Isolation and amino acid sequence of the TRH-potentiating peptide from bovine hypothalamus

Modulation of the growth hormone-releasing activity of thyrotropin-releasing hormone in the chicken by its gene-related peptide preproTRH((160-169))(Ps4): enhanced somatostatinergic tone?

Recent research demonstrated that endocrine actions of thyrotropin (TSH)-releasing hormone (TRH) are modulated by gene-related products within proTRH. In the present report we show that the growth hormone (GH) response to TRH is clearly inhibited after the preincubation of chicken pituitary glands with preproTRH((160-169))Ps4, whereas the TSH response is not impaired. Binding sites for(125)I-[Tyr(0)]-Ps4 were, however, not detected on chicken pituitary membranes, although (as a control) they were readily detectable on membranes from rat pituitary glands. An indirect action may therefore take place within the pituitary by modulating the action of somatostatin (SRIH), the inhibitor of GH release in the chicken. This hypothesis is strengthened by the observation that Ps4 increases the binding of(125)I-[Tyr(1)]-SRIH to chicken pituitary membranes in a dose-related way. Since Ps4 is also produced by pituitary tissue, this may reflect a local or paracrine action on the regulation of GH release.

Neuroregulation of ProTRH biosynthesis and processing

This review presents an overview of the current knowledge on proTRH biosynthesis, its processing, its tissue distribution, and the role of known processing enzymes in proTRH maturation. The neuroendocrine regulation of TRH biosynthesis, the biological actions of its products, and the signal transduction and catabolic pathways used by those products are also reviewed. The widespread expression of proTRH, PC1, and PC2 rnRNAs in hypophysiotropic and extrahypophysiotropic areas of the brain, with their overlapping distribution in many areas, indicates the striking versatility provided by tissue-specific processing in generating quantitative and qualitative differences in nonTRH peptide products as well as TRH. Evidence is presented suggesting that differential processing for proTRH at the intracellular level is physiologically relevant. It is clear that control over the diverse range of proTRH-derived peptides within a specific cell is accomplished most from the regulation at the posttranslational level rather than the translational or transcriptional levels. Several examples supporting this hypothesis are presented in this review. A better understanding of proTRH-derived peptides role represents an exciting new frontier in proTRH research. These connecting sequences in between TRH molecules to form the precursor protein may function as structural or targeting elements that guide the folding and sorting of proTRH and its larger intermediates so that subsequent processing and secretion are properly regulated. The particular anatomical distribution of the proTRH end products, as well as regulation of their levels by neuroendocrine or pharmacological manipulations, supports a unique potential biologic role for these peptides.

Is Ps4 (prepro-TRH [160-169]) more than an enhancer for thyrotropin-releasing hormone?

Ps4 (thyrotropin-releasing hormone [TRH]-enhancing peptide), one of the cryptic peptides resulting from the proteolytic processing of prepro-TRH to produce TRH, has a growing list of functions in addition to its well-established ability to enhance the TRH-induced release of thyrotropin (TSH) and prolactin from the pituitary. Intramedullary coadministration of Ps4 and TRH increased gastric acid secretion above the level produced by TRH alone and intracisternal infusion of Ps4 resulted in a substantial reduction in the levels of prepro-TRH-derived peptide levels in the rat pituitary, including Ps4. High-affinity receptors for Ps4 are widely distributed. In addition to the very high Ps4 binding capacity of the folliculo-stellate cells of the anterior pituitary, abundant Ps4 receptors are found in the urinary bladder, vas deferens, central nervous system, reproductive tissues, and pancreas. Targeted prepro-TRH gene disruption results in hyperglycemia as well as the expected hypothyroidism. The observed disregulation of thyroid and glucose homeostasis in the TRH "knockout" mouse clearly demonstrates that prepro-TRH-derived peptides and their cognate receptors within the pituitary, pancreas, and other neural and endocrine systems are of fundamental importance to a variety of physiological systems and merit structural and functional characterization.

Isolation and characterization of four novel bioactive peptides from a polychaete annelid, Perinereis vancaurica

Four bioactive peptides were purified from an extract of the polycheate annelid Perinereis vancaurica using an HPLC system for fractionation of the extract and the esophagus of the worm as bioassay system. The sequences of the peptides were determined to be H-Trp-Val-Val-Gly-Asp-Val-Gln-OH, H-Ala-Thr-Trp-Leu-Asp-Thr-OH, H-Trp-Met-Val-Gly-Asp-Val-Gln-OH and H-Phe-Tyr-Glu-Gly-Asp-Val-Pro-Tyr-OH. These peptides showed an excitatory activity on the esophagus of P. vancaurica. The excitatory effect of the second and fourth peptides was marked. They may be neuropeptides involved in regulation of the esophagus.

Analysis of structural requirements for TRH-potentiating peptide receptor binding by analogue design

Previous studies established that the [125I-Tyr0]Ps4 derivative of TRH-potentiating peptide (Ps4), Ser-Phe-Pro-Trp-Met-Glu-Ser-Asp-Val-Thr, displays high affinity and selectivity for an orphan membrane receptor in rat anterior pituitary. To identify the sites in Ps4 that determine receptor binding affinity, we have synthesized and screened a panel of 15 single-point substituted analogues for their ability to displace bound [125I-Tyr0]Ps4. The affinity of [Tyr0]Ps4 for rat anterior pituitary membranes [inhibitory constant (Ki), approximately 5 nM] was drastically reduced by the substitution of either Tyr0 with Gly or Asp8 with Asn (Ki approximately 95 and approximately 51 nM, respectively). Deamination of [Tyr0]Ps4 also sharply reduced affinity (Ki approximately 1100 nM). In contrast, Ser1-->Ala, Pro3-->Ala and Thr10-->Val substitutions led to analogues showing a tenfold increase in binding affinity relative to the parent peptide. The change of Phe2-->Leu, Trp4-->Ala, Glu6-->Gln, Val9-->Thr and carboxamidation of Thr10 had no effect on binding affinity. The data suggest that substitutions of the amino-terminal group, Asp8 and Tyr0, have a marked effect on the ability of [Tyr0]Ps4 to compete with [125I-Tyr0]Ps4 for binding to TRH-potentiating peptide pituitary receptor.

Modulation of the biological activity of thyrotropin-releasing hormone by alternate processing of pro-TRH

Thyrotropin-releasing hormone prohormone contains multiple copies of TRH linked together by connecting sequences. Like other plurifunctional prohormone proteins, pro-TRH undergoes differential proteolytic processing in various tissues to generate, beside authentic TRH, several other novel peptides corresponding to C-terminally extended forms of TRH and connecting fragments. The pro-TRH connecting peptides are, together with TRH, predominant storage forms of TRH-precursor related peptides in the rat hypothalamus. Connecting peptides are co-localized with TRH in the median eminence nerve endings and co-released through a mechanism involving voltage-operated Ca2+ channels. The connecting peptide Ps4 is involved in potentiation of the action of TRH on thyrotropin hormone release by pituitary in vitro and in vivo through interactions with a specific pituitary cell receptor coupled to dihydropyridine and omega-connotoxin sensitive Ca2+ channels of the L-type. It also causes dose-dependent increases in the steady state levels of mRNAs of TSH and prolactin through stimulation of the respective gene promoter activities. These findings indicate that Ps4 and TRH, two peptides which originate from a single multifunctional biosynthetic precursor, can function on the same target tissues in a coordinate manner to promote hormonal secretion. This suggests that differential processing of the TRH prohormone may have the potential to modulate the biological activities of TRH.