Transfection of avian vitamin D-dependent calbindin-D28K 5' flanking promoter sequence in primary chick kidney cells

Lipid-mediated gene transfection into chick embryo retinal cells in ovo and in vitro

Several lipofection reagents were tested on chick embryo retinal cultures using green fluorescent protein (GFP) as a reporter gene; best results were obtained with the GenePORTER (GP) reagent, which yielded approximately 4.4% of the cells with intense GFP fluorescence. Cell survival and structural differentiation appeared normal, but one of the immunocytochemical markers studied (visinin) was less frequently observed in GP-treated cultures. When similar plasmid-GP mixtures were injected into chick embryo eyes in ovo, bright GFP-fluorescent cells were observed in different retinal layers, without detectable detrimental effects on retinal morphology. Particularly extensive reporter gene expression was obtained upon intraocular injection of GP plus naked DNA from a RCAS retrovirus, which resulted in the development of abundant radial columns of alkaline phosphatase-positive cells, separated by columns of negative cells. We conclude that lipid-based transfection offers a quick, simple and fairly innocuous means for gene delivery into proliferating and postmitotic retinal cells, in vitro as well as in the developing eye in ovo, and that transfection of naked retroviral DNA can lead to extensive expression of foreign genes by retinal cells, bypassing the time-consuming steps required for the generation of high-titer virion stocks.

Identification of sequence elements in mouse calbindin-D28k gene that confer 1,25-dihydroxyvitamin D3- and butyrate-inducible responses

We have examined the 5' flanking region of the mouse calbindin-D28k gene and identified a 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-responsive element by deletion mutant analysis of the native promoter as well as by studies with a heterologous thymidine kinase (TK) promoter. The segment between residues -200 and -169 was found to confer a dose-dependent 1,25-(OH)2D3 responsiveness through the TK promoter in Ros 17/2.8 cells as well as in CV-1 cells cotransfected with pAV-hVDR (human vitamin D receptor expression vector). This region contains sequences homologous to the rat osteocalcin vitamin D response element (VDRE). Incubation of this element with nuclear extracts from 1,25-(OH)2D3-treated Ros 17/2.8 cells or from 1,25-(OH)2D3-treated COS cells that had been transfected with pAV-hVDR resulted in a specific protein-DNA interaction. In addition to 1,25-(OH)2D3, sodium butyrate, a differentiating agent, has also been found to modulate expression of calbindin-D28k. Deletion analysis of the mouse calbindin-D28k promoter as well as studies with a heterologous TK promoter resulted in identification of a butyrate-responsive element between -180 and -150 that was found to bind specifically to nuclear factors from butyrate-treated Ros 17/2.8 cells. This butyrate-responsive element may represent a genetic element acted upon by enhancer binding proteins. In summary, the 5' flanking region of the mouse calbindin-D28k gene contains responsive elements that interact with nuclear factors and may mediate, at least in part, the enhanced expression of this gene by 1,25-(OH)2D3 and butyrate.

The expression of milligram amounts of functional human 1,25-dihydroxyvitamin D3 receptor in a bacterial expression system

We expressed milligram amounts of functional human 1,25-dihydroxyvitamin D3 receptor in a bacterial expression system in which the cloned cDNA for the hVDR was expressed under the control of bacterial T7 polymerase. The hVDR protein comprised approximately 60% of total bacterial protein. It migrated on polyacrylamide-sodium dodecyl sulfate gels with an M(r) of 48,000. It had the predicted amino acid composition and amino acid sequence analysis. The expressed protein was bound by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) with a Kd in the nanomolar range. It sedimented on sucrose density gradients at 3.5S. Furthermore, the expressed protein bound to the osteocalcin vitamin D response element (VDRE) as assessed by a gel mobility shift assay. The expression of large amounts of hVDR protein should allow for the use of this protein in structure-function and x-ray crystallography studies.

1,25(OH)2-vitamin D3, a steroid hormone that produces biologic effects via both genomic and nongenomic pathways

The hormonally active form of vitamin D is 1,25(OH)2-vitamin D3 [1,25(OH)2D3]. This seco-steroid is the key mediator of the vitamin D endocrine system which produces biological effects in over 28 target tissues. In these target tissues, the biological responses may be generated both by a signal transduction mechanism which involves a nuclear receptor for 1,25(OH)2D3 that modulates gene transcription or a signal transduction pathway which involves rapid opening of Ca2+ channels which are externally located on the plasma membrane. This paper reviews the evidence in support of the pleiotropic effects of this steroid hormone and presents evidence that the receptor of the genomic effects is likely to be separate from the receptor/membrane recognition element which initiates the rapid nongenomic biological effects.

Effects of sodium butyrate on 1,25-dihydroxyvitamin D3 receptor activity in primary chick kidney cells

The genomic effects of the steroid hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by high affinity nuclear associated specific receptors that belong to the superfamily of ligand induced transcription factors. The carboxylic acid, sodium butyrate--a potent inhibitor of histone deacetylase--is known to modulate gene expression in a variety of systems. Specific binding of 1,25(OH)2D3 to its receptor was examined in primary chick kidney cells, the chick macrophage cell line HD-11, and other mammalian cell lines such as ROS 17/2.8, HT-29 and CV-1 cells, that were all cultured in the presence or absence of 1 mM sodium butyrate. Treatment with n-butyrate resulted in significant (4.0-4.5-fold) increases in 1,25(OH)2D3 receptor binding without changing binding affinity only in the primary cultures of chick renal epithelial cells and the chick macrophage cell line but not in the other heterologous receptor-positive cell lines. The maximum increase in receptor binding was evident at 1 mM butyrate concentration. This effect reached a maximum at 15 h treatment, beyond which there was slow attenuation in increased binding until 24 h. The butyrate induced increases in receptor activity was associated with increases in the 1,25(OH)2D3-mediated induction of calbindin-D28K protein only in primary chick kidney cultures but not in the macrophage cell line (HD-11). Similarly, calbindin-D28K promoter activity was enhanced only in butyrate-treated primary chick kidney cultures, transfected with chimeric plasmids containing the 5' flanking sequence of the calbindin-D28K promoter fused to the chloramphenicol acetyl transferase (CAT) reporter gene but not in HD-11 cells.(ABSTRACT TRUNCATED AT 250 WORDS)