Identification of Clusterin Domain Involved in NF-κB Pathway Regulation

Abstract

Clusterin (CLU) is a ubiquitous protein that has been implicated in tumorigenesis, apoptosis, inflammation, and cell proliferation. We and others have previously shown that CLU is an inhibitor of the NF-B pathway. However, the exact form of CLU and the region(s) of CLU involved in this effect were unknown. Using newly generated molecular constructs encoding for CLU and various regions of the molecule, we demonstrated that the presecretory form of CLU (psCLU) form bears the NF-B regulatory activity. Sequence comparison analysis showed sequence motif identity between CLU and ␤-transducin repeat-containing protein (␤-TrCP), a main E3 ubiquitin ligase involved in IB-␣ degradation. These homologies were localized in the disulfide constraint region of CLU. We generated a specific molecular construct of this region, named ⌬CLU, and showed that it has the same NF-B regulatory activity as CLU. Neither the ␣-chain nor the ␤-chain of CLU had any NF-B regulatory activity. Furthermore, we showed that following tumor necrosis factor-␣ stimulation of transfected cells, we could co-immunoprecipitate phospho-IB-␣ with ⌬CLU. Moreover, we showed that ⌬CLU could localize both in the cytoplasm and in the nucleus. These results demonstrate the identification of a new CLU activity site involved in NF-B pathway regulation.

The Molecular Chaperone Apolipoprotein J/Clusterin as a Sensor of Oxidative Stress: Implications in Therapeutic Approaches - A Mini-Review

“…1) pathway [36]. A cytosolic function of CLU also correlates with its reported implication in the regulation of the NF-κB nuclear translocation and activity [39,40], while among the recently identified intracellular CLU interacting proteins are the erythrocytic protein Band-3 [41] and the molecular chaperone HSP60 [42]. …”

“…More recently, CLU gene expression was found to be induced during progression of primary osteoarthritis [67]. Interestingly, CLU seems to also directly intervene in NF-κB regulation, although its role remains debated; depending on the experimental model, CLU had either a negative [39] or a positive effect [40] on NF-κB activity.…”

Implication of clusterin in TNF-α response of rheumatoid synovitis: lesson from in vitro knock-down of clusterin in human synovial fibroblast cells

“…Overall, it appeared recently that many previously reported functions are related to the intracellular forms of the protein, especially NF-B signaling and apoptosis. Indeed, intracellular level of CLU are essential for NF-B activity regulation (6,14), via its effect on the modulation of IB expression that seems to be linked to interaction to a ubiquitin ligase. As NF-B induced genes expression contributes to the pathogenesis of inflammatory diseases such as arthritis, CLU appeared to be a protein possibly involved in RA pathophysiology.…”

“…Among the identified genes modulated in RA synovitis, the clusterin (CLU) gene appears to be a potential gene of interest because it has multiple functions related to apoptosis, inflammation, proliferation, and differentiation (4,5,7). The different functions of CLU depend on its final maturation and localization, cytosolic or nuclear, and involve NF-B signaling and juxtanuclear aggregates (3,6,14). The predominant form of CLU is a secreted heterodimeric protein of 80 kDa (sCLU) produced from the full-length RNA.…”

Clusterin confers resistance to TNF-alpha-induced apoptosis in breast cancer cells through NF-kappaB activation and Bcl-2 overexpression

“…However, the exact form of clusterin and the region(s) of clusterin involved in this effect were unknown. Essabani et al 32 has shown the pre-secretory form of clusterin (psClu) form bears the NF-kappaB regulatory activity. Neither the alpha-chain nor the beta-chain alone of clusterin had any NF-kappaB regulatory activity.…”