VDR and the MEK/ERK signaling pathway are involved in cathelicidin induction by vitamin D analogs. To characterize the role of the VDR in increased cathelicidin expression after treatment with vitamin D analogs, NHEK were transfected with siRNA to decrease VDR expression before stimulation with vitamin D analogs ZK191784, ZK203278 and calcipotriol (all at 10 −8 M). Silencing of VDR was confirmed by qPCR (A; left panel) and Western blot (B; middle panel). siRNA suppression of VDR significantly reduced the induction of cathelicidin mRNA by all vitamin D analogs after 24 hours (A; right panel) (* P