Binding of single-mutant epidermal growth factor (EGF) ligands alters the stability of the EGF receptor dimer and promotes growth signaling.

The epidermal growth factor receptor (EGFR) is a membrane-anchored tyrosine kinase that is able to selectively respond to multiple extracellular stimuli. Previous studies have indicated that the modularity of this system may be caused by ligand-induced differences in the stability of the receptor dimer. However, this hypothesis has not been explored using single-mutant ligands thus far. Herein, we developed a new approach to identify residues responsible for functional divergence by selecting residues in the epidermal growth factor (EGF) ligand that are conserved among orthologs yet divergent between paralogs. Then, we mutated these residues and assessed the mutants' effects on the receptor using a combination of molecular dynamics (MD) and biochemical techniques. Although the EGF mutants had binding affinities for the EGFR comparable with the WT ligand, the EGF mutants showed differential patterns of receptor phosphorylation and cell growth in multiple cell lines. The MD simulations of the EGF mutants indicated that mutations had long-range effects on the receptor dimer interface. This study shows for the first time that a single mutation in the EGF is sufficient to alter the activation of the EGFR signaling pathway at the cellular level. These results also support that biased ligand-receptor signaling in the tyrosine kinase receptor system can lead to differential downstream outcomes and demonstrate a promising new method to study ligand-receptor interactions.

Nuclear matrix metalloproteinases: functions resemble the evolution from the intracellular to the extracellular compartment.

Matrix metalloproteinase (MMP) is defined as an endopeptidase in the extracellular matrix (ECM), which plays essential roles in physiological processes such as organogenesis, wound healing, angiogenesis, apoptosis and motility. MMPs are produced and assembled in the cytoplasm as proenzymes with a cytoplasmic domain and require extracellular activation. MMPs can degrade receptors, extracellular matrix proteins, PARPs and release apoptotic substances. MMPs have been found in the cytosol, organelles and extracellular compartments and recently many types of MMPs have been found in the nucleus. However, the mechanisms and roles of MMPs inside the cell nucleus are still poorly understood. Here we summarized the nuclear localization mechanisms of MMPs and their functions in the nucleus such as apoptosis, tissue remodeling upon injury and cancer progression. Most importantly, we found that nuclear MMPs have evolved to translocate to membrane and target ECM possibly through evolution of nuclear localization signal (NLS), natural selection and anti-apoptotic survival. Thus, the knowledge about the evolution and regulation of nuclear MMPs appears to be essential in understanding a variety of cellular processes along with the development of MMP-targeted therapeutic drugs against the progression of certain diseases.