The most common second messenger is Ca2+, which is stored in the type of
endoplasmic reticulum (ER). Some of the other important second messengers include
IP3 and diacyl glycerol (produced by the hydrolysis of phosphoinositides), arachidonic
acid (produced by the hydrolysis of phospholipids that have arachidonoyl on carbon
number 2 of the glycerol backbone), ceramide, eicosanoids, lysophosphatidic acid, NO
(nitric oxide), cAMP and cGMP. The most common type of receptor is the G proteincoupled
receptor (GPCR). Protein kinases can catalyze the addition of a phosphate to
another protein or even to themselves and affect signal transduction. Another class of G
proteins is called the small GTPases. Nuclear receptors (NRs) play key roles in growth,
development and homeostasis. Lipohilic natural hormones diffuse past the cell
membrane and bind to receptors located in either the cytosol (type I NR) or the nucleus
(type II NR). The IP3 receptor, or IP3R is a membrane-bound complex of glycoproteins.
It is a Ca2+ channel that is activated by IP3, which is a secondary intra-cellular
messenger. Inter-and intracellular communication can be considered as a network that
contains many items (nodes) that have about one to thousands of connections. The most
widely connected nodes are called hubs. Probably, the major genetic hub in human and
many other mammalian cells is the gene TP53 which codes for the protein p53. About
50% of all human cancers have one or more mutations in p53 that alter DNA
transcription.
Keywords: Calcium, Ca2+, IP3, diacyl glycerol, arachidonic acid, ceramide,
eicosanoids, lysophosphatidic acid, nitric oxide, cAMP, cGMP, GPCR.
