Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Terminally differentiated cells are characterized by permanent withdrawal from the cell cycle; they do not enter S phase even when stimulated by growth factors or retroviral oncogenes. We have shown, however, that the adenovirus E1A oncogene can reactivate the cell cycle in terminally differentiated cells. In this report, we describe the molecular events triggered by E1A in terminally differentiated skeletal muscle cells. We found that in myotubes infected with the adenovirus mutant dl520, 12S E1A bypasses the early G1 phase and activates the expression of late-G1 genes, such as the cyclin E and cyclin A genes, cdk2, PCNA, and B-myb. Of these, the cyclin E gene and cdk2 were significantly overexpressed in comparison with levels in proliferating, undifferentiated myoblasts. p130 and pRb were phosphorylated before the infected myotubes entered S phase, despite the high expression of the cyclin-dependent kinase inhibitor p21, and E2F was released. Our results suggest that one of the mechanisms that E1A uses to overcome the proliferative block of terminally differentiated cells involves coordinated overexpression of cyclin E and cdk2. Following E1A expression, the myogenic transcription factors MyoD and myogenin and the muscle-specific structural genes encoding muscle creatine kinase and myosin heavy chain were downregulated. The muscle regulatory factors were also silenced in myotubes infected with adenovirus E1A mutants incapable of reactivating the cell cycle in terminally differentiated muscle cells. Thus, the suppression of the differentiation program is not a consequence of cell cycle reactivation in myotubes, and it is induced by an independent mechanism. Our results show that E1A reactivates the cell cycle and suppresses tissue-specific gene expression in terminally differentiated muscle cells, thus causing dedifferentiation.
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PMID:Expression of E1A in terminally differentiated muscle cells reactivates the cell cycle and suppresses tissue-specific genes by separable mechanisms. 881 42

Viral oncoproteins that inactivate the retinoblastoma tumor suppressor protein (pRb) family both block skeletal muscle differentiation and promote cell cycle progression. To clarify the dependence of terminal differentiation on the presence of the different pRb-related proteins, we have studied myogenesis using isogenic primary fibroblasts derived from mouse embryos individually deficient for pRb, p107, or p130. When ectopically expressed in fibroblasts lacking pRb, MyoD induces an aberrant skeletal muscle differentiation program characterized by normal expression of early differentiation markers such as myogenin and p21, but attenuated expression of late differentiation markers such as myosin heavy chain (MHC). Similar defects in MHC expression were not observed in cells lacking either p107 or p130, indicating that the defect is specific to the loss of pRb. In contrast to wild-type, p107-deficient, or p130-deficient differentiated myocytes that are permanently withdrawn from the cell cycle, differentiated myocytes lacking pRb accumulate in S and G2 phases and express extremely high levels of cyclins A and B, cyclin-dependent kinase (Cdk2), and Cdc2, but fail to readily proceed to mitosis. Administration of caffeine, an agent that removes inhibitory phosphorylations on inactive Cdc2/cyclin B complexes, specifically induced mitotic catastrophe in pRb-deficient myocytes, consistent with the observation that the majority of pRb-deficient myocytes arrest in S and G2. Together, these findings indicate that pRb is required for the expression of late skeletal muscle differentiation markers and for the inhibition of DNA synthesis, but that a pRb-independent mechanism restricts entry of differentiated myocytes into mitosis.
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PMID:Skeletal muscle cells lacking the retinoblastoma protein display defects in muscle gene expression and accumulate in S and G2 phases of the cell cycle. 889

We previously showed that C2 myoblasts transformed by simian virus 40 large T antigen (SVLT) stop the myogenic process after the induction of myogenin and of high Rb levels; the induced Rb, however, becomes notably phosphorylated. We have analyzed the protein levels and activities of cyclin-dependent kinases (cdks) in untransformed C2 cells and in transformants of either SVLT or the cytoplasmic mutant NKT1 (which permits differentiation) upon a shift from growth medium (GM) to mitogen-poor differentiation medium (DM). After the shift, cdk4 levels remained constant and cdk6 levels decreased in all cell types; cdk2 minimally increased only in SVLT cells. Cyclin D1 was downregulated in DM in all cell types, and cyclin D3 was upregulated (albeit less strongly in SVLT cells than in the others). In contrast, a dramatic difference between SVLT cells and the other cells was observed for cyclins E and A, which essentially disappeared (as protein and RNA) in normal C2 and NKT1 cells upon the shift from GM to DM, whereas they increased in SVLT cells. Concurrently, cdk2 activity ceased in C2 and NKT1 cells in DM, whereas it persisted at 20% of the GM level in SVLT cells. cdk4 activity was detectable in all cells only in GM. Cyclin E and A induction thus appeared to sustain enough Rb phosphorylation to interfere with tissue-specific expression, with cdk activity not high enough to activate cyclin self-regulation. In DM, cdk2 complexed to D3 was underphosphorylated in all cells, and SVLT allowed strong inductions of p21 and p27 without affecting their complexes with cdks.
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PMID:Induction of cyclins E and A in response to mitogen removal: a basic alteration associated with the arrest of differentiation of C2 myoblasts transformed by simian virus 40 large T antigen. 903 56

