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Identification and characterization of 1,25D3-membrane-associated rapid response, steroid (1,25D3-MARRS)-binding
Benjamin Rohe1, Susan E Safford, Ilka Nemere
1Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA.
Abstract:
We report the presence of a mammalian equivalent of the avian Membrane-Associated Rapid Response, Steroid (1,25D3-MARRS)-binding protein specific for 1,25(OH)2D3 in a rat small intestinal cell line, IEC-6, that demonstrates rapid responses to the steroid hormone. Identification of transcript and protein was achieved using RT-PCR with several specific primer sets, Western blot analysis with two separate antibodies recognizing distinct regions of the protein, ribozyme knockdown and immunohistochemistry. Promoter analysis of the 1000-bp upstream region of the 1,25D3-MARRS gene in several species revealed the presence of a conserved smad-3 element in the 5' proximal promoter region, but no classical vitamin D response element (VDRE). Treatment of IEC-6 cells with transforming growth factor beta1 (TGFbeta1) increased steady-state levels of 1,25D3-MARRS (mRNA and protein) approximately two-fold over a 24-h period. In contrast, treatment with 1,25(OH)2D3 failed to significantly change 1,25D3-MARRS protein or mRNA levels. Localization studies showed rapid nuclear translocation of a pool of 1,25D3-MARRS protein after 1,25(OH)2D3 treatment, suggesting that the protein is subject to membrane-initiated signal pathway activation. Together these data point to complex interactions between the two important 1,25(OH)2D3 sensitive response systems in intestinal cells, 1,25D3-MARRS protein and the well-studied nVDR, that together work to fine tune intestinal Ca2+ absorption in a variety of avian and mammalian species.
Insights
Researchers identified a mammalian protein, 1,25D3-MARRS, in rat intestinal cells that rapidly responds to the steroid hormone 1,25(OH)2D3. This protein interacts with the vitamin D receptor, influencing calcium absorption.
Area of Science:
- Cell Biology
- Endocrinology
- Molecular Biology
Background:
- The steroid hormone 1,25(OH)2D3 plays a crucial role in calcium absorption.
- Avian species possess a Membrane-Associated Rapid Response, Steroid (1,25D3-MARRS)-binding protein involved in 1,25(OH)2D3 signaling.
- The precise mechanisms of 1,25(OH)2D3 action in mammalian intestinal cells are not fully elucidated.
Purpose of the Study:
- To identify and characterize a mammalian equivalent of the avian 1,25D3-MARRS-binding protein in rat intestinal cells.
- To investigate the regulation and function of this protein in response to 1,25(OH)2D3 and other signaling molecules.
- To explore the interplay between 1,25D3-MARRS and the nuclear vitamin D receptor (nVDR) in intestinal calcium absorption.
Main Methods:
- Reverse transcription-polymerase chain reaction (RT-PCR) for transcript identification.
- Western blot analysis using specific antibodies for protein detection.
- Ribozyme knockdown, immunohistochemistry, and promoter analysis.
- Cell treatment with transforming growth factor beta1 (TGFbeta1) and 1,25(OH)2D3.
- Subcellular localization studies.
Main Results:
- A mammalian 1,25D3-MARRS protein was identified in the rat intestinal cell line IEC-6, exhibiting rapid responses to 1,25(OH)2D3.
- Promoter analysis revealed a conserved smad-3 element but no classical vitamin D response element (VDRE).
- TGFbeta1 treatment increased 1,25D3-MARRS mRNA and protein levels, while 1,25(OH)2D3 did not significantly alter them.
- 1,25D3-MARRS protein rapidly translocated to the nucleus upon 1,25(OH)2D3 treatment, indicating membrane-initiated signaling.
Conclusions:
- A mammalian 1,25D3-MARRS protein exists in intestinal cells and is rapidly activated by 1,25(OH)2D3 via a membrane-initiated pathway.
- The 1,25D3-MARRS system interacts with the nVDR, suggesting a coordinated role in fine-tuning intestinal calcium absorption.
- These findings reveal complex interactions between signaling pathways regulating intestinal calcium homeostasis in both avian and mammalian species.
