The cell signaling theory was developed from the analysis of signal transduction from extracellular signals to intracellular effector molecules via G-protein coupled receptors by Rodbell [1] and Gilman [2]. First, an extracellular signal activates a receptor protein or protein complex. Then, this activation promotes the release of second messenger molecules. These molecules might act on transducer proteins, e.g., protein kinases, activate the production or release of third messenger molecules, or directly activate effector molecules.