Biology:Cellular communication

Cellular communication is an umbrella term used in biology and more in depth in biophysics, biochemistry and biosemiotics to identify different types of communication methods between living cellulites. Some of the methods include cell signaling among others. This process allows millions of cells to communicate and work together to perform important bodily processes that are necessary for survival. Both multicellular and unicellular organisms heavily rely on cell-cell communication.

Intercellular communication

Intercellular communication refers to the communication between cells. Membrane vesicle trafficking has an important role in intercellular communications in humans and animals, e.g., in synaptic transmission, hormone secretion via vesicular exocytosis. Inter-species and interkingdom signaling is the latest field of research for microbe-microbe and microbe-animal/plant interactions for variety of purposes at the host-pathogen interface. Membrane receptors function by binding the signal molecule (ligand) and causing the production of a second signal (also known as a second messenger) that then causes a cellular response. These type of receptors transmit information from the extracellular environment to the inside of the cell by changing shape or by joining with another protein once a specific ligand binds to it. Examples of membrane receptors include G Protein-Coupled Receptors and Receptor Tyrosine Kinases.

Intracellular receptors are found inside the cell, either in the cytopolasm or in the nucleus of the target cell (the cell receiving the signal). Chemical messengers that are hydrophobic or very small (steroid hormones for example) can pass through the plasma membrane without assistance and bind these intracellular receptors. Once bound and activated by the signal molecule, the activated receptor can initiate a cellular response, such as a change in gene expression.

Transduction

Since signaling systems need to be responsive to small concentrations of chemical signals and act quickly, cells often use a multi-step pathway that transmits the signal quickly, while amplifying the signal to numerous molecules at each step.

Steps in the signal transduction pathway often involve the addition or removal of phosphate groups which results in the activation of proteins. Enzymes that transfer phosphate groups from ATP to a protein are called protein kinases. Many of the relay molecules in a signal transduction pathway are protein kinases and often act on other protein kinases in the pathway. Often this creates a phosphorylation cascade, where one enzyme phosphorylates another, which then phosphorylates another protein, causing a chain reaction.

Also important to the phosphorylation cascade are a group of proteins known as protein phosphatases. Protein phosphatases are enzymes that can rapidly remove phosphate groups from proteins (dephosphorylation) and thus inactivate protein kinases. Protein phosphatases are the “off switch” in the signal transduction pathway. Turning the signal transduction pathway off when the signal is no longer present is important to ensure that the cellular response is regulated appropriately. Dephosphorylation also makes protein kinases available for reuse and enables the cell to respond again when another signal is received.

Kinases are not the only tools used by cells in signal transduction. Small, nonprotein, water-soluble molecules or ions called second messengers (the ligand that binds the receptor is the first messenger) can also relay signals received by receptors on the cell surface to target molecules in the cytoplasm or the nucleus. Examples of second messengers include cyclic AMP (cAMP) and calcium ions.

  Membrane receptors function by binding the signal molecule (ligand) and causing the production of a second signal (also known as a second messenger) that then causes a cellular response. These type of receptors transmit information from the extracellular environment to the inside of the cell by changing shape or by joining with another protein once a specific ligand binds to it. Examples of membrane receptors include G Protein-Coupled Receptors and Receptor Tyrosine Kinases.

Intracellular receptors are found inside the cell, either in the cytopolasm or in the nucleus of the target cell (the cell receiving the signal). Chemical messengers that are hydrophobic or very small (steroid hormones for example) can pass through the plasma membrane without assistance and bind these intracellular receptors. Once bound and activated by the signal molecule, the activated receptor can initiate a cellular response, such as a change in gene expression.

Transduction

Since signaling systems need to be responsive to small concentrations of chemical signals and act quickly, cells often use a multi-step pathway that transmits the signal quickly, while amplifying the signal to numerous molecules at each step.

Steps in the signal transduction pathway often involve the addition or removal of phosphate groups which results in the activation of proteins. Enzymes that transfer phosphate groups from ATP to a protein are called protein kinases. Many of the relay molecules in a signal transduction pathway are protein kinases and often act on other protein kinases in the pathway. Often this creates a phosphorylation cascade, where one enzyme phosphorylates another, which then phosphorylates another protein, causing a chain reaction.

