Role of MXD3 in Proliferation of DAOY Human Medulloblastoma Cells

Abstract

A subset of medulloblastomas, the most common brain tumor in children, is hypothesized to originate from granule neuron precursors (GNPs) in which the sonic hedgehog (SHH) pathway is over-activated. MXD3, a basic helix-look-helix zipper transcription factor of the MAD family, has been reported to be upregulated during postnatal cerebellar development and to promote GNP proliferation and MYCN expression. Mxd3 is upregulated in mouse models of medulloblastoma as well as in human medulloblastomas. Therefore, we hypothesize that MXD3 plays a role in the cellular events that lead to medulloblastoma biogenesis. In agreement with its proliferative role in GNPs, MXD3 knock-down in DAOY cells resulted in decreased proliferation. Sustained overexpression of MXD3 resulted in decreased cell numbers due to increased apoptosis and cell cycle arrest. Structure-function analysis revealed that the Sin3 interacting domain, the basic domain, and binding to E-boxes are essential for this activity. Microarray-based expression analysis indicated up-regulation of 84 genes and down-regulation of 47 genes. Potential direct MXD3 target genes were identified by ChIP-chip. Our results suggest that MXD3 is necessary for DAOY medulloblastoma cell proliferation. However, increased level and/or duration of MXD3 expression ultimately reduces cell numbers via increased cell death and cell cycle arrest.

Loss of MXD3 induces apoptosis of Reh human precursor B acute lymphoblastic leukemia cells

“…The results presented here suggest that MXD3 may be involved in leukemia biogenesis and/or maintenance, consistent with our reported proliferative role for MXD3 in cerebellum [17] and its overexpression in cerebellar tumors [18]. MXD3 is expressed in transitional IgD − B cells in the spleen, and its expression is reduced during maturation in mice [20].…”

“…While some MXD proteins are MYC antagonists by acting as transcriptional repressors to promote cell differentiation [7, 9, 11, 13], MXD3 is an atypical member that plays a role in proliferation rather than differentiation [6, 14–18]. MXD3 promotes granule neuron precursor (GNP) proliferation through a Sonic Hedgehog-mediated pathway [17], it is expressed in a mouse model of medulloblastoma [17], and its knock-down (KD) reduced proliferation of the human medulloblastoma cell line DAOY [18]. Since MXD3 appears to be associated with a variety of human cancers [15] and pathways related to B cell malignancies [19, 20], we investigated the role of MXD3 in preB ALL.…”

MXD3 regulation of DAOY cell proliferation dictated by time course of activation

“…Such a mechanism exists for oncogenes such as the transcriptional network relative MYC [26,27]. In support of this possibility, both transient overexpression of MXD3 in GNPs [9] and stable MXD3 overexpression in human medulloblastoma cell lines [10] show an increase in apoptosis. When we examined apoptosis activity at 72 hours in our inducible cell lines, we were unable to find any significant difference in caspase 3/7 activity in response to MXD3 activation (Additional file 6: Figure S6); however, there is a trend towards increased caspase 3/7 activity at 72 hours for ER-MXD3, consistent with the decreased cell number observed.…”

Focus Formation: A Cell-based Assay to Determine the Oncogenic Potential of a Gene

“…It is an atypical member of the MAD family [13][14][15] , and it has been reported to be involved in carcinogenesis 16,17 . When compared to pBABEpuro (negative control) and MYC (positive control), the NIH 3T3 dishes where MXD3 was overexpressed had significantly less foci ( Figure 1A).…”