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Hu W, Chen Y, Tsao C, Chen S, Tzeng C. Development of a multifunctional bioreactor to evaluate the promotion effects of cyclic stretching and electrical stimulation on muscle differentiation. Bioeng Transl Med 2024; 9:e10633. [PMID: 38435819 PMCID: PMC10905532 DOI: 10.1002/btm2.10633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 11/17/2023] [Accepted: 11/24/2023] [Indexed: 03/05/2024] Open
Abstract
A multifunctional bioreactor was fabricated in this study to investigate the facilitation efficiency of electrical and mechanical stimulations on myogenic differentiation. This bioreactor consisted of a highly stretchable conductive membrane prepared by depositing polypyrrole (PPy) on a flexible polydimethylsiloxane (PDMS) film. The tensile deformation of the PPy/PDMS membrane can be tuned by adjusting the channel depth. In addition, PPy/PDMS maintained its electrical conductivity under continuous cyclic stretching in the strain range of 6.5%-13% for 24 h. This device can be used to individually or simultaneously perform cyclic stretching and electrical stimulation. The results of single stimulation showed that either cyclic stretching or electrical stimulation upregulated myogenic gene expression and promoted myotube formation, where electrical stimulation improved better than cyclic stretching. However, only cyclic stretching can align C2C12 cells perpendicular to the stretching direction, and electrical stimulation did not affect cell morphology. Myosin heavy chain (MHC) immunostaining demonstrated that oriented cells under cyclic stretching resulted in parallel myotubes. The combination of these two stimuli exhibited synergetic effects on both myogenic gene regulation and myotube formation, and the incorporated electrical field did not affect the orientation effect of the cyclic stretching. These results suggested that these two treatments likely influenced cells through different pathways. Overall, the simultaneous application of cyclic stretching and electrical stimulation preserved both stimuli's advantages, so myo-differentiation can be highly improved to obtain abundant parallel myotubes, suggesting that our developed multifunctional bioreactor should benefit muscle tissue engineering applications.
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Affiliation(s)
- Wei‐Wen Hu
- Department of Chemical and Materials EngineeringNational Central UniversityTaoyuanTaiwan
| | - Yen‐Chi Chen
- Department of Chemical and Materials EngineeringNational Central UniversityTaoyuanTaiwan
| | - Chia‐Wen Tsao
- Department of Mechanical EngineeringNational Central UniversityTaoyuanTaiwan
| | - Shen‐Liang Chen
- Department of Life SciencesNational Central UniversityTaoyuanTaiwan
| | - Chung‐Yuh Tzeng
- Department of OrthopedicsTaichung Veterans General HospitalTaichungTaiwan
- Department of RehabilitationJen‐Teh Junior College of Medicine, Nursing and ManagementMiaoliTaiwan
- Department of Medicinal Botanicals and Foods on Health ApplicationsDa‐Yeh UniversityChanghuaTaiwan
- Institute of Biomedical SciencesNational Chung Hsing UniversityTaichungTaiwan
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Kwon I. Protective effects of endurance exercise on skeletal muscle remodeling against doxorubicin-induced myotoxicity in mice. Phys Act Nutr 2020; 24:11-21. [PMID: 32698257 PMCID: PMC7451836 DOI: 10.20463/pan.2020.0010] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 06/19/2020] [Accepted: 06/22/2020] [Indexed: 12/14/2022] Open
Abstract
PURPOSE Doxorubicin (DOX) is a potent anti-cancer drug that appears to have severe myotoxicity due to accumulation. The skeletal muscle has a regeneration capacity through satellite cell activation when exposed to extracellular stimulus or damage. Endurance exercise (EXE) is a therapeutic strategy that improves pathological features and contributes to muscle homeostasis. Thus, this study investigated the effect of EXE training in mitigating chronic DOX-induced myotoxicity. METHODS Male C57BL/6J mice were housed and allowed to acclimatize with free access to food and water. All the mice were randomly divided into four groups: sedentary control (CON, n=9), exercise training (EXE, n=9), doxorubicin treatment (DOX, n=9), doxorubicin treatment and exercise training (DOX+EXE, n=9) groups. The animals were intraperitoneally injected with 5 mg/kg/week of DOX treatment for 4 weeks, and EXE training was initiated for treadmill adaptation for 1 week and then performed for 4 weeks. Both sides of the soleus (SOL) muscle tissues were dissected and weighed after 24 hours of the last training sessions. RESULTS DOX chemotherapy induced an abnormal myofiber's phenotype and transition of myosin heavy chain (MHC) isoforms. The paired box 7 (PAX7) and myoblast determination protein 1 (MYOD) protein levels were triggered by DOX, while no alterations were shown for the myogenin (MYOG). DOX remarkably impaired the a-actinin (ACTN) protein, but the EXE training seems to repair it. DOX-induced myotoxicity stimulated the expression of the forkhead box O3 (FOXO3a) protein, which was accurately controlled and adjusted by the EXE training. However, the FOXO3a-mediated downstream markers were not associated with DOX and EXE. CONCLUSION EXE postconditioning provides protective effects against chronic DOX-induced myotoxicity, and should be recommended to alleviate cancer chemotherapy-induced late-onset myotoxicity.
