Abballe Luana, Alfano Vincenzo, Antonacci Celeste, Cefalo Maria Giuseppina, Cacchione Antonella, Del Baldo Giada, Pezzullo Marco, Po Agnese, Moretti Marta, Mastronuzzi Angela, De Smaele Enrico, Ferretti Elisabetta, Locatelli Franco, Miele Evelina
Department of Pediatric Hematology/Oncology and Cellular and Gene Therapy, Bambino Gesù Children's Hospital, Istituto di Ricovero e Cura a Carattere Scientifico, Rome, Italy.
Cancer Research Center of Lyon (CRCL), UMR Inserm U1052/CNRS 5286, Lyon, France.
Front Cell Dev Biol. 2023 Feb 27;11:990711. doi: 10.3389/fcell.2023.990711. eCollection 2023.
Development of the cerebellum is characterized by rapid proliferation of cerebellar granule cell precursors (GCPs) induced by paracrine stimulation of Sonic hedgehog (Shh) signaling from Purkinje cells, in the external granular layer (EGL). Then, granule cell precursors differentiate and migrate into the inner granular layer (IGL) of the cerebellum to form a terminally differentiated cell compartment. Aberrant activation of Sonic hedgehog signaling leads to granule cell precursors hyperproliferation and the onset of Sonic hedgehog medulloblastoma (MB), the most common embryonal brain tumor. β-arrestin1 (ARRB1) protein plays an important role downstream of Smoothened, a component of the Sonic hedgehog pathway. In the medulloblastoma context, β-arrestin1 is involved in a regulatory axis in association with the acetyltransferase P300, leading to the acetylated form of the transcription factor E2F1 (E2F1-ac) and redirecting its activity toward pro-apoptotic gene targets. This axis in the granule cell precursors physiological context has not been investigated yet. In this study, we demonstrate that β-arrestin1 has antiproliferative and pro-apoptotic functions in cerebellar development. β-arrestin1 silencing increases proliferation of Sonic hedgehog treated-cerebellar precursor cells while decreases the transcription of E2F1-ac pro-apoptotic targets genes, thus impairing apoptosis. Indeed, chromatin immunoprecipitation experiments show a direct interaction between β-arrestin1 and the promoter regions of the pro-apoptotic E2F1 target gene and , indicating the double role of β-arrestin1 in controlling apoptosis and cell cycle exit in a physiological context. Our data elucidate the role of β-arrestin1 in the early postnatal stages of cerebellar development, in those cell compartments that give rise to medulloblastoma. This series of experiments suggests that the physiological function of β-arrestin1 in neuronal progenitors is to directly control, cooperating with E2F1 acetylated form, transcription of pro-apoptotic genes.
小脑的发育特征是，在浦肯野细胞发出的音猬因子（Shh）信号的旁分泌刺激作用下，小脑颗粒细胞前体（GCPs）在外部颗粒层（EGL）迅速增殖。然后，颗粒细胞前体分化并迁移到小脑的内部颗粒层（IGL），形成终末分化的细胞区室。音猬因子信号的异常激活会导致颗粒细胞前体过度增殖，并引发音猬因子髓母细胞瘤（MB），这是最常见的胚胎性脑肿瘤。β-抑制蛋白1（ARRB1）在音猬因子信号通路的组成部分——平滑受体下游发挥重要作用。在髓母细胞瘤的背景下，β-抑制蛋白1参与了与乙酰转移酶P300相关的调控轴，导致转录因子E2F1的乙酰化形式（E2F1-ac），并将其活性导向促凋亡基因靶点。在颗粒细胞前体的生理背景下，这一轴尚未得到研究。在本研究中，我们证明β-抑制蛋白1在小脑发育中具有抗增殖和促凋亡功能。β-抑制蛋白1沉默会增加经音猬因子处理的小脑前体细胞的增殖，同时降低E2F1-ac促凋亡靶点基因的转录，从而损害细胞凋亡。事实上，染色质免疫沉淀实验表明β-抑制蛋白1与促凋亡E2F1靶点基因的启动子区域之间存在直接相互作用，这表明β-抑制蛋白1在生理背景下对控制细胞凋亡和细胞周期退出具有双重作用。我们的数据阐明了β-抑制蛋白1在小脑发育出生后早期阶段、在那些会引发髓母细胞瘤的细胞区室中的作用。这一系列实验表明，β-抑制蛋白1在神经元祖细胞中的生理功能是与E2F1的乙酰化形式协同，直接控制促凋亡基因的转录。
