Cloning of cDNAs encoding two isoforms of 68-kDa type I phosphatidylinositol-4-phosphate 5-kinase

Accumulating evidence suggests that phosphatidylinositol metabolism is essential for membrane traffic in the cell. Of particular importance, phosphatidylinositol transfer protein and the type I phosphatidylinositol- 4-phosphate 5-kinase (PI4P5K) have been identified as cytosolic components required for ATP-dependent, Ca2+-activated secretion. In order to identify PI4P5K isoforms that may play important roles in regulated insulin secretion from pancreatic beta-cells, we employed the polymerase chain reaction with degenerate primers and screening of a cDNA library of the murine pancreatic beta-cell line MIN6. Two novel cDNAs, designated PI4P5K-Ialpha and PI4P5K-Ibeta, were identified, which contained complete coding sequences encoding 539- or 546-amino acid proteins, respectively. These cDNAs were expressed in mammalian cells with an adenoviral expression vector. Proteins of both isoforms migrated at 68 kDa on SDS-polyacrylamide gel electrophoresis and exhibited phosphatidylinositol-4-phosphate 5-kinase activity, which was activated by phosphatidic acid, indicating that these proteins were type I isoforms. While these isoforms share a marked amino acid sequence homology in their central portion, the amino- and carboxyl-terminal regions differ significantly. Northern blot analysis depicted that tissue distributions differed between the two isoforms. Molecular identification of type I PI4P5K isoforms in insulin-secreting cells should provide insights into the role of phosphatidylinositol metabolism in regulated exocytosis of insulin-containing large dense core vesicles.

Hypoxia and hypoxia/reoxygenation activate Src family tyrosine kinases and p21ras in cultured rat cardiac myocytes

We previously reported that both hypoxia and hypoxia followed by reoxygenation (hypoxia/reoxygenation) rapidly and sequentially activate mitogen-activated protein kinase kinase kinase (MAPKKK) activity of Raf-1. This was followed by the sequential activation of MAP kinase kinase (MAPKK). MAP kinases (p42mopk and p44mopk), and S6 kinase (p90rsk). In this study, we demonstrated that both hypoxia and hypoxia/ reoxygenation caused rapid activation of Src family tyrosine kinases, p60c-src and p59c-fyn, which are upstream mediators of MAP kinase activation. This was followed by the activation of p21ras. Because Src family tyrosine kinases are known to be cell-surface-associated kinases and upstream regulators of p21ras, these results strongly suggested that activation of Src family tyrosine kinases plays a key role in triggering intracellular signaling cascades in cardiac myocytes in response to hypoxia and hypoxia/reoxygenation.

Role of the low density lipoprotein (LDL) receptor pathway in the metabolism of chylomicron remnants. A quantitative study in knockout mice lacking the LDL receptor, apolipoprotein E, or both

Two receptor pathways are thought to mediate the hepatic clearance of chylomicron remnants, (i) the low density lipoprotein receptor (LDLR) pathway and (ii) non-LDLR pathway. The current study was undertaken to quantitatively assess the contribution of each receptor pathway to hepatic catabolism of chylomicron remnants, by using mice that are deficient in apolipoprotein E (apoE) (apoE(-/-)), the LDLR (LDLR(-/-)), and both (apoE(-/-);LDLR(-/-)). Vitamin A fat tolerance tests showed that the area under the curves of the plasma excursions of retinyl ester in the LDLR(-/-), apoE(-/-), and apoE(-/-);LDLR(-/-) mice were 4, 12, and 12 times larger than those in wild-type mice. The retinyl ester accumulated in the plasma of the LDLR(-/-) mice was distributed in larger subfractions of triglyceride-rich lipoproteins, chylomicrons through very low density lipoprotein-C. These results indicate that the LDLR constitutes the major pathway for the clearance of retinyl ester. In support of this, agarose gel electrophoresis revealed that an oral fat load resulted in retention of chylomicrons in the LDLR(-/-) mice, which was not seen in wild-type mice. The observation that the apoE(-/-) mice showed larger retinyl ester excursion than LDLR(-/-) mice indicates that an apoE-dependent non-LDLR pathway is involved in the rest of the clearance of the retinyl ester. Together, we conclude that the LDLR pathway plays a significant role in the chylomicron remnant metabolism in mice fed a normal chow.

