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

Abstract

The inhibitor of growth family member 3 (ING3) has been shown to modulate transcription, cell cycle control and apoptosis. We previously reported that nuclear ING3 expression was remarkably reduced in melanomas, which correlated with a poorer patient survival, suggesting that decreased ING3 expression may be associated with melanoma progression. However, the mechanism of diminished ING3 expression in melanoma is not clear. Here we show that ING3 level was decreased in metastatic melanoma cells because of a rapid degradation. Furthermore, we showed that ING3 undergoes degradation through the ubiquitinproteasome pathway. ING3 physically interacts with subunits of E3 ligase Skp1-Cullin-F-box protein complex (SCF complex). Knockdown of F-box protein S-phase kinaseassociated protein 2 (Skp2) reduces the ubiquitination of ING3 and significantly stabilizes ING3 in melanoma cells. In addition, lysine 96 residue is essential for ING3 ubiquitination as its mutation to arginine dramatically abrogated ING3 degradation. Disruption of ING3 degradation stimulated ING3-induced G1 cell-cycle arrest and enhanced ultravioletinduced apoptosis. Taken together, our data show that ING3 is degraded by the ubiquitin-proteasome pathway through the SCF Skp2 complex and interruption of ING3 degradation enhances the tumor-suppressive function of ING3, which provides a potential cancer therapeutic approach by interfering ING3 degradation.

Modulation of Intracellular Signaling Pathways to Induce Apoptosis in Prostate Cancer Cells

“…It is known that cells expressing oncogenic Ha-or Ki-ras are susceptible to apoptosis following the suppression of endogenous PKC (11)(12)(13)(14)(15). In this Ras-mediated apoptotic process, JNK1 activation is required (16).…”

“…oncogenic Ras is able to induce human or mouse fibroblasts or lymphocytes to undergo apoptosis once endogenous PKC is suppressed (11)(12)(13)(14)(15). In this process, multiple Ras downstream effectors are involved for transmitting apoptotic signaling.…”

“…In the process of transformation, a persistent increase in Ras activity up-regulates its downstream effector pathways, leading to the phosphorylation and activation of pro-growth transcriptional factors (5)(6)(7)(8)(9)(10). Despite its central involvement in cell growth and differentiation, we and others have demonstrated that treatment with PKC 2 inhibitors can induce apoptosis in various types of cells overexpressing oncogenic v-Ha or Ki-ras (11)(12)(13)(14)(15)(16). In addition, stress-related kinases, such as c-Jun kinase (JNK)/p38 functions as Ras downstream effectors to initiate apoptosis (4).…”

“…In mouse embryotic fibroblasts, the up-regulation of GADD153 correlates with the onset of PUMA-or NOXA-induced cell death (51). We previously demonstrated that Ras mutation, together with abrogation of PKC, are synthetically lethal (11)(12)(13)(14)(15)(16). Therefore, in this study, we tested whether abnormalities in Ras downstream effectors are able to induce apoptosis under PKCdeficient conditions in prostate cancer cells.…”

Role of ING Family Tumor Suppressors in Breast Cancer

“…ING3 expression significantly promoted apoptosis by activating the Fas/caspase-8 pathway, suggesting that ING3 may also be involved in the deathreceptor pathways [9,10,15,64]. Recently ING3 has been reported to be degraded by the ubiquitin-proteasome pathway through the SCF (Skp2) complex and interruption of ING3 degradation enhanced the tumor-suppressive function of ING3 [65]. p29ING4 was identified by Shiseki et al [66].…”