Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0029463 (osteosarcoma)
 16,637 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The retinoblastoma susceptibility gene (RB) product, the retinoblastoma protein (pRb), functions as a regulator of cell proliferation. Introduction of the RB gene into SAOS-2 osteosarcoma cells, which lack functional pRb, prevents cell cycle progression. Such growth-suppressive functions can be modulated by phosphorylation of pRb, which occurs via cell cycle-regulated kinases. We show that constitutively expressed cyclins A and E can overcome pRb-mediated suppression of proliferation. pRb becomes hyperphosphorylated in cells overexpressing these cyclins, and this phosphorylation is essential for cyclin A- and cyclin E-mediated rescue of pRb-blocked cells. This suggests that G1 and S phase cyclins can act as regulators of pRb function in the cell cycle by promoting pRb phosphorylation.
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PMID:Regulation of retinoblastoma protein functions by ectopic expression of human cyclins. 138 95

The representation of cyclins and cyclin-dependent kinases (cdks) was analyzed during progressive development of the bone cell phenotype in cultures of normal diploid rat calvarial osteoblasts. Three developmental stages were examined: (a) proliferation; (b) monolayer confluency; and (c) mineralization of the bone extracellular matrix. We demonstrate that the presence of cyclins and cdks is not restricted to the proliferation period. Consistent with their role in cell cycle progression, cdc2 and cdk2 decrease postproliferatively. However, cdk4 and cyclins A, B, and D1 persist in confluent cells. Cyclin E is significantly up-regulated during the extracellular matrix mineralization developmental period. Examination of the cytoplasmic levels of these cell cycle regulatory proteins indicates a marked increase in cyclin B in the late differentiation stage. The elevation of nuclear cyclin E and cytoplasmic cyclin B is not observed in osteoblasts maintained under culture conditions that do not support differentiation. Furthermore, treatment with transforming growth factor beta for 48 h during the proliferation period renders the cells incompetent for differentiation and abrogates the postproliferative up-regulation of cyclins B and E. Density-induced growth inhibition of ROS 17/2.8 osteosarcoma cells is not accompanied by up-regulation of nuclear cyclin E and cytoplasmic cyclin B when compared to the proliferation period. This observation is consistent with abrogation of both growth control and differentiation regulatory mechanisms in tumor cells. These results suggest that cell cycle regulatory proteins function not only during proliferation but may also play a role in normal diploid osteoblast differentiation.
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PMID:Expression of cell cycle regulatory factors in differentiating osteoblasts: postproliferative up-regulation of cyclins B and E. 758 45

Glucocorticoids inhibit proliferation of many cell types, but the events leading from the activated glucocorticoid receptor (GR) to growth arrest are not understood. Ectopic expression and activation of GR in human osteosarcoma cell lines U2OS and SAOS2, which lack endogenous receptors, result in a G1 cell cycle arrest. GR activation in U2OS cells represses expression of the cyclin-dependent kinases (CDKs) CDK4 and CDK6 as well as their regulatory partner, cyclin D3, leading to hypophosphorylation of the retinoblastoma protein (Rb). We also demonstrate a ligand-dependent reduction in the expression of E2F-1 and c-Myc, transcription factors involved in the G1-to-S-phase transition. Mitogen-activated protein kinase, CDK2, cyclin E, and the CDK inhibitors (CDIs) p27 and p21 are unaffected by receptor activation in U2OS cells. The receptor's N-terminal transcriptional activation domain is not required for growth arrest in U2OS cells. In Rb-deficient SAOS2 cells, however, the expression of p27 and p21 is induced upon receptor activation. Remarkably, in SAOS2 cells that express a GR deletion derivative lacking the N-terminal transcriptional activation domain, induction of CDI expression is abolished and the cells fail to undergo ligand-dependent cell cycle arrest. Similarly, murine S49 lymphoma cells, which, like SAOS2 cells, lack Rb, require the N-terminal activation domain for growth arrest and induce CDI expression upon GR activation. These cell-type-specific differences in receptor domains and cellular targets linking GR activation to cell cycle machinery suggest two distinct regulatory mechanisms of GR-mediated cell cycle arrest: one involving transcriptional repression of G1 cyclins and CDKs and the other involving enhanced transcription of CDIs by the activated receptor.
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PMID:Glucocorticoid receptor-mediated cell cycle arrest is achieved through distinct cell-specific transcriptional regulatory mechanisms. 915 17

