Tissue-specific activity of the proximal human calcitonin receptor promoter is mediated by Sp1 and an epigenetic phenomenon

To identify cis-acting sequences transcriptionally regulating the human calcitonin receptor (hCTR) gene, hCTR promoter/luciferase gene constructs were transiently or stably transfected into hCTR-positive and -negative cell lines. Luciferase assays demonstrated that the proximal hCTR promoter (hCTRP1) was transcriptionally active in all cell lines tested. High-level hCTRP1 activity depended on an 11 bp Sp1/Sp3 binding site. Electrophoretic mobility shift assay showed that this region bound the transcription factors Sp1 and Sp3. We further showed that hCTRP1 was strongly activated by the 11 bp Sp1/Sp3 binding site in hCTRP1/luciferase-, Sp1-transfected Drosophila S2 cells. Bisulphite-mediated sequencing of genomic DNA from hCTR-expressing and -non-expressing cell lines demonstrated that the endogenous hCTRP1 was hypomethylated in all cell lines tested. These results suggest that the hCTRP1 is activated by the tissue-ubiquitous transcription factor Sp1 and that an epigenetic process unrelated to CpG methylation represses its activity in hCTR-negative tissues.

Transcriptional regulation of the calcitonin receptor gene

Calcitonin is a 32-amino-acid peptide hormone that is produced by parafollicular cells of the thyroid gland in response to increased levels of extracellular calcium. In this article we review our previous and current research on the transcriptional regulation of the pig and human calcitonin receptor (CTR) gene. Initially, our experiments on the transcriptional analysis of the pig CTR gene in transgenic mice are examined, followed by our studies on the cloning of the human CTR (hCTR) gene promoter and its transcriptional activity in hCTR-positive cell lines. We further describe the activity of the hCTR promoter in transgenic mice and review current experiments to identify transcriptional regulatory elements and the transcription factors they interact with, which direct the tissue-specific expression pattern of hCTR promoter activity.

Calcitonin, angiotensin II and FPP significantly modulate mouse sperm function

Fertilization-promoting peptide (FPP) regulates the adenylyl cyclase (AC)/cAMP pathway to elicit capacitation-dependent responses, stimulating capacitation in uncapacitated spermatozoa and then arresting it in capacitated cells, thereby inhibiting spontaneous acrosome reactions. Like FPP, calcitonin and angiotensin II are found in seminal plasma and so might affect sperm function; this study investigated responses in uncapacitated and capacitated mouse spermatozoa to these three peptides. Both calcitonin (5 ng/ml) and angiotensin II (1 and 10nmol/l), like FPP (100nmol/l), significantly stimulated capacitation, assessed using chlortetracycline (CTC) fluorescence and fertilization in vitro analyses. Combinations of two or three peptides, at high and low, non-stimulatory concentrations, were more stimulatory than the individual peptides, suggesting that they may act on the same signalling pathway, plausibly AC/cAMP; preliminary data indicate that calcitonin does stimulate cAMP production. In capacitated cells, FPP and calcitonin elicited pertussis toxin-sensitive inhibition of spontaneous acrosome loss, suggesting involvement of inhibitory G proteins; angiotensin II had no detectable effect. When all three peptides were used, angiotensin II did not interfere with inhibitory responses to FPP/calcitonin. These results suggest that angiotensin II, calcitonin and FPP may somehow modulate the AC/cAMP signal transduction pathway, but the precise mechanisms involved have yet to be elucidated.

Multiple promoters regulate human calcitonin receptor gene expression

To initiate studies on the transcriptional regulation of the human calcitonin receptor (hCTR) gene, a 4.9-kb hCTR promoter fragment was cloned and hCTR transcriptional initiation sites were mapped in human osteoclasts, kidney, and breast cancer cell line T47D. RT-PCR detected additional hCTR transcripts initiating at least 1 kb 5' to the transcripts mapped above, demonstrating that the hCTR gene is regulated by at least two separate promoters (hCTRP1 and hCTRP2). Transcripts initiating from the upstream promoter (hCTRP2) have a novel 5' untranslated region (5' UTR). Transfection of T47D breast cancer cells with hCTR promoter/luciferase deletion constructs demonstrated that the cloned 4.9-kb hCTR promoter fragment contains both hCTRP1 and hCTRP2 promoters. Fine deletion mapping of the more transcriptionally active hCTRP1 promoter demonstrated that only 97 bp of the hCTRP1 5' flanking region is required for the majority of its transcriptional activity.

Proximal promoter elements of the human zeta-globin gene confer embryonic-specific expression on a linked reporter gene in transgenic mice

We have investigated the transcriptional regulation of the human embryonic zeta-globin gene promoter. First, we examined the effect that deletion of sequences 5' to zeta-globin's CCAAT box have on zeta-promoter activity in erythroid cell lines. Deletions of sequences between -116 and -556 (cap = 0) had little effect while further deletion to -84 reduced zeta-promoter activity by only 2-3-fold in both transiently and stably transfected erythroid cells. Constructs containing 67, 84 and 556 bp of zeta-globin 5' flanking region linked to a beta-galactosidase reporter gene (lacZ) and hypersensitive site -40 (HS-40) of the human alpha-globin gene cluster were then employed for the generation of transgenic mice. LacZ expression from all constructs, including a 67 bp zeta-globin promoter, was erythroid-specific and most active between 8.5 and 10.5 days post-fertilisation. By 16.5 days gestation, lacZ expression dropped 40-100-fold. These results suggest that embryonic-specific activation of the human zeta-globin promoter is conferred by a 67 bp zeta-promoter fragment containing only a CCAAT and TATA box.

