Interactions of Growth Factors, Hormones, and Oncogenes Controlling the Proliferation of Normal and Cancer Cells
Velibor Krsmanović, James F. Whitfield in Malignant Cell Secretion, 2019
Growth factor deprivation signals the immortalized cells of established lines to stop growing and cycling by affecting all aspects of RNA and protein metabolism (for a review see Reference 109). The cell reduces transcription and/or destabilizes the transcripts of cell cycle genes or proto-oncogenes, decreases synthesis and increases degradation of ribosomal RNA, and increases degradation and decreases the translocation to the nucleus of short-lived nonhistone proteins that regulate chromatin structure.109,216,291-295 However, the quiescent cells do continue to express the genes for, but do not produce, histones, and the DNA replication enzymes dCMP kinase, dihydrofolate reductase, DNA polymerase a, NDP kinase, thymidine kinase, and thymidylate synthase.296-299 Some cells even continue to maintain a pool of CDC2(Hs) protein which is the principal component of the MPFs that trigger mitotic prophase.300 On the other hand, they start expressing the genes for factors which keep them in the quiescent state.301-305 In general, only the mRNA needed for minimal housekeeping and the quiescence factors are translated, while the number of polyribosomes drops as the cell shunts a large fraction of its mRNA into a rapidly mobilizable nonpolysomal pool.109,295,306-308
The Ultrastructure And Pathobiology Of Urinary Bladder Cancer
George T. Bryan, Samuel M. Cohen in The Pathology of Bladder Cancer, 2017
Generally, the smooth and rough endoplasmic reticulum (SER and RER) are rather poorly developed. They form primative tubular systems which are somewhat more prominent in the perinuclear cytoplasm than in the cell periphery. The cisternae of the rough endoplasmic reticulum show simple branching and contain fine fibrillar material. Rough endoplasmic reticulum membranes have 12 to 15 nm bound ribosomes. In addition, clusters of free ribosomes are distributed throughout the cytoplasm. These clusters, the polyribosomes or polysomes, consist of 3 to 30 ribosomes which are held together by slender filaments measuring approximately 1 nm in diameter.
Bacteria
Julius P. Kreier in Infection, Resistance, and Immunity, 2022
DNA carries the genetic information to determine heritable properties of an organism (i.e., its phenotype). The DNA is initially transcribed into complementary polymers of ribonucleic acid (RNA) in the form called messenger RNA (mRNA). The mRNA subsequently serves as a template for synthesis of protein molecules; a process that is mediated by ribosomes. Ribosomes are microparticles composed of protein linked to another class of RNA called ribosomal RNA (rRNA). Ribosomes consist of smaller (30S) and larger (50S) subunits and tend to form aggregates or strands called polyribosomes.
Exploring the rationale for thermotherapy in COVID-19
Published in International Journal of Hyperthermia, 2021
Javier Mancilla-Galindo, Norma Galindo-Sevilla
Cells are adapted to perform their functions most efficiently at a specific temperature. For instance, testicles in mice and humans are exposed to lower temperatures than core body temperature (i.e., 34 °C vs 37 °C). After exposure of mice spermatids to 34 °C, 37 °C, and 40 °C for 1 h, protein synthesis decreased in approximately 25% at 37 °C and 50% at 40 °C when compared to 34 °C [24]. RNA templates called messenger RNA (mRNA) are normally used by cell ribosomes to assemble amino acids into proteins, ribosomes can group into polyribosomes to enhance protein synthesis. In the study by Nakamura and Hall, temperature-dependent reductions in polyribosomes were associated to decreased protein synthesis. HeLa cells exposed to 42 °C also had disaggregation of polyribosomes leading to lower protein synthesis [25].
The lethal effects and determinants of microcystin-LR on heart: a mini review
Published in Toxin Reviews, 2021
Muwaffak Alosman, Linghui Cao, Isaac Yaw Massey, Fei Yang
Researchers have used HE stains for more than a century and they are still effective in recognizing a wide range of tissue types and changes in morphology that forms the basis of a cancer diagnosis (He et al. 2014, Iseki et al. 2018). The stain remains unchanged for many years since it is effective with several fixatives and shows a wide range of nuclear, cytoplasmic, and extracellular matrix features. Hematoxylin contains a deep blue color that stains nucleic acids. Eosin, on the other hand, is pink in color and spans proteins nonspecifically. While a typical tissue nucleus has a blue stain, the extracellular matrix and cytoplasm are stained pink but in varying degrees (Rode and Eisel 2004). In the presence of abundant polyribosomes, the cytoplasm is likely to show a distinct blue cast. Additionally, the lack of staining in an area next to the nucleus helps in identifying the Golgi zone (Fischer et al. 2008). This implies that the stain uncovers structural information. Nonetheless, one of the shortcomings of hematoxylin staining is that it is not compatible with immunofluorescence. This notwithstanding, the method is effective in staining one serial paraffin section from an organ or tissue where immunofluorescence is performed. Generally, hematoxylin without eosin helps in counterstaining for numerous hybridizations or immunohistochemical procedures that need colorimetric substrates.
Silica nanoparticles disrupt OPT-2/PEP-2-dependent trafficking of nutrient peptides in the intestinal epithelium
Published in Nanotoxicology, 2019
Annette Piechulek, Lutz C. Berwanger, Anna von Mikecz
From our results, it seems unlikely that nanosilica-induced peptide vesicles mainly function as transport vesicles. In wild type (N2) worms they gradually grow over time to spherical structures of considerable size with average diameters of 6 μm (72 h; Figure 3(H)). A more fitting idea is that β-Ala-Lys-AMCA vesicles represent aberrant vacuoles/vesicles that store and trap di- and tri-peptides immediately after transport from the intestinal lumen via OPT-2/PEP-2. Due to a lack of turnover, e.g. hydrolysis, the peptides accumulate and accordingly the vesicles grow. In turn, nutrient allocation is disturbed and the peptides are not available for supply of amino acids or peptide hormones and respective signaling. Generally, nutrition stress by amino acid deprivation leads to starvation-induced inactivation of the target of rapamycin (TOR) kinase and reduced transcription of ribosomal RNA (rRNA), decreased ribosome subunit production and reduction of translation (Long et al. 2002; Sengupta, Peterson, and Sabatini 2010; Spriggs, Bushell, and Willis 2010). In addition to TOR, the general amino acid control pathway (GAAC) is activated by amino acid starvation. Here, the cascade of accumulation of uncharged tRNA, activation of GCN2, and inactivation of translation initiation factor eIF2 by phosphorylation reduces global protein synthesis and reprograms translation (Zaborske et al. 2009; Spriggs, Bushell, and Willis 2010). Accordingly, polysome profiling in yeast showed changes in the translational state of >600 mRNAs during the global response to amino acid starvation and significant downregulation of transcripts belonging to the gene ontology (GO) group of ribosome biogenesis and translation (Smirnova et al. 2005).