Effect of mitochondrial and/or cytosolic glycerol 3-phosphate dehydrogenase overexpression on glucose-stimulated insulin secretion from MIN6 and HIT cells

The glycerol phosphate shuttle consists of FAD-linked mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH) and its cytosolic NAD-linked isoform (cGPDH). Impaired mGPDH activity has recently been suggested to be one of the primary causes of insulin secretory defects in beta-cells. We found that mGPDH and cGPDH activities in MIN6 cells are comparable to those of isolated islets and higher than those in HIT cells by eightfold and threefold, respectively. Therefore, we selected the MIN6 cell line as a beta-cell model with normally regulated insulin secretion and normal shuttle enzyme activities and the HIT cell line as a beta-cell model with impaired insulin secretion and lower activities of these enzymes. The role of these dehydrogenases in glucose-stimulated insulin secretion was addressed by examining the effects of overexpression of mGPDH and/or cGPDH via recombinant adenoviruses in these cells. Infection with recombinant adenovirus with a cDNA encoding the Escherichia coli beta-galactosidase gene resulted in expression of its gene in 90% of MIN6 and HIT cells. Infection with a recombinant adenovirus with mGPDH cDNA (Adex1CAmGPDH) caused 2.1-fold and 5.7-fold increases in dehydrogenase activity as compared with those of control MIN6 and HIT cells, respectively. Infection with a recombinant adenovirus with cGPDH cDNA (Adex1CAcGPDH) caused a more than 50-fold increase in activity in both cell lines. Glycerol phosphate shuttle flux, as estimated by [2-3H]glycerol conversion to [3H]H2O, was increased to 120-130% by infection with Adex1CAmGPDH, but not with Adex1CAcGPDH infection, in both MIN6 and HIT cells. No further increase in flux through the glycerol phosphate shuttle was detected when the cells were infected with Adex1CAmGPDH together with Adex1CAcGPDH. Furthermore, neither [U-14C]glucose oxidation nor the insulin secretory response to glucose was affected in either cell line. Thus, mGPDH abundance in MIN6 and HIT cells is not directly related to their insulin secretory capacity in response to glucose, and reduced expression of mGPDH is not the primary cause of abnormal insulin secretory responses in HIT cells. The present data indicate that the emerging hypothesis pointing to mGPDH deficiency as a possible cause of NIDDM needs to be carefully evaluated.

Csk enhances insulin-stimulated dephosphorylation of focal adhesion proteins

Insulin has pleiotropic effects on the regulation of cell physiology through binding to its receptor. The wide variety of tyrosine phosphorylation motifs of insulin receptor substrate 1 (IRS-1), a substrate for the activated insulin receptor tyrosine kinase, may account for the multiple functions of insulin. Recent studies have shown that activation of the insulin receptor leads to the regulation of focal adhesion proteins, such as a dephosphorylation of focal adhesion kinase (pp125FAK). We show here that C-terminal Src kinase (Csk), which phosphorylates C-terminal tyrosine residues of Src family protein tyrosine kinases and suppresses their kinase activities, is involved in this insulin-stimulated dephosphorylation of focal adhesion proteins. We demonstrated that the overexpression of Csk enhanced and prolonged the insulin-induced dephosphorylation of pp125FAK. Another focal adhesion protein, paxillin, was also dephosphorylated upon insulin stimulation, and a kinase-negative mutant of Csk was able to inhibit the insulin-induced dephosphorylation of pp125FAK and paxillin. Although we have shown that the Csk Src homology 2 domain can bind to several tyrosine-phosphorylated proteins, including pp125FAK and paxillin, a majority of protein which bound to Csk was IRS-1 when cells were stimulated by insulin. Our data also indicated that tyrosine phosphorylation levels of IRS-1 appear to be paralleled by the dephosphorylation of the focal adhesion proteins. We therefore propose that the kinase activity of Csk, through the insulin-induced complex formation of Csk with IRS-1, is involved in insulin's regulation of the phosphorylation levels of the focal adhesion proteins, possibly through inactivation of the kinase activity of c-Src family kinases.

