Calcineurin regulates the stability and activity of estrogen receptor α

Abstract

Estrogen receptor α (ER-α) mediates estrogen-dependent cancer progression and is expressed in most breast cancer cells. However, the molecular mechanisms underlying the regulation of the cellular abundance and activity of ER-α remain unclear. We here show that the protein phosphatase calcineurin regulates both ER-α stability and activity in human breast cancer cells. Calcineurin depletion or inhibition down-regulated the abundance of ER-α by promoting its polyubiquitination and degradation. Calcineurin inhibition also promoted the binding of ER-α to the E3 ubiquitin ligase E6AP, and calcineurin mediated the dephosphorylation of ER-α at Ser294 in vitro. Moreover, the ER-α (S294A) mutant was more stable and activated the expression of ER-α target genes to a greater extent compared with the wild-type protein, whereas the extents of its interaction with E6AP and polyubiquitination were attenuated. These results suggest that the phosphorylation of ER-α at Ser294 promotes its binding to E6AP and consequent degradation. Calcineurin was also found to be required for the phosphorylation of ER-α at Ser118 by mechanistic target of rapamycin complex 1 and the consequent activation of ER-α in response to β-estradiol treatment. Our study thus indicates that calcineurin controls both the stability and activity of ER-α by regulating its phosphorylation at Ser294 and Ser118. Finally, the expression of the calcineurin A–α gene (PPP3CA) was associated with poor prognosis in ER-α–positive breast cancer patients treated with tamoxifen or other endocrine therapeutic agents. Calcineurin is thus a promising target for the development of therapies for ER-α–positive breast cancer.

Decoding the Therapeutic Implications of the ERα Stability and Subcellular Distribution in Breast Cancer

“…Moreover, calcineurin facilitates the ERα phosphorylation at Ser118 by mTOR to increase its activation. A higher expression of calcineurin is associated with a poor prognosis in patients receiving endocrine therapy, suggesting that it is a key target for breast cancer treatment ( 102 ).…”

Estrogen receptor α revised: Expression, structure, function, and stability

“…Consistent with these observations, high calcineurin expression was associated with shorter recurrence‐free survival in endocrine‐treated ER‐positive breast cancer patients. [ 108 ]…”

“…Consistent with these observations, high calcineurin expression was associated with shorter recurrence-free survival in endocrine-treated ER-positive breast cancer patients. [108] Fulvestrant, the most commonly used SERD, exerts its tumor suppression effect by inhibiting ERα through its full antagonistic action on ERα and promoting ERα degradation through the ubiquitinproteasome system. Regulation of ER stability by ubiquitination has attracted attention as a therapeutic target for breast cancer, and novel therapies targeting ERα degradation, such as proteolysis-targeting chimeric (PROTAC) technology, are being developed.…”

“…[ 89 ] In contrast to the suppressive effects of PP2A and PP5 on ERα, calcineurin, a Ca 2+ ‐dependent serine/threonine phosphatase, stabilizes and activates ERα (Figure 4). [ 108 ] Phosphorylation of ERα S294 promoted polyubiquitination by E3 ligase E6AP and the subsequent degradation of ERα. calcineurin stabilized ERα by directly dephosphorylating ERα S294, thereby releasing E6AP.…”

Estrogen signaling as a bridge between the nucleus and mitochondria in cardiovascular diseases

“…In fact, these TFs have also been reported in both physiological and pathological CH. In this regard, calcineurin directly regulates ERα stability and activity in breast cancer and estrogen upregulates calcineurin expression via overexpression of ER in systemic lupus erythematosus ( Rider et al, 2000 ; Lin et al, 2011 ; Masaki et al, 2021 ). Similarly, in the heart, estrogen inhibits isoproterenol-induced CH via suppression of Ca 2+ -calcineurin signaling, preventing NFATc3 translocation ( Tsai et al, 2017 ).…”