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HCaRG, a novel calcium-regulated gene coding for a nuclear protein, is potentially involved in the regulation of cell
1Centre de recherche, Centre hospitalier de l'Université de Montréal, Montréal, Québec H2W 1T8, Canada.
Abstract:
Since a negative calcium balance is present in spontaneously hypertensive rats, we searched for the gene(s) involved in this dysregulation. A cDNA library was constructed from the spontaneously hypertensive rat parathyroid gland, which is a key regulator of serum-ionized calcium. From seven overlapping DNA fragments, a 1100-base pair novel cDNA containing an open reading frame of 224 codons was reconstituted. This novel gene, named HCaRG (hypertension-related, calcium-regulated gene), was negatively regulated by extracellular calcium concentration, and its basal mRNA levels were higher in hypertensive animals. The deduced protein showed no transmembrane domain, 67% alpha-helix content, a mutated calcium-binding site (EF-hand motif), four putative "leucine zipper" motifs, and a nuclear receptor-binding domain. At the subcellular level, HCaRG had a nuclear localization. We cloned the human homolog of this gene. Sequence comparison revealed 80% homology between rats and humans at the nucleotide and amino acid sequences. Tissue distribution showed a preponderance in the heart, stomach, jejunum, kidney (tubular fraction), liver, and adrenal gland (mainly in the medulla). HCaRG mRNA was significantly more expressed in adult than in fetal organs, and its levels were decreased in tumors and cancerous cell lines. We observed that after 60-min ischemia followed by reperfusion, HCaRG mRNA declined rapidly in contrast with an increase in c-myc mRNA. Its levels then rose steadily to exceed base line at 48 h of reperfusion. HEK293 cells stably transfected with HCaRG exhibited much lower proliferation, as shown by cell count and [(3)H]thymidine incorporation. Taken together, our results suggest that HCaRG is a nuclear protein potentially involved in the control of cell proliferation.
Insights
Researchers identified a novel gene, hypertension-related, calcium-regulated gene (HCaRG), linked to calcium regulation in hypertensive rats. This gene, found in human tissues, appears to control cell proliferation and is downregulated in cancerous cells.
Area of Science:
- Molecular Biology
- Genetics
- Physiology
Background:
- Spontaneously hypertensive rats exhibit a negative calcium balance, suggesting a genetic basis for calcium dysregulation.
- The parathyroid gland plays a crucial role in regulating serum-ionized calcium levels.
Purpose of the Study:
- To identify and characterize novel genes involved in calcium regulation and hypertension.
- To investigate the function and regulation of the newly discovered HCaRG gene.
Main Methods:
- Construction of a cDNA library from spontaneously hypertensive rat parathyroid glands.
- Gene cloning, sequencing, and homology analysis with human counterparts.
- Analysis of HCaRG mRNA expression in various tissues, developmental stages, and cell lines.
- Investigation of HCaRG's role in cell proliferation using transfected HEK293 cells.
Main Results:
- A novel gene, HCaRG, was identified and characterized, showing higher basal mRNA levels in hypertensive rats and negative regulation by extracellular calcium.
- HCaRG encodes a nuclear protein with structural motifs suggesting interaction with nuclear receptors and calcium binding.
- HCaRG exhibits significant homology between rats and humans, with specific tissue distribution and decreased expression in tumors.
- HCaRG expression is altered during ischemia-reperfusion injury and its presence in HEK293 cells significantly reduces cell proliferation.
Conclusions:
- HCaRG is a novel calcium-regulated gene potentially involved in hypertension and cell proliferation control.
- The findings suggest HCaRG as a potential therapeutic target for hypertension and cancer.