In vitro and in vivo antitumor effects of vitamin K5 on hepatocellular carcinoma

Although a number of studies have shown that vitamins K1, K2 and K3 exerted antitumor effects on various types of rodent- and human-derived neoplastic cell lines, it has not been examined whether or not vitamin K5 also possesses antitumor activity. In the present study, we examined the antitumor effects of vitamin K5 on PLC/PRF/5 human hepatocellular carcinoma (HCC) cells in vitro and in vivo. Furthermore, we examined the mechanisms of antitumor actions of vitamin K5 not only in vitro but also in vivo. Vitamin K5 was shown to suppress the proliferation of PLC/PRF/5 cells at a concentration of 30 microM. By a flow cytometric analysis, it was shown that although vitamin K5 did not induce apoptosis on PLC/PRF/5 cells, it did induce G1 arrest on PLC/PRF/5 cells. Subsequent in vivo study using subcutaneous HCC-bearing athymic nude mice demonstrated that vitamin K5 markedly suppressed the growth of HCC tumors. Although protein expression levels of cyclin D1 and p16INK4a cyclin-dependent kinase (Cdk) inhibitor in HCC tumors were not decreased by vitamin K5 treatment, those of Cdk4 were reduced significantly by the treatment. Taken collectively, vitamin K5 could induce potent antitumor effects on HCC not only in vitro but also in vivo, at least in part by inducing G1 arrest of cell cycle through downregulation of Cdk4 expression. The results demonstrated here indicate that vitamin K5 may be a useful agent for the treatment of patients with HCC.

Antitumor effects of vitamins K1, K2 and K3 on hepatocellular carcinoma in vitro and in vivo

A number of studies have shown that various K vitamins, specifically vitamins K2 and K3, possess antitumor activity on various types of rodent- and human-derived neoplastic cell lines. In the present study, we examined the antitumor effects of vitamins K1, K2 and K3 on PLC/PRF/5 human hepatocellular carcinoma (HCC) cells in vitro and in vivo. Furthermore, we examined the mechanisms of antitumor actions of these vitamins in vitro and in vivo. Although vitamin K1 did not inhibit proliferation of PLC/PRF/5 cells at a 90-microM concentration (the highest tested), vitamins K2 and K3 suppressed proliferation of the cells at concentrations of 90 and 9 microM, respectively. By flow cytometric analysis, it was shown that not only vitamin K1, but also vitamin K2 did not induce apoptosis or cell cycle arrest on PLC/PRF/5 cells. In contrast, vitamin K3 induced G1 arrest, but not apoptosis on PLC/PRF/5 cells. Subsequent in vivo study using subcutaneous HCC-bearing athymic nude mice demonstrated that both vitamins K2 and K3 markedly suppressed the growth of HCC tumors to similar extent. Protein expression of cyclin D1 and cyclin-dependent kinase 4 (Cdk4), but not p16INK4a Cdk inhibitor in the tumor was significantly reduced by vitamin K2 or K3 treatment, indicating that vitamins K2 and K3 may induce G1 arrest of cell cycle on PLC/PRF/5 cells in vivo. Taken collectively, vitamins K2 and K3 were able to induce potent antitumor effects on HCC in vitro and in vivo, at least in part, by inducing G1 arrest of the cell cycle. The results indicate that vitamins K2 and K3 may be useful agents for the treatment of patients with HCC.

Proliferative capability of hepatocytes and expression of G1-related cell cycle molecules in the development of liver cirrhosis in rats

