Publications (8)40.9 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: Serine-threonine Ca2+/calmodulin-dependent protein kinase II (CaMKII) is the key component in noncanonical Wnt5a signaling and has been shown to regulate its signaling. In this study, we found that CaMKII induced by Wnt5a remarkably reduced the protein stability of the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT), a co-repressor of Notch signaling, through proteasomal degradation. Wnt5a was found to enhance Notch1 intracellular domain (Notch1-IC) transcription activity, which could be inhibited by treatment with KN93, a CaMKII inhibitor. The kinase activity of CaMKII was essential for the activation of Notch signaling. We also determined that CaMKII could enhance the association between Notch1-IC and RBP-Jk. Furthermore, the physical association between RBP-Jk and SMRT was substantially suppressed by CaMKII. We demonstrated that CaMKII directly bound and phosphorylated SMRT at Ser-1407, thereby facilitating SMRT translocation from the nucleus to the cytoplasm and proteasome-dependent degradation. These results suggest that CaMKII down-regulated the protein stability of SMRT through proteasomal degradation.
- [Show abstract] [Hide abstract] ABSTRACT: Notch1 genes encode receptors for a signaling pathway that regulates cell growth and differentiation in various contexts, but the role of Notch1 signaling in osteogenesis is not well defined. Notch1 controls osteoblast differentiation by affecting Runx2, but the question arises whether normal osteoblastic differentiation can occur regardless of the presence of Notch1. In this study, we observed the downregulation of Notch1 signaling during osteoblastic differentiation. BMPR-IB/Alk6-induced Runx2 proteins reduced Notch1 activity to a marked degree. Accumulated Runx2 suppressed Notch1 transcriptional activity by dissociating the Notch1-IC-RBP-Jk complex. Using deletion mutants, we also determined that the N-terminal domain of Runx2 was crucial to the binding and inhibition of the N-terminus of the Notch1 intracellular domain. Notably, upregulation of the Runx2 protein level paralleled reduced expression of Hes1, which is a downstream target of Notch1, during osteoblast differentiation. Collectively, our data suggest that Runx2 is an inhibitor of the Notch1 signaling pathway during normal osteoblast differentiation.
- [Show abstract] [Hide abstract] ABSTRACT: Notch is a transmembrane protein that acts as a transcriptional factor in the Notch signaling pathway for cell survival, cell death and cell differentiation. Notch1 and Fbw7 mutations both lead the activation of the Notch1 pathway and are found in the majority of patients with the leukemia T-ALL. However, little is known about the mechanisms and regulators that are responsible for attenuating the Notch signaling pathway through Fbw7. Here, we report that the serum- and glucocorticoid-inducible protein kinase SGK1 remarkably reduced the protein stability of the active form of Notch1 through Fbw7. The protein level and transcriptional activity of the Notch1 intracellular domain (Notch1-IC) were higher in SGK1-deficient cells than in SGK1 wild-type cells. Notch1-IC was able to form a trimeric complex with Fbw7 and SGK1, thereby SGK1 enhanced the protein degradation of Notch1-IC via a Fbw7-dependent proteasomal pathway. Furthermore, activated SGK1 phosphorylated Fbw7 at serine 227, an effect inducing Notch1-IC protein degradation and ubiquitylation. Moreover, accumulated dexamethasone-induced SGK1 facilitated the degradation of Notch1-IC through phosphorylation of Fbw7. Together our results suggest that SGK1 inhibits the Notch1 signaling pathway via phosphorylation of Fbw7.
- [Show abstract] [Hide abstract] ABSTRACT: DJ-1 has been reported as a gene linked to early onset familial Parkinson's disease, and is functionally involved in transcriptional regulation and oxidative stress-induced cell death. To understand the role of DJ-1 in cellular stress, this study investigated DJ-1's effect on stress-activated protein kinase signaling and H(2)O(2)-induced activation of apoptosis signal-regulating kinase 1 (ASK1). According to the results, the overexpression of DJ-1 inhibited H(2)O(2)-induced activation of ASK1 as well as the activation of downstream kinases in the p38 mitogen-activated protein kinase (MAPK) signaling cascade. The results of both in vivo binding and kinase studies have revealed that ASK1 is the direct target of DJ-1, whereas it has shown no effect on either MKK3 or p38. DJ-1 blocked both the homo-oligomerization of ASK1 and inhibited ASK1 activity. Taken together, our data strongly suggest that DJ-1, by directly inhibiting ASK1, may act as a negative regulator in ASK1 signaling cascades.