Sp1 functions in a chromatin-dependent manner to augment human alpha-globin promoter activity

The 5' flanking region of the human alpha-globin gene is highly G + C rich and contains multiple copies of the consensus sequence for the Sp1 binding site. We investigated the role of this G + C-rich region in augmenting alpha-globin promoter activity in the presence of the far-upstream alpha-globin enhancer, HS-40. We show that in transiently transfected erythroid cells, deletion of the alpha-globin G + C-rich 5' flanking region has no effect on alpha-globin promoter activity. However, upon stable integration into chromatin, deletion of this region causes a nearly 90% decrease in promoter activity compared with expression from an alpha-globin promoter retaining this region. These results suggest that the alpha-globin G + C-rich 5' flanking region augments alpha-globin promoter activity in a chromatin-dependent manner. We further show that this G + C-rich region is required for the activation of alpha-globin gene expression during erythroid differentiation. Finally, we show by both footprint analysis and functional assays that the ability of the G + C-rich region to increase alpha-globin promoter activity from a stably integrated alpha-globin gene is mediated by its multiple binding sites for the transcription factor Sp1.

The developmental regulation of the human zeta-globin gene in transgenic mice employing beta-galactosidase as a reporter gene

We have investigated the developmental and tissue specific expression of the human embryonic zeta-globin gene in transgenic mice. A construct containing 550 bp of zeta-globin 5' flanking region, fused to a beta-galactosidase (lacZ) reporter gene and linked to the locus control region (LCR)-like alpha positive regulatory element (alpha PRE) was employed for the production of transgenic mice. Firstly, we compared the number of live born transgenic mice containing this construct to the number of live born transgenic mice containing the entire zeta-globin gene linked to the alpha PRE or the beta LCR. Data showed that 12% of mice generated from eggs injected with zeta-promoter/lacZ/alpha PRE DNA were transgenic compared to only 2% of mice generated from eggs injected with the entire zeta-globin gene linked to the alpha PRE or the beta LCR. The reduced number of live born transgenic mice containing the latter constructs suggests that death of transgenic embryos, possibly due to thalassaemia, may be occurring. X-gal staining of whole embryos containing the lacZ gene revealed that zeta-globin promoter activity was most pronounced at 8.5-9.5 days of development and was restricted to erythroid cells. By 15 days of development, no zeta-globin promoter activity was detected. These results suggest that the alpha PRE can direct high level expression from the zeta-globin promoter and that sequences required for the correct tissue and developmental specific expression of the human zeta-globin gene are present within 550 bp's of 5' flanking region. Sequences within the body of the zeta-globin gene or 3' of the cap site do not appear to be necessary for correct zeta-globin developmental regulation.

The LCR-like alpha-globin positive regulatory element functions as an enhancer in transiently transfected cells during erythroid differentiation

A positive regulatory element (PRE) similar to the locus control region (LCR) of the human beta-globin gene cluster has recently been identified 40 kb upstream of the human zeta-globin mRNA cap site (Higgs D.R. W.G. Wood, A.P. Jarman, J. Sharpe, J. Lida, I.M. Pretorius, and H. Ayyub. 1990). We investigated the influence of the alpha PRE on human alpha-globin promoter activity in transiently transfected cells. The introduction of the alpha PRE into alpha-globin promoter/CAT expression constructs increased alpha-globin promoter activity by 15-30 fold in a human erythroid cell line (Putko) as well as in mouse erythroleukemia cells (MELCs) induced with hexamethylene bisacetamide (HMBA). When these constructs were introduced into uninduced MELCs or HeLa cells, only a 2-3 fold increase in alpha-globin promoter activity was observed. Deletion of 600 bp of alpha-globin 5' flanking sequences containing six putative SP1-binding sites had no significant effect on levels of alpha-globin promoter enhancement by the alpha PRE. We further demonstrated that the alpha PRE and HS2 of the beta-LCR could similarly enhance transcriptional activity of the SV40 early promoter in HMBA induced MELCs. Finally, we showed that alpha-globin promoter activity in the presence of the alpha PRE increased with continued HMBA exposure and was coincident with transcriptional activation of endogenous globin genes.

Localized maternal mRNA related to transforming growth factor beta mRNA is concentrated in a cytokeratin-enriched fraction from Xenopus oocytes

The localized maternal RNA Vg1 resides in the cortical region of the vegetal pole of fully grown Xenopus oocytes and is inherited by only a subset of blastomeres in the early embryo [Weeks, D. L. & Melton, D. A. (1987) Cell 51, 861-867]. Because RNA-cytoskeletal interactions may play a role in RNA localization, we have examined the association of Vg1 RNA with components of the oocyte's cytoskeleton. Gel and immunoblot analysis of a detergent-insoluble fraction revealed a greatly simplified protein pattern composed largely of cytokeratins and vimentin. In sharp contrast to the nonlocalized histone H3 mRNA, Vg1 RNA was concentrated some 35- to 50-fold in this insoluble fraction. Extractions at higher salt concentrations yielded preparations further enriched in cytokeratins and in the Vg1 RNA. Upon ovulation, VG1 RNA is released into the soluble fraction. This change in Vg1 RNA distribution coincides with the observed breakdown of cortical cytokeratin filaments [Klymkowsky, M. W., Maynell, L. A. & Polson, A. G. (1987) Development 100, 543-557] and the loss of Vg1 RNA from the cortical region. Our findings are consistent with the hypothesis that RNA-cytoskeletal interactions are involved in the localization and segregation of information during development.