title: p53 and Egr-1 additively suppress transformed growth in HT1080 cells but Egr-1 counteracts p53-dependent apoptosis.
abstract: The human fibrosarcoma cell line, HT1080, clone H4, was used to determine if the transformation suppressive functions of p53 and Egr-1 have the same underlying mechanism. This cell line expresses only mutant p53 and no detectable Egr-1. H4 clones stably expressing Egr-1 are less transformed in proportion to the level of Egr-1 expressed, acting through the induction of the TGFbeta1 gene. Here, H4 cells and the highest Egr-1 expressing clone were transfected with a vector expressing normal human p53 to derive stable clones expressing p53. The expression of p53 in H4 cells inhibited transformed growth and reduced tumorigenicity. The effect of coexpression of both p53 and Egr-1 was additive, producing cell lines with 30% of normal growth rate and sevenfold reduced tumorigenicity compared with control lines. These results indicated that each factor may act independently by different pathways, although each additively increased the level of p21WAF1 cell cycle inhibitor. However, exposure of the H4-derived cells to UV-C irradiation produced contrasting effects. Cell cycle analyses showed that the presence of p53 was associated with loss of the G1 and S cells to apoptosis after irradiation. In contrast, the expression of Egr-1 increased entry into S/G2 phase of the cell cycle with little apoptosis via a mechanism involving elevated FAK and low caspase activities. Apoptosis was observed only in the cell lines that expressed no Egr-1, especially those expressing wt-p53, and was preceded by high caspase activity. In summary, Egr-1 suppressed transformation and counteracted apoptosis by the coordinated activation of TGFbeta1, FN, p21 and FAK, leading to enhanced cell attachment and reduced caspase activity. In the doubly expressing cell line, the survival effect of Egr-1 was dominant over the apoptotic effect of p53.
authors.affiliation: La Jolla Cancer Research Center, The Burnham Institute, California 92037, USA.
authors.forename: I
authors.initials: I
authors.lastname: de Belle
authors.forename: R P
authors.initials: RP
authors.lastname: Huang
authors.forename: Y
authors.initials: Y
authors.lastname: Fan
authors.forename: C
authors.initials: C
authors.lastname: Liu
authors.forename: D
authors.initials: D
authors.lastname: Mercola
authors.forename: E D
authors.initials: ED
authors.lastname: Adamson
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D015197:Carcinogenicity Tests; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002453:Cell Cycle / Q000528:radiation effects; D002455:Cell Division / Q000528:radiation effects; D002471:Cell Transformation, Neoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D053938:DNA Fragmentation / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051766:Early Growth Response Protein 1; D005354:Fibrosarcoma; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D017874:Immediate-Early Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D009154:Mutation; D011494:Protein Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: C493956:CDKN1A protein, human; D015815:Cell Adhesion Molecules; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases