Biological Role and Therapeutic Targeting of TGF-β3 in Glioblastoma

Abstract

Transforming growth factor (TGF)-β contributes to the malignant phenotype of glioblastoma by promoting invasiveness and angiogenesis and creating an immunosuppressive microenvironment. So far, TGF-β₁ and TGF-β₂ isoforms have been considered to act in a similar fashion without isoform-specific function in glioblastoma. A pathogenic role for TGF-β₃ in glioblastoma has not been defined yet. Here, we studied the expression and functional role of endogenous and exogenous TGF-β₃ in glioblastoma models. <i>TGF-β₃</i> mRNA is expressed in human and murine long-term glioma cell lines as well as in human glioma-initiating cell cultures with expression levels lower than <i>TGF-β₁</i> or <i>TGF-β₂</i> in most cell lines. Inhibition of <i>TGF-β₃</i> mRNA expression by ISTH2020 or ISTH2023, two different isoform-specific phosphorothioate locked nucleic acid (LNA)-modified antisense oligonucleotide gapmers, blocks downstream SMAD2 and SMAD1/5 phosphorylation in human LN-308 cells, without affecting <i>TGF-β₁</i> or <i>TGF-β₂</i> mRNA expression or protein levels. Moreover, inhibition of <i>TGF-β₃</i> expression reduces invasiveness <i>in vitro</i> Interestingly, depletion of <i>TGF-β₃</i> also attenuates signaling evoked by TGF-β₁ or TGF-β₂ In orthotopic syngeneic (SMA-560) and xenograft (LN-308) <i>in vivo</i> glioma models, expression of <i>TGF-β₃</i> as well as of the downstream target, <i>plasminogen-activator-inhibitor (PAI)-1</i>, was reduced, while <i>TGF-β₁</i> and <i>TGF-β₂</i> levels were unaffected following systemic treatment with <i>TGF-β₃</i> -specific antisense oligonucleotides. We conclude that TGF-β₃ might function as a gatekeeper controlling downstream signaling despite high expression of TGF-β₁ and TGF-β₂ isoforms. Targeting TGF-β₃<i>in vivo</i> may represent a promising strategy interfering with aberrant TGF-β signaling in glioblastoma. <i>Mol Cancer Ther; 16(6); 1177-86. ©2017 AACR</i>.