91. In an experiment, various soluble mediators are added to a cell culture containing epidermal cells to determine which of the mediators might be useful for promoting epidermal cell growth. When epidermal growth factor (EGF) is added, it binds to epidermal cell surface receptors, inducing RAS protein activation, with subsequent transcription factor translocation andDNA transcription activation. This effect in the epidermal cells is most likely to be mediated through which of the following intracellular pathways?
Calcium ion channel
Mitogen-activated protein kinase
Answer: D Mitogen-activated protein kinase
The mitogen-activated protein (MAP) kinase cascade is involved in signaling from activation via cell surface receptors for growth factors. This pathway is particularly important for signaling of epidermal growth factor and fibroblast growth factor.
Ligand binding, such as occurs with acetylcholine at a nerve-muscle junction, alters the conformation of ion channel receptors to allow flow of specific ions such as calcium into the cell, changing the electric potential across the cell membrane.
Cyclic AMP is a “second messenger” that is typically activated via ligand binding to receptors with seven transmembrane segments that associate with GTP-hydrolyzing proteins; chemokine receptors function in this fashion. Cyclin-dependent kinases act within the nucleus.