Aspects Of Cell Growth Research Articles

Nucellar-cell-specific expression of a lipid transfer protein gene in barley ( Hordeum vulgare L.)

Plant lipid transfer proteins (LTPs) are thought to participate in many aspects of cell growth and development. We have identified a novel LTP gene (LTP-ne) from barley (Hordeum vulgare) through differential screening of an ovary cDNA library. LTP-ne was mapped to the distal region of the long arm of barley chromosome 4, distinct from the genomic location of other known LTPs. Sequence comparison indicated that LTP-ne was more closely related to the 7-kDa LTPs than to the 9-kDa LTPs in barley. In Northern hybridization, LTP-ne transcripts were detected in ovary, but not in other tissues, and were most abundant 3–4 days after pollination. Furthermore, RNA in situ hybridization showed that within the ovary, the LTP-ne gene was specifically expressed in the outer cell layer of the nucellus. These results showed that the newly identified barley LTP was ovular cell specific and regulated by pollination/fertilization.

Biochemical genetics of plant growth

The plant growth hormones are ubiquitous compounds that act at low concentrations to regulate various aspects of cell growth. Genetic strategies have led to the identification of diverse proteins involved in hormone signaling or response. Included in this group are proteins that directly regulate transcription, enzymes involved in protein modification, receptor kinases, and the first plant adenylyl cyclase.

Nlk is a murine protein kinase related to Erk/MAP kinases and localized in the nucleus.

Extracellular-signal regulated kinases/microtubule-associated protein kinases (Erk/MAPKs) and cyclin-directed kinases (Cdks) are key regulators of many aspects of cell growth and division, as well as apoptosis. We have cloned a kinase, Nlk, that is a murine homolog of the Drosophila nemo (nmo) gene. The Nlk amino acid sequence is 54. 5% similar and 41.7% identical to murine Erk-2, and 49.6% similar and 38.4% identical to human Cdc2. It possesses an extended amino-terminal domain that is very rich in glutamine, alanine, proline, and histidine. This region bears similarity to repetitive regions found in many transcription factors. Nlk is expressed as a 4. 0-kb transcript at high levels in adult mouse brain tissue, with low levels in other tissues examined, including lung, where two smaller transcripts of 1.0 and 1.5 kb are expressed as well. A 4.0-kb Nlk message is also present during embryogenesis, detectable at day E10. 5, reaching maximal steady state levels at day E12.5, and then decreasing. Nlk transiently expressed in COS7 cells is a 60-kDa kinase detectable by its ability to autophosphorylate. Mutation of the ATP-binding Lys-155 to methionine abolishes its ability to autophosphorylate, as does mutation of a putative activating threonine in kinase domain VIII, to valine, aspartic, or glutamic acid. Subcellular fractionation indicates that 60-70% of Nlk is localized to the nucleus, whereas 30-40% of Nlk is cytoplasmic. Immunofluorescence microscopy confirms that Nlk resides predominantly in the nucleus. Nlk and Nmo may be the first members of a family of kinases with homology to both Erk/MAPKs and Cdks.

A candidate molecule approach to defining developmental pathology in schizophrenia.

The evidence that schizophrenia may have its origins from early in life, possibly during prenatal brain development, is based primarily on a constellation of nonspecific anatomical findings and on the results of surveys of obstetrical complications and of childhood neurological and psychological adjustment. The developmental processes implicated by this evidence are uncertain, but speculation has centered around abnormalities of neuronal proliferation, migration, and connection formation. These developmental milestones are the results of complicated cellular processes involving molecular interactions between cells and between the extracellular and intracellular milieus. To understand how these abnormalities could relate to schizophrenia, it is necessary to characterize the molecular events that define the processes. In this article, we discuss the potential impact of a number of molecules that are important in the sequence of cellular events implicated in schizophrenia. In particular, we focus on molecular mechanisms related to cell proliferation, axonal outgrowth, cell migration, cell survival, synaptic regression, myelination, and developmental aspects of early adult life. These various candidate molecules regulate different aspects of cell growth and cell-cell interactions and are involved in the regulation of deoxyribonucleic acid (DNA) expression. Very few of these molecules have been studied in the schizophrenic brain.

