Dissection of differentially regulated (G+C)-rich promoters of the human parathyroid hormone (PTH)/PTH-related peptide receptor gene

Pleckstrin homology (PH) domain and Leucine Rich Repeat Phosphatase 1 (Phlpp1) Suppresses Parathyroid Hormone Receptor 1 (Pth1r) Expression and Signaling During Bone Growth

Endochondral ossification is tightly controlled by a coordinated network of signaling cascades including parathyroid hormone (PTH). Pleckstrin homology (PH) domain and leucine rich repeat phosphatase 1 (Phlpp1) affects endochondral ossification by suppressing chondrocyte proliferation in the growth plate, longitudinal bone growth, and bone mineralization. As such, Phlpp1-/- mice have shorter long bones, thicker growth plates, and proportionally larger growth plate proliferative zones. The goal of this study was to determine how Phlpp1 deficiency affects PTH signaling during bone growth. Transcriptomic analysis revealed greater PTH receptor 1 (Pth1r) expression and enrichment of histone 3 lysine 27 acetylation (H3K27ac) at the Pth1r promoter in Phlpp1-deficient chondrocytes. PTH (1-34) enhanced and PTH (7-34) attenuated cell proliferation, cAMP signaling, cAMP response element-binding protein (CREB) phosphorylation, and cell metabolic activity in Phlpp1-inhibited chondrocytes. To understand the role of Pth1r action in the endochondral phenotypes of Phlpp1-deficient mice, Phlpp1-/- mice were injected with Pth1r ligand PTH (7-34) daily for the first 4 weeks of life. PTH (7-34) reversed the abnormal growth plate and long-bone growth phenotypes of Phlpp1-/- mice but did not rescue deficits in bone mineral density or trabecular number. These results show that elevated Pth1r expression and signaling contributes to increased proliferation in Phlpp1-/- chondrocytes and shorter bones in Phlpp1-deficient mice. Our data reveal a novel molecular relationship between Phlpp1 and Pth1r in chondrocytes during growth plate development and longitudinal bone growth. © 2021 American Society for Bone and Mineral Research (ASBMR).

Characterisation of the mouse vasoactive intestinal peptide receptor type 2 gene, Vipr2, and identification of a polymorphic LINE-1-like sequence that confers altered promoter activity

The VPAC(2) receptor is a seven transmembrane spanning G protein-coupled receptor for two neuropeptides, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP). It has a distinct tissue-specific, developmental and inducible expression that underlies an important neuroendocrine role. Here, we report the characterisation of the gene that encodes the mouse VPAC(2) receptor (Vipr2), localisation of the transcriptional start site and functional analysis of the promoter region. The Vipr2 gene contains 12 introns within its protein-coding region and spans 68.6 kb. Comparison of the 5' untranslated region sequences for cloned 5'-RACE products amplified from different tissues showed they all were contained within the same exon, with the longest extending 111 bp upstream of the ATG start site. Functional analysis of the 3.2-kb 5'-flanking region using sequentially deleted sequences cloned into a luciferase gene reporter vector revealed that this region is active as a promoter in mouse AtT20 D16:16 and rat GH4C1 cell lines. The core promoter is located within a 180-bp GC-rich region proximal to the ATG start codon and contains potential binding sites for Sp1 and AP2, but no TATA-box. Further upstream, in two out of three mice strains examined, we have discovered a 496-bp polymorphic DNA sequence that bears a significant identity to mouse LINE-1 DNA. Comparison of the promoter activity between luciferase reporter gene constructs derived from the BALB/c (which contains this sequence) and C57BL/6J (which lacks this sequence) Vipr2 promoter regions has shown three-fold difference in luciferase gene activity when expressed in mouse AtT20 D16:16 and alphaT3-1 cells, but not when expressed in the rat GH4C1 cells or in COS 7 cells. Our results suggest that the mouse Vipr2 gene may be differentially active in different mouse strains, depending on the presence of this LINE-1-like sequence in the promoter region.

Identification of the promoter region of the parathyroid hormone receptor gene responsible for transcriptional suppression by insulin-like growth factor-I

We investigated parathyroid hormone (PTH)/PTH-related protein receptor (PTH1R) gene suppression induced by insulin-like growth factor (IGF)-I using a rat osteoblast-like cell line (UMR-106). Observations were made with PD98059, a specific ERK signaling pathway inhibitor, and UMR-106 cells transfected with dominant negative or constitutively active forms of MAP kinase kinase. IGF-I inhibited PTH1R gene expression via an ERK1/2 MAP kinase pathway. We cloned the 8-kb promoter region of the rat PTH1R gene and characterized the U3 promoter, a major IGF-I-responsive promoter among the two present in rat osteoblasts. The IGF-I-suppressive region was between +1 and +25, identical to the previously described PTH-suppressive region (PTHSR). Gel mobility-shift detected a specific DNA-protein complex decreased by IGF-I. Mutation involving a three base sequence (+1 to +3) among more than 3.5 kb constituting the PTH1R promoter region completely abolished IGF-I action. Thus, IGF-I signaling may act at the osteoblast exon U3 transcription initiation site to repress the transcriptional activity.

