ABSTRACT
The epidermal growth factor receptor (EGFR) functions in various cellular physiological processes such as proliferation, differentiation, and motility. Although recent studies have reported that EGFR signaling is involved in osteoclast recruitment and formation, the molecular mechanism of EGFR signaling for the regulation of osteoclastogenesis remains unclear. We investigated the role of the EGFR in osteoclast differentiation and survival and show that the expression of the EGFR was highly up-regulated by receptor activator of nuclear factor-kappaB ligand (RANKL) during osteoclast differentiation. EGFR-specific tyrosine kinase inhibitors and EGFR knockdown blocked RANKL-dependent osteoclast formation, suggesting that EGFR signaling plays an important role in osteoclastogenesis. EGFR inhibition impaired the RANKL-mediated activation of osteoclastogenic signaling pathways, including c-Jun N-terminal kinase (JNK), NF-kappaB, and Akt/protein kinase B (PKB). In addition, EGFR inhibition in differentiated osteoclasts caused apoptosis through caspase activation. Inhibition of the phosphoinositide-3 kinase (PI3K)-Akt/PKB pathway and subsequent activation of BAD and caspases-9 and -3 may be responsible for the EGFR inhibition-induced apoptosis. The EGFR physically associated with receptor activator of nuclear factor-kappaB (RANK) and Grb2-associated binder 2 (Gab2). Moreover, RANKL transactivated EGFR. These data indicate that EGFR regulates RANKL-activated signaling pathways by cross-talking with RANK, suggesting that the EGFR may play a crucial role as a RANK downstream signal and/or a novel type of RANK co-receptor in osteoclast differentiation and survival.
Subject(s)
Cell Differentiation , ErbB Receptors/metabolism , Osteoclasts/metabolism , RANK Ligand/metabolism , Receptor Activator of Nuclear Factor-kappa B/metabolism , Signal Transduction , Adaptor Proteins, Signal Transducing , Animals , Apoptosis , Caspases/metabolism , Cell Differentiation/drug effects , Cell Survival , Cells, Cultured , Enzyme Activation , ErbB Receptors/antagonists & inhibitors , ErbB Receptors/genetics , Female , JNK Mitogen-Activated Protein Kinases/metabolism , Mice , Mice, Inbred ICR , NF-kappa B/metabolism , Osteoclasts/drug effects , Osteoclasts/enzymology , Phosphatidylinositol 3-Kinases/metabolism , Phosphoproteins/metabolism , Phosphorylation , Protein Binding , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins c-akt/metabolism , RNA Interference , RNA, Small Interfering/metabolism , Recombinant Proteins/metabolism , Signal Transduction/drug effects , Time Factors , Up-RegulationABSTRACT
The proto-oncogene protein DEK has been implicated in the t(6;9) chromosomal translocation associated with a subtype of acute myelogenous leukemia (AML), which results in the formation of a DEK-CAN fusion protein. Histone acetylation is an important post-translational modification which is involved in transcriptional regulation. In this study, we report that the acidic domain containing protein DEK interacts with histones and exerts a potent inhibitory effect on both p300 and PCAF-mediated histone acetyltransferase activity and transcription. Using chromatin immunoprecipitation assays, we have demonstrated that the recruitment of DEK to the appropriate promoter induces the histone H3 and H4 hypoacetylation of chromatin. Collectively, our data illustrate the important regulatory role played by protein DEK in transcriptional regulation, and suggest that transcription-regulating acidic domain regions may play a role in leukemogenesis.
