Phosphorylation by p38 mitogen-activated protein kinase promotes estrogen receptor α turnover and functional activity via the SCF(Skp2) proteasomal complex

Integrative genomics of gene and metabolic regulation by estrogen receptors α and β, and their coregulators

The closely related transcription factors (TFs), estrogen receptors ERα and ERβ, regulate divergent gene expression programs and proliferative outcomes in breast cancer. Utilizing breast cancer cells with ERα, ERβ, or both receptors as a model system to define the basis for differing response specification by related TFs, we show that these TFs and their key coregulators, SRC3 and RIP140, generate overlapping as well as unique chromatin-binding and transcription-regulating modules. Cistrome and transcriptome analyses and the use of clustering algorithms delineated 11 clusters representing different chromatin-bound receptor and coregulator assemblies that could be functionally associated through enrichment analysis with distinct patterns of gene regulation and preferential coregulator usage, RIP140 with ERβ and SRC3 with ERα. The receptors modified each other's transcriptional effect, and ERβ countered the proliferative drive of ERα through several novel mechanisms associated with specific binding-site clusters. Our findings delineate distinct TF-coregulator assemblies that function as control nodes, specifying precise patterns of gene regulation, proliferation, and metabolism, as exemplified by two of the most important nuclear hormone receptors in human breast cancer.

ERα, SKP2 and E2F-1 form a feed forward loop driving late ERα targets and G1 cell cycle progression

Estrogen triggers transactivation coupled estrogen receptor α (ERα) proteolysis, but mechanisms thereof remain obscure. Present data link estrogen:ERα-driven transcription with cell cycle progression. Although liganded ERα induces many genes within 1-4 h, gene activation after 6 h is thought to be indirect. Here, we identify SKP2 as a late-acting coactivator that drives ERα targets to promote G1-to-S progression. Data support a model in which estrogen-activated cyclin E-CDK2 binds and phosphorylates ERαS341, to prime ERα-SCF(SKP2) binding via SKP2-L248QTLL252 in late G1. SKP2 activates ERα ubiquitylation and proteolysis. Putative late ERα targets were identified by expression profiling. SKP2 knockdown attenuated E2F-1 and BLM induction. SKP2 overexpression, but not coactivator motif mutant SKP2-L248QTAA252, enhanced estrogen-induced E2F-1 and BLM expression. SKP2 knockdown impaired estrogen-stimulated ERα, SKP2, SRC3 and RNA polymerase II recruitment to E2F-1 and BLM promoters. This work not only identifies these late-activated genes as bona fide ERα targets but describes a novel mechanism for their periodic activation. SKP2 serves as dual ERα E3 ligase/coactivator for late-activated target genes, revealing a novel mechanism whereby ERα/SCF(SKP2) transactivation of E2F-1 feeds forward to drive G1-to-S.

Pin1 modulates ERα levels in breast cancer through inhibition of phosphorylation-dependent ubiquitination and degradation

Estrogen receptor-alpha (ERα) is an important biomarker used to classify and direct therapy decisions in breast cancer (BC). Both ERα protein and its transcript, ESR1, are used to predict response to tamoxifen therapy, yet certain tumors have discordant levels of ERα protein and ESR1, which is currently unexplained. Cellular ERα protein levels can be controlled post-translationally by the ubiquitin-proteasome pathway through a mechanism that depends on phosphorylation at residue S118. Phospho-S118 (pS118-ERα) is a substrate for the peptidyl prolyl isomerase, Pin1, which mediates cis-trans isomerization of the pS118-P119 bond to enhance ERα transcriptional function. Here, we demonstrate that Pin1 can increase ERα protein without affecting ESR1 transcript levels by inhibiting proteasome-dependent receptor degradation. Pin1 disrupts ERα ubiquitination by interfering with receptor interactions with the E3 ligase, E6AP, which also is shown to bind pS118-ERα. Quantitative in situ assessments of ERα protein, ESR1, and Pin1 in human tumors from a retrospective cohort show that Pin1 levels correlate with ERα protein but not to ESR1 levels. These data show that ERα protein is post-translationally regulated by Pin1 in a proportion of breast carcinomas. As Pin1 impacts both ERα protein levels and transactivation function, these data implicate Pin1 as a potential surrogate marker for predicting outcome of ERα-positive BC.

Prognostic impact of Jab1, p16, p21, p62, Ki67 and Skp2 in soft tissue sarcomas

PURPOSE

The purpose of this study is to clarify the prognostic significance of expression of Jab1, p16, p21, p62, Ki67 and Skp2 in soft tissue sarcomas (STS). Optimised treatment of STS requires better identification of high risk patients who will benefit from adjuvant therapy. The prognostic significance of Jab1, p16, p21, p62, Ki67 and Skp2 in STS has not been sufficiently investigated.

EXPERIMENTAL DESIGN

Tissue microarrays from 193 STS patients were constructed from duplicate cores of viable and representative neoplastic tumor areas. Immunohistochemistry was used to evaluate the expression of Jab1, p16, p21, p62, Ki67 and Skp2.

RESULTS

In univariate analyses, high tumor expression of Ki67 (P = 0.007) and Skp2 (P = 0.050) correlated with shorter disease-specific survival (DSS). In subgroup analysis, a correlation between Skp2 and DSS was seen in patients with malignancy grade 1 or 2 (P = 0.027), tumor size >5 cm (P = 0.018), no radiotherapy given (P = 0.029) and no chemotherapy given (P = 0.017). No such relationship was apparent for Jab1, p16, p21 and p62; but p62 showed a positive correlation to malignancy grade (P = 0.019). Ki67 was strongly positively correlated to malignancy grade (P = 0.001). In multivariate analyses, Skp2 was an independent negative prognostic factor for DSS in women (P = 0.009) and in patients without administered chemotherapy or radiotherapy (P = 0.026).

CONCLUSIONS

Increased expression of Skp2 in patients with soft tissue sarcomas is an independent negative prognostic factor for disease-specific survival in women and in patients not administered chemotherapy or radiotherapy. Besides, further studies are warranted to explore if adjuvant chemotherapy or radiotherapy improve the poor prognosis of STS with high Skp2 expression.

Clinical significance of Cullin 1 protein expression in gastric cancer

AIM: To examine the expression of Cullin 1 protein in gastric cancer cells and tissues and to analyze the correlation between Cullin 1 protein expression and clinicopathologic variables and patient survival.

METHODS: Cullin 1 protein expression in BGC-823, SGC-7901, and GES-1 cells was determined by Western blot. In addition, we constructed a tissue microarray that included 792 primary gastric cancer tissues and evaluated Cullin 1 expression in tumor biopsies by immunohistochemistry.

RESULTS: Cullin 1 protein expression levels were higher in BGC-823 and SGC-7901 cells than in GES-1 cells (both P < 0.01), and in gastric cancer tissues than in adjacent tissues (P < 0.01). Cullin 1 overexpression was significantly correlated with TNM stage (P = 0.011), depth of invasion (P = 0.035, T1-T3 vs T4), and lymph node metastasis (P = 0.036). Furthermore, we found a strong correlation between high Cullin 1 expression and worse overall and 3-year survival rates in gastric cancer patients (P = 0.042, 0.026). Cox regression analysis revealed that Cullin 1 expression was an independent prognostic factor predicting 3-year outcome in patients with gastric cancer (P = 0.028).

CONCLUSION: Cullin 1 may be an important marker for lymph node metastasis and prognosis in gastric cancer, representing a potential treatment target for this malignancy.