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

Abstract

Estrogen receptor-alpha (ERα) is an important biomarker used to classify and direct therapy decisions in breast cancer. 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 (UPP) 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. Since Pin1 impacts both ERα protein levels and transactivation function, these data implicate Pin1 as a potential surrogate marker for predicting outcome of ERα-positive breast cancer.

Prolyl isomerase Pin1 in cancer

“…This isomerization stabilizes ERα protein by blocking ERα interaction with the E3 ligase, E6AP, and thus inhibiting the E6AP-mediated ubiquitylation and degradation of ERα. In addition, Pin1 and ERα levels are positively correlated in human breast carcinoma specimens [100,101].…”

In Situ Tumor PD-L1 mRNA Expression Is Associated with Increased TILs and Better Outcome in Breast Carcinomas

“…Patient cohorts, tissue microarrays, and control preparations Two previously reported (33,34) retrospective stage I-III breast cancer collections from Yale University (New Haven, CT) represented in tissue microarray (TMA) format were used in this study, termed YTMA128 (N ¼ 238) and YTMA201 (N ¼ 398). Clinicopathologic information from patients in both cohorts was collected from clinical records and pathology reports.…”

“…In situ detection of PD-L1 transcripts in FFPE TMA samples was performed using the RNAscope assay with custom-designed in situ hybridization probes (Advanced Cell Diagnostics) coupled to automated quantitative fluorescence (QIF) detection as described (33)(34)(35). Briefly, 5 mm sections were deparaffinized, boiled with preamplification reagent for 15 minutes, and submitted to protease digestion followed by hybridization for 2 hours with target probes to human PD-L1 mRNA, Ubiquitin C (UbC) as a positive control, or the bacterial gene DapB mRNA as a negative control.…”

Peptidylprolyl Isomerase Pin1 Directly Enhances the DNA Binding Functions of Estrogen Receptor α

“…Our studies indicate that high levels of Pin1 expression are associated with worse outcomes in ER␣ ϩ breast tumors as well as increased ER␣ signaling and transcriptional activity (25,31). Pin1 is recruited to phosphorylated ER␣ at Ser 118 in response to estrogen, tamoxifen, and EGF (25).…”

“…Phosphorylation-dependent isomerization by Pin1 affects diverse cellular processes, such as protein-protein interactions, subcellular localization, dephosphorylation, and transcription (30). We previously identified cis-trans isomerization of the Ser(P) 118 -Pro 119 bond in AF1 by Pin1 as a novel post-translational modification regulating ER␣ conformation, protein stability, and transcriptional function (25,31). Ser 118 in the AF1 region of ER␣ is a major site of phosphorylation by proline-directed kinases in response to estrogen, growth factors, and anti-estrogens, such as tamoxifen (11)(12)(13)(14)(15).…”