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Beta-Arrestin 2 Is Required for Dopamine Receptor Type 2 Inhibitory Effects on AKT Phosphorylation and Cell
Federica Mangili1, Elena Giardino1, Donatella Treppiedi1
1Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy.
Abstract:
Dopamine receptor type 2 (DRD2) agonists are the first-choice treatment for prolactin-secreting pituitary tumors but are poorly effective in nonfunctioning pituitary neuroendocrine tumors (NF-PitNETs). DRD2 reduces AKT phosphorylation in lactotrophs, but no data are available in NF-PitNETs. DRD2 effects on AKT are mediated by a β-arrestin 2-dependent mechanism in mouse striatum. The aim of this study was to investigate DRD2 effects on AKT phosphorylation and cell proliferation in human primary cultured NF-PitNET cells and in rat tumoral lactotroph cells MMQ, and to test β-arrestin 2 involvement. We found that the DRD2 agonist BIM53097 induced a reduction of the p-AKT/total-AKT ratio in MMQ (-32.8 ± 17.6%, p < 0.001 vs. basal) and in a subset (n = 15/41, 36.6%) of NF-PitNETs (subgroup 1). In the remaining NF-PitNETs (subgroup 2), BIM53097 induced an increase in p-AKT. The ability of BIM53097 to reduce p-AKT correlated with its antimitotic effect, since the majority of subgroup 1 NF-PitNETs was responsive to BIM53097, and nearly all subgroup 2 NF-PitNETs were resistant. β-Arrestin 2 was expressed in MMQ and in 80% of subgroup 1 NF-PitNETs, whereas it was undetectable in 77% of subgroup 2 NF-PitNETs. In MMQ, β-arrestin 2 silencing prevented DRD2 inhibitory effects on p-AKT and cell proliferation. Accordingly, β-arrestin 2 transfection in subgroup 2 NF-PitNETs conferred to BIM53097 the ability to inhibit both p-AKT and cell growth. In conclusion, we demonstrated that β-arrestin 2 is required for DRD2 inhibitory effects on AKT phosphorylation and cell proliferation in MMQ and NF-PitNETs, paving the way for a potential role of β-arrestin 2 as a biomarker predicting NF-PitNETs' responsiveness to treatment with dopamine agonists.
Insights
Dopamine receptor type 2 (DRD2) agonists inhibit AKT phosphorylation and cell growth in some pituitary tumors. Beta-arrestin 2 is crucial for this effect, potentially serving as a biomarker for treatment response in nonfunctioning pituitary neuroendocrine tumors (NF-PitNETs).
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- Dopamine receptor type 2 (DRD2) agonists effectively treat prolactin-secreting pituitary tumors but show limited efficacy in nonfunctioning pituitary neuroendocrine tumors (NF-PitNETs).
- While DRD2 signaling inhibits AKT phosphorylation in lactotrophs, its role in NF-PitNETs remains uncharacterized.
- DRD2-mediated effects on AKT are known to involve beta-arrestin 2 in other cellular contexts.
Purpose of the Study:
- To investigate the impact of DRD2 agonists on AKT phosphorylation and cell proliferation in human NF-PitNET cells and rat MMQ cells.
- To determine the involvement of beta-arrestin 2 in mediating DRD2's effects on AKT signaling and cell growth.
- To explore beta-arrestin 2 as a potential predictive biomarker for NF-PitNET response to dopamine agonists.
Main Methods:
- Utilized human primary cultured NF-PitNET cells and rat MMQ cells.
- Administered the DRD2 agonist BIM53097 to assess effects on AKT phosphorylation (p-AKT/total-AKT ratio) and cell proliferation.
- Investigated the role of beta-arrestin 2 through expression analysis, silencing, and transfection experiments.
Main Results:
- BIM53097 reduced p-AKT levels and inhibited cell proliferation in MMQ cells and a subset (36.6%) of NF-PITNETs (subgroup 1).
- In the remaining NF-PITNETs (subgroup 2), BIM53097 increased p-AKT and showed no antiproliferative effect.
- Beta-arrestin 2 expression correlated with DRD2 agonist responsiveness; silencing or absence of beta-arrestin 2 abrogated the inhibitory effects of BIM53097 on p-AKT and cell growth.
Conclusions:
- Beta-arrestin 2 is essential for the inhibitory effects of DRD2 agonists on AKT phosphorylation and cell proliferation in both MMQ and NF-PITNET cells.
- The presence or absence of beta-arrestin 2 expression can predict NF-PITNETs' responsiveness to dopamine agonist therapy.
- Beta-arrestin 2 may serve as a valuable biomarker for guiding treatment decisions in NF-PITNET patients.
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