NF-Y is composed of three subunits, NF-YA, NF-YB, and NF-YC, all required for DNA binding. All subunits are expressed in proliferating skeletal muscle cells, whereas NF-YA alone is undetectable in terminally differentiated cells in vitro. By immunohistochemistry, we show that the NF-YA protein is not expressed in the nuclei of skeletal and cardiac muscle cells in vivo. By chromatin immunoprecipitation experiments, we demonstrate herein that NF-Y does not bind to the CCAAT boxes of target promoters in differentiated muscle cells. Consistent with this, the activity of these promoters is down-regulated in differentiated muscle cells. Finally, forced expression of the NF-YA protein in cells committed to differentiate leads to an impairment in the down-regulation of cyclin A, cyclin B1, and cdk1 expression and is accompanied by a delay in myogenin expression. Thus, our results indicate that the suppression of NF-Y function is of crucial importance for the inhibition of several cell cycle genes and the induction of the early muscle-specific program in postmitotic muscle cells.
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PMID:Requirement for down-regulation of the CCAAT-binding activity of the NF-Y transcription factor during skeletal muscle differentiation. 1285 58

Satellite cells are quiescent muscle stem cells that promote postnatal muscle growth and repair. Here we show that myostatin, a TGF-beta member, signals satellite cell quiescence and also negatively regulates satellite cell self-renewal. BrdU labeling in vivo revealed that, among the Myostatin-deficient satellite cells, higher numbers of satellite cells are activated as compared with wild type. In contrast, addition of Myostatin to myofiber explant cultures inhibits satellite cell activation. Cell cycle analysis confirms that Myostatin up-regulated p21, a Cdk inhibitor, and decreased the levels and activity of Cdk2 protein in satellite cells. Hence, Myostatin negatively regulates the G1 to S progression and thus maintains the quiescent status of satellite cells. Immunohistochemical analysis with CD34 antibodies indicates that there is an increased number of satellite cells per unit length of freshly isolated Mstn-/- muscle fibers. Determination of proliferation rate suggests that this elevation in satellite cell number could be due to increased self-renewal and delayed expression of the differentiation gene (myogenin) in Mstn-/- adult myoblasts. Taken together, these results suggest that Myostatin is a potent negative regulator of satellite cell activation and thus signals the quiescence of satellite cells.
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PMID:Myostatin negatively regulates satellite cell activation and self-renewal. 1296 5

Dedifferentiated areas of dedifferentiated liposarcoma (DDL) usually show malignant fibrous histiocytoma (MFH)- or fibrosarcoma-like features and lack any histologic signs of specific differentiation. However, some reports have demonstrated specific differentiation in these areas, with histologic features resembling those of rhabdomyosarcoma, leiomyosarcoma, and osteosarcoma. We report here a pathologic and genetic analysis of three cases of DDLs with rhabdomyosarcomatous areas. MFH- or fibrosarcoma-like areas of one primary DDL and two recurrent DDLs contained various amounts of rhabdomyoblasts, which were immunoreactive for desmin, myoglobin, muscle actin (HHF-35), and myogenin. An ultrastructural examination demonstrated rhabdomyoblasts with abundant cytoplasm containing thin and thick filaments and Z-bands. By real-time PCR, amplification of mdm2 and cdk4 was confirmed in both well-differentiated and dedifferentiated areas with rhabdomyoblasts of all cases. To our knowledge, only seven cases of DDLs with rhabdomyosarcomatous components have been reported, and furthermore, the genetic profiles of the rhabdomyosarcomatous components in DDLs have not been investigated. This study demonstrates that DDLs with rhabdomyosarcomatous areas have genetic alterations that are common to well-differentiated/dedifferentiated liposarcomas.
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PMID:Dedifferentiated liposarcoma with rhabdomyoblastic differentiation. 1601 47

Myocyte differentiation is due to transcription of genes that characterize the phenotypic and biochemical identity of differentiated muscle cells. These are the myogenic regulatory factors (MRFs) MyoD, Myf5, myogenin and MRF4. Overexpression of cdk/cyclins has been reported to inhibit the activity of MyoD and prevent myogenic differentiation by different modalities. Unlike other cdk/cyclin complexes, overexpression of cdk9/cyclin T2a, enhances MyoD function and promotes myogenic differentiation. In addition, cyclin T2a interacting with a novel partner, PKN alpha, is able to strongly enhance the expression of myogenic differentiation markers, such as myogenin and Myosin Heavy Chain. So, cyclin T2a could stimulate myogenic differentiation interacting with different kinase partners Cdk9 or PKN alpha in a synergistic or antagonistic way.
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PMID:Involvement of cdks and cyclins in muscle differentiation. 1658 81

