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October, 2006
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Receptors, Growth Factor: Cell surface receptors that bind growth or trophic factors with high affinity, triggering intracellular responses which influence the growth, differentiation, or survival of cells.

Enzyme-linked Receptors

JoVE 10723

Enzyme-linked receptors are proteins which act as both receptor and enzyme, activating multiple intracellular signals. This is a large group of receptors that include the receptor tyrosine kinase (RTK) family. Many growth factors and hormones bind to and activate the RTKs.

RTKs are also called neurotrophin (NT) receptors because they bind nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), NT-3, NT-4/5, NT-6, and NT-7. The growth factors typically bind to an RTK subfamily of tropomyosin-related kinase receptors (Trk): Trk A, Trk B, and Trk C. Trk A is specific for NGF, NT-6, and NT-7. Trk B binds BDNF and NT-4/5, while Trk C is specific for NT-3. NT-3 can also bind with low affinity to Trk A and TrkB. The Trk receptors have a single transmembrane domain, with a growth factor binding site on the extracellular portion and an enzyme activation site intracellularly. Trk receptors can be monomeric or dimerized, where two Trk receptors are bound together. To activate the receptor, a single growth factor molecule either binds two monomeric receptors, causing them to dimerize, or it binds both sites on a pre-dimerized receptor. Once the receptors are bound, the tyrosines phosphorylate by pulling phosphates from ATP and donating them to each other, a process called “autophosphorylation.” This opens docking sites along the i

 Core: Biology

Endocrine Signaling

JoVE 10719

Endocrine cells produce hormones to communicate with remote target cells found in other organs. The hormone reaches these distant areas using the circulatory system. This exposes the whole organism to the hormone but only those cells expressing hormone receptors or target cells are affected. Thus, endocrine signaling induces slow responses from its target cells but these effects also last longer. There are two types of endocrine receptors: cell surface receptors and intracellular receptors. Cell surface receptors work similarly to other membrane bound receptors. Hormones, the ligand, bind to a hormone specific G-protein coupled receptor. This initiates conformational changes in the receptor, releasing a subunit of the G-protein. The protein activates second messengers which internalize the message by triggering signaling cascades and transcription factors. Many hormones work through cell surface receptors, including epinephrine, norepinephrine, insulin, prostaglandins, prolactin, and growth hormones. Steroid hormones, like testosterone, estrogen, and progesterone, transmit signals using intracellular receptors. These hormones are small hydrophobic molecules so they move directly past the outer cell membrane. Once inside, and if that cell is a target cell, the hormone binds to its receptor. Binding creates a conformational change in the receptor

 Core: Biology

Autocrine Signaling

JoVE 10973

Secreted signals can act on a variety of target cells. In some cases, the cell that secretes a signal also detects and responds to the signaling molecule it produces; this is called Autocrine Signaling.

Under normal physiological conditions, autocrine signaling is important for homeostasis. This process is well characterized in the macrophages of the immune system. Macrophages secrete a variety of signals including the cytokine Interleukin-1, IL-1. The secreting macrophages also possess membrane receptors for IL-1 that, when bound, can activate an intracellular signaling cascade. The resulting intracellular signals trigger the secretion of additional cytokines including more IL-1 from the target cell. Though IL-1 secreted by these macrophages can also bind to receptors on other cells and cell types, binding to the signaling cell is important in the regulation of signal production. Autocrine signaling is also a major mechanism of cancer cell proliferation. Cancerous cells secrete a variety of growth signals to themselves, through autocrine signaling, and to nearby tissues. For example, progesterone appears to act in an autocrine manner in breast cancer, whereby progesterone binds to progesterone receptors on the signaling cell, stimulating the action of growth-promoting genes. Autocrine signaling can also play a role in the development of skin cancer by stim

 Core: Biology

Physiology of the Circulatory System- Concept

JoVE 10625


Conditions in the external environment of an organism can change rapidly and drastically. To survive, organisms must maintain a fairly constant internal environment, which involves continuous regulation of temperature, pH, and other factors. This balanced state is known as homeostasis, which describes the processes by which organisms maintain their optimal internal…

 Lab Bio

Bacterial Signaling

JoVE 10713

At times, a group of bacteria behaves like a community. To achieve this, they engage in quorum sensing, the perception of higher cell density that results in a shift in gene expression. Quorum sensing involves both extracellular and intracellular signaling. The signaling cascade starts with a molecule called an autoinducer (AI). Individual bacteria produce AIs that move out of the bacterial cell membrane into the extracellular space. AIs can move passively along a concentration gradient out of the cell, or be actively transported across the bacterial membrane. When cell density in the bacterial populations is low, the AIs diffuse away from the bacteria, keeping the environmental concentration of AIs low. As bacteria reproduce and continue to excrete AIs, the concentration of AIs increases, eventually reaching a threshold concentration. This threshold permits AIs to bind membrane receptors on the bacteria, triggering changes in gene expression across the whole bacterial community. Many bacteria are broadly classified as gram positive or gram negative. These terms refer to the color that the bacteria take on when treated with a series of staining solutions which were developed by Hans Christian Joachim Gram over a century ago. If bacteria pick up a purple color, they are gram-positive; if they look red, they are gram-negative. These stain colors are pic

 Core: Biology

An Introduction to Developmental Neurobiology

JoVE 5207

Developmental neuroscience is a field that explores how the nervous system is formed, from early embryonic stages through adulthood. Although it is known that neural progenitor cells follow predictable stages of proliferation, differentiation, migration, and maturation, the mechanisms controlling the progression through each stage are incompletely understood. Studying…


Real-time Live-cell Flow Cytometry to Investigate Calcium Influx, Pore Formation, and Phagocytosis by P2X7 Receptors in Adult Neural Progenitor Cells

1Griffith Institute for Drug Discovery, Griffith University, 2Australian Institute for Bioengineering and Nanotechnology, University of Queensland, 3Discipline of Anatomy and Histology, School of Medical Science, University of Sydney, 4Bosch Institute, University of Sydney, 5Applied Neurosciences Program, Peter Duncan Neurosciences Research Unit, St. Vincent's Centre for Applied Medical Research, 6School of Medical Sciences, The University of New South Wales (UNSW) Medicine, Sydney, New South Wales, 7School of Environment and Science, Griffith University, Brisbane, Queensland, 8Florey Institute of Neuroscience and Mental Health, University of Melbourne

JoVE 59313

 Developmental Biology
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