Satoshi Kanazawa

c-Myc recruits P-TEFb for transcription, cellular proliferation and apoptosis.

c-Myc promotes cellular proliferation, sensitizes cells to apoptosis and prevents differentiation. It binds cyclin T1 structurally and functionally from the positive transcription elongation factor b (P-TEFb). The cyclin-dependent kinase 9 (Cdk9) in P-TEFb then phosporylates the C-terminal domain of RNA polymerase II, which is required for the transition from initiation to elongation of eukaryotic transcription. Inhibiting P-TEFb blocks the transcription of its target genes as well as cellular proliferation and apoptosis induced by c-Myc.

Induction of Notch signaling by tumor necrosis factor in rheumatoid synovial fibroblasts.

Rheumatoid arthritis (RA) is characterized by progressive inflammation associated with abberrant proliferation of synoviocytes. In order to explore the characteristics of rheumatoid synovial fibroblasts (RSF), we performed the comparative gene expression profile analysis between RSF and normal synovial fibroblasts (NSF) upon tumor necrosis factor (TNF) stimulation. As an initial screening for the genes preferentially induced by TNF in RSF compared with NSF, we have adopted a cDNA array containing well-defined sets of genes responsible for cell growth, cell fate determination, and cellular invasiveness. Differentially expressed genes of interest were confirmed using real-time RT–PCR. We found that TNF induced the expression of Notch-1, Notch-4, and Jagged-2 in RSF. The expression of these proteins was detected in the RA synovial tissues. The nucleus of RA synoviocytes showed strong staining with anti-Notch-1 and Notch-4 antibody. TNF induced the nuclear translocation of Notch intracellular domain in RSF, indicating the elicitation of the Notch signaling. Notch-1, Notch-4, and Jagged-2 proteins were also detected in the developing synovium of mouse embryo. Thus, RSF may have re-acquired the primordial phenotype, accounting for the hyperproliferation and aggressive invasiveness, exhibiting tumor-like phenotype.

53BP2 induces apoptosis through the mitochondrial death pathway.

The p53 binding protein 2 (53BP2) has been identified as the interacting protein to p53, Bcl‐2, and p65 subunit of nuclear factor κB (NF‐κB). The TP53BP2 gene encodes two splicing variants, 53BP2S and 53BP2L, previously known as apoptosis stimulating protein 2 of p53 (ASPP2). We found that these 53BP2 proteins are located predominantly in the cytoplasm and induce apoptosis as demonstrated by cleavage of poly ADP ribose polymerase (PARP) and annexin V staining. Furthermore, we demonstrate that 53BP2 is located in the mitochondria and induces apoptosis associated with depression of the mitochondrial trans‐membrane potential (ΔΨm) and activation of caspase‐9. From these findings we conclude that 53BP2 induces apoptosis through the mitochondrial death pathway.