Perforin-positive leukemic cell infiltration in the aortic tissue of a patient with T-cell prolymphocytic leukemia

Here we report a rare case of T-cell prolymphocytic leukemia in which leukemic killer cells, expressing a cytolytic factor perforin, infiltrated the aorta as well as the heart and may have directly injured aortic vascular cells which strongly expressed human leukocyte antigens (HLAs) and intercellular adhesion molecule-1 (ICAM-1) as well as costimulatory molecules B7 and B70, which are ligands for CD28 expressed on T-cells. In spite of chemotherapy against leukemic cells, this autoimmune process finally caused fatal multi-organ failure.

Nonmuscle and smooth muscle myosin heavy chain expression in rejected cardiac allografts. A study in rat and monkey models

BACKGROUND

Diagnosis of acute rejection and graft arteriosclerosis (chronic rejection) is critical to the success of cardiac transplantation, but accurate diagnosis is often difficult. We have reported that there are three types of vascular myosin heavy chain (MHC) isoforms: SM1, SM2, and SMemb. SM2 is specifically expressed in differentiated smooth muscle cells (SMCs). SMemb is a nonmuscle-type MHC abundantly expressed in SMCs of fetal aorta.

METHODS AND RESULTS

To evaluate the usefulness of MHC expression for diagnosis and analysis of acute and chronic rejection, heterotopic cardiac transplantation was performed in rats and monkeys. Immunohistochemistry, electron microscopy, and Northern blot assay were performed to evaluate MHC expression. SMemb was expressed in spindle-shaped cells located in acutely rejected myocardium in the rats and monkeys. These cells were also observed in areas lacking cellular infiltration. These SMemb-positive cells were activated fibroblasts or myofibroblasts. SMemb mRNA was enhanced parallel to the progression of acute rejection. In the coronary arteries of chronically rejected allografts, enhanced SMemb and reduced SM2 expression was observed in both thickened intima and media. The reduced medial SM2 expression was observed before the intimal thickening occurred. These cells were phenotypically modulated SMCs.

CONCLUSIONS

Altered expression of MHC isoforms is a sensitive indicator in the diagnosis of acute and chronic cardiac rejection. The pathophysiology of this alteration in MHC isoform expression should be studied further to elucidate the pathogenesis of cardiac rejection.

Molecular genetic approach to the pathophysiology of cardiovascular disease

The delineation of the molecular mechanisms of cardiovascular disease is an important initial step in developing improved methods of screening and therapy. Recently, progress has been made in characterizing the molecular basis of several inherited cardiovascular diseases, particularly as to the diseases caused by defects in single gene. When the disease under study has a complex etiology with multiple genetic and environmental components, it becomes much more difficult to dissect out the genetic factors and to distinguish between causation and correlation. Gene targeting in mice provides a means to test the effect of a precise genetic change completely free from the effects of differences in any other genes. Models of several human genetic diseases have been produced by gene targeting and the resulting "knockout" mice have often confirmed that the disease is the consequence of the defect of a gene of interest. The review will focus on the how molecular genetic approach is useful to understand the basic mechanism of complex genetic diseases, including essential hypertension, atherosclerosis, congenital heart disease. Particular emphasis will be given to the renin angiotensin system because a large body of evidence indicates its greater role in the pathogenesis of many complex cardiovascular diseases than has been recognized.

