WNT3 Inhibits Cerebellar Granule Neuron Progenitor Proliferation and Medulloblastoma Formation via MAPK Activation

Abstract

During normal cerebellar development, the remarkable expansion of granule cell progenitors (GCPs) generates a population of granule neurons that outnumbers the total neuronal population of the cerebral cortex, and provides a model for identifying signaling pathways that may be defective in medulloblastoma. While many studies focus on identifying pathways that promote growth of GCPs, a critical unanswered question concerns the identification of signaling pathways that block mitogenic stimulation and induce early steps in differentiation. Here we identify WNT3 as a novel suppressor of GCP proliferation during cerebellar development and an inhibitor of medulloblastoma growth in mice. WNT3, produced in early postnatal cerebellum, inhibits GCP proliferation by down-regulating pro-proliferative target genes of the mitogen Sonic Hedgehog (SHH) and the bHLH transcription factor Atoh1. WNT3 suppresses GCP growth through a non-canonical Wnt signaling pathway, activating prototypic mitogen-activated protein kinases (MAPKs), the Ras-dependent extracellular-signal-regulated kinases 1/2 (ERK1/2) and ERK5, instead of the classical β-catenin pathway. Inhibition of MAPK activity using a MAPK kinase (MEK) inhibitor reversed the inhibitory effect of WNT3 on GCP proliferation. Importantly, WNT3 inhibits proliferation of medulloblastoma tumor growth in mouse models by a similar mechanism. Thus, the present study suggests a novel role for WNT3 as a regulator of neurogenesis and repressor of neural tumors.

Development of the cerebellum: simple steps to make a ‘little brain’

“…The lack of an internal cell division clock (Espinosa and Luo, 2008) has focussed attention on cell non-autonomous factors such Wnt and bone morphogenetic protein (BMP) pathway signals in the EGL. For example, non-canonical Wnt signalling via Wnt3 has recently been shown to be capable of decreasing proliferation independently of BMP signalling (Anne et al, 2013). Conversely, multiple BMPs are expressed in the cerebellum during EGL development and can antagonise the Shh-dependent proliferation of granule progenitors both in vitro and in slice cultures (Rios et al, 2004) through regulation of Atoh1 (Zhao et al, 2008) and via miR22 (Berenguer et al, 2013).…”

Modulating expression level of secreted Wnt3 influences cerebellum development in zebrafish transgenics

“…S2F-G) confirms their localization to a proliferation niche. The role of Wnt3 in inhibiting proliferation of cultured cerebellar granule progenitors and regulating its neurogenesis has been documented in mice (Anne et al, 2013). We investigated whether a similar role exists for Wnt3 by assessing its impact on cerebellum neurogenesis in zebrafish.…”

“…Cerebellar vermis hypoplasia in Joubert syndrome, for example, is linked to defective canonical Wnt signaling (Lancaster et al, 2011). Wnt3 is expressed in the developing cerebellum and the dorsal spinal cord of all vertebrates (Roelink and Nusse, 1991;Bulfone et al, 1993;Garriock et al, 2007;Clements et al, 2009;Anne et al, 2013). In mice, Wnt3 is expressed prior to gastrulation and its targeted deletion causes an early developmental arrest (Liu et al, 1999).…”

“…In human, homozygous nonsense mutation within the WNT3 coding region (Q83X) resulted in the loss of all limbs with concomitant CNS, craniofacial and urogenital defects in affected fetuses (Niemann et al, 2004). Wnt3 was identified as an extracellular regulator of granule cell progenitor proliferation and differentiation during mouse cerebellar development (Anne et al, 2013). Depending on cellular context, Wnt3 either acts via the canonical Wnt pathway by activating the nuclear translocation of β-catenin (Kim et al, 2008), or via the RhoA pathway (Kobune et al, 2007).…”

Pigment epithelium-derived factor regulation by human chorionic gonadotropin in granulosa cells

“…It is accepted that transactivation of LH receptor is downstream of PKC cascade (Leserer et al 2000, Cattaneo et al 2014; it is also suggested that PKC can act downstream to EGF and that EGF-like growth factors can activate PKC directly (Li et al 1991, Anne et al 2013, Liu et al 2014. To determine whether inhibition of PKC will hamper the ability of AREG to downregulate PEDF expression, we followed the expression of PEDF in AREG-stimulated LH-15 cells with or without pretreatment with a PKC inhibitor (GF; 10 mM).…”