ISSN:1065-7541    

DOI:10.1002/roi.2970030602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe combination of in vitro transformation protocols and transfection assays allowed us to isolate a new transforming gene,cph, from neoplastic Syrian hamster embryo fibroblasts chemically initiated with a single dose of 3‐methylcholanthrene. Cosmid clones encompassingcphgenomic sequences were able to transform NIH/3T3 cells and showed a synergistic action with H‐rasin the transformation of the murine fibroblasts. In the present study, we describe the molecular cloning of the hamstercphoncogene cDNA. Nucleotide sequence analysis of a full‐length cDNA clone (pBl‐19), isolated from a cDNA library from neoplastic hamster cells withcphgenomic probes demonstrated that the clonedcphcDNA does not show any significant global homology to sequences deposited in established databases, confirming thatcphis a novel gene. ThecphcDNA contained an open reading frame with coding capacity for a protein of about 26 kDa, which was synthesized from pBl‐19 by using in vitro transcription‐translation assays. The cph protein deduced from the cDNA nucleotide sequence contained a dbl‐homologous (DH) domain. The fact that the DH domain has been found primarily among GDP‐exchange factors suggests that cph may be a new member of this family of proteins. © 1995

ISSN:1065-7541    

DOI:10.1002/roi.2970030603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1065-7541    

DOI:10.1002/roi.2970030604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractBy using vector‐mediated gene transfer and expression cloning, cDNAs of dominantly acting genes have been identified that cause phenotypic conversion of cells from flat, contact‐inhibited growth to focus formation and anchorage‐independent growth. Such morphologic growth changes are consistent with carcinogenic progression steps. Plasmid rescue and polymerase chain reaction amplification have permitted the identification of four candidate cDNAs (two unknown and two known) that are present in these transformed cells. Partial sequence analysis shows that one unknown gene contains sequence homology to the envelope sequences of the human retrovirus (HIV‐1). This characteristic suggests that the isolated cDNA may be a putative oncogene. The model system reported here permits identification and characterization of genes that may be associated with progression steps from the immortal state to anchorage independence and tumorigenicity. © 1995 Wiley

ISSN:1065-7541    

DOI:10.1002/roi.2970030605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractUltraviolet (UV)‐induced nonmelanoma skin cancer requires a number of genetic changes before tumors can develop. To determine the sequence of these changes; we performed a series of functional studies by investigating the spontaneously immortalized human skin keratinocyte HaCaT cell line. We established a multistep in vitro carcinogenesis model that allowed us to place known (mutational inactivation of the tumor suppressor genep53, rasoncogene activation) and novel (loss of chromosome 3p as carrier of “senescence” gene(s) and chromosome 15 as carrier of a tumor suppressor gene as well as telomerase up‐regulation) genetic alterations involved in the process of skin carcinogenesis in chronological order. © 1995 Wiley

ISSN:1065-7541    

DOI:10.1002/roi.2970030606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe two‐stage model of cellular senescence, M1 (mortality stage 1) and M2 (mortality stage 2), represents independent mechanisms limiting the proliferative capacity of normal somatic cells. The cellular proteins p53 and either pRB or an RB‐like activity appear to be important in the inhibition of cell proliferation that occurs when the M1 mechanism is activated. Because telomeres (the ends of chromosomes) shorten progressively with each cell division in normal somatic cells, it has been proposed that telomere attrition is the molecular measure (clock) of the proliferative potential remaining in cells. However, the M1 mechanism is activated when there are several kilobases of telomeric repeats left; thus, presently, it is not understood how or if telomere shortening controls the onset of the M1 mechanism. In the presence of viral oncogenes or somatic mutations that block cellular senescence, cells divide beyond M1 (extension of life span), and telomere erosion continues. This process persists until a second independent mechanism, M2, is activated, again resulting in inhibition of cell proliferation. The M2 mechanism may result from terminal telomere shortening, when there are so few telomeric repeats remaining that cells either stop dividing or die. In tumor‐derived cell lines, telomeres do not continue to shorten and are maintained by the ribonucleoprotein enzyme telomerase. In almost all normal human somatic cells, telomerase activity is repressed. A hypothesis that is gaining momentum is that a rare cell escapes M2 by inactivating the pathway repressing telomerase. The reactivation of telomerase may be a necessary event for the sustained growth of most human tumors. © 1995 Wiley‐L