Insulin resistance and growth retardation in mice lacking insulin receptor substrate-1 and identification of insulin receptor substrate-2

To clarify the physiological roles of insulin receptor substrate-1 (IRS-1) in vivo, we made mice with a targeted disruption of the IRS-1 gene locus. Mice homozygous for targeted disruption of the IRS-1 gene were born alive but were retarded in embryonal and postnatal growth. They also had resistance to the glucose-lowering effects of insulin, insulin-like growth factor-1 (IGF-1) and factor-2 (IGF-2). These data suggest the existence of both IRS-1-dependent and IRS-1-independent pathways for signal transduction of insulin and IGFs. Moreover, we identified tyrosine phosphorylation of a 190-kDa protein (pp 190) as a novel substrate (IRS-2) for insulin receptor kinase in livers of IRS-1 deficient mice which can bind both P13-kinase and Ash/Grb2.

Tyrosine phosphorylation of p130Cas in cell adhesion and transformation

Integrins comprise the major class of receptors used by cells to interact with the extracellular matrix. Integrin/matrix interactions play a critical role in a variety of biological processes, including embryonic development, wound healing, tumor metastasis, cell growth and differentiation. It is now evident that integrins can transduce biochemical signals across the plasma membrane to the cell interior. Protein tyrosine phosphorylation has attracted much attention as an important regulator for integrin-mediated signal transduction. Recently, we have identified a novel signaling molecule, p130Cas, which participates in integrin-mediated signal transduction. p130Cas was originally identified as a protein hyperphosphorylated in cells expressing transforming gene products p47v-crk (v-Crk) and p60v-crk (v-Src). In this brief review, we will discuss about a role of p130Cas in signal transduction triggered by cell adhesion and transformation.

Elevated platelet count features the variant type of BCR/ABL junction in chronic myelogenous leukaemia

A variant form of BCR/ABL junction was identified in a patient with chronic myelogenous leukaemia (CML). The BCR/ABL fusion mRNA of this patient showed in-frame junction between BCR exon c3 and ABL exon 2. Although the diagnosis of CML was made, the patient showed clinical features of essential thrombocythaemia (ET) rather than that of typical CML. Treatment with interferon-alpha showed no cytogenetic response. The c3-a2 type of BCR/ABL junction seems to be associated with elevated platelet count and thus could form a novel clinical entity different from typical CML.

Overexpression of catalytic subunit p110alpha of phosphatidylinositol 3-kinase increases glucose transport activity with translocation of glucose transporters in 3T3-L1 adipocytes

To elucidate the mechanisms of phosphatidylinositol (PI) 3-kinase involvement in insulin-stimulated glucose transport activity, the epitope-tagged p110alpha subunit of PI 3-kinase was overexpressed in 3T3-L1 adipocytes using an adenovirus-mediated gene transduction system. Overexpression of p110alpha was confirmed by immunoblot using anti-tagged epitope antibody. p110alpha overexpression induced a 2.5-fold increase in PI 3-kinase activity associated with its regulatory subunits in the basal state, an increase exceeding that of the maximally insulin-stimulated control cells, while PI 3-kinase activity associated with phosphotyrosyl protein was only modestly elevated. Overexpression of p110alpha induced an approximately 14-fold increase in the basal glucose transport rate, which was also greater than that observed in the stimulated control. No apparent difference was observed in the cellular expression level of either GLUT1 or GLUT4 proteins between control and p110alpha-overexpressing 3T3-L1 adipocytes. Subcellular fractionation revealed translocation of glucose transporters from intracellular to plasma membranes in basal p110alpha-overexpressing cells. The translocation of GLUT4 protein to the plasma membrane was further confirmed using a membrane sheet assay. These findings indicate that an increment in PI 3-kinase activity induced by overexpression of p110alpha of PI 3-kinase stimulates glucose transport activity with translocation of glucose transporters, i.e., mimics the effect of insulin.

