It is well established that Vitamin D essential for proper regeneration of epidermal barrier and immunomodulation. The active form of vitamin D, calcitriol (1,25(OH)2D3) thought the binding to vitamin D nuclear receptor (VDR), modulates expression of hundreds of genes. In an additions activity of VDR could be regulated on various levels. Here we presenting our preliminary results concerning effects of VDR expression, alternative splicing, expression of coactivator RXR on the activity of 1,25(OH)2D3 in human keratinocytes (HaCaT, A431 and primary cells). At least three splicing variants of VDR receptor mRNA were expressed in human keratinocyte cells, and its expression was modulated by 1,25(OH)2D3. Interestingly, keratinocytes cell lines used in the study differ in the patter of expressed VDR isoforms, which could at least partially explain observed various response to 1,25(OH)D3. Next it was shown, that overexpression of VDR splicing variants (VDR1 or VDR3) in keratinocytes had a modulatory effect on VDR signalling including delayed translocation of VDR to the nucleus and partial selectivity in target genes. The translocation of VDR1 and VDR3 was observed live by using fusion constructs of VDR isoform with green fluorescent protein (GFP). On the other hand, attenuation of VDR expression by RNAi resulted in downregulation of classic VDR targets in keratinocytes, however some phenotypic changes including induction of differentiation by 1,25(OH)2D3 were not full diminished what suggested involvement of alternative pathways. Thus, we are planning to investigate non geneomic pathways activated by vitamin D.
Summarising, our preliminary results suggest that alternative splicing of VDR may modulate response of keratinocytes to 1,25(OH)2D3 and could be essential regulatory factor in maintenance of epidermal barrier and skin physiology

On the role of vitamin D receptor alternative splicing in human keratinocytes