Vitamin D3/Vitamin A Receptor Interactions
The interaction between vitamin D3 and vitamin A receptors is complex. Since I am going to be spending some time discussing the role of this interaction in AIDS, allergy and asthma, I need to make the basics of this interation understandable to the reader.
The active form of vitamin D3 is 1,25 Vitamin D3. The active form of vitamin A is all-trans retinoic acid. Retinol is a form of vitamin A found in the eyes and has a slightly different structure.
Although there is only one basic form of vitamin D3 receptor, there are multiple forms of vitamin A receptors.
The vitamin D3 receptor or VDR interacts with the vitamin A RXR receptor before the complex enters the nucleus. Apparently, the interaction is stabilized by vitamin D3 binding to VDR. The RXR receptor is NOT bound to any form of vitamin A in this process. Apparently, the VDR/RXR interaction is required for maximal vitamin D3 signaling.
A form of vitamin A called 9-cis-retinoic acid can bind RXR and prevent heterodimer formation with the VDR receptor. Under these circumstances RXR, found to 9-cis RA, forms a complex with another RXR receptor, also found to 9-cis RA, called a homodimer. This complex binds to unique DNA sites on specific genes.
Although I have referred to vitamin D3 and vitamin A as synergistic hormones, this might be an incorrect characterization. The RXR receptor that is bound to VDR is NOT bound to a vitamin A molecule. In fact, if it does bind 9-cis RA, the vitamin D3 receptor becomes relatively inactive.
Vitamin D3 is required for normal functioning of the immune system. In its absence, the cell mediated immune, or Th1, response fails.
Vitamin A, on the other hand, shifts the immune response in another direction toward a Th2 or antibody mediated immune response. This immune response is associated with allergy, asthma and HIV infections.
Although the concentrations of vitamins D3 and A play a role in these immune dysfunctions, other factors are also at work to modulate hormone responsiveness.
I will discuss these issues in the context of HIV infections first. Allergy and asthma essays will follow.
Stay tuned...
Grouppe Kurosawa, Medicine in the Public Interest
(http://www.grouppekurosawa.com)
The active form of vitamin D3 is 1,25 Vitamin D3. The active form of vitamin A is all-trans retinoic acid. Retinol is a form of vitamin A found in the eyes and has a slightly different structure.
Although there is only one basic form of vitamin D3 receptor, there are multiple forms of vitamin A receptors.
The vitamin D3 receptor or VDR interacts with the vitamin A RXR receptor before the complex enters the nucleus. Apparently, the interaction is stabilized by vitamin D3 binding to VDR. The RXR receptor is NOT bound to any form of vitamin A in this process. Apparently, the VDR/RXR interaction is required for maximal vitamin D3 signaling.
A form of vitamin A called 9-cis-retinoic acid can bind RXR and prevent heterodimer formation with the VDR receptor. Under these circumstances RXR, found to 9-cis RA, forms a complex with another RXR receptor, also found to 9-cis RA, called a homodimer. This complex binds to unique DNA sites on specific genes.
Although I have referred to vitamin D3 and vitamin A as synergistic hormones, this might be an incorrect characterization. The RXR receptor that is bound to VDR is NOT bound to a vitamin A molecule. In fact, if it does bind 9-cis RA, the vitamin D3 receptor becomes relatively inactive.
Vitamin D3 is required for normal functioning of the immune system. In its absence, the cell mediated immune, or Th1, response fails.
Vitamin A, on the other hand, shifts the immune response in another direction toward a Th2 or antibody mediated immune response. This immune response is associated with allergy, asthma and HIV infections.
Although the concentrations of vitamins D3 and A play a role in these immune dysfunctions, other factors are also at work to modulate hormone responsiveness.
I will discuss these issues in the context of HIV infections first. Allergy and asthma essays will follow.
Stay tuned...
Grouppe Kurosawa, Medicine in the Public Interest
(http://www.grouppekurosawa.com)
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