LAUSR

Hypoxia is a condition of oxygen deficiency which occurs in most growing solid tumors and stimulates a cascade of cell signals through a family of transcription factors named as hypoxia inducible factors (HIFs) that transactivate several regulatory genes involved in tumor proliferation. β3-adrenoceptors (β3-ARs) are involved in several hypoxic scenarios and in pathological conditions where hypoxia leads to important steps for cancer progression. Studies showed that β-AR blockade of mice suppressed hypoxia induction of renal HIF-1α accumulation, erythropoietin production, and erythropoiesis in vivo. In this work we assumed that β3-AR mediates hypoxia sensing and that it was necessary for HIF-1α stabilization thus we investigated a putative correlation between β3-AR/HIF-1α. Data showed a similar outcome of β3-ARs and HIF-1α at short time of hypoxia, and that β3-AR antagonist, SR59230A reduced HIF-1α protein expression under hypoxia. β3-AR silencing under hypoxia revealed an evident reduction of HIF-1α protein expression that confirmed the β3-AR modulation of HIF-1α expression. SR59230A treatment strongly reduced the HIF-1α target genes as GLUT1, HK-2 and HIF-1α expression at long time treatment confirming the β3-AR modulation of HIF-1α transcriptional activity. Conversely, the HIF-1α-transcriptional inhibitor Topotecan did not affect β3-AR expression confirming that is β3-AR that mediates HIF-1α activation. Immunofluorescence analysis showed that β3-AR co-localized with the nucleus under hypoxia more than normoxia. These results were confirmed by nuclear-cytoplasmic fragmentation that showed the presence of both β3-AR and HIF-1α proteins in the nucleus under hypoxia. Co-immunoprecipitation of β3-AR/HIF-1α revealed that under hypoxia, HIF-1α dissociates from β3-AR binding, but this process was abrogated by SR59230A. HIF-1α, released under hypoxia from the link with β3-AR, can play its transcriptional activity in the nucleus, while the binding with β3-AR blocks its transcriptional activity. Moreover, β3-AR regulation on HIF-1α was exerted through PHD2 activity at short time as SR59230A treatment under hypoxia increased the PHD2 protein expression but not at long time treatment, thus showing a different regulation of HIF-1α at different time points. In conclusion, the β3-AR upstream of the signaling β3-AR/HIF-1α axis exerts its role by PHD2 activity. Citation Format: Amada Pasha, Claudia Masi, Francesco Carrozzo, Martina Rosati, Alessia Boaretto, Alessandro Pini, Claudio Favre, Maura Calvani. Hypoxic HIF-1α stabilization dependent on β3-adrenoceptor localization in Ewing sarcoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4808.