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Affiliation(s)
- Insu Kwon
- Research Institute of Sports Science and Industry, Hanyang University, SeoulRepublic of Korea
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Torok ZA, Busekrus RB, Hydock DS. Effects of Creatine Supplementation on Muscle Fatigue in Rats Receiving Doxorubicin Treatment. Nutr Cancer 2019; 72:252-259. [PMID: 31184509 DOI: 10.1080/01635581.2019.1623900] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The purpose of this study was to investigate the effects of in vivo creatine monohydrate (Cr) supplementation on doxorubicin (Dox)-induced muscle dysfunction. Male rats were fed a diet supplemented with 3% Cr or a standard chow for 2 wk. After 2 wk of feeding, animals received Dox or saline as a placebo. Five days post-injection, grip strength was measured, and muscle fatigue was analyzed ex vivo. When compared with controls, a significantly lower grip strength was observed with Dox treatment, but no significant handgrip difference was observed with Cr feeding prior to Dox treatment when compared to controls. In the isolated muscle fatigue experiments, solei (primarily type I muscle) from controls produced significantly less force than baseline at 60 s and solei from Dox treated rats produced significantly less force than baseline at 30 s; however, Cr feeding prior to Dox produced significantly less force than baseline at 60 s. In the primarily type II EDL, a decline in force production from baseline was observed at 50 s in controls and Cr + Dox and at 20 s in standard chow + Dox. Cr attenuated the increase in fatigue that accompanies Dox treatment suggesting that Cr supplementation may have use in managing Dox myotoxicity.
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Affiliation(s)
- Zoltan A Torok
- School of Sport and Exercise Science, University of Northern Colorado, Greeley, Colorado, USA
| | - Raquel B Busekrus
- School of Sport and Exercise Science, University of Northern Colorado, Greeley, Colorado, USA
| | - David S Hydock
- School of Sport and Exercise Science, University of Northern Colorado, Greeley, Colorado, USA.,The University of Northern Colorado Cancer Rehabilitation Institute, University of Northern Colorado, Greeley, Colorado, USA
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D'Lugos AC, Fry CS, Ormsby JC, Sweeney KR, Brightwell CR, Hale TM, Gonzales RJ, Angadi SS, Carroll CC, Dickinson JM. Chronic doxorubicin administration impacts satellite cell and capillary abundance in a muscle-specific manner. Physiol Rep 2019; 7:e14052. [PMID: 30963722 PMCID: PMC6453819 DOI: 10.14814/phy2.14052] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 03/15/2019] [Accepted: 03/16/2019] [Indexed: 01/23/2023] Open
Abstract
Anthracycline chemotherapies are effective at reducing disease recurrence and mortality in cancer patients. However, these drugs also contribute to skeletal muscle wasting and dysfunction. The purpose of this study was to assess the impact of chronic doxorubicin (DOX) administration on satellite cell and capillary densities in different skeletal muscles. We hypothesized that DOX would reduce satellite cell and capillary densities of the soleus (SOL) and extensor digitorum longus (EDL) muscles, along with muscle fiber size. Ovariectomized female Sprague-Dawley rats were randomized to receive three bi-weekly intraperitoneal injections of DOX (4 mg∙kg-1 ; cumulative dose 12 mg∙kg-1 ) or vehicle (VEH; saline). Animals were euthanized 5d following the last injection and the SOL and EDL were dissected and prepared for immunohistochemical and RT-qPCR analyses. Relative to VEH, CSA of the SOL and EDL fibers were 26% and 33% smaller, respectively, in DOX (P < 0.05). In the SOL, satellite cell and capillary densities were 39% and 35% lower, respectively, in DOX (P < 0.05), whereas in the EDL satellite cell and capillary densities were unaffected by DOX administration (P > 0.05). Proliferating satellite cells were unaffected by DOX in the SOL (P > 0.05). In the SOL, MYF5 mRNA expression was increased in DOX (P < 0.05), while in the EDL MGF mRNA expression was reduced in DOX (P < 0.05). Chronic DOX administration is associated with reduced fiber size in the SOL and EDL; however, DOX appeared to reduce satellite cell and capillary densities only in the SOL. These findings highlight that therapeutic targets to protect skeletal muscle from DOX may vary across muscles.
