The receptor activator of NF-κB ligand (RANKL) induces various osteoclast-specific marker genes during osteoclast differentiation mediated by mitogen-activated protein (MAP) kinase cascades. However, the results of transcriptional programming of an osteoclast-specific cathepsin K gene are inconclusive. Here we report the regulatory mechanisms of RANKL-induced cathepsin K gene expression during osteoclastogenesis in a p38 MAP kinase-dependent manner. The reporter gene analysis with sequential 5′-deletion constructs of the cathepsin K gene promoter indicates that limited sets of the transcription factors such as NFATc1, PU.1, and microphthalmia transcription factor indeed enhance synergistically the gene expression when overexpressed in RAW264 cells. In addition, the activation of p38 MAP kinase is required for the maximum enhancement of the gene expression. RANKL-induced NFATc1 forms a complex with PU.1 in nuclei of osteoclasts following the nuclear accumulation of NFATc1 phosphorylated by the activated p38 MAP kinase. These results suggest that the RANKL-induced cathepsin K gene expression is cooperatively regulated by the combination of the transcription factors and p38 MAP kinase in a gradual manner.

Transcription elongation factor DSIF/Spt4–Spt5 is capable of promoting and inhibiting RNA polymerase II elongation and is involved in the expression of various genes. While it has been known for many years that DSIF inhibits elongation in collaboration with the negative elongation factor NELF, how DSIF promotes elongation is largely unknown. Here, an activity-based biochemical approach was taken to understand the mechanism of elongation activation by DSIF. We show that the Paf1 complex (Paf1C) and Tat-SF1, two factors implicated previously in elongation control, collaborate with DSIF to facilitate efficient elongation. In human cells, these factors are recruited to the FOS gene in a temporally coordinated manner and contribute to its high-level expression. We also show that elongation activation by these factors depends on P-TEFb-mediated phosphorylation of the Spt5 C-terminal region. A clear conclusion emerging from this study is that a set of elongation factors plays nonredundant, cooperative roles in elongation. This study also shows unambiguously that Paf1C, which is generally thought to have chromatin-related functions, is involve directlyd in elongation control.

Fibrodysplasia ossificans progressiva (FOP) patients carry a missense mutation in ACVR1 [617G > A (R206H)] that leads to hyperactivation of BMP-SMAD signaling. Contrary to a previous study, here we show that FOP fibroblasts showed an increased efficiency of induced pluripotent stem cell (iPSC) generation. This positive effect was attenuated by inhibitors of BMP-SMAD signaling (Dorsomorphin or LDN1931890) or transducing inhibitory SMADs (SMAD6 or SMAD7). In normal fibroblasts, the efficiency of iPSC generation was enhanced by transducing mutant ACVR1 (617G > A) or SMAD1 or adding BMP4 protein at early times during the reprogramming. In contrast, adding BMP4 at later times decreased iPSC generation. ID genes, transcriptional targets of BMP-SMAD signaling, were critical for iPSC generation. The BMP-SMAD-ID signaling axis suppressed p16/INK4A-mediated cell senescence, a major barrier to reprogramming. These results using patient cells carrying the ACVR1 R206H mutation reveal how cellular signaling and gene expression change during the reprogramming processes. Significance The development of iPSCs provides unprecedented opportunities for life sciences, drug discovery, and regenerative medicine. The efficiency of iPSC generation is quite low: typically less than 1% of human primary somatic cells that have received reprogramming factors turn into iPSCs. Previous studies revealed that cellular senescence was a major barrier to iPSC generation. In this study using human FOP mutant cells, we provide evidence that the BMP-SMAD-ID signaling suppressed p16/INK4A-mediated cellular senescence during the early phase in iPSC generation. These results are unexpected because BMP-SMAD signaling has negative effects on the self-renewal of human iPSCs. Here, we show that a human natural mutation increases the efficiency of iPSC generation.