Fig. 8: CDK9 is dissociated from HEXIM1 upon KL or TPA treatment.

a–c Keratinocytes expressing HA-CDK9 were treated with DMSO control, KL, or TPA. Immunoprecipitation using the HA antibody was performed from the lysate of these keratinocytes, followed by western blot probing for HA and HEXIM1. d–g Violin and ECDF plots showing HA-CDK9 traveling ratio (TR) with KL or TPA relative to DMSO control at 92, direct, rapid-response genes (****P < 0.001 ***P < 0.01, d, e KL P = 0.0002, f, g P = 0.0041, two-tailed, unpaired t test). A higher travel ratio indicates high proportion of CDK9 binding in the gene body. h Genome browser tracks comparing HA-CDK9 ChIP-seq enrichment at ATF3 among the DMSO control, KL treatment, or TPA treatment. i Illustration of the working model. In the progenitor state, AFF1 and HEXIM1 cooperatively hold CDK9 in an inactive state. With SEC disruption (KL) or PKC signaling (TPA), CDK9 from SEC-AFF1 is rapidly released into an active form. This rapid switch allows the activation of SEC-direct-target genes such as ATF3, which can further promote the expression of differentiation-activating transcription factors (GRHL3, PRDM1, ZNF750, and OVOL1, etc) to advance the terminal differentiation process. Source data are provided as a Source Data file.