Transforming Growth Factor-β System and Its Regulation by Members of the Steroid-Thyroid Hormone Superfamily

TGF-beta s and their receptors are expressed ubiquitously, and they act as key regulators of many aspects of cell growth, differentiation, and function. Steroid action on target tissues is often associated with increase in TGF-beta isoforms. Regulation of TGF-beta expression and activation is crucial for normal development and growth control. The loss of responsiveness of different tumor cells to the antiproliferative effects of TGF-beta is a common feature in carcinogenesis. Multiple changes are required for the cells to gain complete resistance to TGF-beta growth inhibition (Fynan and Reiss, 1993; Kimchi et al., 1988; Samuel et al., 1992). Although many tumor cells are not growth inhibited by TGF-beta, they respond to TGF-beta treatment by changes in the expression of matrix components and enhanced proteolytic activity (KeskiOja et al., 1988). Agents that induce TGF-beta production in target tissues can have a chemopreventive or chemotherapeutic value for the management of epithelial malignancies. Conversely, data supporting a positive role for TGF-beta in established tumor progression are beginning to emerge (Arteaga et al., 1993a,b; Barrett-Lee et al., 1990; Arrick et al., 1992 ; E. A. Thompson et al., 1991). In later stages of tumor development, cell proliferation is often not inhibited by TGF-beta, and tumor cells secrete large amounts of this growth factor (Fynan and Reiss, 1993). In vivo TGF-beta secreted by tumor or stromal cells can influence host responses such as a natural killer cell function and thus indirctly support tumor cell viability (Arteaga et al., 1993b). TGF-beta may also affect tumor growth indirectly by stromal effects and promotion of angiogenesis. TGF-beta may also be involved in the progression of breast tumors from the steroid-sensitive to steroid-insensitive state (King et al., 1989). Understanding of the net effect of TGF-beta in different stages of tumor development is critical for the evaluation of its therapeutic value in cancer treatment.

Proteins regulating Ras and its relatives.

GTPases of the Ras superfamily regulate many aspects of cell growth, differentiation and action. Their functions depend on their ability to alternate between inactive and active forms, and on their cellular localization. Numerous proteins affecting the GTPase activity, nucleotide exchange rates and membrane localization of Ras superfamily members have now been identified. Many of these proteins are much larger and more complex than their targets, containing multiple domains capable of interacting with an intricate network of cellular enzymes and structures.

Carboxyl-terminal proteolytic processing of matrix Gla protein.

The present study was undertaken to determine the extent of COOH-terminal proteolytic processing in matrix Gla protein (MGP), a 10-kDa protein which contains 5 residues of the vitamin K-dependent Ca2+ binding amino acid, gamma-carboxyglutamic acid (Gla). Two forms of MGP were isolated from demineralization and urea extracts of bovine cortical bone, one 79 residues in length with the COOH terminus Phe-Arg-Gln and the other 83 residues in length with the COOH terminus Phe-Arg-Gln-Arg-Arg-Gly-Ala. The 84-residue form of bovine MGP predicted from the message structure could not be detected in the bone extracellular matrix extracts, and it therefore seems probable that the lysine at position 84 was removed by the action of a carboxypeptidase B-like enzyme prior to secretion. A plausible sequence of proteolytic cleavages that could generate the 79-residue form of MGP would be a trypsin-like cleavage at Arg80-Arg81 or Arg81-Gly82 followed by carboxypeptidase B-like cleavage to remove COOH-terminal arginine(s). Since essentially equal amounts of the 79- and 83-residue forms of MGP were also detected in bovine articular cartilage and plasma, it seems likely that the COOH-terminal processing events identified in bone apply to many of the other tissues which synthesize this protein. Only one form of MGP was detected in human bone extracts, a 77-residue protein that lacks the COOH-terminal residues Arg-Lys-Arg-Arg-Gly-Thr-Lys. This shortened version of human MGP is consistent with the proposed model for COOH-terminal processing, since the amino acid substitution in the COOH terminus of the human protein, Lys79 for Gln79, would allow removal of the additional basic residues from the human MGP COOH terminus by the action of the carboxypeptidase B-like enzymic activity. Recent studies have shown that MGP is strongly induced by retinoic acid in fibroblasts, chondrocytes, and osteoblasts, a response which suggests that MGP mediates an action of retinoic acid on an aspect of cell growth or differentiation. If this hypothesis is true, the present evidence for complex COOH-terminal processing events could provide a means to regulate the as yet unknown activity of MGP in the extracellular environment in a mechanism similar to the activation of hormones such as anaphlotoxins and kinins.