Liver cirrhosis is the end stage of various chronic liver diseases and its prognosis is very poor. One of the most important causes of liver cirrhosis appears to be impaired proliferative capability of hepatocytes caused by continuous hepatic damage. Cell cycle-related molecules have been shown to play essential roles in cell proliferation. Specifically, G1-related cell cycle molecules are important, because they are requisite for the entry into the cell cycle from the quiescent state. However, the role of these cell cycle molecules during the development of liver cirrhosis remains to be examined. In the present study, liver cirrhosis was produced in rats by intraperitoneally administering dimethylnitrosamine (DMN). Proliferative capability of hepatocytes estimated immunohistochemically by proliferating cell nuclear antigen staining was markedly increased at an early stage of cirrhosis development. However, it was gradually decreased thereafter and suppressed substantially at the time of cirrhosis manifestation. Cyclin D1 expression estimated by a real-time reverse transcription-polymerase chain reaction (RT-PCR) method was also increased markedly at an early stage of cirrhosis development but decreased substantially thereafter. mRNA levels of catalytic subunits of cyclin D1, cyclin-dependent kinase 4 (Cdk4) and Cdk6, did not show significant changes during the development of liver cirrhosis. Among G1-specific Cdk inhibitors, expression of p15INK4b and p16INK4a estimated by an RT-PCR method was increased according to the progression of cirrhosis and reached a peak at the time of cirrhosis manifestation. Conversely, p18INK4c expression did not change significantly during the development of liver cirrhosis. These results suggest that cyclin D1 plays an essential role in hepatocyte proliferation in response to hepatic damage. However, with the decrease of cyclin D1 expression and increase of p15INK4b and p16INK4a expression, proliferative capability of hepatocytes is severely impaired and extracellular matrix components are deposited to retrieve space lost by the destruction of hepatic parenchyma, resulting in establishment of liver cirrhosis.

Ras-dependent cell cycle commitment during G2 phase

Synchronization used to study cell cycle progression may change the characteristics of rapidly proliferating cells. By combining time-lapse, quantitative fluorescent microscopy and microinjection, we have established a method to analyze the cell cycle progression of individual cells without synchronization. This new approach revealed that rapidly growing NIH3T3 cells make a Ras-dependent commitment for completion of the next cell cycle while they are in G2 phase of the preceding cell cycle. Thus, Ras activity during G2 phase induces cyclin D1 expression. This expression continues through the next G1 phase even in the absence of Ras activity, and drives cells into S phase.

The p38 pathway provides negative feedback for Ras proliferative signaling

Ras activates three mitogen-activated protein kinases (MAPKs) including ERK, JNK, and p38. Whereas the essential roles of ERK and JNK in Ras signaling has been established, the contribution of p38 remains unclear. Here we demonstrate that the p38 pathway functions as a negative regulator of Ras proliferative signaling via a feedback mechanism. Oncogenic Ras activated p38 and two p38-activated protein kinases, MAPK-activated protein kinase 2 (MK2) and p38-related/activated protein kinase (PRAK). MK2 and PRAK in turn suppressed Ras-induced gene expression and cell proliferation, whereas two mutant PRAKs, unresponsive to Ras, had little effect. Moreover, the constitutive p38 activator MKK6 also suppressed Ras activity in a p38-dependent manner whereas arsenite, a potent chemical inducer of p38, inhibited proliferation only in a tumor cell line that required Ras activity. MEK was required for Ras stimulation of the p38 pathway. The p38 pathway inhibited Ras activity by blocking activation of JNK, without effect upon ERK, as evidenced by the fact that PRAK-mediated suppression of Ras-induced cell proliferation was reversed by coexpression of JNKK2 or JNK1. These studies thus establish a negative feedback mechanism by which Ras proliferative activity is regulated via signaling integrations of MAPK pathways.

Influence of cell cycle and oncogene activity upon topoisomerase IIalpha expression and drug toxicity