Also important to the phosphorylation cascade are a group of proteins known as protein phosphatases. Protein phosphatases are enzymes that can rapidly remove phosphate groups from proteins (dephosphorylation) and thus inactivate protein kinases. Protein phosphatases are the “off switch” in the signal transduction pathway. Turning the signal transduction pathway off when the signal is no longer present is important to ensure that the cellular response is regulated appropriately. Dephosphorylation also makes protein kinases available for reuse and enables the cell to respond again when another signal is received.

Kinases are not the only tools used by cells in signal transduction. Small, nonprotein, water-soluble molecules or ions called second messengers (the ligand that binds the receptor is the first messenger) can also relay signals received by receptors on the cell surface to target molecules in the cytoplasm or the nucleus. Examples of second messengers include cyclic AMP (cAMP) and calcium ions.

Membrane receptors function by binding the signal molecule (ligand) and causing the production of a second signal (also known as a second messenger) that then causes a cellular response. These type of receptors transmit information from the extracellular environment to the inside of the cell by changing shape or by joining with another protein once a specific ligand binds to it. Examples of membrane receptors include G Protein-Coupled Receptors and Receptor Tyrosine Kinases.

Intracellular receptors are found inside the cell, either in the cytopolasm or in the nucleus of the target cell (the cell receiving the signal). Chemical messengers that are hydrophobic or very small (steroid hormones for example) can pass through the plasma membrane without assistance and bind these intracellular receptors. Once bound and activated by the signal molecule, the activated receptor can initiate a cellular response, such as a change in gene expression.

Transduction

Since signaling systems need to be responsive to small concentrations of chemical signals and act quickly, cells often use a multi-step pathway that transmits the signal quickly, while amplifying the signal to numerous molecules at each step.

Steps in the signal transduction pathway often involve the addition or removal of phosphate groups which results in the activation of proteins. Enzymes that transfer phosphate groups from ATP to a protein are called protein kinases. Many of the relay molecules in a signal transduction pathway are protein kinases and often act on other protein kinases in the pathway. Often this creates a phosphorylation cascade, where one enzyme phosphorylates another, which then phosphorylates another protein, causing a chain reaction.

Also important to the phosphorylation cascade are a group of proteins known as protein phosphatases. Protein phosphatases are enzymes that can rapidly remove phosphate groups from proteins (dephosphorylation) and thus inactivate protein kinases. Protein phosphatases are the “off switch” in the signal transduction pathway. Turning the signal transduction pathway off when the signal is no longer present is important to ensure that the cellular response is regulated appropriately. Dephosphorylation also makes protein kinases available for reuse and enables the cell to respond again when another signal is received.

Kinases are not the only tools used by cells in signal transduction. Small, nonprotein, water-soluble molecules or ions called second messengers (the ligand that binds the receptor is the first messenger) can also relay signals received by receptors on the cell surface to target molecules in the cytoplasm or the nucleus. Examples of second messengers include cyclic AMP (cAMP) and calcium ions.

Responseslide_49

Cell signaling ultimately leads to the regulation of one or more cellular activities. Regulation of gene expression (turning transcription of specific genes on or off) is a common outcome of cell signaling. A signaling pathway may also regulate the activity of a protein, for example opening or closing an ion channel in the plasma membrane or promoting a change in cell metabolism such as catalyzing the breakdown of glycogen. Signaling pathways can also lead to important cellular events such as cell division or apoptosis (programmed cell death). Responseslide_49

Cell signaling ultimately leads to the regulation of one or more cellular activities. Regulation of gene expression (turning transcription of specific genes on or off) is a common outcome of cell signaling. A signaling pathway may also regulate the activity of a protein, for example opening or closing an ion channel in the plasma membrane or promoting a change in cell metabolism such as catalyzing the breakdown of glycogen. Signaling pathways can also lead to important cellular events such as cell division or apoptosis (programmed cell death). Response

Cell signaling ultimately leads to the regulation of one or more cellular activities. Regulation of gene expression (turning transcription of specific genes on or off) is a common outcome of cell signaling. A signaling pathway may also regulate the activity of a protein, for example opening or closing an ion channel in the plasma membrane or promoting a change in cell metabolism such as catalyzing the breakdown of glycogen. Signaling pathways can also lead to important cellular events such as cell division or apoptosis (programmed cell death).