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Affiliation(s)
| | - Christopher S. Fry
- Department of Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTexas
| | - Jordan C. Ormsby
- College of Health SolutionsArizona State UniversityPhoenixArizona
| | | | - Camille R. Brightwell
- Department of Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTexas
| | - Taben M. Hale
- Department of Basic Medical SciencesCollege of Medicine‐PhoenixUniversity of ArizonaPhoenixArizona
| | - Rayna J. Gonzales
- Department of Basic Medical SciencesCollege of Medicine‐PhoenixUniversity of ArizonaPhoenixArizona
| | | | - Chad C. Carroll
- Department of PhysiologyMidwestern UniversityGlendaleArizona
- Department of Health and KinesiologyPurdue UniversityWest LafayetteIndiana
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Bredahl EC, Hydock DS. Creatine Supplementation and Doxorubicin-Induced Skeletal Muscle Dysfunction: An Ex Vivo Investigation. Nutr Cancer 2017; 69:607-615. [PMID: 28323480 DOI: 10.1080/01635581.2017.1295089] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Supplementing the diet with creatine (Cr) to manage chemotherapy-induced skeletal muscle weakness and fatigue has potential, but little has been done exploring it as an intervention. This study examined the effects of Cr on skeletal muscle dysfunction induced by the chemotherapy drug doxorubicin (Dox). Soleus and extensor digitorum longus (EDL) from male Sprague-Dawley rats maintained in an organ bath were incubated in Krebs-Henseleit (KH) buffer with or without creatine monohydrate (25 mM) for 30 min. Skeletal muscle was then incubated in KH buffer with or without Dox (24 μM) for an additional 30 min. Baths were then refreshed with KH buffer, and a 100-s fatigue protocol was administered. At baseline (0 s time point), no significant differences in force production were observed in the slow, type I soleus, but the Dox-treated soleus fatigued quicker than the non-Dox-treated soleus; however, pretreatment with Cr extended the time to fatigue in the Dox-treated soleus. In the fast, type II EDL, Dox treatment decreased force production at baseline and increased fatigue, and Cr treatment prior to Dox attenuated this dysfunction. Creatine pretreatment mitigated Dox-induced skeletal muscle dysfunction ex vivo suggesting that Cr may play a role in managing Dox-induced skeletal muscle side effects.
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Affiliation(s)
- Eric C Bredahl
- a Department of Exercise Science and Pre-Health Professions , Creighton University , Omaha , Nebraska , USA
| | - David S Hydock
- b School of Sport and Exercise Science, University of Northern Colorado , Greeley , Colorado , USA.,c The University of Northern Colorado Cancer Rehabilitation Institute, University of Northern Colorado , Greeley , Colorado , USA
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Schonn I, Hennesen J, Dartsch DC. Ku70 and Rad51 vary in their importance for the repair of doxorubicin- versus etoposide-induced DNA damage. Apoptosis 2011; 16:359-69. [PMID: 21107697 DOI: 10.1007/s10495-010-0564-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
For DNA targeting anticancer drugs, cellular DNA repair mechanisms may cause resistance and hamper the therapeutic outcome. DNA damage induced by topoisomerase IIα inhibitors like etoposide and anthracyclines, which are a mainstay of cancer therapy, is also repaired in many cell types, but the impact and precise mechanisms of this repair are still obscure. To investigate the DNA damage response of human adenocarcinoma HT29-cells to doxorubicin and to compare the involvement of Ku70 and Rad51 in the repair of doxorubicin- versus etoposide-induced DNA damage, we assessed cell cycle distribution and cell death, DNA damage, proteins relevant for repair by homologous recombination and non-homologous end-joining, and clonogenicity following exposure to doxorubicin at clinically achievable concentrations. Also, we assessed changes in the repair kinetics after siRNA-mediated attenuation of Ku70 or Rad51 expression. We found that exposure to doxorubicin for 24 h induced a substantial amount of DNA damage that was largely repaired when doxorubicin was removed and the cells were maintained in drug-free medium. Nevertheless, a pronounced G(2)/M arrest occurred at times when repair was maximal. This was followed by a distinct increase in cell death and loss of clonogenicity. In this regard, responses to doxorubicin and etoposide were similar. However, distinct differences in the repair process following doxorubicin versus etoposide were seen in concentration dependency, time-course and requirement of Ku70 and Rad51 proteins. In spite of the shared molecular target of doxorubicin and etoposide, DNA lesions induced by these compounds are repaired differently.