The cell cycle, oncogenic signaling, and topoisomerase (topo) IIalpha levels all influence sensitivity to anti-topo II drugs. Because the cell cycle and oncogenic signaling influence each other as well as topo IIalpha levels, it is difficult to assess the importance of any one of these factors independently of the others during drug treatment. Such information, however, is vital to an understanding of the cellular basis of drug toxicity. We, therefore, developed a series of analytical procedures to individually assess the role of each of these factors during treatment with the anti-topo II drug etoposide. All studies were performed with asynchronously proliferating cultures by the use of time-lapse and quantitative fluorescence staining procedures. To our surprise, we found that neither oncogene action nor the cell cycle altered topo IIalpha protein levels in actively cycling cells. Only a minor population of slowly cycling cells within these cultures responded to constitutively active oncogenes by elevating topo IIalpha production. Thus, it was possible to study the effects of the cell cycle and oncogene action on drug-treated cells while topo IIalpha levels remained constant. Toxicity analyses were performed with two consecutive time-lapse observations separated by a brief drug treatment. The cell cycle phase was determined from the first observation, and cell fate was determined from the second. Cells were most sensitive to drug treatment from mid-S phase through G(2) phase, with G(1) phase cells nearly threefold less sensitive. In addition, the presence of an oncogenic src gene or microinjected Ras protein increased drug toxicity by approximately threefold in actively cycling cells and by at least this level in the small population of slowly cycling cells. We conclude that both cell cycle phase and oncogenic signaling influence drug toxicity independently of alterations in topo IIalpha levels.

Characteristics of Cyclodextrin Adsorption onto Activated Carbons

Whereas the amount of cyclodextrin (CD) adsorbed onto the large-pore activated carbon A (AC-A) increased with the number of glucose units, the amount adsorbed onto the small-pore activated carbon B (AC-B) showed the opposite tendency. This behavior can be accounted for in terms of a molecular exclusion. It is known that a good linear relationship is obtained between the Freundlich constants log K and 1/N for hydrophobic adsorption. The adsorption of CDs onto AC-A obeyed this relation, but, because of the molecular exclusion, the plots of AC-B deviated greatly. The adsorption of CDs onto AC-A was not explainable in terms of solubility. This could be because, in the case of a solid compound, adsorbability depends on the chemical potential of the molecule in aqueous solution whereas solubility depends also on the heat of fusion of the solid. In order to estimate the relative chemical potential of CDs in water, a method based on the numbers of carbon atoms and oxygen atoms in the molecule was devised which allowed a more accurate estimation of CD adsorbability than did solubility. The mean pore diameter of AC-A increased after CD adsorption, while that of AC-B showed little change. Copyright 2000 Academic Press.

[Serum leptin levels in normal pregnant women and their babies]

OBJECTIVE

To investigate serum leptin levels in normal pregnant women and their babies.

METHODS

Immunoradioassay was used to measure the serum levels of leptin in 10 non-pregnant women, 63 pregnant women (31 in the firs, 10 in the second, and 22 in the third trimester), 27 women at delivery, 18 women in the first week after delivery and in 18 newborns' cord serum. Serum leptin levels were correlated with body weight, body mass index (BMI), fasting insulin levels and lipids.

RESULTS

Serum insulin, cholesterol, triglyceride were increased since the second trimester during pregnancy. One week after delivery serum insulin but not cholesterol and triglicetride level was decreased to the levels of non-pregnancy. Serum leptin levels were (7.98 +/- 4.42) micrograms/L in non-pregnant women and (7.03 +/- 3.42) micrograms/L in the first trimester. Then the levels were increased to (13.97 +/- 8.03) micrograms/L in second trimester and (14.86 +/- 6.25) micrograms/L in the third trimester, (19.89 +/- 9.66) micrograms/L at the delivery time and returned to (10.86 +/- 9.18) micrograms/L in the first week after delivery, respectively. Cord serum leptin levels of newborns were (8.93 +/- 6.95) micrograms/L. Serum leptin levels in pregnant women were positively correlated with their body weight, BMI, fasting serum insulin and glycerol levels. Cord serum leptin levels was positively correlated with newborn birth weights as well as their insulin levels.

CONCLUSIONS

(1) Serum leptin levels increase in the second and third trimester, and may contribute to the inhibition of increased food intake, body weight and body fat. (2) Newborn serum leptin may come from themselves, and the levels were lower than those in their mothers. (3) Birth weight, possibly adiposity, as well as serum insulin positively regulates serum leptin levels in neonates as in adults.