Myostatin decreases muscle mass and this is accomplished, in part, by inhibiting muscle satellite cell proliferation and differentiation by regulating the expression of cell cycle-related proteins (e.g. p21 and cdk2) and myogenic regulatory factors (e.g. myogenin and MyoD). The purpose of this investigation was to determine whether protein ingestion before and after a resistance exercise (RE) bout affects myostatin and cell cycle-related gene expression. Strength-trained middle-aged to older men were divided into a protein group (61.4 +/- 4.3 years, n = 9) or a placebo group (62.1 +/- 4.2 years, n = 9). Muscle biopsies from the vastus lateralis muscle were taken at rest and 1 and 48 h after a 5 x 10 repetition leg press RE bout. Protein (15 g whey) or non-caloric placebo was taken immediately before and after the RE bout. mRNA expression levels of myostatin and related genes (AcvrIIb, FLRG, p21, p27, cdk2, myogenin and MyoD) were determined by Taqman probe-based real-time RT-PCR and normalized to GAPDH mRNA. Myostatin mRNA decreased after a RE bout, but only in the placebo group (P < or = 0.05). Conversely, myostatin-binding protein FLRG and cell-cycle kinase cdk2 mRNA increased only in the protein group (P < or = 0.05). p21 mRNA was increased at 1 h post-RE in placebo (P < or = 0.05) and tended to be increased in the protein group (P = 0.08). Myostatin, its binding protein and cell cycle-related gene expressions are affected by single RE bout and these responses are further modified by whey protein intake. Therefore, controlling nutrition intake is important when studying gene expression responses to exercise.
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PMID:The effects of whey protein on myostatin and cell cycle-related gene expression responses to a single heavy resistance exercise bout in trained older men. 1792 33

Differentiation of myocytes is impaired in patients with myotonic dystrophy type 1, DM1. CUG repeat binding protein, CUGBP1, is a key regulator of translation of proteins that are involved in muscle development and differentiation. In this paper, we present evidence that RNA-binding activity of CUGBP1 and its interactions with initiation translation complex eIF2 are differentially regulated during myogenesis by specific phosphorylation and that this regulation is altered in DM1. In normal myoblasts, Akt kinase phosphorylates CUGBP1 at Ser28 and increases interactions of CUGBP1 with cyclin D1 mRNA. During differentiation, CUGBP1 is phosphorylated by cyclinD3-cdk4/6 at Ser302, which increases CUGBP1 binding with p21 and C/EBPbeta mRNAs. While cyclin D3 and cdk4 are elevated in normal myotubes; DM1 differentiating cells do not increase these proteins. In normal myotubes, CUGBP1 interacts with cyclin D3/cdk4/6 and eIF2; however, interactions of CUGBP1 with eIF2 are reduced in DM1 differentiating cells and correlate with impaired muscle differentiation in DM1. Ectopic expression of cyclin D3 in DM1 cells increases the CUGBP1-eIF2 complex, corrects expression of differentiation markers, myogenin and desmin, and enhances fusion of DM1 myoblasts. Thus, normalization of cyclin D3 might be a therapeutic approach to correct differentiation of skeletal muscle in DM1 patients.
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PMID:Ectopic expression of cyclin D3 corrects differentiation of DM1 myoblasts through activation of RNA CUG-binding protein, CUGBP1. 1857 Sep 22

The effects of timed ingestion of high-quality protein before and after resistance exercise are not well known. In this study, young men were randomized to protein (n = 11), placebo (n = 10) and control (n = 10) groups. Muscle cross-sectional area by MRI and muscle forces were analyzed before and after 21 weeks of either heavy resistance training (RT) or control period. Muscle biopsies were taken before, and 1 and 48 h after 5 x 10 repetition leg press exercise (RE) as well as 21 weeks after RT. Protein (15 g of whey both before and after exercise) or non-energetic placebo were provided to subjects in the context of both single RE bout (acute responses) as well as each RE workout twice a week throughout the 21-week-RT. Protein intake increased (P < or = 0.05) RT-induced muscle cross-sectional area enlargement and cell-cycle kinase cdk2 mRNA expression in the vastus lateralis muscle suggesting higher proliferating cell activation response with protein supplementation. Moreover, protein intake seemed to prevent 1 h post-RE decrease in myostatin and myogenin mRNA expression but did not affect activin receptor IIb, p21, FLRG, MAFbx or MyoD expression. In conclusion, protein intake close to resistance exercise workout may alter mRNA expression in a manner advantageous for muscle hypertrophy.
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PMID:Acute and long-term effects of resistance exercise with or without protein ingestion on muscle hypertrophy and gene expression. 1866 Dec 58


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