Three stages of cell communication

Reception

A G Protein-coupled receptor within the plasma membrane.

Reception occurs when the target cell (any cell with a receptor protein specific to the signal molecule) detects a signal, usually in the form of a small, water-soluble molecule, via binding to a receptor protein. Reception is the target cell's detection of a signal via binding of a signaling molecule, or ligand. Receptor proteins span the cell’s plasma membrane and provide specific sites for water-soluble signaling molecules to bind to. These trans-membrane receptors are able to transmit information from outside the cell to the inside because they change conformation when a specific ligand binds to it. By looking at three major types of receptors, (G protein coupled receptors, receptor tyrosine kinases, and ion channel receptors) scientists are able to see how trans-membrane receptors contribute to the complexity of cells and the work that these cells do. Other well-known receptor includes Ser Thr Kinase Receptor (known as TGFB signaling), TNFR and adhesion and mechanotransduction receptor. Cell surface receptors play an essential role in the biological systems of single- and multi-cellular organisms and malfunction or damage to these proteins is associated with cancer, heart disease, and asthma.

Transduction

When binding to the signaling molecule, the receptor protein changes in some way and starts the process of transduction. A specific cellular response is the result of the newly converted signal. Usually, transduction requires a series of changes in a sequence of different molecules (called a signal transduction pathway) but sometimes can occur in a single step. The molecules that compose these pathways are known as relay molecules. The multistep process of the transduction stage is often composed of the activation of proteins by addition or removal of phosphate groups or even the release of other small molecules or ions that can act as messengers. The amplifying of a signal is one of the benefits to this multiple step sequence. Other benefits include more opportunities for regulation than simpler systems do and the fine- tuning of the response, in both unicellular and multicellular organism.

Response

A specific cellular response is the result of the transduced signal in the final stage of cell signaling. This response can essentially be any cellular activity that is present in a body. It can spur the rearrangement of the cytoskeleton, or even as catalysis by an enzyme. These three steps of cell signaling all ensure that the right cells are behaving as told, at the right time, and in synchronization with other cells and their own functions within the organism. At the end, the end of a signal pathway leads to the regulation of a cellular activity. This response can take place in the nucleus or in the cytoplasm of the cell. A majority of signaling pathways control protein synthesis by turning certain genes on and off in the nucleus.

Local and long distance signaling

Local

Communicating through direct contact is one form of local signaling for eukaryotic cells. Plant and animal cells possess junctions that connect the cytoplasm of cells adjacent to one another. These connections allow for signaling substances that were dissolved in the cytosol to easily pass between the cells that are connected. Animal cells contain gap junctions and can communicate through these junctions in a process called cell–cell recognition. Plant cells are connected through plasmodesmata. Embryonic development and the immune response rely heavily on this type of local signaling. In other types of local signaling, the signaling cell secretes messenger molecules that only travel short distances. These local regulators influence cells in the vicinity and can stimulate nearby target cells to perform an action. A number of cells can receive messages and respond to another molecule within their vicinity at the same time. This process of local signaling within animal cells is known as paracrine signaling.

Long distance

Hormones are used by both plant and animal cells for long-distance signaling. In animal cells, specialized cells release these hormones and send them through the circulatory system to other parts of the body. They then reach target cells, which can recognize and respond to the hormones and produce a result. This is also known as endocrine signaling. Plant growth regulators, or plant hormones, move through cells or by diffusing through the air as a gas to reach their targets.

Cell signaling and impacts

There are three different types of basic cell communication: surface membrane to surface membrane; exterior, which is between receptors on the cell; and direct communication, which means signals pass inside the cell itself. The junctions of these cells are important because they are the means by which cells communicate with one another. Epithelial cells especially rely on these junctions because when one is injured, these junctions provide the means and communication to seal these injuries. These junctions are especially present in the organs of most species. However, it is also through cell signaling that tumors and cancer can also develop. Stem cells and tumor-causing cells, however, do not have gap junctions so they cannot be affected in the way that one would control a typical epithelial cell. Upstream cells signaling pathways control the proteins and genes that are expressed, which can both create a means for cancer to develop without stopping or a means for treatment for these diseases by targeting these specific upstream signaling pathways. Much of cell communication happens when ligands bind to the receptors of the cell membrane and control the actions of the cell through this binding. Genes can be suppressed, they can be over expressed, or they can be partially inhibited through cell signaling transduction pathways. Some research has found that when gap junction genes were transfected into tumor cells that did not have the gap junction genes, the tumor cells became stable and points to the ability of gap junction genes to inhibit tumors. This stability leads researchers to believe that gap junctions will be a part of cancer treatment in the future.

