Growth-Inhibitory Activity of Bone Morphogenetic Protein 4 in Human Glioblastoma Cell Lines Is Heterogeneous and Dependent on Reduced SOX2 Expression

Abstract

Glioblastoma multiforme (GBM) continues to have a dismal prognosis. Even though detailed information on the genetic aberrations in cell signaling and cell cycle checkpoint control is available, no effective targeted treatment has been developed. Despite the advanced molecular defects, glioblastoma cells may have remnants of normal growth inhibitory pathways, such as the bone morphogenetic protein (BMP) signaling pathway. We have evaluated the growth inhibitory effect of BMP4 across a broad spectrum of patient samples, using a panel of 40 human glioblastoma initiating cell (GIC) cultures. A wide range of responsiveness was observed. BMP4 sensitivity was positively correlated with a proneural mRNA expression profile, high SOX2 activity, and BMP4-dependent up-regulation of genes associated with inhibition of the MAPK pathway, as demonstrated by gene set enrichment analysis (GSEA). BMP4 response in sensitive cells was mediated by the canonical BMP receptor pathway involving SMAD1/5/9 phosphorylation and SMAD4 expression. SOX2 was consistently down-regulated in BMP4treated cells. Forced expression of SOX2 attenuated the BMP4 sensitivity including a reduced upregulation of MAPK inhibitory genes, implying a functional relationship between SOX2 downregulation and sensitivity. The results show an extensive heterogeneity in BMP4 responsiveness among GICs, and identify a BMP4 sensitive subgroup, in which SOX2 is a mediator of the response. Implications: Development of agonists targeting the BMP signaling pathway in glioblastoma is an attractive avenue towards a better treatment-our study may help find biomarkers that predict the outcome of such treatment and enable stratification of patients.

Canonical BMP2/4 signaling degrades SOX2 in glioblastoma propagating cells

“…Our own observations align closely with the work of Dalmo et al, 2020. We observed that exposure of glioblastoma TPCs (5 primary lines) to BMP2/4 resulted in rapid downregulation of SOX2 followed by reduction in Ki67 and induction of GFAP (Fig.…”

“…In contrast, Dalmo et al, 2020 concluded that response is heterogenous among 40 primary human glioblastomas analyzed [5]. Invariably, such response in sensitive cells induced SMAD1/5/9 phosphorylation, SMAD4 expression, and consistent downregulation of SOX2 [5].…”

“…Developmental pathways controlling self-renewal and differentiation of normal NSCs may be relevant to GPCs. For instance, the transcription factor SRY (sex-determining region)box 2 (SOX2), which is required for self-renewal, proliferation and neurogenic differentiation of different type of NSCs [6,7,17,18], is highly expressed in vivo in hyperproliferative areas of glioblastoma [19], marks proliferating GPCs ex vivo [16], expressed, albeit to variable extent, in cultured GPCs [5,11] and functions as an oncogene by supporting their proliferation and tumor initiation capability [20]. On the other end, Bone Morphogenetic Proteins (BMPs), a group of cytokines of the TGF-β superfamily implicated in differentiation, apoptosis and proliferation of NSCs according to their developmental stage and microenvironment [21,22], have been shown to exert a tumor suppressor activity on glioblastoma due to their ability to promote differentiation of GPCs and loss of their tumorigenic potential [1][2][3].…”

Modeling glioblastoma heterogeneity as a dynamic network of cell states

“…Temozolomide (TMZ) was chosen as the standard‐of‐care drug and added at a concentration found in the cerebrospinal fluid of GBM patients (1 µg/ml), to reflect a clinically relevant dose (Ostermann et al , 2004). The cytokine BMP4 was chosen for its inhibitory effect on GBM growth (Piccirillo et al , 2006; Dalmo et al , 2020) and was administered at a dosage (1 ng/ml) shown to elicit a receptor response (Heemskerk et al , 2019) and to have an effect on cell fate choice (Lim et al , 2000), while not causing a complete stop of cell proliferation.…”

The evolution of the cancer stem cell state in glioblastoma: emerging insights into the next generation of functional interactions

“…This was ascribed to reduction in self-renewal through the induction of asymmetric cell division, diminishing the CSC pool, and pushing cells into mature post-mitotic states. 55 However, extensive heterogeneity has been observed in BMP4 responsiveness in other studies, 56,57 highlighting the importance of assessing therapeutic responses across multiple CSC populations.…”