Cellular Signaling

Cellular Signaling

It is the response generated by a cell in the presence of a ligand.

Type of signaling are given below.

A)     Endocrine Signaling

B)     Paracrine

C)     Autocrine

D)     Juxtracrine

E)      Neurocine signaling.

Endocrine Signaling:- In this signaling the signaling molecules is produce by endocrine glands. Which interacts with the receptor present on distantly located target cell. The receptor might be intracellular and extracellular . But they are high efficiency receptor .This is hormones mediated signaling. It is a long- range signaling in which signal molecule is transported by the blood stream.

Paracrine Signaling:- It is a signaling between neighbor cell and adjusting cell  for example  Transmission of action potential across the neuron by the help of neurotransmitter like Acetylcoline  e.g  T-cell activate B-cell or T-cell activate NK cell.

Autocrine Signaling:- This is within the cell signaling. In this type of signaling the ligand produce by the same cell having receptor for the ligand e.g Foreign antigen stimulate the production of T-Lymphocytes. Unregulated autocrine signaling can lead to Cancer development . It induce cell division and regenerate e.g  Liver .

Juxtracrine Signaling:- It is a cellular communication which involves cell to cell contact. Several intracellular and extracellular matrix proteins(ECM) participates in this signaling e.g Delta-Notch pathway in which Delta is ligand and Notch is receptor.

Mode of Ligand interaction is two types

v  Intracellular Receptor (Cytosolic/Nuclear) e.g Thyroxine, Retenoic Acid,  Vit.D3 etc.

v  Extracellular Receptor (Cell surface) e.g GPCR, RTK, Wnt, Hedgehog etc.

Intracellular Receptor:- These receptor are broadly classified into two categories which are given below.

ü Cytosolic Receptor Signaling:-  Which mainly interact with steroid hormones.

Ø  In the absence of estrogen estrogen receptor is conjugated with HSP90 which protect the receptor from degradation.

Ø  Estrogen molecules cross the plasma membrane(PM) by the simple diffusion.

Ø  In the cytosol estrogen displaces HSP90 and interacts with is receptor. And active receptor ligand dimer complex is formed.  

Ø  A signal sequence known as NLS (Nuclear Localize Sequence) present in the cytosol interact with the active dimer and promotes its movement in to the nucleus.

Ø  Active dimer in the nucleus interact with the HRE (Hormones Response Element) of primary responsive genes. HRE is a conserved nucleotide sequence present in the promoter region of primary response genes.

Ø  Zink finger motif present in the receptor promotes the receptor interactions with the HRE of the target gene.

Ø  A co-activator known as HAT is recruited by active dimer on HRE.

Ø  HAT promotes the expression of primary responsive gene.

Ø  Product of primary gene may produce physiological effect or it may act as a transcription factor which control the expression of the secondary genes. Diagram are given below.

ü Nuclear Receptor Signaling:-  Which interact with Thyroxin hormone.

Thyroxin Signaling

Ø  It is hydrophilic in nature which can not cross the plasma membrane . It is divided from tyrosine amino acid.

Ø  Carrier mediator transporter are responsible transporting thyroxin inside the cell its known as facilated diffusion .

Ø   Inside the cell thyroxin interact with its nuclear receptor directly inside the nucleus.

Ø  Receptor ligand dimer complex is form which interact with HRE of target gene and promote gene expression. Diagram are given below.

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