A conserved cysteine residue in the runt homology domain of AML1 is required for the DNA binding ability and the transforming activity on fibroblasts

The AML1 gene encodes DNA-binding proteins that contain the runt homology domain and is found at the breakpoints of t(8;21), t(3;21), and t(12;21) translocations associated with myelogenous leukemias. AML1 heterodimerizes with PEBP2beta/CBFbeta, resulting in the enhanced affinity with DNA. The runt homology domain is responsible for binding with DNA and heterodimerizing with PEBP2beta/CBFbeta. AML1 is suggested to perform a pivotal role in myeloid cell differentiation, whereas it can cause neoplastic transformation when overexpressed in fibroblasts. In this study, we demonstrated that the reducing reagent, dithiothreitol (DTT), markedly enhances the DNA binding of AML1 expressed in COS7 cells. Oxidation by diamide or modification by N-ethylmaleimide of the free sulfhydryl residues inhibited the interaction of AML1 with DNA. The diamide effect was reversible with excess of DTT, whereas DTT could not restore the DNA binding of AML1 treated with N-ethylmaleimide. Site-directed mutagenesis of the amino acid residue 72, a highly conserved cysteine in the runt homology domain of AML1, to serine almost completely abolished DNA binding without altering the interaction with PEBP2beta/CBFbeta. This substitution also impaired transactivation through the consensus DNA sequence and transformation of fibroblasts induced by AML1b. These data indicate an essential role of the conserved cysteine residue in DNA binding of AML1, and it is possible that the redox state of AML1 could contribute to the regulation of its function.

Suppression of diet-induced atherosclerosis in low density lipoprotein receptor knockout mice overexpressing lipoprotein lipase

Lipoprotein lipase (LPL) is a key enzyme in the hydrolysis of triglyceride-rich lipoproteins. Conflicting results have been reported concerning its role in atherogenesis. To determine the effects of the overexpressed LPL on diet-induced atherosclerosis, we have generated low density lipoprotein receptor (LDLR) knockout mice that overexpressed human LPL transgene (LPL/LDLRKO) and compared their plasma lipoproteins and atherosclerosis with those in nonexpressing LDLR-knockout mice (LDLRKO). On a normal chow diet, LPL/LDLRKO mice showed marked suppression of mean plasma triglyceride levels (32 versus 236 mg/dl) and modest decrease in mean cholesterol levels (300 versus 386 mg/dl) as compared with LDLRKO mice. Larger lipoprotein particles of intermediate density lipoprotein (IDL)/LDL were selectively reduced in LPL/LDLRKO mice. On an atherogenic diet, both mice exhibited severe hypercholesterolemia. But, mean plasma cholesterol levels in LPL/ LDLRKO mice were still suppressed as compared with that in LDLRKO mice (1357 versus 2187 mg/dl). Marked reduction in a larger subfraction of IDL/LDL, which conceivably corresponds to remnant lipoproteins, was observed in the LPL/LDLRKO mice. LDLRKO mice developed severe fatty streak lesions in the aortic sinus after feeding with the atherogenic diet for 8 weeks. In contrast, mean lesion area in the LPL/LDLRKO mice was 18-fold smaller than that in LDLRKO mice. We suggest that the altered lipoprotein profile, in particular the reduced level of remnant lipoproteins, is mainly responsible for the protection by LPL against atherosclerosis.

