Neuromedin B

Neuromedin B (NMB) is a bombesin-related peptide in mammals. It was originally purified from pig spinal cord, and later shown to be present in human central nervous system and gastrointestinal tract.

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Functions of Neuromedin B

Neuromedin has the following functions:

• (1) Regulation of exocrine and endocrine secretions
• (2) Regulation of cell growth
• (3) Regulation of body temperature
• (4) Regulation of blood pressure and glucose level

Neuromedin Signaling Pathway

NMB exerts it's effects by binding to a cell surface receptor. A high affinity receptor called the neuromedin B receptor (NMBR) has been identified. This receptor is a G protein-coupled receptor with seven transmembrane spanning regions, hence the receptor is also denoted as 7-TMR or 7 Transmembrane Receptor. Upon binding several intracellular signaling cascades are induced, which are mentioned below (see Figure 2 for signal cascade).

When NMB binds to 7-TMR, the heterotrimeric G-protein that is attached to the receptor gets activated. The G-protein is called heterotrimeric because it consists of 3 polypeptides: α subunit, β subunit and γ subunit. Out of which G-β and G-γ subunits function as a monomer. And G-α has a GDP bound to it. When the NMB binds to 7-TMR, there occurs GTP exchange for GDP bound to G-α subunit and thus it gets activated, dissociates from the G-βγ. The activated G-α in turn activates adenylate cyclase(AC) which in turn catalyzes the conversion of ATP to cAMP second messenger. cAMP helps in the activation of the enzyme Protein Kinase A (PKA). PKA enters the nucleus and activates the cAMP response element-binding protein. The activated CREB binds along with CREB binding protein, co-activator to the CRE region of the DNA in the nucleus. CREB and CBP are held together by leucine zippers. CRE is the control that activates number of growth factors, and thus cell proliferation and some anti-apoptotic genes.In the brain, CREB plays a role in long-term memory and learning.