Communication in cancer

cells will often communicate via gap junctions, which are proteins known as connexins. These connexins have been shown to suppress cancer cells, but this suppression is not the only thing that connexins facilitate. Connexins can also promote tumor progression; therefore, this makes connexins only conditional tumor suppressors.^[5] However, this relationship that connects cells makes the spreading of drugs through a system much more effective as small molecules can pass through gap junctions and spread the drug much more quickly and efficiently. The idea that increasing cell communication, or more specifically, connexins, to suppress tumors has been a long, ongoing debate that is supported by the fact that so many types of cancer, including liver cancer, lack the cell communication that characterizes normal cells.

See also

• Signal Transduction
• Membrane vesicle trafficking
• Communication
• Biochemistry
• Biophysics
• Translation
• Calcium buffering
• Host-pathogen interface

Further reading

• "Analysis of connexin expression during mouse Schwann cell development identifies connexin29 as a novel marker for the transition of neural crest to precursor cells". Glia 55 (1): 93–103. January 2007. doi:10.1002/glia.20427. PMID 17024657. 
• "A rate equation approach to elucidate the kinetics and robustness of the TGF-beta pathway". Biophysical Journal 91 (12): 4368–80. December 2006. doi:10.1529/biophysj.105.080408. PMID 17012329. Bibcode: 2006BpJ....91.4368M. 
• "Man1, an inner nuclear membrane protein, regulates vascular remodeling by modulating transforming growth factor beta signaling". Development (Cambridge, England) 133 (19): 3919–28. October 2006. doi:10.1242/dev.02538. PMID 16943282. 
• "Protein expression changes in the nucleus accumbens and amygdala of inbred alcohol-preferring rats given either continuous or scheduled access to ethanol". Alcohol (Fayetteville, N.Y.) 40 (1): 3–17. August 2006. doi:10.1016/j.alcohol.2006.10.001. PMID 17157716. 
• Handbook of Cell Signaling. Academic Press. 2009. ISBN 978-0-12-374145-5. 
• Cell communication. New York: Wiley. 1974. ISBN 0-471-18135-8. 
• "Cell communication in health and disease". Readings from Scientific American Magazine. WH Freeman. 1991. ISBN 0-7167-2224-0. 
• Cell communication in nervous and immune system (1st ed.). New York: Springer. 2006. ISBN 3-540-36828-0. 
• "Cell Adhesion & Communication". Cell Communication & Adhesion (Yverdon, Switzerland ; New York: Harwood Academic Publishers) 7 (6). May 1993. ISSN 1061-5385. 
• Cell Communication & Adhesion. 8. Basingstoke, Hants, UK: Harwood Academic Publishers. 2001. 
• Cell communication : understanding how information is stored and used in cells (1st ed.). New York: Rosen Pub. Group. 2005. ISBN 1-4042-0319-2. 
• Intercellular communication. Manchester: Manchester University Press. 1991. ISBN 0-7190-3269-5. 
• Intercellular communication. New York: Plenum Press. 1977. ISBN 0-306-30958-0. 
• "Intercellular communication in leucocyte function". proceedings of the 15th International Leucocyte Culture Conference, Asilomar and Pacific Grove, Calif. (15th ed.). Chichester ; New York: Wiley. December 1982. ISBN 0-471-90161-X. 
• Intercellular communication in plants. Oxford: Blackwell. 2005. ISBN 1-4051-2068-1. 
• Intercellular communication in plants : studies on plasmodesmata. Berlin ; New York: Springer-Verlag. 1976. ISBN 0-387-07570-4. 
• Intercellular communication through gap junctions. Amsterdam ; New York: Elsevier. 1995. ISBN 0-444-81929-0.