Subcellular fate of the lnt-2 oncoprotein is determined by choice of initiation codon

Fibroblast growth factors (FGFs) have been implicated in many aspects of cell growth and differentiation both in normal and neoplastic settings. For example, the mouse int-2 gene, which encodes an FGF-related product, is a frequent target of proviral activation in carcinomas induced by mouse mammary tumour virus, but apparently functions at discrete stages of normal embryonic development. Six classes of int-2 messenger RNA have been identified in embryonic cells, each of which is predicted to encode the same 245-amino-acid protein. But all known int-2 transcripts include sequences upstream of the AUG codon presumed to be the initiation codon. Here we report an additional N-terminally extended int-2 gene product initiated at an in-frame CUG codon. In COS-1 cells transiently transfected with appropriate int-2 complementary DNAs, the AUG-initiated product is found predominantly in the secretory pathway, whereas the CUG-initiated form is localized to the nucleus. These data indicate that the Int-2 oncoprotein could influence cellular behaviour by two distinct mechanisms.

Polyamine levels in gynecologic malignancies.

Polyamines are closely related to many aspects of cell growth. Since increased amounts of polyamines in the urine of human cancer patients were reported in 1971, polyamines have been studied from the standpoint of tumor markers. In this study, polyamines in erythrocytes, plasma and urine were determined in 42 controls and 105 patients with gynecologic malignant tumors. The changes in polyamine levels were investigated before and after treatment. With advances in the stage of uterine cervical cancer, the frequency of abnormal levels of polyamines (concentrations greater than two standard deviations above the mean control level) became greater, and reached nearly 80% in recurrent and ovarian cancer. In the early stage of cancer, the diagnostic value was low. Comparison with carcinoembryonic antigen (CEA) was also performed. The polyamines lack specificity for malignant diseases, but they can be used to some extent as a tumor marker in the gynecologic field.

Positive correlation between size at initiation of chromosome replication in Escherichia coli and size at initiation of cell constriction.

The variability of (i) the length (size) at which cells initiate chromosome replication, (ii) the length at which they initiate cell constriction, and (iii) the time interval between these events has been estimated for Escherichia coli B/r K at two different slow growth rates. Steady-state cultures were pulse-labeled with [3H]thymidine and, after fixation, analyzed by electron microscopic radioautography. The coefficient of variation of length at initiation of chromosome replication was found to be 15 to 22%, the coefficient of variation of length at initiation of cell constriction was 10%, and the coefficient of variation of the time interval between both events was 25%. With the help of these values we calculated a high positive coefficient of correlation (rho) between the length at which a round of chromosome replication is initiated and that at which the onset of cell constriction occurs. At both growth rates rho has a value of 0.6 to 1.0. This correlation excludes a model in which chromosome initiation and cell constriction are independently triggered by some aspects of cell growth. It favors a model in which an event before or at chromosome initiation triggers both.