E3 Ubiquitin Ligase RNF126 Promotes Cancer Cell Proliferation by Targeting the Tumor Suppressor p21 for Ubiquitin-Mediated Degradation

Abstract

To identify novel oncogenic E3 ubiquitin ligases as anticancer targets, we screened an E3 ubiquitin ligase siRNA library containing siRNA pools against 555 individual E3s using the sulphorhodamine B assay in the MDA-MB-231 breast cancer cell line and the PC3 prostate cancer cell line. RNF126 was identified and validated as a candidate from this screening. Knockdown of RNF126 dramatically decreased cell viability in these cancer cell lines. Consistently, RNF126 knockdown delayed cell-cycle G 1 -S progression and decreased cell proliferation. Using protein array analysis we found that RNF126 silencing increased cell-cycle dependent kinase inhibitor p21 cip protein levels in both MDA-MB-231 and PC3. Knockdown of RNF126 stabilized the p21 protein rather than increased p21 mRNA levels. We showed that RNF126 interacts with p21 and RNF126 overexpression increased p21 protein ubiquitination in an E3 ligase activity-dependent manner. RNF126 knockdown induced loss of cell viability in MDA-MB-231 and PC-3 can be partially rescued by depletion of p21. RNF126 stable knockdown in PC3 inhibited tumor growth in SCID mice. Finally, we found that RNF126 is highly expressed in a subset of breast cancer cell lines and negatively correlated with p21 expression levels. These findings suggest that RNF126 promotes cancer cell proliferation by targeting p21 for ubiquitin-mediated degradation. RNF126 could be a novel therapeutic target in breast and prostate cancers. Cancer Res; 73(1); 385-94. Ó2012 AACR.

Stabilization of p21 (Cip1/WAF1) following Tip60-dependent acetylation is required for p21-mediated DNA damage response

“…11,13,14 The interaction of histone deacetylases (HDACs) with p21 was also identified in a recent study, suggesting a possible acetylation process for p21.…”

“…9 In addition to these ligases, p21 levels are closely monitored under normal cellular conditions by other E3 ligases, such as MKRN1, p53RFP, and RNF126, in order to facilitate senescent-free progression. 11,13,14 The interaction of histone deacetylases (HDACs) with p21 was also identified in a recent study, suggesting a possible acetylation process for p21. 15 Tip60, originally identified as HIV-1 interacting acetyltransferase, is a member of the MYST family, which contains MOZ, Ybf2/Sas2, and Sas2 motifs.…”

Cytosolic Quality Control of Mislocalized Proteins Requires RNF126 Recruitment to Bag6

“…This interaction was markedly reduced (but not entirely eliminated) by deleting the Ubl domain of Bag6 (ΔUbl). RNF126 contains two recognizable domains: a Zn finger domain near the N terminus (residues 10–40), and a RING domain near the C terminus (residues 229–270) shown before to possess E3 ligase activity (Zhi et al., 2013). Deletion constructs of RNF126 in the Zn finger region abolished the Bag6 interaction, while a construct encoding only the first 100 residues of RNF126 (RNF126F) could be coimmunoprecipitated with Bag6 (Figure 3D).…”

E3 Ubiquitin ligase RNF126 regulates the progression of tongue cancer

“…First, the substrates of RNF126, like p21 14, Bag6 15, and EGFR 9 are involved in oncogenesis. It promotes cell proliferation partially through degrading p21 14.…”

“…First, the substrates of RNF126, like p21 14, Bag6 15, and EGFR 9 are involved in oncogenesis. It promotes cell proliferation partially through degrading p21 14. Second, it shares similar protein domains and structure with the E3 ligases, BCA2, which is involved in the progression of breast cancer 16.…”