1,25-Dihydroxyvitamin D3 exerts its effects by binding to the vitamin D receptor (VDR), which regulates transcription of target genes by recruiting various coactivators. Bikle and colleagues examined the role of several coactivators in human epidermal keratinocytes and found that, although these coactivators differentially associate with the VDR in proliferating versus differentiating keratinocytes, each is required for both early and late differentiation.