Molecular organization of the mouse gastrin-releasing peptide receptor gene and its promoter

Estrogens influence female itch sensitivity via the spinal gastrin-releasing peptide receptor neurons

Many women exhibit a dramatic increase in itch during pregnancy, but the underlying mechanism is unknown. Here, we demonstrate that the female sex steroid hormone estradiol, but not progesterone, enhances itch-related scratching behavior in female rats elicited by histamine, the prototypical itch mediator in humans. This is associated with an enhancement in histamine-evoked activity of a subset of spinal dorsal horn neurons that express a neuropeptide receptor, gastrin-releasing peptide receptor (GRPR), that was previously shown to be involved in spinal cord processing of itch. These findings may account for why itch sensation varies with estrogen levels and provide a basis for treating histamine-related itch diseases in females by targeting GRPR.

There are sex differences in somatosensory sensitivity. Circulating estrogens appear to have a pronociceptive effect that explains why females are reported to be more sensitive to pain than males. Although itch symptoms develop during pregnancy in many women, the underlying mechanism of female-specific pruritus is unknown. Here, we demonstrate that estradiol, but not progesterone, enhances histamine-evoked scratching behavior indicative of itch in female rats. Estradiol increased the expression of the spinal itch mediator, gastrin-releasing peptide (GRP), and increased the histamine-evoked activity of itch-processing neurons that express the GRP receptor (GRPR) in the spinal dorsal horn. The enhancement of itch behavior by estradiol was suppressed by intrathecal administration of a GRPR blocker. In vivo electrophysiological analysis showed that estradiol increased the histamine-evoked firing frequency and prolonged the response of spinal GRP-sensitive neurons in female rats. On the other hand, estradiol did not affect the threshold of noxious thermal pain and decreased touch sensitivity, indicating that estradiol separately affects itch, pain, and touch modalities. Thus, estrogens selectively enhance histamine-evoked itch in females via the spinal GRP/GRPR system. This may explain why itch sensation varies with estrogen levels and provides a basis for treating itch in females by targeting GRPR.

Involvement of Gastrin-Releasing Peptide Receptor in the Regulation of Adipocyte Differentiation in 3T3-L1 Cells

Gastrin-releasing peptide (GRP), a member of bombesin-like peptides, and its receptor (GRP-R) play an important role in various physiological and pathological conditions. In this work, we investigated the role of GRP-R on adipogenesis in 3T3-L1 adipocytes. The expression of GRP-R was significantly increased during the adipocyte differentiation of 3T3-L1 cells. The inhibition of GRP-R by the antagonist RC-3095 affected adipogenesis in 3T3-L1 cells, which reduced lipid accumulation and regulated the expression of adipogenic genes. Moreover, cyclic AMP response element-binding protein (CREB) directly bound to the GRP-R promoter upon exposure to adipogenic stimuli. The down-regulation of GRP-R by the knockdown of CREB inhibited adipocyte differentiation of 3T3-L1 cells. Together these results suggest that the regulation of GRP-R activity or expression has an influence on adipogenesis through regulating adipogenic related genes.

Breast Cancer Takes up 99mTc Bombesin. A Preliminary Report

Background

Several tumors including lung, prostate, ovarian, colon, and exocrine pancreatic cancer show receptors for the amphibian neurotransmitter and growth factor bombesin (BN) and its mammalian counterparts gastrin-releasing peptide and neuromedin B. Also breast cancer has been reported to show such receptors: the presence of BN receptors in primary breast cancer has been demonstrated on cultured cells and by autoradiography on breast tissue samples. Authors who have studied BN receptors in breast cancer do not agree on their frequency in primary cancer, but indicate that 100% of metastatic breast cancers show such receptors.

Methods

We examined three primary breast cancer patients with 99mTc BN and 99mTc sestamibi one week before surgery. One of them showed axillary node invasion. The same acquisition technique was used for breast and chest imaging with both radiopharmaceuticals, whereas total body images were acquired only with 99mTc BN. Also the administered radioactivity was different: 20 mCi of 99mTc sestamibi and 5-8 mCi of 99mTc BN. Dynamic images were acquired for 20 mins after iv injection with the patient in ventral decubitus and the gamma camera positioned in lateral view, as is generally done in Khakhali's prone scintimammography. Anterior chest images were acquired for 30 mins. Prone scintimammography was performed one hour after administration of both tracers. ROIs were drawn on tumors and surrounding breast with the same technique in order to calculate the tumor to breast ratio (T/B). In addition, total body scan was performed one hour and three hours after 99mTc BN administration. All three patients underwent breast conserving surgery with lymphadenectomy. Postoperative pathologic assessment showed the following T and N stages in the three patients: T1bN0, T1cN0. and T1cN1.

Results

All three cancers were imaged with both tracers. The T/B of 99mTc BN was always higher than that of 99mTc sestamibi. Chest uptake was always much higher with 99mTc sestamibi than with 99mTc BN. Comparison between 99mTc BN and 99mTc sestamibi images gave other intriguing results: in the N1 patient both tracers clearly imaged the invaded node, but on the 99mTc BN image the primary tumor was larger than on the 99mTc sestamibi image and the node was smaller. It is known that 99mTc BN is not taken up by vessels and inflammatory tissue. The time activity curves of the two tracers were significantly different in all patients, with an increase in 99mTc BN uptake in the first three to five minutes, followed by a less sharp uprise of the curve, quite similar to a plateau.

