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38 - Cell cycle: mechanisms of control and dysregulation in cancer
- from Part 2.5 - Molecular pathways underlying carcinogenesis: cell cycle
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- By Erik S. Knudsen, Department of Pathology, UT Southwestern Medical Center, Dallas, TX, USA, Ryan J. Bourgo, Kimmel Cancer Center, Department of Cancer Biology, Thomas Jeferson University, Philadelphia, PA, USA, Elizabeth L. Gosnell, Kimmel Cancer Center, Department of Cancer Biology, Thomas Jeferson University, Philadelphia, PA, USA, Jeffry L. Dean, Kimmel Cancer Center, Department of Cancer Biology, Thomas Jeferson University, Philadelphia, PA, USA, A. Kathleen McClendon, Kimmel Cancer Center, Department of Cancer Biology, Thomas Jeferson University, Philadelphia, PA, USA
- Edited by Edward P. Gelmann, Columbia University, New York, Charles L. Sawyers, Memorial Sloan-Kettering Cancer Center, New York, Frank J. Rauscher, III
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- Book:
- Molecular Oncology
- Published online:
- 05 February 2015
- Print publication:
- 19 December 2013, pp 452-464
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Summary
Introduction
The mitotic cell cycle consists of four discrete phases that comprise the ordered processes required for the accurate division and partition of the genetic material into viable daughter cells (Figure 38.1). These processes are tightly controlled by cellular machinery, which not only orchestrates regulation of the various cell-cycle phases, but also integrates environmental cues to ensure that proliferation occurs only when conditions are favorable. The integrity of these processes is of utmost significance, and deregulation of cell-cycle regulatory mechanisms can contribute to tumorigenesis through a variety of discrete mechanisms, as will be discussed.
Mechanisms of G1 control
The majority of cells in adult tissues harbor a diploid (2N) DNA content, and have generally exited from the cell cycle. These cells exist outside the conventional active cell cycle in a phase termed G0. This G0 stage encompasses a variety of biological states, including terminal differentiation, quiescence, and senescence. Upon the engagement of appropriate physiological signals, G0 cells can commit to subsequent mitotic cell division. Typically, this entry into the cell cycle is mediated by an increase in mitogenic signaling and/or the removal of intrinsic barriers to proliferation (1). In the case of complex tissues, this stimulation of proliferation could be part of intrinsic tissue homeostasis (e.g. proliferation in the crypt to maintain epithelial integrity), response to injury (e.g. liver regeneration), or response to hormonal stimuli (e.g. expansion of mammary epithelia during pregnancy). Although it is widely accepted that such signaling leads to a transition from G0 into G1, the first gap phase, the factors that specify the G0-phase are poorly understood. In addition to a handful of molecular markers, one clear distinction between the G0- and G1-phases is the relative metabolic activity of cells. As such, analyses of gene expression has been suggested to differentiate G0 cells from their G1 counterparts, which are engaged in biosynthetic processes for cell division (2). In contrast with the G0 to G1 transition, those events that mediate progression through G1 have been extensively studied and the general processes involved are comparatively well defined.
New insight into butyrate metabolism
- Knud Erik Bach Knudsen, Anja Serena, Nuria Canibe, Katri S. Juntunen
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- Journal:
- Proceedings of the Nutrition Society / Volume 62 / Issue 1 / February 2003
- Published online by Cambridge University Press:
- 05 March 2007, pp. 81-86
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- Article
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Butyrate is a C4 acid produced by microbial fermentation of carbohydrates and protein in the large intestine of all animal species. The factor of prime importance for the production rate of butyrate in the lower gut is type and levels of non-digestible carbohydrates entering the large intestine. It was previously believed that 85–90% of the butyrate produced in the gut was cleared when passing the gut epithelium, but recent studies with catheterised pigs have shown that the concentration of butyrate in the portal vein is strongly influenced by the production rate in the large intestine. Increased gut production of butyrate further raises the circulating level of butyrate. For good reason it is not possible with current technologies to perform direct measurements of the variation in the butyrate concentration in the portal vein of human subjects, but short-chain fatty acid levels in portal blood from sudden-death victims, subjects undergoing emergency surgery or planned surgery have indicated a higher gut production and absolute and relative concentration of butyrate in non-fasted as compared with fasted human subjects. However, despite an expected higher gut production of butyrate when feeding a high-fibre rye-bread-based diet as compared with a low-fibre wheat-bread-based diet, there was no difference in absolute or relative levels of butyrate in the peripheral blood of human subjects.