Efp targets 14-3-3σ for proteolysis and promotes breast tumour growth

Abstract

Oestrogen exerts its influence on target organs through activating oestrogen receptors (ERs) and regulating downstream genes by means of their oestrogen-responsive elements. Efp, a target gene product of ER alpha, is a member of the RING-finger B-box coiled-coil (RBCC) motif family. Efp is predominantly expressed in various female organs as well as in breast cancers, and is thought to be essential for oestrogen-dependent cell proliferation and organ development Efp-disrupted mice display underdeveloped uteri and reduced oestrogen responsiveness. Here we show that Efp is a RING-finger-dependent ubiquitin ligase (E3) that targets proteolysis of 14-3-3 sigma, a negative cell cycle regulator that causes G2 arrest. We demonstrate that tumour growth of breast cancer MCF7 cells implanted in female athymic mice is reduced by treatment with antisense Efp oligonucleotide. Efp-overexpressing MCF7 cells in ovariectomized athymic mice generate tumours in the absence of oestrogen. Loss of Efp function in mouse embryonic fibroblasts results in an accumulation of 14-3-3 sigma, which is responsible for reduced cell growth. These data provide an insight into the cell-cycle machinery and tumorigenesis of breast cancer by identifying 14-3-3 sigma as a target for proteolysis by Efp, leading to cell proliferation.

Downregulation of 14-3-3σ in ovary, prostate and endometrial carcinomas is associated with CpG island methylation

“…The EFP is a target gene of the estrogen receptor acting as an ubiquitin ligase of 14-3-3s. 6 Whether EFP, widely expressed in hormone-sensitive tissues like uterus, ovary and mammary glands may play a role in 14-3-3s regulation of urological and gynecological cancers is subject of ongoing studies.…”

“…Furthermore, overexpression of EFP in vivo can induce tumors presumably by inducing genomic instability due to 14-3-3s loss. 6 Finally, in skin epithelia, expression of 14-3-3s is upregulated upon differentiation in cells of the poststem cell compartment and immortalization of keratinocytes by experimental inactivation of 14-3-3s, underlines furthermore its role as tumor suppressor gene. 7 Significant progress has been made in understanding the molecular genetics of urological and gynecological malignancies.…”

Frequent downregulation of 14-3-3 σ protein and hypermethylation of 14-3-3 σ gene in salivary gland adenoid cystic carcinoma

“…Although most of ACC tissue simultaneously showed high methylation index of 14-3-3 s gene and downregulation of 14-3-3 s protein, some cases did not show the correlation between the methylation index and expression level of 14-3-3 s. The reason for this discrepancy was unclear at present, however, it might be due to contamination of the stromal cells for analysis or the presence of another pre-or post-transcriptional regulation of 14-3-3 s. Recently, Urano et al (2002) demonstrated that Efp, a RINGfinger-dependent ubiquitin ligase (E3) targeted proteolysis of 14-3-3 s. In SGC cells, proteolysis of 14-3-3 s by ubiquitin -proteasome pathway might contribute to regulate the level of 14-3-3 s protein.…”

Knockdown of Efp by DNA-modified small interfering RNA inhibits breast cancer cell proliferation and in vivo tumor growth

“…The cell lysates were resolved by 12% sodium dodecyl sulfate polyacrylamide gel electrophoresis and transferred to polyvinylidene difluoride membranes (Millipore, Bedford, MA). The membranes were probed with a rabbit anti-Efp antibody 8 or rabbit anti-14-3-3s antibody (Santa Cruz, Santa Cruz, CA), incubated with horseradish peroxidase-conjugated anti-rabbit immunoglobulin G (GE Healthcare, Buckinghamshire, UK) and visualized using enhanced chemiluminescence (GE Healthcare). Membranes were stripped and reprobed with a mouse anti-b-actin antibody (AC-74; SigmaAldrich, St Louis, MO) to verify equal loading of the protein across the lanes.…”

“…7 Moreover, we showed that Efp promotes the growth of breast tumors by functioning as a ubiquitin E3 ligase that targets the G2/M cell-cycle checkpoint 14-3-3s. 8 Therefore, Efp is considered to be a factor essential in estrogen-dependent cancer proliferation and is a new target of breast cancer therapy.…”