An unexpected link between the secretory path and the organization of the nucleus

Yeast sec mutations define the machinery of vesicular traffic. Surprisingly, many of these mutations also inhibit ribosome biogenesis by reducing transcription of rRNA and genes encoding ribosomal proteins. We observe that these mutants reversibly inhibit protein import into the nucleus, with import cargo accumulating at the nucleoplasmic face of nuclear pore complexes, as when Ran-GTP cannot bind importins. They also rapidly and reversibly relocate multiple nucleolar and nucleoplasmic proteins to the cytoplasm. The import block and relocation are antagonized by overexpression of yeast Ran, Hog1p kinase, or Ssa/Hsp70 proteins or by inhibition of protein synthesis. These nucleocytoplasmic signaling events document an extraordinary plasticity of nuclear organization.

Cyclin D1 production in cycling cells depends on ras in a cell-cycle-specific manner

BACKGROUND

Cellular Ras and cyclin D1 are required at similar times of the cell cycle in quiescent NIH3T3 cells that have been induced to proliferate, but not in the case of cycling NIH3T3 cells. In asynchronous cultures, Ras activity has been found to be required only during G2 phase to promote passage through the entire upcoming cell cycle, whereas cyclin D1 is required through G1 phase until DNA synthesis begins. To explain these results in molecular terms, we propose a model whereby continuous cell cycle progression in NIH3T3 cells requires cellular Ras activity to promote the synthesis of cyclin D1 during G2 phase. Cyclin D1 expression then continues through G1 phase independently of Ras activity, and drives the G1-S phase transition.

RESULTS

We found high levels of cyclin D1 expression during the G2, M and G1 phases of the cell cycle in cycling NIH3T3 cells, using quantitative fluorescent antibody measurements of individual cells. By microinjecting anti-Ras antibody, we found that the induction of cyclin D1 expression beginning in G2 phase was dependent on Ras activity. Consistent with our model, cyclin D1 expression during G1 phase was particularly stable following neutralization of cellular Ras. Finally, ectopic expression of cyclin D1 largely overcame the requirement for cellular Ras activity during the continuous proliferation of cycling NIH3T3 cells.

CONCLUSIONS

Ras-dependent induction of cyclin D1 expression beginning in G2 phase is critical for continuous cell cycle progression in NIH3T3 cells.

Cell cycle arrest and morphological alterations following microinjection of NIH3T3 cells with Pur alpha

Levels of Pur alpha, a protein implicated in control of both DNA replication and gene transcription, fluctuate during the cell cycle, being lowest in early S phase and highest just after mitosis. Here we have employed a new video time-lapse technique enabling us to determine the cell cycle position of each cell in an asynchronous culture at a given time and to ask whether introduction of Pur alpha protein at specific times can affect cell cycle progression. Approximately 80% of all NIH3T3 cells injected with Pur alpha were inhibited from passing through mitosis. Cells injected with Pur alpha during S or G2 phases were efficiently blocked with a 4N (G2 phase) DNA level, as determined by quantitative DNA photometry of individual cells. Of the cells injected with Pur alpha during G1 phase, 40% experienced a rapid cell death characterized by extreme cellular fragmentation. Of those G1 injected cells which remained viable, approximately equal numbers were arrested with either 2N or 4N DNA levels. Cells arrested by Pur alpha in G2 phase grew to cover a large surface area. These results link fluctuations in Pur alpha levels to aspects of cell cycle control.

Cellular ras and cyclin D1 are required during different cell cycle periods in cycling NIH 3T3 cells