Structurally altered Evi-1 protein generated in the 3q21q26 syndrome

Overexpression of the Evi-1 gene appears to be a consistent feature of the 3q21q26 syndrome, an association of myeloid leukemias/myelodysplastic syndrome with a specific chromosomal aberration involving both 3q21 and 3q26, such as t(3;3)(q21;q26) or inv(3)(q21q26). The rearrangement in 3q26 has been reported to occur near the Evi-1 locus, implicating that it is the critical gene deregulated in the 3q21q26 syndrome. Here we present a structural abnormality of Evi-1 protein in a case with the 3q21q26 syndrome. In this case carrying typical inv(3)(q21q26), the 3q26 breakpoint is located within an intron of the Evi-1 gene, and resulted in overexpression of normally unexpressed, an aberrant form of Evi-1 protein, in which the C-terminal 44 amino acids of wild-type Evi-1 protein were truncated and replaced by five amino acids. The truncated Evi-1 protein is shown to increase AP1 activity when expressed in NIH3T3 cells as its wild-type counterpart. We also show that the origin of this peculiar type of rearrangement of the Evi-1 gene is not an artifact during establishment of the cell line, but is the event that occurred in the primary leukemic cells. Our results strongly support that the primary target for the 3q21q26 syndrome is the Evi-1 gene, and provide the first evidence that the structurally altered Evi-1 gene may be involved in the 3q21q26 syndrome.

Extensive pulmonary metastases in malignant pleural mesothelioma. A rare clinical and radiographic presentation

We report a case of malignant pleural mesothelioma in a patient who presented with pleural effusion and reticulonodular shadow on chest radiograph. Pulmonary metastases were diagnosed by transbronchial lung biopsy specimen and the patient died of extensive pulmonary metastases. This pattern of clinical and radiographic presentation is seldom reported for malignant pleural mesothelioma.

The extracellular signal-regulated kinase pathway phosphorylates AML1, an acute myeloid leukemia gene product, and potentially regulates its transactivation ability

AML1 (also called PEBP2alphaB, CBFA2, or CBFalpha2) is one of the most frequently disrupted genes in chromosome abnormalities seen in human leukemias. It has been reported that AML1 plays several pivotal roles in myeloid hematopoietic differentiation and other biological phenomena, probably through the transcriptional regulation of various relevant genes. Here, we investigated the mechanism of regulation of AML1 functions through signal transduction pathways. The results showed that AML1 is phosphorylated in vivo on two serine residues within the proline-, serine-, and threonine-rich region, with dependence on the activation of extracellular signal-regulated kinase (ERK) and with interleukin-3 stimulation in a hematopoietic cell line. These in vivo phosphorylation sites of AML1 were phosphorylated directly in vitro by ERK. Although differences between wild-type AML1 and phosphorylation site mutants in DNA-binding affinity were not observed, we have shown that ERK-dependent phosphorylation potentiates the transactivation ability of AML1. Furthermore the phosphorylation site mutations reduced the transforming capacity of AML1 in fibroblast cells. These data indicate that AML1 functions are potentially regulated by ERK, which is activated by cytokine and growth factor stimuli. This study provides some important clues for clarifying unidentified facets of the regulatory mechanism of AML1 function.

Construction of a normalized directionally cloned cDNA library from adult heart and analysis of 3040 clones by partial sequencing

Large-scale sequencing of clones from cDNA libraries derived from specific tissues is a rapid and efficient way of discovering novel genes expressed in those tissues. However, because the heart is continually contracting and relaxing, it strongly expresses muscle-contractile genes and/or mitochondrial genes, a bias that reduces the efficiency of this method. To improve the efficiency of identifying novel genes expressed in the heart, we constructed a normalized directionally cloned cDNA library from adult heart and partially sequenced 3040 clones. Comparisons of these sequence data with known DNA sequences in the database revealed that 57.1% of the clones matched human genes already known, 23.4% were identical or almost identical to human expressed sequence tags (ESTs), 14.2% bore no significant homology to any sequences in the database, and 1.2% represented repetitive sequences. The remaining 4.1% showed some homology with known genes, and Northern blot analysis of several clones in this category revealed that most of them were expressed mainly in the heart and skeletal muscle. After redundancy was excluded, the 3040 clones accounted for 1395 distinctive ESTs, 446 of which exhibited no match to any known sequence. Our results suggest that our normalized library is less redundant than standard libraries and is a useful resource for cataloging genes expressed in the heart.

