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The biology of prostate cancer is still poorly understood. Allelic loss studies indicate that there likely exist multiple sites harbouring candidate tumour suppressor genes (TSG), some of which may have an important role in primary tumours, and some in late stages of prostate cancer. The recent studies on the localization of potential TSG in neoplastic transformation of prostate comprise chromosome regions 7q, 8p, l0p/q, 16q, 17q, and 18q. In connection with accumulation of genetic changes affecting functioning of critical TSG, the multistep cancer progression hypothesis is a useful starting point in efforts to understand the biology of the neoplastic lesions of prostate.
We recently observed an interaction between poly(ADP-ribose) polymerase-1 (PARP-1) and the tumor suppressor p53 protein. However, more extensive studies on both proteins, especially those on characterization of their domains involved in the interaction were difficult due to very low expression levels of p53 in mammalian cells. Therefore, we generated recombinant proteins for such studies. To clarify which domains of human PARP-1 and of human wild-type (wt) p53 were involved in this protein-protein interaction, we generated baculoviral constructs encoding full length or distinct functional domains of both proteins. Full length PARP-1 was simultaneously coexpressed in insect cells with full length wt p53 protein or its distinct truncated fragments and vice versa. Reciprocal immunoprecipitation of Sf9 cell lysates revealed that the central and carboxy-terminal fragments of p53 each were sufficient to confer binding to PARP-1, whereas the amino-terminal part harbouring the transactivation functional domain was dispensable. On the other hand, the amino-terminal and central fragments of PARP-1 were both necessary for complex formation with p53 protein. Since the most important features of p53 protein are regulated by phosphorylation, we addressed the question whether its phosphorylation is essential for the binding between the two proteins. Baculovirally expressed wt p53 was post-translationally modified. At least six distinct p53 isomers were resolved by immunoblotting following two-dimensional separation of baculovirally expressed wt p53 protein. Using specific phospho-serine antibodies, we identified phosphorylation of baculovirally expressed p53 protein at five distinct sites. To define the role of p53 phosphorylation, pull-down assays using untreated and dephosphorylated p53 protein were performed. Dephosphorylated p53 failed to bind PARP-1, indicating that complex formation between the two proteins was regulated by phosphorylation of p53. The marked phosphorylation of p53 at Ser392 observed in unstressed cells suggests that the phosphorylated carboxy-terminal part of p53 undergoes complex formation with PARP-1 resulting in masking of the NES and thereby preventing its export.
The p53 tumor suppressor plays the role of a cellular hub which gathers stress signals such as damage to DNA or hypoxia and translates them into a complex response. p53 exerts its action mainly as a potent transcription factor. The two major outcomes of p53 activity are highlighted: cell cycle arrest and apoptosis. During malignant transformation p53 or p53-pathway related molecules are disabled extremely often. Mutations in p53 gene are present in every second human tumor. A mutant form of p53 may not only negate the wild type p53 function but may play additional role in tumor progression. Therefore p53 represents a relatively unique and specific target for anticancer drug design. Current approaches include several different molecules able to restore p53 wild-type conformation and activity. Such small molecule drugs hold great promise in treating human tumors with dysfunction of p53 pathway in the near future.
Human platelets diadenosine triphosphatase was characterised and compared with the Fhit protein, a human tumour suppressor with diadenosine triphosphatase activity. Both enzymes exhibit similar Km, are similarly activated by Mg2+, Ca2+ and Mn2+, and inhibited by Zn2+ and suramin. However, they are differentially inhibited by Fhit antibodies and exhibit differences in gel-filtration behaviour.
Nuclear bodies are electron dense, spherical structures with a diameter between 0.2 and 1.0 µm. The function of these nuclear domains is unclear. One class of nuclear bodies contains the tumor suppressor protein PML. Besides in the nucleus, a small number of PML-containing structures of about the same size as nuclear bodies is also present in the cytoplasm. We have investigated whether PML is transported from the nucleus to the cytoplasm and/or vice versa. To this end we injected the PML-specific mAb 5E10 into the cytoplasm of living cells. Subsequently, we monitored translocation of the antibody across the nuclear envelope by indirect immunofluorescent microscopy. It is well known that antibodies in the cytoplasm of living cells do not enter the nucleus, unless as a complex with a karyophilic protein. We observed accumulation into PML-containing nuclear bodies of 5E10 microinjected into the cytoplasm. Control rabbit IgG and a mAb specific for lamin B2 were not translocated to the nucleus. All nuclear PML bodies were labeled simultaneously by 5E10 with gradually increased intensity in time. Labeling of PML-containing nuclear bodies by 5E10 microinjected into the cytoplasm was not affected by inhibition of protein synthesis. These results suggest that the 5E10 antigen PML shuttles between the nucleus and cytoplasm, indicating that nuclear bodies are dynamic structures.
Multiple and diverse cell adhesion molecules take part in intercellular and cell-extracellular matrix interactions of cancer. Cancer progression is a multi-step process in which some adhesion molecules play a pivotal role in the development of recurrent, invasive, and distant metastasis. A growing body of evidence indicates that alterations in the adhesion properties of neoplastic cells play a pivotal role in the development and progression of cancer. Loss of intercellular adhesion and the des­quamation of cells from the underlying lamina propria allows malignant cells to es­cape from their site of origin, degrade the extracellular matrix, acquire a more motile and invasion phenotype, and finally, invade and metastasize. In addition to partici­pating in tumor invasiveness and metastasis, adhesion molecules regulate or signifi­cantly contribute to a variety of functions including signal transduction, cell growth, differentiation, site-specific gene expression, morphogenesis, immunologic function, cell motility, wound healing, and inflammation. Cell adhesion molecule (CAM), a di­verse system of transmembrane glycoproteins has been identified that mediates the cell–cell and cell–extracellular matrix adhesion and also serves as the receptor for different kinds of virus. We summarize recent progress regarding the role of CAM, particularly, immunoglobulin-CAMs and cadherins in the progression of cancer and discuss the potential application of CAMs in the development of cancer therapy mainly on urogenital cancer.
Many models of tumour formation have been put forth so far. In general they involve mutations in at least three elements within the cell: oncogenes, tumour suppressors and regulators of telomere replication. Recently numerous mutations in mitochondria have been found in many tumours, whereas they were absent in normal tissues from the same individual. The presence of mutations, of course, does not prove that they play a causative role in development of neoplastic lesions and progression; however, the key role played by mitochondria in both apoptosis and generation of DNA-damaging reactive oxygen species might indicate that the observed mutations contribute to tumour development. Recent experiments with nude mice have proven that mtDNA mutations are indeed responsible for tumour growth and exacerbated ROS production. This review describes mtDNA mutations in main types of human neoplasia.
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