Figure 1. CDK4 and CDK6 regulate the expression of IκBζ and its proinflammatory target genes in IL-36α– and IL-17A/TNF-α–stimulated keratinocytes.

(A) Human primary keratinocytes were treated for 1 hour with 100 ng/mL IL-36α or 200 ng/mL IL-17A and 10 ng/mL TNF-α. The CDK4/6 inhibitor abemaciclib (Abe) or an ethanol vehicle control (Ctrl) were added in parallel. Phosphorylation of RB (pRB) served as a control for CDK4/6 inhibition, and actin as a loading control. Relative mRNA levels of IκBζ (NFKBIZ) were normalized to the reference gene RPL37A. (B) Luciferase assay of IκBζ (NFKBIZ) promoter activity in HaCaT cells that were cytokine-stimulated for 24 hours in the presence or absence of the CDK4/6 inhibitors abemaciclib or palbociclib (Pal). Relative luciferase (luc) activity was normalized to an internal Renilla luciferase control that was transfected in parallel. Endogenous protein levels were analyzed as input controls by immunoblotting (bottom). (C and D) CDK4 and CDK6 were depleted in primary human keratinocytes by lentiviral transduction of shRNA. Ctrl shRNA– or CDK4/6 shRNA–depleted cells were treated with (C) IL-36α or (D) IL-17A/TNF-α, similar as in A. (E and F) Human primary keratinocytes were stimulated with IL-36α as in A. (E) Cytokine gene expression in CDK4/6 inhibitor–treated cells. (F) Relative gene expression levels in IL-36α–treated control or CDK4/6-depleted cells. (G) Transient overexpression of CDK4, CDK6, or CDK9 in HaCaT cells, treated for 1 hour with 100 ng/mL IL-36α. (H) Cytokine gene expression in IL-36α–treated primary keratinocytes overexpressing IκBζ in the presence or absence of abemaciclib. For all analyses, n = 3 ± SD. Significance was calculated using a 1-way ANOVA for multiple groups and a 2-tailed Student’s t test for comparing 2 groups: *P < 0.05; **P < 0.01; ***P < 0.001.