Expression of costimulatory molecules in human leukemias

In order to determine the indication of B7 (B7-1 and B7-2) molecules-mediated immuno-gene therapy for human leukemias, we investigated 94 human leukemic samples for the expression of MHC molecules required for tumor antigen-specific signals and of B7-1, B7-2, and ICAM-1 molecules required for non-specific costimulatory signals. All samples were strongly positive for MHC class I and 84% for class II antigen. B7-1, B7-2 and ICAM-1 were expressed in 5%, 22% and 16% of the total cases, respectively. Especially in 54 AML samples, B7-1 was only expressed in one case, while B7-2 was detected in as many as 15 cases (28%). We have also examined 13 human myelo/monocytic cell lines for the expression of class II and costimulatory molecules and found that significant expression of costimulatory molecules was induced in human leukemic cells by some suitable drugs, among which interferon-gamma (IFN-gamma) was the most potent inducer. Our results indicate that when the B7-mediated immuno-gene therapy was applied to human leukemias, especially to AML, B7-1 was rather preferable to B7-2 in that the latter was more widely expressed on human leukemic cells. Furthermore, since gene-transfer systems occasionally accompany serious problems, it should be taken into account that costimulatory molecules on human myelo/monocytic leukemic cells could be induced ex vivo without the introduction of exogenous genes.

Inactivation of multiple tumor-suppressor genes involved in negative regulation of the cell cycle, MTS1/p16INK4A/CDKN2, MTS2/p15INK4B, p53, and Rb genes in primary lymphoid malignancies

It is now evident that the cell cycle machinery has a variety of elements negatively regulating cell cycle progression. However, among these negative regulators in cell cycle control, only 4 have been shown to be consistently involved in the development of human cancers as tumor suppressors: Rb (Retinoblastoma susceptibility protein), p53, and two recently identified cyclin-dependent kinase inhibitors, p16INK4A/MTS1 and p15INK4B/MTS2. Because there are functional interrelations among these negative regulators in the cell cycle machinery, it is particularly interesting to investigate the multiplicity of inactivations of these tumor suppressors in human cancers, including leukemias/lymphomas. To address this point, we examined inactivations of these four genes in primary lymphoid malignancies by Southern blot and polymerase chain reaction-single-strand conformation polymorphism analyses. We also analyzed Rb protein expression by Western blot analysis. The p16INK4A and p15INK4B genes were homozygously deleted in 45 and 42 of 230 lymphoid tumor specimens, respectively. Inactivations of the Rb and p53 genes were 27 of 91 and 9 of 173 specimens, respectively. Forty-one (45.1%) of 91 samples examined for inactivations of all four tumor suppressors had one or more abnormalities of these four tumor-suppressor genes, indicating that dysregulation of cell cycle control is important for tumor development. Statistical analysis of interrelations among impairments of these four genes indicated that inactivations of the individual tumor-suppressor genes might occur almost independently. In some patients, disruptions of multiple tumor-suppressor genes occurred; 4 cases with p16INK4A, p15INK4B, and Rb inactivations; 2 cases with p16INK4A, p15INK4B, and p53 inactivations; and 1 case with Rb and p53 inactivations. It is suggested that disruptions of multiple tumor suppressors in a tumor cell confer an additional growth advantage on the tumor.

Impaired ventilatory responses to hypoxia and hypercapnia in mutant mice deficient in endothelin-1

We studied respiratory functions in mutant mice deficient in endothelin-1 (ET-1) generated by gene targeting. In conscious adult mice heterozygous for ET-1 gene mutation (ET+/- heterozygous mice), arterial PO2 was significantly lower, PCO2 tended to be higher, and pH tended to be lower than in wild-type littermates. When these conscious mice breathed room air, respiratory minute volume and rate, determined by body plethysmography, were not significantly different between the two groups. However, when ET+/- heterozygous mice were subjected to systemic hypoxia (1:1 air-N2) or hypercapnia (5% CO2-95% O2), increases in respiratory minute volume were significantly attenuated. In conscious newborn ET-/- homozygous mice delivered by cesarean section and tracheotomized, ventilatory responses to systemic hypoxia and hypercapnia, regularly observed in newborn wild-type mice, were almost totally absent. In urethan-anesthetized adult ET+/- heterozygous mice, increases in phrenic nerve discharges in response to hypoxia and hypercapnia were significantly attenuated. Our results demonstrate that ventilatory responses to hypoxia and hypercapnia are impaired in ET-1-deficient mice and suggest that endogenous ET-1 participates in the physiological control of ventilation.

