Biology 107 Cellular Communication October 6, 2003

Cellular Communication Student Objectives:As a result of this lecture and the assigned reading, you should understand the following: 1.A cell communicates and interacts with other cells (cell-cell interactions) and with its extracellular matrix (ECM) (cell-matrix interactions) 2.Extracellular communication factors are of two general types: 1) those that get through the lipid bilayer on their own (e.g., steroid hormones) or 2) those that act on the outside of the membrane (e.g., peptide hormones) and require a receptor and transduction of the signal across the membrane to produce an intracellular response. 3.Extracellular communication factors influence such cellular functions as cell division, metabolism, and gene expression.

Cellular Communication 4.Cell-cell interactions are achieved by direct cell-cell contact, or by indirect associations among cells separated by greater or lesser distances. In addition to communication, direct cell-cell interactions may be adhesive interactions through cell adhesion molecules (CAMs), cadherins, or adhering-types of intercellular junctions. a.Direct cell-cell communication may occur through transmembrane molecular signaling or through intercellular connections - gap (communicating) intercellular junctions (animals) or plasmodesmata (plants). b.Indirect interactions are mediated by soluble factors that diffuse over greater or lesser distances and interact with specific cell membrane-associated receptor molecules.

Cellular Communication 5.Signal transduction may lead to receptor changes that directly affect intracellular events (e.g., altered permeability of an ion channel) or may indirectly affect intracellular events through second messenger systems (e.g., cyclic AMP and diacylglycerol/inositol triphosphate messengers). 6.Second messengers are small molecules that diffuse rapidly and amplify the cellular response by acting to directly or indirectly activate protein kinases, enzymes that attach phosphate groups from ATP to specific target proteins. 7.Protein phosphorylation/dephosphorylation is a common mode of rapid, reversible regulation of protein function. The protein kinases transfer phosphate groups to proteins, while specific protein phosphatases remove phosphate groups.

Cells May Interact and Attach to Their Non-cellular Extracellular Matrix (ECM)

Cells May Interact Directly with Other Cells Through Intercellular Junctions or Through Cell Surface Molecules

Cadherins are Examples of Adhesive Cell Surface Molecules that Link Adjacent Cells Together Attachment

Mating-type signaling in yeast

Cell May Interact Indirectly with Other Cells Through Secreted Signal That Diffuse to the Target

Three Major Components of Signaling are Reception, Transduction, and the Response

Signals Received on the Outside of the Cell May Influence Intracellular Events such as Gene Transcription

Receptors Provide Specificity to Signaling

Receptor Type Determines the Intracellular Response to Ligand Binding

One Consequence of Signal Transduction is Amplification of the Response

Second Messenger Systems Amplify the Initial Signal and Usually Work Through a Protein Kinase

A Common Second Messenger is cAMP cAMP is a nucleotide cAMP activates a protein kinase

DAG and IP 3 are Common Second Messengers

Both cAMP and DAG/IP 3 Pathways Work Through G-Protein Intermediates

Interactions of Different Transduction Pathways Lead to Diversity of Responses