Evidence for Homodimerization of the c-Fos Transcription Factor in Live Cells Revealed by Fluorescence Microscopy and Computer Modeling.

Abstract

The c-Fos and c-Jun transcription factors, members of the activator protein 1 (AP-1) complex, form heterodimers and bind to DNA via a basic leucine zipper and regulate the cell cycle, apoptosis, differentiation, etc. Purified c-Jun leucine zipper fragments could also form stable homodimers, whereas c-Fos leucine zipper homodimers were found to be much less stable in earlier in vitro studies. The importance of c-Fos overexpression in tumors and the controversy in the literature concerning c-Fos homodimerization prompted us to investigate Fos homodimerization. Förster resonance energy transfer (FRET) and molecular brightness analysis of fluorescence correlation spectroscopy data from live HeLa cells transfected with fluorescent-protein-tagged c-Fos indicated that c-Fos formed homodimers. We developed a method to determine the absolute concentrations of transfected and endogenous c-Fos and c-Jun, which allowed us to determine dissociation constants of c-Fos homodimers (Kd = 6.7 ± 1.7 μM) and c-Fos-c-Jun heterodimers (on the order of 10 to 100 nM) from FRET titrations. Imaging fluorescence cross-correlation spectroscopy (SPIM-FCCS) and molecular dynamics modeling confirmed that c-Fos homodimers were stably associated and could bind to the chromatin. Our results establish c-Fos homodimers as a novel form of the AP-1 complex that may be an autonomous transcription factor in c-Fos-overexpressing tissues and could contribute to tumor development.

DOI: 10.1128/MCB.00346-15

Cite this paper

@article{Szalki2015EvidenceFH, title={Evidence for Homodimerization of the c-Fos Transcription Factor in Live Cells Revealed by Fluorescence Microscopy and Computer Modeling.}, author={Nikoletta Szal{\'o}ki and Jan Wolfgang Krieger and Istv{\'a}n Kom{\'a}romi and Katalin Toth and Gy{\"{o}rgy V{\'a}mosi}, journal={Molecular and cellular biology}, year={2015}, volume={35 21}, pages={3785-98} }