- [Show abstract] [Hide abstract] ABSTRACT: Notch proteins perform a critical function in cell-fate decisions and in differentiation. In this study, we determined that indirubin-3'-monoxime reduced Notch1 signaling to a remarkable extent. Indirubin-3'-monoxime has been shown to inhibit both constitutive active mutants of Notch1 and Notch1-IC-mediated transactivation activity. However, in such cases, neither the Notch cleavage pattern nor the protein stability of Notch1-IC was determined to have been significantly altered. Indirubin-3'-monoxime suppresses Notch1 transcriptional activity via the dissociation of the Notch1-IC-RBP-Jk complex. Notably, the transcriptional activity of Notch1-IC was not suppressed significantly in the GSK-3beta null cells by indirubin-3'-monoxime as compared to what was observed with GSK-3beta wild-type cells. In the previous study, we synthesized a series of indirubin derivatives. Interestingly, some of these indirubin derivatives were characterized as potent inhibitors of Notch1 signaling. Taken together, the results of this study indicate that indirubin-3'-monoxime downregulated Notch1 signaling in a GSK-3beta-dependent and proteosomal degradation-independent manner.
- [Show abstract] [Hide abstract] ABSTRACT: The Notch signaling pathway appears to perform an important function in the determination of cell fate and in differentiation, in a wide variety of organisms and cell types. In this study, we provide evidence that the inactivation of Notch signaling by zinc is achieved via a PI3K-Akt-dependent, cytoplasmic retention of Notch1-IC and RBP-Jk. Extracellular zinc has been determined to inhibit constitutive active mutants of both Notch1 (DeltaEN1) and Notch1-IC-mediated transcription. However, in such cases, neither the cleavage pattern of Notch nor the protein stability of Notch1-IC and RBP-Jk was found to have significantly changed. With regard to the modulation of Notch signaling, zinc appears to exert a significant negative influence on the binding occurring between Notch1 and RBP-Jk, both in vivo and in vitro. The zinc-induced inhibition of Notch signaling can be rescued via pretreatment with wortmannin or LY294002, both of which are specific PI3K signaling pathway inhibitors. Furthermore, we ascertained that zinc triggers the cytoplasmic retention of Notch1-IC and RBP-Jk, and that cytoplasmic retention could be rescued via treatment with wortmannin. Overall, we have determined that an important relationship exists between zinc and the Notch1 signaling pathway, and that this relationship is intimately involved with the cytoplasmic retention of Notch and RBP-Jk.
- [Show abstract] [Hide abstract] ABSTRACT: The Notch signaling pathway appears to perform an important function in a wide variety of organisms and cell types. In our present study, we provide evidence that UV irradiation-induced Tip60 proteins reduced Notch1 activity to a marked degree. Accumulated UV irradiation-induced Tip60 suppresses Notch1 transcriptional activity via the dissociation of the Notch1-IC-CSL complex. The binding between endogenous Tip60 and Notch1-IC in UV radiation-exposed cells was verified in this study by coimmunoprecipitation. Interestingly, the physical interaction of Tip60 with Notch1-IC occurs to a more profound degree in the presence of CSL but does not exist in a trimeric complex. Using Notch1-IC and Tip60 deletion mutants, we also determined that the N terminus, which harbors the RAM domain and seven ankyrin repeats of Notch1-IC, interacts with the zinc finger and acetyl coenzyme A domains of Tip60. Furthermore, here we report that Notch1-IC is a direct target of the acetyltransferase activity of Tip60. Collectively, our data suggest that Tip60 is an inhibitor of the Notch1 signaling pathway and that Tip60-dependent acetylation of Notch1-IC may be relevant to the mechanism by which Tip60 suppresses Notch1 signaling.
- [Show abstract] [Hide abstract] ABSTRACT: Integrin-linked kinase (ILK) is a scaffold and protein kinase that acts as a pivotal effector in integrin signaling for various cellular functions. In this study, we found that ILK remarkably reduced the protein stability of Notch1 through Fbw7. The kinase activity of ILK was essential for the inhibition of Notch1 signaling. Notably, the protein level and transcriptional activity of the endogenous Notch1 intracellular domain (Notch1-IC) were higher in ILK-null cells than in ILK wild-type cells, and the level of endogenous Notch1-IC was increased by the blocking of the proteasome, suggesting that ILK enhances the proteasomal degradation of Notch1-IC. ILK directly bound and phosphorylated Notch1-IC, thereby facilitating proteasomal protein degradation through Fbw7. Furthermore, we found down-regulation of Notch1-IC and up-regulation of ILK in basal cell carcinoma and melanoma patients but not in squamous cell carcinoma patients. These results suggest that ILK down-regulated the protein stability of Notch1-IC through the ubiquitin-proteasome pathway by means of Fbw7.
Chonnam National University
Gwangju, Gwangju, South Korea
- School of Biological Sciences and Technology