Spontaneous differentiation of normal diploid osteoblasts in culture is accompanied by increased cyclin E associated kinase activity on (1) the retinoblastoma susceptibility protein pRB, (2) the p107 RB related protein, and (3) two endogenous cyclin E-associated substrates of 78 and 105 kD. Activity of the differentiation-related cyclin E complexes (diff.ECx) is not recovered in cdc2 or cdk2 immunoprecipitates. Phosphorylation of both the 105 kD endogenous substrate and the p107 exogenous substrate is sensitive to inhibitory activity (diff.ECx-i) present in proliferating osteoblasts. This inhibitory activity is readily recruited by the cyclin E complexes of differentiated osteoblasts but is not found in cyclin E immunoprecipitates of the proliferating cells themselves. Strong inhibitory activity on diff.ECx kinase activity is excerted by proliferating ROS 17/2.8 osteosarcoma cells. However, unlike the normal diploid cells, the diff.ECx-i activity of proliferating ROS 17/2.8 cells is recovered by cyclin E immunoprecipitation. The cyclin-dependent kinase inhibitor p21CIP1/WAF1 inhibits diff.ECx kinase activity. Thus, our results suggest the existence of a unique regulatory system, possibly involving p21CIP1/WAF1, in which inhibitory activity residing in proliferating cells is preferentially targeted towards differentiation-related cyclin E-associated kinase activity.
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PMID:Post-proliferative cyclin E-associated kinase activity in differentiated osteoblasts: inhibition by proliferating osteoblasts and osteosarcoma cells. 921 16

In mammalian cells, the retinoblastoma protein (Rb) is thought to negatively regulate progression through the G1 phase of the cell cycle by its association with the transcription factor E2F [1-3]. Rb-E2F complexes suppress transcription of genes required for DNA synthesis ([4], reviewed in [3,5]), and the prevailing view is that phosphorylation of Rb by complexes of cyclin-dependent kinases (Cdks) and their regulatory cyclin subunits, and the subsequent release of active E2F, is required for S-phase entry [1-3]. This view is based, in part, on the fact that ectopic expression of cyclin-Cdks leads to Rb phosphorylation and that this modification correlates with S-phase entry [6-8]. In Drosophila, however, cyclin E expression can bypass a requirement for E2F, suggesting that cyclins may activate replication independently of the Rb/E2F pathway [9]. We sought to examine whether Rb phosphorylation is a prerequisite for S-phase entry in Rb-deficient SAOS-2 osteosarcoma cells, using a commonly used cotransfection assay [6-8,10]. We find that a G1 arrest in SAOS-2 cells mediated by an Rb mutant lacking all 14 consensus Cdk phosphorylation sites is bypassed by coexpressing G1-specific E-type or D-type cyclin-Cdk complexes, and that injection of purified cyclin-Cdks during G1 accelerates S-phase entry. Our results indicate that Rb phosphorylation is not essential for S-phase entry when G1 cyclin-Cdks are overexpressed, and that other substrates of these kinases can be rate-limiting for the G1 to S-phase transition. These data also reveal that the SAOS-2 cotransfection assay is complicated by Rb-independent effects of the coexpressed Cdks.
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PMID:S-Phase entry upon ectopic expression of G1 cyclin-dependent kinases in the absence of retinoblastoma protein phosphorylation. 928 20

