Somatostatin gene synthesis

Another common mechanism for modulating hormonal response involves two (or more) hormonal inputs with both positive and negative effects (see fig. 24.21). The hypothalamic peptides, somatostatin and GRF, have opposite effects on GH synthesis and secretion. Similarly, glucagon and insulin have opposite effects on gluconeogenesis in the liver (see the discussion earlier in this chapter), and some of the effects of ecdysone on gene expression in insects are blocked by juvenile hormone (a terpene derivative fig. 24.22). 

Fig. 24.9 Production of recombinant somatostatin. The small size of somatostatin allows the chemical synthesis of the gene coding for it. This gene can be cloned into an expression fused to [i-galactosidasc. The fusion protein generated in E. coli is then purified and the somatostatin polypeptide is released by treatment with cyanogen bromide.

In mammalian cells, an elevation In the cytosolic cAMP level stimulates the expression of many genes. For instance, increased cAMP in certain endocrine cells Induces production of somatostatin, a peptide that inhibits release of various hormones in liver cells, cAMP Induces synthesis of several enzymes involved in converting three-carbon compounds to glucose. 

Some genes which show late expression after addition of CDF/LIF have been identified. For example, in cultured sympathetic neurons CDF/LIF induces transcription of not only the acetylcholine gene, but also the genes coding for substance P, somatostatin, cholecystokinin, enkephalin and vasoactive intestinal polypeptide (Nawa and Patterson, 1990 Fann and Patterson, 1994). The transcription of muscarinic acetylcholine receptor genes and substance P receptor genes is also induced (Ludlam et al., 1994). On the other hand, CDF/LIF suppresses catecholamine synthesis. In osteoblast-like cells, LIF suppresses alkaline... 

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