Subcellular Targeting of p33^ING1b by Phosphorylation-Dependent 14-3-3 Binding Regulates p21^WAF1 Expression

Abstract

ING1 is a type II tumor suppressor that affects cell growth, stress signaling, apoptosis, and DNA repair by altering chromatin structure and regulating transcription. Decreased ING1 expression is seen in several human cancers, and mislocalization has been noted in diverse types of cancer cells. Aberrant targeting may, therefore, functionally inactivate ING1. Bioinformatics analysis identified a sequence between the nuclear localization sequence and plant homeodomain domains of ING1 that closely matched the binding motif of 14-3-3 proteins that target cargo proteins to specific subcellular locales. We find that the widely expressed p33ING1b splicing isoform of ING1 interacts with members of the 14-3-3 family of proteins and that this interaction is regulated by the phosphorylation status of ING1. 14-3-3 binding resulted in significant amounts of p33ING1b protein being tethered in the cytoplasm. As shown previously, ectopic expression of p33 ING1bincreased levels of the p21 Waf1 cyclin-dependent kinase inhibitor upon UV-induced DNA damage. Overexpression of 14-3-3 inhibited the up-regulation of p21Waf1 by p33 ING1b , consistent with the idea that mislocalization blocks at least one of ING1's biological activities. These data support the idea that the 14-3-3 proteins play a crucial role in regulating the activity of p33ING1b by directing its subcellular localization.

Sumoylation of ING2 regulates the transcription mediated by Sin3A

“…As the potential PDSMs of ING2 and p33ING1b are sumoylated or phosphorylated, respectively, this strongly suggests that ING2 sumoylation could be regulated by an adjacent phosphorylation site and, reciprocally, that ING1 phosphorylation could regulate its potential sumoylation. Gong et al (2006) observed p33ING1b exportation from the nucleus after 14-3-3Z overexpression. Thus, even if under our experimental conditions we observed that ING2 subcellular localization is independent on its sumoylation, we cannot exclude that in other conditions sumoylation of ING2 could be involved in this process.…”

“…p33ING1b has been reported to be phosphorylated on serine 199 (S199) to regulate its amount in the nucleus. Indeed, this phosphorylation event was shown to be required for p33ING1 binding to the 14-3-3Z cargo protein in order to be exported from the nucleus (Gong et al, 2006). Interestingly, the serine 199 of ING1 is the serine residue belonging to the potential PDSM.…”

The tumor suppressor ING3 is degraded by SCFSkp2-mediated ubiquitin–proteasome system

“…In this study, we found that rapid ING3 degradation has an important role in the loss of ING3 expression in advanced melanomas, thereby providing another explanation of aberrant ING3 expression in melanomas in addition to our previous finding that subcellular relocalization of ING3 causes its deregulation in both primary and metastatic melanomas (Wang et al, 2007). Meanwhile, ING1b has been shown to be shifted from the nucleus to the cytoplasm in melanocytic lesions (Nouman et al, 2002), which may be mediated by 14-3-3 proteins (Gong et al, 2006). Both nuclear ING2 and overall ING4 expressions are also downregulated in melanomas, although only the reduced ING4 expression was significantly associated with melanoma progression (Lu et al, 2006;Li et al, 2008).…”

Cytoplasmic expression of p33ING1b is correlated with tumorigenesis and progression of human esophageal squamous cell carcinoma

“…Studies revealed that 14-3-3 family members primarily reside in the cytoplasm and are associated with phosphorylated ligands involved in numerous cellular processes, including regulation of the cell cycle and DNA damage checkpoints. Binding to 14-3-3 causes tethering of significant amounts of p33 ING1b in the cytoplasm (33,34). Moreover, other studies have demonstrated that cytoplasmic p33…”

“…ING1b particularly binds to members of the 14-3-3 family through phosphorylation at serine residue 199 (33). Studies revealed that 14-3-3 family members primarily reside in the cytoplasm and are associated with phosphorylated ligands involved in numerous cellular processes, including regulation of the cell cycle and DNA damage checkpoints.…”