Novel techniques were used to determine when in the cell cycle of proliferating NIH 3T3 cells cellular Ras and cyclin D1 are required. For comparison, in quiescent cells, all four of the inhibitors of cell cycle progression tested (anti-Ras, anti-cyclin D1, serum removal, and cycloheximide) became ineffective at essentially the same point in G1 phase, approximately 4 h prior to the beginning of DNA synthesis. To extend these studies to cycling cells, a time-lapse approach was used to determine the approximate cell cycle position of individual cells in an asynchronous culture at the time of inhibitor treatment and then to determine the effects of the inhibitor upon recipient cells. With this approach, anti-Ras antibody efficiently inhibited entry into S phase only when introduced into cells prior to the preceding mitosis, several hours before the beginning of S phase. Anti-cyclin D1, on the other hand, was an efficient inhibitor when introduced up until just before the initiation of DNA synthesis. Cycloheximide treatment, like anti-cyclin D1 microinjection, was inhibitory throughout G1 phase (which lasts a total of 4 to 5 h in these cells). Finally, serum removal blocked entry into S phase only during the first hour following mitosis. Kinetic analysis and a novel dual-labeling technique were used to confirm the differences in cell cycle requirements for Ras, cyclin D1, and cycloheximide. These studies demonstrate a fundamental difference in mitogenic signal transduction between quiescent and cycling NIH 3T3 cells and reveal a sequence of signaling events required for cell cycle progression in proliferating NIH 3T3 cells.

Dissociation of CDK2 from cyclin A in response to the topoisomerase II inhibitor etoposide in v-src-transformed but not normal NIH 3T3 cells

Our previous work has demonstrated that treatment of NIH 3T3 cells with etoposide (VP16), an inhibitor of DNA topoisomerase II and widely used anticancer agent, results in G2/M-phase arrest, whereas treatment of cells transformed by v-src, v-ras, or v-raf results in an S-phase blockage. The present studies describe the mechanistic aspects of this selective S-phase arrest in the v-src-transformed cells. The S-phase arrest in these cells was found to be coupled with depletion of cyclin A-dependent kinase activity. This decrease could not be explained by changes in the overall level of cyclin A, CDK2, p27, or p21 proteins. Rather, it was associated with a time-dependent reduction of CDK2 protein complexed with cyclin A following VP16 treatment. It was further shown that the decrease of cyclin A-associated CDK2 was linked to an increase of CDK2 protein in cyclin E immunocomplexes, which suggests that CDK2 might become redistributed following treatment with VP16. Thus, oncogenic transformation by v-src can trigger separation of CDK2 protein from cyclin A in response to VP16. This might contribute to the depletion of cyclin A-dependent kinase activity and the selective S-phase arrest by VP16 in v-src-transformed cells.

p21Waf1 inhibits the activity of cyclin dependent kinase 2 by preventing its activating phosphorylation

Prostaglandin A2 (PGA2), a potent inhibitor of the growth of many cell types, inhibits G1 phase cyclin dependent kinases (cdk). Although PGA2 suppresses cyclin D1 and elevates p21Waf1 levels, it was the failure of cdk2 to become activated by phosphorylation which correlated best with growth inhibition. In kinetic studies, cdk2 activation was inhibited efficiently only if p21Waf1 levels increased prior to the activating phosphorylation; suggesting that p21Waf1 had blocked this phosphorylation. This model was confirmed in cells from p21Waf1 knockout mice where PGA2 was completely unable to block the activating phosphorylation of cdk2, or inhibit cdk2 activity. As expected, growth inhibition of p21Waf1(-/-) cells was not observed at PGA2 concentrations which inhibited cdk2 activity and growth of p21Waf1(+/+) cells.

FADD gene therapy for malignant gliomas in vitro and in vivo

Fas/APO-1 (CD95), a cell surface cytokine receptor, triggers apoptotic cell death by specific agonist antibody, suggesting that Fas/APO-1 may be a promising target for treatment of tumors. In this study, we show that treatment with anti-Fas antibody effectively induced apoptosis in malignant glioma cell lines with high expression of Fas/APO-1 (n = 3). Malignant glioma cells with low or undetectable expression of Fas/APO-1 (n = 6), however, were resistant to Fas/APO-1-dependent cytotoxicity. The purpose of this study, therefore, was to determine whether resistant tumors could be made susceptible to apoptosis. FADD/MORT1 constitutes a novel protein that associates specifically with the cytoplasmic death domain of Fas/APO-1 and induces apoptosis. We investigated whether overexpression of FADD would induce apoptosis in malignant glioma cells without activating Fas/APO-1. Results indicated that about 85% of malignant glioma cells, regardless of Fas/APO-1 expression levels, underwent apoptosis after transient transfection with FADD expression vector. To further improve gene transfer of FADD into malignant glioma cells, we constructed a retroviral vector containing the FADD gene. The retroviral transfer of FADD gene significantly enhanced the transduction efficiency and effectively inhibited both in vitro and in vivo survival of malignant glioma cells through induction of apoptosis. These findings suggest that the FADD gene is a novel and useful tool for the treatment of malignant gliomas.