Structure and characterization of the 5'-flanking region of the mouse smooth muscle myosin heavy chain (SM1/2) gene

We have previously shown that smooth muscle myosin heavy chain isoforms (SMs), including SM1, SM2, and SMemb, are differentially expressed during vascular development, and in vascular lesions, such as atherosclerosis. The SM1/2 gene is expressed exclusively in smooth muscle cells and generates SM1 and SM2 mRNAs by alternative splicing. Whereas SM1 is constitutively expressed from early development, SM2 appears only after birth. In this study, we have isolated and characterized the 5'-flanking region of the mouse SM1/2 gene. Transient transfection assays using a series of promoter-luciferase chimeric constructs demonstrated that tandem elements of the CCTCCC sequence, located at -89 and -61 bp relative to the transcription start site, were essential for transcriptional activity of the SM1/2 gene in primary cultured rabbit aortic smooth muscle cells and smooth muscle cell lines derived from the rabbit aorta but not in non-smooth muscle cells. Gel mobility shift assays indicated that CCTCCC was a binding site for nuclear proteins prepared from smooth muscle cells. Double-stranded oligonucleotides containing either the CACC box or the Sp1 consensus sequence efficiently competed with the CCTCCC elements for binding the nuclear extracts. Site-specific mutations of CCTCCC elements resulted in a significant reduction of the promoter activity. Moreover, CCTCCC elements are evolutionary conserved between mouse and rabbit. In conclusion, the results of this study indicate an important role for the interaction of the CCTCCC sequence with Sp1 or related factors in activating transcription from the SM1/2 gene promoter.

Insulin signalling and insulin actions in the muscles and livers of insulin-resistant, insulin receptor substrate 1-deficient mice

We and others recently generated mice with a targeted disruption of the insulin receptor substrate 1 (IRS-1) gene and demonstrated that they exhibited growth retardation and had resistance to the glucose-lowering effect of insulin. Insulin initiates its biological effects by activating at least two major signalling pathways, one involving phosphatidylinositol 3-kinase (PI3-kinase) and the other involving a ras/mitogen-activated protein kinase (MAP kinase) cascade. In this study, we investigated the roles of IRS-1 and IRS-2 in the biological action in the physiological target organs of insulin by comparing the effects of insulin in wild-type and IRS-1-deficient mice. In muscles from IRS-1-deficient mice, the responses to insulin-induced PI3-kinase activation, glucose transport, p70 S6 kinase and MAP kinase activation, mRNA translation, and protein synthesis were significantly impaired compared with those in wild-type mice. Insulin-induced protein synthesis was both wortmannin sensitive and insensitive in wild-type and IRS-1 deficient mice. However, in another target organ, the liver, the responses to insulin-induced PI3-kinase and MAP kinase activation were not significantly reduced. The amount of tyrosine-phosphorylated IRS-2 (in IRS-1-deficient mice) was roughly equal to that of IRS-1 (in wild-type mice) in the liver, whereas it only 20 to 30% of that of IRS-1 in the muscles. In conclusion, (i) IRS-1 plays central roles in two major biological actions of insulin in muscles, glucose transport and protein synthesis; (ii) the insulin resistance of IRS-1-deficient mice is mainly due to resistance in the muscles; and (iii) the degree of compensation for IRS-1 deficiency appears to be correlated with the amount of tyrosine-phosphorylated IRS-2 (in IRS-1-deficient mice) relative to that of IRS-1 (in wild-type mice).