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Affiliation(s)
- Ilona Schonn
- Clinical Pharmacy, Institute of Pharmacy, Hamburg University, Bundesstrasse 45, Hamburg, Germany.
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Harmon EB, Harmon ML, Larsen TD, Paulson AF, Perryman MB. Myotonic dystrophy protein kinase is expressed in embryonic myocytes and is required for myotube formation. Dev Dyn 2008; 237:2353-66. [DOI: 10.1002/dvdy.21653] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
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Dhawan J, Helfman DM. Modulation of acto-myosin contractility in skeletal muscle myoblasts uncouples growth arrest from differentiation. J Cell Sci 2004; 117:3735-48. [PMID: 15252113 DOI: 10.1242/jcs.01197] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Cell-substratum interactions trigger key signaling pathways that modulate growth control and tissue-specific gene expression. We have previously shown that abolishing adhesive interactions by suspension culture results in G0 arrest of myoblasts. We report that blocking intracellular transmission of adhesion-dependent signals in adherent cells mimics the absence of adhesive contacts. We investigated the effects of pharmacological inhibitors of acto-myosin contractility on growth and differentiation of C2C12 myogenic cells. ML7 (5-iodonaphthalene-1-sulfonyl homopiperazine) and BDM (2,3, butanedione monoxime) are specific inhibitors of myosin light chain kinase, and myosin heavy chain ATPase, respectively. ML7 and BDM affected cell shape by reducing focal adhesions and stress fibers. Both inhibitors rapidly blocked DNA synthesis in a dose-dependent, reversible fashion. Furthermore, both ML7 and BDM suppressed expression of MyoD and myogenin, induced p27kip1 but not p21cip1, and inhibited differentiation. Thus, as with suspension-arrest, inhibition of acto-myosin contractility in adherent cells led to arrest uncoupled from differentiation. Over-expression of inhibitors of the small GTPase RhoA (dominant negative RhoA and C3 transferase) mimicked the effects of myosin inhibitors. By contrast, wild-type RhoA induced arrest, maintained MyoD and activated myogenin and p21 expression. The Rho effector kinase ROCK did not appear to mediate Rho's effects on MyoD. Thus, ROCK and MLCK play different roles in the myogenic program. Signals regulated by MLCK are critical, since inhibition of MLCK suppressed MyoD expression but inhibition of ROCK did not. Inhibition of contractility suppressed MyoD but did not reduce actin polymer levels. However, actin depolymerization with latrunculin B inhibited MyoD expression. Taken together, our observations indicate that actin polymer status and contractility regulate MyoD expression. We suggest that in myoblasts, the Rho pathway and regulation of acto-myosin contractility may define a control point for conditional uncoupling of differentiation and the cell cycle.
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Affiliation(s)
- Jyotsna Dhawan
- Center for Cellular and Molecular Biology, Uppal Road, Hyderabad, 500 007, India.
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9
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Puri PL, Bhakta K, Wood LD, Costanzo A, Zhu J, Wang JYJ. A myogenic differentiation checkpoint activated by genotoxic stress. Nat Genet 2002; 32:585-93. [PMID: 12415271 DOI: 10.1038/ng1023] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2002] [Accepted: 09/18/2002] [Indexed: 11/08/2022]
Abstract
Cell-cycle checkpoints help to protect the genomes of proliferating cells under genotoxic stress. In multicellular organisms, cell proliferation is often directed toward differentiation during development and throughout adult homeostasis. To prevent the formation of differentiated cells with genetic instability, we hypothesized that genotoxic stress may trigger a differentiation checkpoint. Here we show that exposure to genotoxic agents causes a reversible inhibition of myogenic differentiation. Muscle-specific gene expression is suppressed by DNA-damaging agents if applied prior to differentiation induction but not after the differentiation program is established. The myogenic determination factor, MyoD (encoded by Myod1), is a target of the differentiation checkpoint in myoblasts. The inhibition of MyoD by DNA damage requires a functional c-Abl tyrosine kinase (encoded by Abl1), but occurs in cells deficient for p53 (transformation-related protein 53, encoded by Trp53) or c-Jun (encoded by the oncogene Jun). These results support the idea that genotoxic stress can regulate differentiation, and identify a new biological function for DNA damage-activated signaling network.
