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Nuclear factor I interferes with transformation induced by nuclear oncogenes
E R Schuur1, U Kruse, J S Iacovoni
1Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California 92037, USA.
Abstract:
The four nuclear factor I genes (NFI-A, NFI-B, NFI-C, and NFI-X) give rise to multiple isoforms by alternative splicing in many tissues. These NFI proteins cooperate with AP-1, Myc, and other transcription factors in regulating transcription of numerous cellular and viral genes. We have investigated the growth-regulatory potential of NFI by overexpressing cDNAs from chicken NFI genes -A, -B, -C, and -X in chicken embryo fibroblasts (CEF). None of the NFI cDNAs induced oncogenic transformation of CEF. However, overexpression of each of the NFI proteins caused similar morphological alteration of the cells, inducing them to become flattened and polygonal and to show increased adherence. The growth properties of these cells were similar to normal CEF. When these morphologically altered CEF were challenged by superinfection with oncogenic retroviruses, they were resistant to transformation by the nuclear oncogenes jun, fos, junD, myc, and qin but were readily transformed by cytoplasmic oncogenes src, mil/raf, ras, and fps. The NFI-A1 protein was able to alter transactivation by the cellular and viral Jun proteins in a promoter-dependent manner. The changes in cell morphology and reduced susceptibility to nuclear oncogenes were not seen with a carboxy-terminal truncation in the transactivation domain of NFI, suggesting that this region of the protein is essential for the observed effects. The dichotomy between the activities of nuclear and of cytoplasmic oncogenes in this system is discussed.
Insights
Overexpressing nuclear factor I (NFI) proteins in chicken cells altered their shape and adherence. These cells resisted transformation by nuclear oncogenes but remained susceptible to cytoplasmic oncogenes.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Nuclear Factor I (NFI) proteins, encoded by four genes (NFI-A, NFI-B, NFI-C, NFI-X), produce multiple isoforms via alternative splicing.
- NFI proteins interact with transcription factors like AP-1 and Myc to regulate gene expression.
Purpose of the Study:
- To investigate the growth-regulatory potential of NFI proteins.
- To determine the effects of NFI overexpression on chicken embryo fibroblasts (CEF) and their susceptibility to oncogenic transformation.
Main Methods:
- Overexpression of chicken NFI cDNAs (-A, -B, -C, -X) in CEF.
- Assessment of cell morphology, adherence, and growth properties.
- Challenging morphologically altered CEF with oncogenic retroviruses encoding nuclear and cytoplasmic oncogenes.
- Analysis of NFI-A1 protein's effect on Jun protein transactivation.
Main Results:
- NFI overexpression did not induce oncogenic transformation but caused significant morphological changes (flattening, increased adherence) in CEF.
- Morphologically altered CEF exhibited resistance to transformation by nuclear oncogenes (jun, fos, myc) but remained susceptible to cytoplasmic oncogenes (src, ras).
- NFI-A1 protein modulated Jun protein transactivation in a promoter-dependent manner, with the transactivation domain being crucial for observed effects.
Conclusions:
- The transactivation domain of NFI proteins is essential for inducing morphological changes and altering oncogene susceptibility.
- NFI proteins play a role in regulating cellular responses to different classes of oncogenes, highlighting a dichotomy between nuclear and cytoplasmic oncogene activities.