Association between AAAG repeat polymorphism in the P3 promoter of the human parathyroid hormone (PTH)/PTH-related peptide receptor gene and adult height, urinary pyridinoline excretion, and promoter activity

The PTH/PTHrP receptor (PTHR1) plays an essential role in skeletal development and mediates many other functions of PTH and PTHrP. Human PTHR1 gene transcription is controlled by three promoters, P1-P3. The most proximal promoter, P3, is active in bone and osteoblast-like cell lines and accounts for the majority of renal transcripts in adults. We have identified a tetranucleotide repeat (AAAG)n polymorphism in the P3 promoter. In 214 unrelated Japanese, the repeat number (n) ranged from 3-8, with the AAAG5 allele being the most frequent (59%). In 55 unrelated Caucasians, n ranged from 5-7, and the frequency of the AAAG5 allele was 78%. The most frequent genotypes in a cohort of 85 young (18-20 yr) female Japanese were 5/5, 5/6, and 6/6. The 6/6 genotype was associated with greater height (5/5 vs. 6/6; P < 0.02) and lower urinary deoxypyridinoline and pyridinoline (P < 0.02), which are markers of bone resorption. The height of an additional 71 healthy female Japanese subjects, aged 14-17 yr, having genotype 5/5, 5/6, or 6/6 was also in the order of genotype 5/5 < 5/6 < 6/6 (5/5 vs. 6/6, P < 0.05). There was no significant difference in lumbar and femoral bone mineral density between genotypes. Likewise, there was no difference in circulating intact PTH levels between groups. The activity of P3 promoter-luciferase reporter constructs in transcription assays in 2 human osteoblast-like cell-lines varied according to repeat number, with AAAG6 being the least active. In conclusion, the P3 promoter (AAAG)n polymorphism is frequent in both Japanese and Caucasians and has potential as a linkage marker for the PTHR1 locus. In addition, it may influence the expression of the receptor in target tissues and have functional consequences on the developing skeleton.

Parathyroid hormone (PTH) suppresses rat PTH/PTH-related protein receptor gene promoter

Parathyroid hormone (PTH) regulates osteoblasts via a G protein-linked PTH/PTH-related protein (PTHrP) receptor. PTH effects on PTH/PTHrP receptor gene expression were studied in UMR 106 osteoblast-like cells. In heterogeneous nuclear RNA and Northern analysis, PTH suppressed PTH/PTHrP receptor transcription. We cloned the 7-kb promoter region of the rat PTH/PTHrP receptor gene and transiently transfected chimeric deletion constructs containing the 5'-flanking region and the luciferase gene into UMR 106 cells. In transfected cells the minimal region for basal promoter activity was between positions -128 and +103. The 5'-flanking region of exon U1 contained several putative-binding sites for Sp1 and the myc-associated zinc finger protein (MAZ). The minimal PTH-suppressive region (PTHSR) was between +1 and +25 in exon U1, but the 5'-flanking region or Sp1 and MAZ-binding sites also were required for PTH-mediated repression. By gel mobility shift assay PTH markedly decreased binding of PTHSR-protein complex in UMR 106 cells. The mutation experiments showed that the most critical sequence for the repression of PTH was 5'-GGGGGAGGGGAG-3' (+1 to +12) of PTHSR. This represents the first characterization of a PTH-suppressive region of the PTH/PTHrP receptor gene in rat.

Analysis of the P3 promoter of the human parathyroid hormone (PTH)/PTH-related peptide receptor gene in pseudohypoparathyroidism type 1b

Hypocalcemia and hyperphosphatemia caused by PTH resistance are the only discernible abnormalities in pseudohypoparathyroidism type 1b (PHP-1b). Because of the selective resistance toward PTH, inactivating mutations in its receptor, the PTH/PTH-related peptide receptor (PTHR1), were thought to be responsible for PHP-1b. However, gene abnormalities responsible for PHP-1b have not been identified in the coding region and well conserved promoters (P1 and P2) of the PTHR1 gene. The purpose of the present study was to analyze the structure of the P3 promoter, the main promoter of the human PTHR1 gene in kidney, in patients with PHP-1b. Southern analysis of genomic DNA from lymphoblastoid cell lines of eight nonfamilial patients with PHP-1b revealed neither gross rearrangements nor methylation abnormalities in the P3 promoter region of the PTHR1 gene. Sequencing revealed no abnormalities in the P3 promoter region, although one patient was homozygous for an (AAAG)n polymorphic variant. In conclusion, despite the selective resistance toward PTH in the kidney, which mainly uses the PTHR1 P3 promoter, PHP-1b in eight cases is not associated with structural abnormalities in this promoter. This study also indicates that inactivation of the P3 promoter is not achieved by methylation as tested in patients' genomic DNA from lymphoblastoid cell lines. The influence of alterations in the polymorphic A-rich repeat sequence on promoter activity warrants further study.