ISSN:1065-7541    

DOI:10.1002/roi.2970030607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractTelomeric DNA safeguards chromosomes from genetic damage and rearrangement. Normal somatic cells lose telomeric DNA with each division and during normal human aging. Immortal cancer cells typically express the enzyme telomerase, a ribonucleoprotein polymerase that adds new telomere repeats onto the chromosome ends. To study the role of telomerase in cancer cells, the RNA component of human telomerase (hTR) was recently cloned. HeLa cells expressing antisense hTR exhibited reduced telomerase activity, gradual loss of telomeric DNA, and cell death after 23–26 doublings. These results demonstrate that telomerase is a critical enzyme for the continued proliferation of metastatic tumor cells. Whereas telomere loss occurs in both normal and precancerous cells, telomere shortening with age can lead to genetic damage, which may underlie the age‐related increases in cancer rates. © 1995 Wiley‐Lis

ISSN:1065-7541    

DOI:10.1002/roi.2970030608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mutant p53 gene (mp53; codon 273Arg‐His) was introduced into normal human fibroblasts (OUMS‐24 strain), and a G418‐resistant clone, OUMS‐24/P6, was obtained. This clone expressed mp53 and showed an extended life span, but it senesced at the 79th population‐doubling level (PDL). When these cells were subjected to eight intermittent treatments with 2 Gy of x‐rays, they were immortalized, whereas normal fibroblasts (OUMS‐24) into which mp53 had not been introduced were not immortalized by the same x‐ray treatment. These results indicate that the introduction of mp53 alone is not sufficient for immortalization of human cells and that mutations of the remaining wild‐type p53 or other genes are also necessary. © 19

ISSN:1065-7541    

DOI:10.1002/roi.2970030609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractSpontaneous immortalization of fibroblasts containing an inherited mutation of one p53 allele was associated with loss of the wild‐type p53 allele and loss of p16INK4gene expression, but this combination of genetic events was insufficient for immortalization. Loss of p16INK4expression appears to be an alternative to loss of functional retinoblastoma gene product. In all cell lines studied, immortalization was associated either with stabilization of telomere length in the presence of telomerase activity or with the acquisition of long and heterogeneous telomeres in the absence of detectable telomerase. The role of other genes, such as human stanniocalcin, in the immortalization process is under investigation. © 1995 Wiley‐Liss,

ISSN:1065-7541    

DOI:10.1002/roi.2970030610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractLoss of adhesion leads to cell cycle arrest at the G1/S boundary in normal, adhesion‐dependent, mesenchymal cells. This arrest is accompanied by the inability to produce cyclin A. Using deletional and mutational analysis of the cyclin A promoter, we have identified a CCAAT element that mediates the adhesion‐dependent transcriptional activation of cyclin A. Specific binding of a novel 40/115 kDa heteromeric protein complex, which we have named CBP/cycA, to this CCAAT element was detectable only in cycling cells, not in cells arrested in G0or at the anchorage checkpoint at the G1/S boundary. However, during the G0and G1phases of the cell cycle, CBP/cycA appeared to be present but sequestered by a retinoblastoma (Rb) family member. Activity of Rb family members is generally thought to be controlled by the cyclin D‐cdk4/cdk6 and cyclin E‐cdk2 kinases. We have found that cyclin E‐cdk2 complexes from cells G1‐arrested by adhesion deprivation, though present at normal levels, are catalytically inactive. These results suggest that control of cell cycle progression by adhesion is mediated by a pathway involving cyclin E‐cdk2, Rb, and CBP/cycA, ultimately controlling transcriptional activation of cyclin A at the G1/S boundary. © 1995 W

ISSN:1065-7541    

DOI:10.1002/roi.2970030611

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY