|
I think these agents (viruses and also throw in heavy metals) could be related in that they can induce stress-related gene expression in a cell. If the cell has suffered chromosome damage from low levels of vitamin D and the resulting genomic instability that can entail, then the cell's stress response could be exaggerated and lead to an over-reaction, over-expression of some genes that have lost their normal control.
Mutation Research 475 (2001) 69–88
Review
Vitamin D and genomic stability
Malay Chatterjee
Abstract
1a,25-dihydroxyvitaminD3 [1,25(OH)2D3] has been shown to act on novel target tissues not related to calcium homeostasis.
There have been reports characterizing 1,25(OH)2D3 receptors and activities in diverse tissues such as brain, pancreas, pituitary,
skin, muscle, placenta, immune cells and parathyroid. The receptor hormone complex becomes localized in the nucleus, and
undergoes phosphorylation by reacting with a kinase. This form of the receptor then interacts with the Vitamin D responsive
element of target gene and modifies the transcription of those genes to develop the action. The modulation of gene transcription
results in either the induction or repression of specific messenger RNAs (m-RNAs), ultimately resulting in changes in protein
expression needed to produce biological responses. Genes for carbonic anhydrase that are expressed at high levels in osteoclast
are known to be involved in bone resorption and Id genes role in osteoblast–osteoclast differentiation reflects the genomic effect
of Vitamin D on bones. Genomic action of Vitamin D also explains the biosynthesis of oncogenes, polyamines, lymphokines
and calcium binding proteins. However, there is a possibility that some of the actions of 1,25(OH)2D3 may be mediated by
non-genomic mechanisms and may not require the binding to Vitamin D receptor (VDR).
Vitamin D offers a protection from genotoxic effects of Vitamin D deficiency by increasing the insulin receptor gene expression
and BSP (bone sialoprotein), bone-remodeling by decreasing the osteopontin (OPN) m-RNAs, maintaining the normal
epidermal structure and enamel matrix. Gonadal insufficiency in Vitamin D deficiency was corrected by vitamin mediated
direct regulation of the expression of aramotase gene. The supportive role of Vitamin D in placental function is also evident
by its influence on human placental lactogen (hpl) gene transcription accompanied by increase hpl m-RNA levels. Further
role of Vitamin D is envisaged in identifying cyclin C as an important target for Vitamin D in cell-cycle regulation.
Vitamin D at physiological concentration has been found to protect cell proteins and membranes against oxidative stress by
inhibiting the peroxidative attack on membrane lipids. Vitamin D, at a concentration range of 210−8–510−8 M, induces
apoptosis in most cancer cells, stabilizes chromosomal structure and prevents DNA double-strand breaks induced either
by endogenous or exogenous factors. Vitamin D is also effective in stimulating DNA synthesis in adult alveolar II cells and
provides a novelmechanism of modulation of epithelial cell proliferation in the context of lung development and repair against
injury. The regulation of various proto-oncogenes (c-myc, c-fos, c-jun), differentiation inducing properties, antiproliferative
effects on keratinocytes and inhibitory effects in several human malignancy ranks Vitamin D as a novel hormone that may
have physiological and clinical implication in the carcinogenic process.
Notice the expression with regards to vitamin D "stabilizes chromosomal structure and prevents DNA double-strand breaks induced either by endogenous or exogenous factors."
So someone who has low vitamin D could have an accumulation of DNA double-strand breaks and other damage that can lead to chromosomal fragmentation, improper distribution of chromatin to daughter cells, and opening up of previously sequestered genes. One gene I have pointed to previously is spermine synthase on the X chromosome. With two X chromosomes, normally one is inactive the other active. But with chromosome instability, leading to fragmentation and/or low methylation, perhaps both become active leading to over expression of spermine synthase from both copies of the gene instead of just one. Look at the following:
'Methylthioadenosine, a potent inhibitor of spermine synthase from bovine brain' Pajula RL and Raina A, FEBS Letters (1979) 99:343-345.
'Methylthioadenosine reverses brain autoimmune disease' Moreno et al. Ann Neurol 2006;60:323-334.
Granted, these authors used EAE rats and attribute the reversal to suppression of the immune system's autoimmune attack but at least someone is finally talking about the right enzyme as far as I'm concerned. If spermine synthase is over-active it can reduce S-adenosylmethionine needed for methylation and reduce the spermidine needed for myelin formation and hypusine formation that is essential for translation. It can also alter the inactions of vitamin D receptor with its targets. An excess of spermine can stabilize Z-DNA, which is a major auto-antigen in lupus. The genomic instability could also lead to expression of LINEs and SINEs which then give the appearance of reverse transcriptase activity and would put a big strain on the cell's S-adenosylmethionine needed for methylation. See: 'The long (LINEs) and the short (SINEs) of it: Altered methylation as a precursor to toxicity' Carnell AN and Goodman JI Toxicological Sciences (2003) 75:229-235.
Does disruption of the X chromosome as I am proposing have a relation to autoimmune diseases? See:
ARTHRITIS & RHEUMATISM
Vol. 54, No. 4, April 2006, pp 1270–1278
Identification and Characterization of an Xp22.33;Yp11.2
Translocation Causing a Triplication of Several Genes of the
Pseudoautosomal Region 1 in an XX Male Patient
With Severe Systemic Lupus Erythematosus
Pierre Chagnon,et al.
The X;Y translocation break point sequence in
an XX male patient with prepubertal systemic lupus
erythematosus (SLE) was characterized with the intention
of identifying a predisposing gene(s) for SLE.
Spectral karyotyping of the patient’s metaphase chromosomes
showed normal autosomes and 2 X chromosomes,
one of which displayed a small portion of the Y
chromosome. Using a Y chromosome polymerase chain
reaction (PCR) walking strategy and inverse PCR, we
found that the abnormal recombination occurred between
retroviral long terminal repeats located at
Xp22.33 (position 0.95 Mb; inside the pseudoautosomal
regions) and Yp11.2 (4.20 Mb) downstream of the
sex-determining region Y (SRY) gene. The complete
DNA sequence of the break point was determined,
revealing a partial duplication of the pseudoautosomal
region 1 (PAR1) in the derivative X chromosome and
causing a partial trisomy of the 12 known genes located
between the interleukin-3 receptor (IL3RA; position
1.1 Mb on the X and Y chromosomes) and CD99
(position 2.2 Mb) genes inclusively. All other X chromosome
genes were present as 2 copies. Real-time quantitative
PCR confirmed the presence of 3 copies of each of
the 12 genes in the patient’s genomic DNA. We also
found that RNA for 1 of the candidate genes was indeed
overexpressed in the patient’s blood as compared with
normal subjects. Taken together, the uniqueness of the
translocation, the rarity of severe prepubertal SLE in
males, and the presence of SLE in some patients with
Klinefelter’s syndrome (who have a triplication of the 2
PAR regions) point to a possible relationship between
the partial triplication of the PAR1 region and the
development of SLE.
This disruption of the X by insertion of a small fragment of the Y in an XX male is enough to give the person a male phenotype but also appears to give the person a susceptibility for lupus. This insertion location is near the spermine synthase gene at Xp22.1. Although the insertion is distal to Xp22.1, my belief is that it disrupts the overall X inactivation (chromatin structure) process in that region, including proximally into Xp22.1. There are other case of X-linked chronic granulomatous disease with disruptions at Xp21.2 leading to lupus. The authors of the Arthritis & Rheumatism article above cite two genes that are particularly interesting: the IL3RA gene for a subunit of the interleukin-3 receptor and CD99, a cell surface molecule involved in adhesion and T cell apoptosis. These two genes would be more easily seen as culprits than the spermine synthase I'll admit but they all could be problems when the chromatin is disrupted.
It's been two years since I wrote about polyamines in detail. I probably should try to write out my theory again with the newer material I am finding and get it published somewhere. It just doesn't seem to interest the autoimmune research world. I get more interest from the cancer researchers though in relating genome instability, polyamines, and tumor growth.
Wesley
|