Divergent regulation of theOsteopontinpromoter by the estrogen receptor-related receptors is isoform- and cell context dependent

Abstract

We sought to determine whether the estrogen receptor-related receptor gamma (mEsrrg) regulated the Osteopontin (Opn) promoter through the same AP1/CAAT box element that we have previously described for mEsrra. In HeLa cells mEsrrg used an additional site present in the 5'UTR, while in ROS17/2.8 cells the AP1/CAAT site was not used, but a completely novel site surrounding the transcription start site was used. We also find that in ROS17/2.8 cells mEsrra repressed, while mEsrrg activated the Opn promoter. None of the sites identified conform to established Esrr response elements (ERREs). Additionally, the two reported mEsrrg protein isoforms showed differences in their activation potential. Mutations in the activation function 2 (AF2) of mEsrra, predicted to abolish activation, surprisingly turned mEsrra into a better activator. In contrast, similar AF2 mutations in Esrrg2 abolished its ability to activate the Opn promoter. Mutation of the DNA binding domain of mEsrra/g2 abolished transcriptional activity in HeLa and ROS17/2.8 cells. Our data indicate, first, that the two Esrr isoforms regulate Opn in a cell context-dependent manner. Second, they suggest that although the DNA binding domains of mEsrra and mEsrrg are 93% identical and required for regulation, the receptors bind to distinct Opn promoter elements, suggesting that the two isoforms may co-regulate Opn, and perhaps other genes, without competing for the same site in the promoter. Finally, the results suggest that each isoform interacts differently with co-activators and co-repressors, as highlighted by the AF2 mutation that turns mEsrra into a better activator but abolishes activity of Esrrg2.

Osteopontin is linked with AKT, FoxO1, and myostatin in skeletal muscle cells

“…Germane to OPN's role in muscle, a promoter polymorphism (rs28357094) alters transcription factor binding and baseline gene transcription in multiple cell types. The rs28357094 genotype was associated with an increase in biceps muscle size in women but not men, in keeping with an effect of estrogens on OPN expression . In healthy human muscle, OPN expression increased with acute mechanical loading, further suggesting a role of OPN in muscle injury and hypertrophic remodeling .…”

“…Therefore, OPN could more efficiently exert its downstream effects, leading to myofiber hypertrophy. Potential drawbacks were the use of female mdx mice, as males are predominantly affected in DMD, but also possible hormonal influences on OPN expression, and the lack of a blinded observer to measure minimal Feret diameter.…”

Estrogen adversely affects the prognosis of patients with lung adenocarcinoma

“…Enhanced OPN expression has been noted in the plasma of advanced lung cancer patients, and OPN has also been speculated to be involved in the formation of malignant pleural effusions . Estrogen‐related receptors (ERR) have been known to regulate the synthesis of osteopontin and ERRalpha response elements have been identified in the OPN promoter . Estrogen was demonstrated to regulate OPN expression and lead to angiogenesis and metastasis in breast cancer .…”

Estrogen, Estrogen Receptor and Lung Cancer

“…We demonstrated ERβ was the predominant ER in the A549 and PE089 lung cancer cell lines, and malignant pleural effusions from the patients with lung adenocarcinoma. Osteopontin (OPN) is a small integrin-binding ligand N -linked glycoprotein regulating signaling pathways involved in tumor progression and metastasis [ 37 , 38 , 39 ]. Enhanced OPN expression has been noted in the plasma of advanced lung cancer patients, and OPN has also been speculated to be involved in the formation of malignant pleural effusion [ 40 , 41 ].…”