Cell cycle deregulation and xeroderma pigmentosum group C cell transformation.
We previously described a genetically unstable human fibroblast cell strain (GM2995), isolated from normal appearing skin of a xeroderma pigmentosum group C patient that repeatedly underwent changes characteristic of the transformed phenotype upon serial cultivation in vitro. In order to gain information concerning genetic changes associated with the transformation of this xeroderma pigmentosum group C cell strain, we examined the expression/function of several cell cycle regulators during its serial cultivation. A mutation in exon 8 of the P53 gene was associated with loss of function of the p53 protein and appeared at about the same time that transformation occurred. Abnormal P53 function was confirmed by the lack of upregulation of p53 as well as activation of its downstream effectors p21Waf1 and HDM2 in high passage cells exposed to either gamma irradiation or ultraviolet C irradiation. Consistent with deregulation in cell cycle control, persistent hyper-phosphorylation of the retinoblastoma protein and lack of a decrease in p34cdc2 were observed in irradiated cells. Furthermore, retinoblastoma protein remained hyperphosphorylated in control high passage confluent cultures that were serum starved for 72 h. Compared with low passage cells, the expression levels of the cyclin-dependent kinase inhibitor p27Kip1 were significantly reduced and the pattern of expression of the von Hippel-Lindau protein was aberrant. These data indicate that the process of cellular transformation of this xeroderma pigmentosum group C cell strain involves the progressive acquisition of mutations and abnormalities in the expression/function of several cell cycle regulators.
Azzam
Edouard I
EI
Laboratory of Radiobiology, Department of Cancer Cell Biology, Harvard School of Public Health, Boston, MA 02115, USA.
Nagasawa
Hatsumi
H
Yu
Yongjia
Y
Li
Chuan-Yuan
CY
Little
John B
JB
D016203:CDC2 Protein Kinase / Q000235:genetics; D002450:Cell Communication; D018797:Cell Cycle Proteins / Q000235:genetics; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D002648:Child; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000235:genetics; D005347:Fibroblasts / Q000166:cytology*; D006801:Humans; D007223:Infant; D008025:Ligases / Q000235:genetics; D008297:Male; D009154:Mutation; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000235:genetics; D051736:Proto-Oncogene Proteins c-mdm2; D016160:Retinoblastoma Protein / Q000235:genetics; D012867:Skin / Q000166:cytology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D014983:Xeroderma Pigmentosum / Q000473:pathology / Q000503:physiopathology*
C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D016203:CDC2 Protein Kinase; D008025:Ligases; C497446:VHL protein, human