CH 03 Cell Signaling.indd

This mechanism, called cell signaling, allows cell-cell communication and is necessary for the functional regulation and integration of multicellular organisms. Our discussion in this chapter not only provides the basis for understanding normal cell function but serves also as an introduction to the role of abnormal cell signaling in human disease. Signaling molecules are either secreted or expressed at the cell surface of one cell. Signaling molecules can bind to receptors on the surface of another cell or the same cell. Different types of signaling molecules transmit information in multicellular organisms, and their mechanisms of action on their target cells can be diverse. Some signaling molecules can act on the cell surface after binding to cell surface receptors; others can cross the plasma membrane and bind to intracellular receptors in the cytoplasm and nucleus. When a signaling molecule binds to its receptor, it initiates a cascade of intracellular reactions to regulate critical functions such as cell proliferation, differentiation, movement, metabolism, and behavior. Because of their critical role in the control of normal cell growth and differentiation, signaling molecules have acquired signifi cant relevance in cancer research.