User:Chingla/Paracrine Signaling

Introduction
Paracrine factors are proteins made by a cell or a group of cells that alter the behavior or differentiation of adjacent cells. They are produced by the inducer in order to effect the responder in the process of cell induction.

Paracrine factors function by binding to a receptor that initiates a series an enzymatic reactions within the cell. These pathways of responses to the paracrine factor often have several endpoints and are called signal induction pathways.

Cell Induction and Competence
A. Cell induction: interaction at close range between two or more cells or tissues of different histories and properties
 * 1. Inducer: Tissues that produces the signal(s) that changes the cellular behavior of the other tissue
 * 2. Responder: Tissue that is being induced
 * Receptor Protein
 * Competence
 * Cells of the responding tissue must have both a receptor protein for the inducing factor and the ability to respond to a specific inductive signal. This ability is called competence

Major Types of Paracrine Signaling
A. Fibroblast Growth Factor (FGF) Family
 * 1. Receptor Tyrosine Kinase (RTK) Pathway
 * 2. JAK-STAT Pathway

B. Hedgehog Family

C. Wnt Family
 * 1. Canonical Pathway: sends messages to the nucleus
 * 2. Noncanonical Pathway: sends messages to the actin and microtubule cytoskeleton

D. TGF-β Superfamily
 * 1. SMAD Pathway

Other Paracrine Factors
A. Epidermal Growth Factors

B. Hepatocyte Growth Factors

C. Neurotrophins

D. Stem Cell Factors

E. Erythopoietin

F. Cytokines

G. Interleukins

Other Types of Signaling
A. Endocrine

B. Juxtacrine

C. Autocrine


 * They differ from endocrine factors, such as hormones. Endocrine factors travel through the blood and exert their effects on cells and tissues far away. However, paracrine factors are secreted into the extracellular space and influence their close neighbors. Another means of cellular interaction is achieved through juxtacrine signaling, in which proteins from the inducing cell interacts with receptor proteins of adjacent responding cells without diffusing from the cell producing it. Another type called autocrine signaling uses the same paracrine factors for induction of its own receptor.