Cell Signaling Pathway: Definition, MOA and Functions

It is universally known that cells are the building blocks our body, just like the bricks making a wall. However, cells can actually do more. Serving as chemical signaling molecules, they keep a close watch for what's going on around them. Once there is any change in their neighbors and environment, these cells will receive and process signals immediately, leading to a quick response. More often than not, many signals are received simultaneously, but cells are able to integrate all these information into a unified action plan by sending out messages to other cells near or far.

What is cell signaling pathway?
Cell signaling pathway refers to a group of molecules in a cell, which, in together, control certain cell functions, such as cell division. As a matter of fact, activities like cell growth, proliferation, differentiation and aging are all controlled by a complex network of signaling pathways.

After the first molecule in a pathway receives a signal, it activates another molecule. Such process is repeated until the last molecule is activated and the anticipated cell function is realized. On the other hand, abnormal activation of signaling pathways can lead to cancer, which might help explain how cancer occurs. Currently, drugs are being developed to block these pathways so as to help block cancer cell growth and kill cancer cells.

What is the MOA of cell signaling pathway？
The mechanism of action of these molecules is as follows:

A basic fact about cell signaling pathway is cells typically receive signals in chemical form via various signaling molecules. When a signaling molecule binds with an appropriate receptor on a cell surface, chain of events will be triggered and the amplified signal will be carried to the cell interior. Another fact you may not know is that cells can also send signaling molecules to other cells. Some of these chemical signals only need to travel a short distance to reach their targets, for example, neurotransmitters, but others may go much farther before their travel purpose is carried out.

Different signaling pathway has different effects on the growth, proliferation, differentiation and aging of cells. Over the past decade, many signaling pathways have been unveiled by scientists. Next, we’ll elaborate three of them: JNK signaling pathway, RAS signaling pathway as well as mTOR signaling pathway.

JNK Signaling Pathway
The c-Jun N-terminal kinases (JNK) are a family of serine/threonine protein kinases in the mitogen-activated protein kinase (MAPK) regime. As one of the major signaling cassettes of the MAPK signaling pathway, the JNK signaling pathway plays an important role in the control of a number of cellular processes, including proliferation, embryonic development and apoptosis.

According to clinical data, JNK are clearly involved in ischemia-induced cell death and reperfusion injury in several different tissues and the control of insulin sensitivity in metabolic regulation. Other literature also suggests a link between JNK signaling to diseases like type I diabetes, osteosarcoma, ataxia and immune system dysfunction. Also, JNKs might play a role in chronic inflammation. In addition, researches have proved the importance of JNKs in neurodegenerative diseases. There are findings from in vitro and in vivo studies which reported likely association between alterations of JNK pathways with pathogenesis and neuronal death in AD. In recent years, a great number of JNK inhibitors are identified and further developed as promising therapeutics targeting a wide range of diseases.

RAS Signaling Pathway
RAS signaling pathway, together with RAS proteins, plays a critical role in normal cellular proliferation. In circumstances where these signaling pathways are constitutively activated or over expressed, cancer often occurs. Composed of more than 150 members, the RAS superfamily is huge and all members share similar structures and biochemical properties, but at the same time, these proteins play multiple and divergent roles while serving as versatile and key regulators of virtually all fundamental cellular processes. As mentioned earlier, dysfunction of them might possibly result in the pathogenesis of serious human diseases, developmental syndromes and cancer included.

mTOR Signaling Pathway
The mammalian target of rapamycin (mTOR) is an atypical serine/threonine protein kinase, which belongs to the phosphatidylinositol kinase-related kinase (PIKK) family. mTOR can interact with several proteins to form two distinct complexes- mTOR complex 1 (mTORC1) and 2 (mTORC2) respectively. Much attention are drawn by mTOR considering its essential role in cell growth control and involvement in human tumorigenesis. mTOR deregulation has been detected in human diseases like cancer, obesity, type 2 diabetes, and neurodegeneration, so it might be another clinical implication to target the mTOR signaling pathway and new treatment approaches are expected to be found.