Conclusions

Our first impression is that 99mTc BN is a useful breast cancer seeking agent and very promising for lymph node staging.

Distribution of the pig gastrin-releasing peptide receptor and the effect of GRP on porcine Leydig cells

Gastrin-releasing peptide (GRP) is a mammalian bombesin (BN)-like peptide which plays a role in a number of important physiological functions via its receptor (gastrin-releasing peptide receptor, GRPR) in most animals. However, little is known about the gene encoding GRPR and its functions (especially reproduction) in pigs. In this study, we first cloned and analyzed the pig GRPR cDNA. Then we systematically investigated the expression levels of GRPR mRNA by relative real-time PCR (RT-PCR), and analyzed the distribution of the GRPR protein in pig tissues via immunohistochemistry (IHC). Finally, we studied the effect of GRP on testosterone secretion and GRPR (mRNA and protein) expression in Leydig cells. Results showed that the pig GRPR cDNA cloned at 1487bp, including one open reading frame (ORF) of 1155bp and encodes 384 amino acids. Significantly, compared with other species, the cDNA sequence and amino acid sequence of the pig GRPR were highly homologous and conservative. The RT-PCR results showed that: in the central nervous system (CNS) and the pituitary, GRPR mRNA was found in the cerebellum, hypophysis, spinal cord and hypothalamus; in the peripheral tissues, GRPR mRNA was mainly expressed in the pancreas, esophagus, ovary, testis, spleen, thymus, jejunum lymph node, muscle and fat. Moreover, the IHC results showed that GRPR immunoreactivity was widely distributed in the pig tissues and organs, such as the pancreas, esophagus, testis, ovary, spleen, pituitary gland and adrenal gland. In addition, we found that GRP promotes testosterone secretion, and increases GRPR mRNA and protein expression in cultured Leydig cells in vitro. These molecular and morphological data not only describe the anatomical locations of GRPR in pigs, but also provide the theoretical foundation for further research into its possible physiological functions in pigs. These results suggest that the GRP/GRPR system may play an important role in regulating the reproductive system of the boar.

Regulation and signaling of human bombesin receptors and their biological effects

PURPOSE OF REVIEW

This review will highlight recent advances in the understanding of molecular mechanisms by which mammalian bombesin receptors are regulated and which intracellular signaling pathways have been characterized to mediate agonist-dependent receptor biological effects.

RECENT FINDINGS

Mammalian bombesin receptors have been demonstrated to be involved in a larger array of physiological and pathophysiological conditions than previously reported. Pharmacological experiments in vitro and in vivo as well as utilization of animals genetically deficient of the gastrin-releasing peptide receptor demonstrated roles in memory and fear behavior, lung development and injury, small intestinal cell repair, autocrine tumor growth, and mediating signals for pruritus and penile reflexes. Intracellular signaling studies predominantly of the gastrin-releasing peptide receptor owing to its frequent overexpression in some human malignancies showed that PI3 kinase activation is an important mechanism of cell proliferation. Tumor cell treatment including gastrin-releasing peptide receptor antagonists combined with inhibition of epidermal growth factor receptor resulted in an additive effect on blocking cell proliferation. Novel molecular mechanisms of the orphan bombesin receptor subtype-3 and gastrin-releasing peptide receptor gene regulation have been elucidated.

SUMMARY

Inhibition of gastrin-releasing peptide receptor signaling in human malignancies represents an attractive target for pharmacological treatment. Novel functions of bombesin related peptides have been identified including processes in the central nervous system, lung and intestinal tract.

The human gastrin-releasing peptide receptor gene structure, its tissue expression and promoter

The human gastrin-releasing peptide receptor (hGRP-R) is aberrantly expressed in cancers of the colon, lung and prostate and mediates signals of cellular proliferation. However, the underlying mechanisms of aberrant and/or activation of hGRP-R expression are unknown. Therefore, a genomic clone is identified, the hGRP-R gene is characterized, and the hGRP-R promoter is defined. The protein coding region is divided into three exons and exon/intron splice sites occur in the proximal 2nd and distal 3rd intracellular loops of the receptor molecule. The hGRP-R locus extends over more than 27 kb and is assigned to the chromosomal band Xp22 by fluorescence in situ hybridization. With primer extension experiments, we demonstrate two major transcription start sites in gastrointestinal and breast cancer cells, located 43 and 36 bp downstream of a TTTAAA motif which is identified 407 to 402 bp upstream of the ATG start codon. The hGRP-R is found most abundantly expressed in the normal human pancreas, where four gene-specific transcripts can be detected by Northern blot analysis, whereas only two transcripts are detected in the human stomach and, very weakly, in the adrenal cortex and the brain. In contrast, the human GRP-R is not expressed in the normal human colon, lung, and prostate. Steady state hGRP-R mRNA can also be detected in some cultured cells from breast, lung, and duodenal cancer. Robust hGRP-R promoter activity is demonstrated in a duodenal carcinoma cell line that natively expresses the functional hGRP-R. Truncation studies suggest a CRE motif, located 112 bp upstream of the major transcription start site, is required to confer basal hGRP-R promoter activity in duodenal cancer cells. These studies provide the necessary data to further elucidate molecular mechanisms of aberrant hGRP-R expression in human cancers.