is the ®rst report that a squalene synthase inhibitor is superior to an HMG-CoA reductase inhibitor in lowering plasma nonHDL-C level in rhesus monkeys and is superior to a ®brate in signi®cantly lowering plasma triglyceride level. YM-53601 may therefore prove useful in treating hypercholesterolemia and hypertriglyceridemia in humans.

Elevated plasma lipoprotein(a) [Lp(a)]levels constitute an independent risk factor for the development of atherosclerosis. However, the mechanism underlying Lp(a) atherogenicity is unclear. Recently, we demonstrated that Lp(a) may potentially be proatherogenic in transgenic rabbits expressing human apolipoprotein(a) [apo(a)]. In this study, we further investigated atherosclerotic lesions of transgenic rabbits by morphometry and immunohistochemistry. On a cholesterol diet, human apo(a) transgenic rabbits had more extensive atherosclerotic lesions of the aorta, carotid artery, iliac artery, and coronary artery than did nontransgenic littermate rabbits as defined by increased intimal lesion area. Enhanced lesion development in transgenic rabbits was characterized by increased accumulation of smooth muscle cells, that was often associated with the Lp(a) deposition. To explore the possibility that Lp(a) may be involved in the smoothmuscle cell phenotypic modulation, we stained the lesions using a panel of monoclonal antibodies against smooth-muscle myosin heavy-chain isoforms (SM1, SM2, and SMemb) and basic transcriptional element binding protein-2 (BTEB2). We found that a large number of smooth muscle cells located in the apo(a)-containing areas of transgenic rabbits were positive for SMemb and BTEB2, suggesting that these smooth muscle cells were either immature or in the state of activation. In addition, transgenic rabbits showed delayed fibrinolytic activity accompanied by increased plasma plasminogen activator inhibitor-1. Lipoprotein(a) [Lp(a)] closely resembles low-density lipoprotein (LDL) in both lipid composition and the presence of apolipoprotein (apo) B-100 (apoB-100). Lp(a) is distinguished from LDL by the presence of an additional protein designated as apolipoprotein(a) [apo(a)], which is complexed to apoB-100 by disulfide linkage.