Antisense telomerase treatment: induction of two distinct pathways, apoptosis and differentiation

Telomerase, the enzyme that elongates telomeric DNA (TTAGGG)n, may be involved in cellular immortality and oncogenesis. To investigate the effect of inhibition of telomerase on tumor cells, we transfected the antisense vector against the human telomerase RNA into human malignant glioma cells exhibiting telomerase activity. After 30 doublings, some subpopulations of transfectants expressed a high level of interleukin-1beta-converting enzyme (ICE) protein and underwent apoptosis. In contrast, other subpopulations also showed enhanced ICE protein but escaped from apoptotic crisis and continued to grow, although their DNA synthesis, invasive ability, and tumorigenicity in nude mice were significantly reduced. Surviving cells demonstrated increased expression of glial fibrillary acidic protein and decreased motility, consistent with a more differentiated state. These cells also contained enhanced expression of the cyclin-dependent kinase inhibitors (CDKIs) p21 and p27. Treatment of surviving nonapoptotic cells with antisense oligonucleotides against p27, but not p21, induced apoptotic cell death, suggesting that p27 may have protected differentiating glioma cells from apoptosis. These data show that treatment with antisense telomerase inhibits telomerase activity and subsequently induces either apoptosis or differentiation. Regulation of these two distinct pathways may be dependent on the expression of ICE or CDKIs.

Dbp5p, a cytosolic RNA helicase, is required for poly(A)+ RNA export

The DBP5 gene encodes a putative RNA helicase of unknown function in the yeast Saccharomyces cerevisiae. It is shown here that Dbp5p is an ATP-dependent RNA helicase required for polyadenylated [poly(A)+] RNA export. Surprisingly, Dbp5p is present predominantly, if not exclusively, in the cytoplasm, and is highly enriched around the nuclear envelope. This observation raises the possibility that Dbp5p may play a role in unloading or remodeling messenger RNA particles (mRNPs) upon arrival in the cytoplasm and in coupling mRNP export and translation. The functions of Dbp5p are likely to be conserved, since its potential homologues can be found in a variety of eukaryotic cells.

Retroviral transfer of CPP32beta gene into malignant gliomas in vitro and in vivo

Malignant gliomas are highly aggressive neoplasms that are very resistant to current therapeutic approaches, including irradiation, chemotherapy, and immunotherapy. To improve the prognosis, it is absolutely essential to explore novel modalities of treatment. Recently, we have demonstrated that interleukin 1beta-converting enzyme (ICE), a mammalian homologue of the Caenorhabditis elegans cell death gene ced-3, induces apoptotic cell death in malignant glioma cells. To date, ICE and ICE-like proteases (the ICE family), such as Ich-1L, CPP32beta, Mch2alpha, and Mch3alpha, have been shown to mediate apoptosis in some cells. The purpose of this study is to determine whether the ICE gene family functions as a useful tool for the treatment of malignant glioma cells through induction of apoptosis. The transient transfection assays showed that CPP32beta and Mch2alpha genes induced apoptotic cell death in malignant glioma cells more effectively than did the ICE, Ich-1L, and Mch3alpha genes. To improve the efficiency of gene transfer into malignant glioma cells, we constructed the retroviral vectors containing the ICE gene family. The retroviral transfer of CPP32beta or Mch2alpha gene effectively induced apoptosis in malignant glioma cells in vitro. Furthermore, treatment of tumors grown in mice with retrovirus containing CPP32beta significantly inhibited growth of the tumors through induction of apoptosis. The retroviral transfer of CPP32beta or Mch2alpha, therefore, may be a novel and promising approach for the treatment of malignant glioma, an invariably fatal tumor.

