The growth of normal cells is arrested when they come in contact with each other, a process known as contact inhibition. Contact inhibition is lost during tumorigenesis, resulting in uncontrolled cell growth. Here, we investigated the role of the tetraspanin transmembrane 4 superfamily member 5 (TM4SF5) in contact inhibition and tumorigenesis. We found that TM4SF5 was overexpressed in human hepatocarcinoma tissue. TM4SF5 expression in clinical samples and in human hepatocellular carcinoma cell lines correlated with enhanced p27 Kip1 expression and cytosolic stabilization as well as morphological elongation mediated by RhoA inactivation. These TM4SF5-mediated effects resulted in epithelial-mesenchymal transition (EMT) via loss of E-cadherin expression. The consequence of this was aberrant cell growth, as assessed by S-phase transition in confluent conditions, anchorage-independent growth, and tumor formation in nude mice. The TM4SF5-mediated effects were abolished by suppressing the expression of either TM4SF5 or cytosolic p27 Kip1 , as well as by reconstituting the expression of E-cadherin. Our observations have revealed a role for TM4SF5 in causing uncontrolled growth of human hepatocarcinoma cells through EMT.

Human p32, originally cloned as a splicing factor 2-associated protein, has been reported to interact with a variety of molecules including human immunodeficiency virus Tat and complement 1q (C1q). p32 protein is supposed to be in the nucleus and on the plasma membrane for the association with human immunodeficiency virus Tat and C1q, respectively. None of the interactions, however, is proven to have a physiological role. To investigate the physiological function of p32, we determined the intracellular localization of p32. The fractionation of cells, fluorescent immunocytochemistry, and electron microscopic immunostaining show that p32 is exclusively localized in the mitochondrial matrix. We cloned a Saccharomyces cerevisiae homologue of human p32 gene, referred to yeast p30 gene. The yeast p30 protein is also localized in the mitochondrial matrix. The disruption of the p30 gene caused the growth retardation of yeast cells in a glycerol medium but not in a glucose medium, i.e. the impairment of the mitochondrial ATP synthesis. The growth impairment was restored by the introduction of the human p32 cDNA, indicating that p30 is a functional yeast counterpart of human p32. Taken together, both p32 and p30 reside in mitochondrial matrix and play an important role in maintaining mitochondrial oxidative phosphorylation.

Severe hyperhomocysteinemia is associated with endothelial cell injury that may contribute to an increased incidence of thromboembolic disease. In this study, homocysteine induced programmed cell death in human umbilical vein endothelial cells as measured by TdTmediated dUTP nick end labeling assay, DNA ladder formation, induction of caspase 3-like activity, and cleavage of procaspase 3. Homocysteine-induced cell death was specific to homocysteine, was not mediated by oxidative stress, and was mimicked by inducers of the unfolded protein response (UPR), a signal transduction pathway activated by the accumulation of unfolded proteins in the lumen of the endoplasmic reticulum. Dominant negative forms of the endoplasmic reticulum-resident protein kinases IRE1␣ and -␤, which function as signal transducers of the UPR, prevented the activation of glucose-regulated protein 78/immunoglobulin chain-binding protein and C/EBP homologous protein/growth arrest and DNA damage-inducible protein 153 in response to homocysteine. Furthermore, overexpression of the point mutants of IRE1 with defective RNase more effectively suppressed the cell death than the kinase-defective mutant. These results indicate that homocysteine induces apoptosis in human umbilical vein endothelial cells by activation of the UPR and is signaled through IRE1. The studies implicate that the UPR may cause endothelial cell injury associated with severe hyperhomocysteinemia.

