CAMP response protein

All the DNA-binding proteins discussed thus far function by inhibiting transcription until some environmental condition, such as the presence of lactose, is met. There are also DNA-binding proteins that stimulate transcription. One particularly well studied example is the catabolite activator protein (CAP), which is also known as the cAMP response protein (CRP). When bound to cAMP, CAP, which also is a sequence-specific DNA-binding protein, stimulates the transcription of lactose- and arabinose-catabolizing genes. Within the lac operon, CAP binds to an inverted repeat that is centered near position -61 relative to the start site for transcription (Figure 31.10). CAP functions as a dimer of identical subunits. 

Biosynthesis. CRE is derived from a precursor of 196 amino acids (84,85). This gene contains one copy of CRE, which is flanked by double basic amino acids. The amino acid sequence of the CRE precursor suggests that it may arise from proteins related to POMC and neurophysins (31). The CRE precursor contains a cAMP responsive element which aHows stimulation of mRNA synthesis when intraceHular levels of cAMP are increased (86). 

The cAMP responsive element binding factor (CREB) is also activated by phosphorylation. Depending on the stimuli, CREB is the target of a cAMP dependent protein kinase or of kinases called MAPKs, RSK, and CamKIV. As in AP-1, CREB carries a basic leucine zipper motif (bZDP), which mediates homo dimerization of CREB when bound to the CRE. 

Shumilla, A.J., Broderick, J.R., Wang, Y., and Barchowsky, A., Chromium Cr(VI) inhibits the transcriptional activity of nuclear factor B by decreasing the interaction of p65 with cAMP-responsive elementbinding protein, Journal of Biological Chemistry, 274 (51), 36207-36212, 1999. 

Adenovirus transcription factor (ATF) is a protein activated by the adenovirus protein E2a and has turned out to be CREB (cAMP-responsive, element-binding protein) Jun is named for avian sarcoma virus 17 (I am told that junana is 17 in Japanese). 

Nibuya M., Nestlr E. J., Duman R. S. (1996). Chronic antidepressant administration increases the expression of cAMP response element binding protein (CREB) in rat hippocampus. J. Neurosci. 16, 2365-72. 

Newton, S.S., Thome, J., Wallace, T.L. et al. Inhibition of cAMP response element-binding protein or dynorphin in the nucleus accumbens produces an antidepressant-like effect. J. Neurosci. 22 10883, 2002. 

Alreja M, Aghajanian G. Pacemaker activity of locus coeruleus neurons whole-cell recordings in brain slices show dependence on cAMP and protein kinase A. Brain Res 1991 556 339—343. Shiekhattar R, Aston-Jones G. Modulation of opiate responses in brain noradrenergic neurons by cAMP cascade changes with chronic morphine. Neuroscience 1993 57 879-885. 

Cyclic nucleotides are made in response to receptor activation. The receptor activates a G-protein that, in turn, activates adenylyl cyclase to make the cyclic nucleotide. To complete the signaling, the increase in cAMP concentration activates a specific protein kinase (serine/threo-nine), cAMP-dependent protein kinase (A kinase) (Fig. 9-7). To turn off the signaling pathway, the cyclic nucleotides are destroyed by enzymes called phosphodiesterases. These cleave cAMP to AMP. 

L The answer is a. (Hardman, pp 1460, 14642) Cosyntropin is related to adrenocorticotropin. It corresponds to the first 24 amino acids of adreno-corticotropin. Cosyntropin complexes with a plasma membrane receptor that brings about the activation of adenylyl cyclase. Adenylyl cyclase catalyzes the formation of cAMP from ATP In the cytoplasm, cAMP activates cAMP-dependent protein kinase, which participates in the phosphorylation of specific substrate proteins (e.g., enzymes). The phosphorylated protein eventually induces the particular response on the target cell. 

The synthesis of 5-HT can increase markedly under conditions requiring more neurotransmitter. Plasticity is an important concept in neurobiology. In general, this refers to the ability of neuronal systems to conform to either short- or long-term demands placed upon their activity or function (see Plasticity in Ch. 53). One of the processes contributing to neuronal plasticity is the ability to increase the rate of neurotransmitter synthesis and release in response to increased neuronal activity. Serotonergic neurons have this capability the synthesis of 5-HT from tryptophan is increased in a frequency-dependent manner in response to electrical stimulation of serotonergic soma [7]. The increase in synthesis results from the enhanced conversion of tryptophan to 5-HTP and is dependent on extracellular calcium ion. It is likely that the increased 5-HT synthesis results in part from alterations in the kinetic properties of tryptophan hydroxylase, perhaps due to calcium-dependent phosphorylation of the enzyme by calmodulin-dependent protein kinase II or cAMP-dependent protein kinase (PKA see Ch. 23). 

This list is not intended to be comprehensive but to indicate the wide array of neuronal proteins regulated by phosphorylation. Some of the proteins are specific to neurons but most are present in many cell types in addition to neurons and are included because their multiple functions in the nervous system include the regulation of neuron-specific phenomena. Not included are the many phosphoproteins present in diverse tissues, including brain, that play a role in generalized cellular processes, such as intermediary metabolism, and that do not appear to play a role in neuron-specific phenomena. NMDA, N-methyl-D-aspartate CREB, cAMP response element-binding proteins STAT, signal-transducing activators of transcription ... 

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