Activation of JNK/SAPK pathway is not directly inhibitory for cell cycle progression in NIH3T3 cells

In this study the induction of stress activated protein kinase (SAPK) activity by protein synthesis inhibitors was shown not to inhibit cellular proliferation. Anisomycin induced strong SAPK activity at non-inhibitory concentrations for either protein or DNA synthesis, while the other two inhibitors, emetine and cycloheximide, blocked cell cycle progression without strong SAPK induction. With all three inhibitors, the induction of SAPK activity was always accompanied by protein synthesis inhibition to some extent. Stimulation of mRNA expression of the genes c-jun, c-fos and c-myc correlated well with SAPK induction, but not with cell cycle inhibition. With concentrations of each inhibitor able to block DNA synthesis, no induction of message for the cyclin dependent kinase inhibitor waf-1 was observed; while induction of gadd45 message indicated that the cells might be responding to growth-arrest or DNA damage. The inability of microinjected E2F/DP1 transcription factor proteins to overcome the inhibition of DNA synthesis induced by protein synthesis inhibitors indicate that blockage of an early event in cell cycle progression had occurred. These results indicate that the SAPK induction by protein synthesis inhibitors has no proliferative consequences.

A yeast acetyl coenzyme A carboxylase mutant links very-long-chain fatty acid synthesis to the structure and function of the nuclear membrane-pore complex

The conditional mRNA transport mutant of Saccharomyces cerevisiae, acc1-7-1 (mtr7-1), displays a unique alteration of the nuclear envelope. Unlike nucleoporin mutants and other RNA transport mutants, the intermembrane space expands, protuberances extend from the inner membrane into the intermembrane space, and vesicles accumulate in the intermembrane space. MTR7 is the same gene as ACC1, encoding acetyl coenzyme A (CoA) carboxylase (Acc1p), the rate-limiting enzyme of de novo fatty acid synthesis. Genetic and biochemical analyses of fatty acid synthesis mutants and acc1-7-1 indicate that the continued synthesis of malonyl-CoA, the enzymatic product of acetyl-CoA carboxylase, is required for an essential pathway which is independent from de novo synthesis of fatty acids. We provide evidence that synthesis of very-long-chain fatty acids (C26 atoms) is inhibited in acc1-7-1, suggesting that very-long-chain fatty acid synthesis is required to maintain a functional nuclear envelope.

A DEAD-box-family protein is required for nucleocytoplasmic transport of yeast mRNA

An enormous variety of primary and secondary mRNA structures are compatible with export from the nucleus to the cytoplasm. Therefore, there seems to be a mechanism for RNA export which is independent of sequence recognition. There nevertheless is likely to be some relatively uniform mechanism which allows transcripts to be packaged as ribonucleoprotein particles, to gain access to the periphery of the nucleus and ultimately to translocate across nuclear pores. To study these events, we and others have generated temperature-sensitive recessive mRNA transport (mtr) mutants of Saccharomyces cerevisiae which accumulate poly(A)+ RNA in the nucleus at 37 degrees C. Several of the corresponding genes have been cloned. Upon depletion of one of these proteins, Mtr4p, conspicuous amounts of nuclear poly(A)+ RNA accumulate in association with the nucleolus. Corresponding dense material is also seen by electron microscopy. MTR4 is essential for growth and encodes a novel nuclear protein with a size of approximately 120 kDa. Mtr4p shares characteristic motifs with DEAD-box RNA helicases and associates with RNA. It therefore may well affect RNA conformation. It shows extensive homology to a human predicted gene product and the yeast antiviral protein Ski2p. Critical residues of Mtr4p, including the mtr4-1 point mutation, have been identified. Mtr4p may serve as a chaperone which translocates or normalizes the structure of mRNAs in preparation for export.