The Hakata antigen is a novel, thermolabile ␤ 2 -macroglycoprotein that reacts with sera from patients suffering from systemic lupus erythematosus. In this study we present the structure and the function of the Hakata antigen. We have identified cDNA clones encoding the Hakata antigen and analyzed its function. The cDNA included a possible open reading frame of 897 nucleotides, encoding 299 amino acids. The Hakata antigen consisted of a collagen-like domain in the middle section and a fibrinogen-like domain in the COOH terminus, both of which are homologous to human ficolin-1 and opsonin P35, indicating that these three molecules form a distinct family. The molecular mass of the Hakata antigen expressed in transfected cells was 35 kDa under reduced conditions, and it formed ladder bands under nonreducing conditions compatible with the previous result that the Hakata antigen exists in serum as homopolymers. Purified Hakata antigen sustained lectin activity, showing affinity with GalNAc, GlcNAc, D-fucose as mono/oligosaccharide, and lipopolysaccharides from Salmonella typhimurium and Salmonella minnesota. These results suggest that the Hakata antigen, a new member of the ficolin/opsonin P35 family, plays a role in the serum exerting lectin activity under physiological conditions. Inaba and Okochi (1) reported that sera from patients with systemic lupus erythematosus (SLE) 1 contained an antibody that reacted with normal sera. The antibody was shown to react against a novel thermolabile ␤ 2 -macroglycoprotein, designated the "Hakata antigen" (2). A similar thermolabile substance had been reported by Epstein and Tan (3), but it was not known whether the two proteins are the same. The molecular mass of the Hakata antigen in serum was 650 kDa as determined by gel filtration. The antigen was thermolabile because it lost antigenicity upon heating to 56°C for 1 min. The Hakata antigen was separated as a single band of 35 kDa by SDS-PAGE under reducing conditions. However, under nonreducing conditions it separated as ladder bands from 35 kDa to nearly the top of the gel, suggesting that the Hakata antigen exists in serum as homopolymers consisting of the 35 kDa subunit (2). All sera from 10,050 Japanese healthy blood donors, 99.99% of 751,352 Japanese patients' sera, and 99.98% of 41,430 Swedish patients' sera contained the Hakata antigen (4), thus implying that the Hakata antigen is a normal serum protein. The reference range of the Hakata antigen was 7-23 g/ml (2). The antibody against the Hakata antigen was possessed by 4.3% of 349 SLE patients and 0.3% of 703 patients with other autoimmune diseases (4). Among patients with other autoimmune diseases who possessed the antibody against the Hakata antigen, one patient was found among those with chronic glomerulonephritis and another in the group with primary biliary cirrhosis.In this study, we have cloned and characterized cDNA clones encoding the Hakata antigen revealing that the Hakata antigen is a novel serum protein that has Ca 2ϩ -independent lectin activity. The pri...

Glycogen synthase kinase-3 (GSK-3) is a master regulator of growth and death in cardiac myocytes. GSK-3 is inactivated by hypertrophic stimuli through phosphorylation-dependent and -independent mechanisms. Inactivation of GSK-3 removes the negative constraint of GSK-3 on hypertrophy, thereby stimulating cardiac hypertrophy. N-terminal phosphorylation of the GSK-3 isoforms GSK-3␣ and GSK-3␤ by upstream kinases (e.g., Akt) is a major mechanism of GSK-3 inhibition. Nonetheless, its role in mediating cardiac hypertrophy and failure remains to be established. Here we evaluated the role of Serine(S)21 and S9 phosphorylation of GSK-3␣ and GSK-3␤ in the regulation of cardiac hypertrophy and function during pressure overload (PO), using GSK-3␣ S21A knock-in (␣KI) and GSK-3␤ S9A knock-in (␤KI) mice. Although inhibition of S9 phosphorylation during PO in the ␤KI mice attenuated hypertrophy and heart failure (HF), inhibition of S21 phosphorylation in the ␣KI mice unexpectedly promoted hypertrophy and HF. Inhibition of S21 phosphorylation in GSK-3␣, but not of S9 phosphorylation in GSK-3␤, caused phosphorylation and down-regulation of G1-cyclins, due to preferential localization of GSK-3␣ in the nucleus, and suppressed E2F and markers of cell proliferation, including phosphorylated histone H3, under PO, thereby contributing to decreases in the total number of myocytes in the heart. Restoration of the E2F activity by injection of adenovirus harboring cyclin D1 with a nuclear localization signal attenuated HF under PO in the ␣KI mice. Collectively, our results reveal that whereas S9 phosphorylation of GSK-3␤ mediates pathological hypertrophy, S21 phosphorylation of GSK-3␣ plays a compensatory role during PO, in part by alleviating the negative constraint on the cell cycle machinery in cardiac myocytes.cardiac hypertrophy ͉ heart failure ͉ mouse model ͉ signal transduction