A mathematical model integrating the roles of cyclin D, cdk4, cyclin E, cdk2, E2F and RB in control of the G1 phase of the cell cycle is described. Experimental results described with murine embryo fibroblasts (MEFs), either Rb+/+ or Rb-/-, and with the RB-deficient osteosarcoma cell line, Saos-2, served as the basis for the formulation of this mathematical model. A model employing the known interactions of these six proteins does not reproduce the experimental observations described in the MEFs. The appropriate modelling of G1 requires the inclusion of a sensing mechanism which adjusts the activity of cyclin E/cdk2 in response to both RB concentration and growth factors. Incorporation of this sensing mechanism into the model allows it to reproduce most of the experimental results observed in Saos-2 cells, Rb-/- MEFS, and Rb+/+ MEFs. The model also makes specific predictions which have not been tested experimentally.
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PMID:A mathematical model of the regulation of the G1 phase of Rb+/+ and Rb-/- mouse embryonic fibroblasts and an osteosarcoma cell line. 937 29

To evaluate the distribution of cyclin protein expression, in relation to cell proliferation rate and clinical behavior, an immunohistochemical study was performed on 92 tumor samples of patients with high grade osteosarcoma (OS). A large cyclin A- and cyclin E-positive fraction was found respectively in 59% and 47% of the osteosarcomas, while immunostaining for cyclin D1 was weak or absent in most tumor samples. A positive, statistically significant correlation was found between A and E cyclins and Ki67 expression (p<0.001). Disease-free survival (DFS) analysis included 69 of the 92 patients. A significantly higher probability of metastasis was seen in patients lacking cyclin D1 compared to those in which cyclin D1 was positive (p<0.01). Conversely, patients with >40% of cyclin A-positive cells relapsed more frequently than those with <40% of cyclin A-positive cells (p<0.05). The multivariate analysis demonstrated that cyclin A had a lower predective risk in terms of disease-free survival as opposed to the loss of cyclin D1 that is considered a powerful prognostic factor.
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PMID:Prognostic significance of cyclin expression in human osteosarcoma. 953 20

We have used c-Fos transgenic mice which develop osteosarcomas to determine the expression patterns of cyclins, cyclin-dependent kinases (CDKs), and cyclin-dependent kinase inhibitors (CKIs) in different bone cell populations in order to define the potential mechanisms of c-Fos transformation. Immunohistochemical analysis in embryonic and early postnatal bone demonstrated that cyclin E and its kinase partner CDK2 were expressed specifically in bone-forming osteoblasts. Cyclin D1 expression was absent despite high levels of CDK4 and CDK6, and the CKI p27 was expressed in chondrocytes, osteoclasts, and at lower levels in osteoblasts. Following activation of the c-fos transgene in vivo and before overt tumor formation, cyclin D1 expression increased dramatically and was colocalized with exogenous c-Fos protein specifically in osteoblasts and chondrocytes, but not in osteoclasts. Prolonged activation of c-Fos resulted in osteosarcoma formation wherein the levels of cyclin D1, cyclin E, and CDKs 2, 4, and 6 were high in a wide spectrum of malignant cell types, especially in transformed osteoblasts. The CKI p27 was expressed at very high levels in bone-resorbing osteoclasts, and to a lesser extent in chondrocytes and osteoblasts. These in vivo observations suggest that cyclin D1 may be a target for c-Fos action and that elevation of cyclin D1 in osteoblasts which already express cyclin E/CDK2 and the cyclin D1 partners CDKs-4 and 6, may predispose cells to uncontrolled cell growth leading to osteosarcoma development. This study implicates altered cell cycle control as a potential mechanism through which c-Fos causes osteoblast transformation and bone tumor formation.
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PMID:Control of cell cycle gene expression in bone development and during c-Fos-induced osteosarcoma formation. 966 90

