Differential regulation of nuclear factor‐kappa B subunits on epidermal keratinocytes by ultraviolet B and tacrolimus

Modulation of nuclear factor-kappa B (NF-κB) expression has important clinical implications including anti-inflammation. Recently, we have shown that direct regulation of NF-κB/p65 subunit may account for tacrolimus ointment's remarkable clinical efficacy on treating inflammatory dermatoses. However, NF-κB is a dimeric transcription factor formed by hetero- or homodimeration of the five Rel family proteins. The complete operational scheme of different NF-κB subunits remains obscure. It has been shown that homodimers consist of NF-κB/p50 may serve an inhibitory role in suppressing inflammation while dimers consisting of NF-κB/p65 activate inflammatory pathway. Our current study aimed to explore the effects of ultraviolet B (UVB) on epidermal keratinocytes in terms of specific NF-κB subunits NF-κB/p50 and NF-κB/p65. Additionally, the effects of tacrolimus on differential regulation of NF-κB subunits of UVB irradiated keratinocytes were also investigated. Our result showed that UVB sequentially regulated the activities of different subunits of NF-κB: the activity of NF-κB/p50 was downregulated in the early stage (6 hours), followed by upregulation of NF-κB/p65 in the later stage (12 hours). The results from immunofluorescence, immunocytochemical, and immunohistochemical analyses indicated that the nuclear expression of NF-κB/p50 could be seen constitutively while the nuclear expression of NF-κB/p65 could only be seen after UVB irradiation. Furthermore, treatment with tacrolimus didn't affect the nuclear activation and translocation of NF-κB/p50, while the UVB induced NF-κB/p65 nuclear expression was suppressed by tacrolimus. In summary, we have shown that UVB irradiation sequentially regulated different NF-κB subunits. The clinical efficacy of tacrolimus may be attributed to its specific regulatory effect on NF-κB/p65 but not NF-κB/p50 of the NF-κB pathway.