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Affiliation(s)
- Pier Lorenzo Puri
- Dulbecco Telethon Institute at Laboratory of Gene Expression, Fondazione Andrea Cesalpino University of Rome La Sapienza, 00161 Rome, Italy
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Horenstein MS, Vander Heide RS, L'Ecuyer TJ. Molecular basis of anthracycline-induced cardiotoxicity and its prevention. Mol Genet Metab 2000; 71:436-44. [PMID: 11001837 DOI: 10.1006/mgme.2000.3043] [Citation(s) in RCA: 160] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Anthracyclines are a class of highly potent antitumor antibiotics utilized against hematologic and solid tumors in children and in adults. Their use has been limited primarily by their cardiotoxic side effects, which may lead to congestive heart failure. Although there is a linear relationship between the cumulative dose received and the incidence of cardiotoxicity, in some patients cardiotoxicity may develop at doses below the generally accepted threshold level. Anthracycline-induced cardiotoxicity is believed to be related to the generation of highly reactive oxygen species, which, by means of membrane lipid peroxidation, cause direct damage to cardiac myocyte membranes. Another important factor may be the relatively poor antioxidant defense system of the heart. In an attempt to circumvent these toxic effects, a wide variety of antioxidants have been used in cell culture, animal, and human studies without consistent beneficial effects. Moreover, none of the agents used to date are designed to act selectively upon the heart. If the cardiac complications resulting from anthracyclines could be reduced and/or prevented, higher doses could potentially be used, thereby increasing cancer cure rates. Furthermore, the incidence of cardiac toxicity resulting in congestive heart failure or even heart transplantation would be reduced, therefore increasing the quality and extent of life for cancer survivors. This article will review the basic science of free radical biology, the biology of oxygen-derived free radicals and antioxidant proteins, and explore some new and innovative approaches to limiting and/or preventing anthracycline-induced cardiotoxicity.
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Affiliation(s)
- M S Horenstein
- Division of Pediatric Cardiology, Children's Hospital of Michigan and Wayne State University, Detroit, Michigan 48201, USA
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Pantazis P, Chatterjee D, Han Z, Wyche J. Differentiation of human malignant melanoma cells that escape apoptosis after treatment with 9-nitrocamptothecin in vitro. Neoplasia 1999; 1:231-40. [PMID: 10935478 PMCID: PMC1508080 DOI: 10.1038/sj.neo.7900025] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
After in-vitro exposure to 0.05 micromol/L 9-nitrocamptothecin (9NC) for periods of time longer than 5 days, 65% to 80% of the human malignant melanoma SB1B cells die by apoptosis, whereas the remaining cells are arrested at the G2-phase of the cell cycle. Upon discontinuation of exposure to 9NC the G2-arrested cells resume cell cycling or remain arrested depending on the duration of 9NC exposure. In contrast to cycling malignant cells, the cells irreversibly arrested at G2 exhibit features of normal-like cells, the melanocytes, as assessed by the appearance of dendrite-like structures; loss of proliferative activity; synthesis of the characteristic pigment, melanin; and, particularly, loss of tumorigenic ability after xenografting in immunodeficient mice. Further, the expression of the cyclin-dependent kinase inhibitor p16 is upregulated in the 9NC-treated, G2-arrested, but downregulated in density G1-arrested cells, whereas the reverse is observed in the expression of another cyclin-dependent kinase inhibitor, p21. These results suggest that malignant melanoma SB1B cells that escape 9NC-induced death by apoptosis undergo differentiation toward nonmalignant, normal-like cells.
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Affiliation(s)
- P Pantazis
- Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912, USA.
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Studzinski GP, Harrison LE. Differentiation-related changes in the cell cycle traverse. INTERNATIONAL REVIEW OF CYTOLOGY 1999; 189:1-58. [PMID: 10333577 DOI: 10.1016/s0074-7696(08)61384-4] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
This review examines recent developments relating to the interface between cell proliferation and differentiation. It is suggested that the mechanism responsible for this transition is more akin to a "dimmer" than to a "switch," that it is more useful to refer to early and late stages of differentiation rather than to "terminal" differentiation, and examples of the reversibility of differentiation are provided. An outline of the established paradigm of cell cycle regulation is followed by summaries of recent studies that suggest that this paradigm is overly simplified and should be interpreted in the context of different cell types. The role of inhibitors of cyclin-dependent kinases in differentiation is discussed, but the data are still inconclusive. An increasing interest in the changes in G2/M transition during differentiation is illustrated by examples of polyploidization during differentiation, such as megakaryocyte maturation. Although the retinoblastoma protein is currently maintaining its prominent role in control of proliferation and differentiation, it is anticipated that equally important regulators will be discovered and provide an explanation at the molecular level for the gradual transition from proliferation to differentiation.
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Affiliation(s)
- G P Studzinski
- Department of Pathology and Laboratory Medicine, University of Medicine and Dentistry, New Jersey Medical School, Newark 07103, USA
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