We previously demonstrated that P16Ink4a (p16) expression in p16-deficient U343 astrocytoma cells causes a G1 cell cycle arrest, profound changes in cytoskeletal proteins and alterations in expression and activity of the pRB and E2F family proteins. We examine here the effects of expressing wild type or mutant versions of the downstream targets of p16 in U343 astrocytomas. We first attempted to block proliferation of U343 cells using the dominant mutant of pRB, deltap34. Expression of this mutant in the human osteosarcoma, SAOS-2, potently blocked proliferation but did not affect the cell cycle of U343 cells. We next showed that expression of E2F-1, E2F-2, E2F-3 and E2F-4 are each able to overcome this p16-dependent cell cycle arrest but exhibit distinct biological activities. Adenoviral-mediated expression of E2F-1, E2F-2, E2F-3, or E2F-4 overcame the p16-dependent cell cycle block and induced alterations in cell morphology. E2F-5, only in conjunction with DP1, promoted cell cycle progression. For both E2F-1 and E2F-2, but not E2F-3 or E2F-5/DP1, cell cycle re-entry was associated with almost quantitative cell death. Only small numbers of dying cells were observed in E2F-4-expressing cultures. Expression of the different E2F's altered the expression of distinct sets of cell cycle regulatory proteins. E2F-1 induced endogenous E2F-4 expression and also caused an increase in pRB, p107 and cyclin E levels. Expression of E2F-4 caused a weak increase in E2F-1 levels but also strongly induced pRB, p107, p130 and cyclin E. However, E2F-1 and E2F-4 clearly regulate expression of distinct genes, demonstrated when E2F-4 caused a threefold increase in the levels of cdk2 whereas E2F-1 failed to increase in this cyclin dependent kinase. Similarly, expression of E2F-1 or E2F-2 were shown to have distinct effects on the expression of cdk2, cyclin E and pRB despite both of these closely related E2F-family members potently inducing cell death. Thus, E2F-1, E2F-2, E2F-3 and E2F-4 are able to overcome the p16-dependent proliferative block in U343 astrocytoma cells. While overcoming this cell cycle block, each of the E2F's uniquely affect the expression of a number of cell cycle regulatory proteins and have distinct abilities to promote cell death.
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PMID:The E2F-family proteins induce distinct cell cycle regulatory factors in p16-arrested, U343 astrocytoma cells. 978 3

The human BTG1 protein is thought to be a potential tumour suppressor because its overexpression inhibits NIH 3T3 cell proliferation. However, little is known about how BTG1 exerts its anti-proliferative activity. In this study, we used the yeast 'two-hybrid' system to screen for interacting protein partners and identified human carbon catabolite repressor protein (CCR4)-associative factor 1 (hCAF-1), a homologue of mouse CAF-1 (mCAF-1) and Saccharomyces cerevisiae yCAF-1/POP2. In vitro the hCAF-1/BTG1 complex formation was dependent on the phosphorylation of a putative p34cdc2 kinase site on BTG1 (Ser-159). In yeast, the Ala-159 mutant did not interact with hCAF-1. In addition, phosphorylation of Ser-159 in vitro showed specificity for the cell cycle kinases p34CDK2/cyclin E and p34CDK2/cyclin A, but not for p34CDK4/cyclin D1 or p34cdc2/cyclin B. Cell synchrony experiments with primary cultures of rat aortic smooth-muscle cells (RSMCs) demonstrated that message and protein levels of rat CAF-1 (rCAF-1) were up-regulated under conditions of cell contact, as previously reported for BTG1 [Wilcox, Scott, Subramanian, Ross, Adams-Burton, Stoltenborg and Corjay (1995) Circulation 92, I34-I35]. Western blot and immunohistochemical analysis showed that rCAF-1 localizes to the nucleus of contact-inhibited RSMCs, where it was physically associated with BTG1, as determined by co-immunoprecipitation with anti-hCAF-1 antisera. Overexpression of hCAF-1 in NIH 3T3 and osteosarcoma (U-2-OS) cells was itself anti-proliferative with colony formation reduced by 67% and 90% respectively. Taken together, these results indicate that formation of the hCAF-1/BTG1 complex is driven by phosphorylation at BTG1 (Ser-159) and implicates this complex in the signalling events of cell division that lead to changes in cellular proliferation associated with cell-cell contact.
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PMID:Human carbon catabolite repressor protein (CCR4)-associative factor 1: cloning, expression and characterization of its interaction with the B-cell translocation protein BTG1. 982 Aug 26


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