Mohammad G. Hossain

Glioblastoma angiogenesis and tumor cell invasiveness are differentially regulated by β8 integrin

Glioblastoma multiforme (GBM) is a highly invasive brain tumor that develops florid microvascular proliferation and hemorrhage. However, mechanisms that favor invasion versus angiogenesis in this setting remain largely uncharacterized. Here, we show that integrin β8 is an essential regulator of both GBM-induced angiogenesis and tumor cell invasiveness. Highly angiogenic and poorly invasive tumors expressed low levels of β8 integrin, whereas highly invasive tumors with limited neovascularization expressed high levels of β8 integrin. Manipulating β8 integrin protein levels altered the angiogenic and invasive growth properties of GBMs, in part, reflected by a diminished activation of latent TGFβs, which are extracellular matrix protein ligands for β8 integrin. Taken together, these results establish a role for β8 integrin in differential control of angiogenesis versus tumor cell invasion in GBM. Our findings suggest that inhibiting β8 integrin or TGFβ signaling may diminish tumor cell invasiveness during malignant progression and following antivascular therapies.

The astrocyte-expressed integrin αvβ8 governs blood vessel sprouting in the developing retina.

The mouse retina is vascularized after birth when angiogenic blood vessels grow and sprout along a pre-formed latticework of astrocytes. How astrocyte-derived cues control patterns of blood vessel growth and sprouting, however, remains enigmatic. Here, we have used molecular genetic strategies in mice to demonstrate that αvβ8 integrin expressed in astrocytes is essential for neovascularization of the developing retina. Selective ablation of αv or β8 integrin gene expression in astrocytes leads to impaired blood vessel sprouting and intraretinal hemorrhage, particularly during formation of the secondary vascular plexus. These pathologies correlate, in part, with diminished αvβ8 integrin-mediated activation of extracellular matrix-bound latent transforming growth factor βs (TGFβs) and defective TGFβ signaling in vascular endothelial cells, but not astrocytes. Collectively, our data demonstrate that αvβ8 integrin is a component of a paracrine signaling axis that links astrocytes to blood vessels and is essential for proper regulation of retinal angiogenesis.

A mosaic mouse model of astrocytoma identifies alphavbeta8 integrin as a negative regulator of tumor angiogenesis.

Angiogenesis involves a complex set of cell–cell and cell–extracellular matrix (ECM) interactions that coordinately promote and inhibit blood vessel growth and sprouting. Although many factors that promote angiogenesis have been characterized, the identities and mechanisms of action of endogenous inhibitors of angiogenesis remain unclear. Furthermore, little is known about how cancer cells selectively circumvent the actions of these inhibitors to promote pathological angiogenesis, a requisite event for tumor progression. Using mosaic mouse models of the malignant brain cancer, astrocytoma, we report that tumor cells induce pathological angiogenesis by suppressing expression of the ECM protein receptor αvβ8 integrin. Diminished integrin expression in astrocytoma cells leads to reduced activation of latent TGFβs, resulting in impaired TGFβ receptor signaling in tumor-associated endothelial cells. These data reveal that astrocytoma cells manipulate their angiogenic balance by selectively suppressing αvβ8 integrin expression and function. Finally, these results show that an adhesion and signaling axis normally involved in developmental brain angiogenesis is pathologically exploited in adult brain tumors.

A mosaic mouse model of astrocytoma identifies αvβ8 integrin as a negative regulator of tumor angiogenesis

Angiogenesis involves a complex set of cell–cell and cell–extracellular matrix (ECM) interactions that coordinately promote and inhibit blood vessel growth and sprouting. Although many factors that promote angiogenesis have been characterized, the identities and mechanisms of action of endogenous inhibitors of angiogenesis remain unclear. Furthermore, little is known about how cancer cells selectively circumvent the actions of these inhibitors to promote pathological angiogenesis, a requisite event for tumor progression. Using mosaic mouse models of the malignant brain cancer, astrocytoma, we report that tumor cells induce pathological angiogenesis by suppressing expression of the ECM protein receptor αvβ8 integrin. Diminished integrin expression in astrocytoma cells leads to reduced activation of latent TGFβs, resulting in impaired TGFβ receptor signaling in tumor-associated endothelial cells. These data reveal that astrocytoma cells manipulate their angiogenic balance by selectively suppressing αvβ8 integrin expression and function. Finally, these results show that an adhesion and signaling axis normally involved in developmental brain angiogenesis is pathologically exploited in adult brain tumors.

Analysis of αv integrin protein expression in human eyelid and periorbital squamous cell carcinomas

Background: Alpha v integrins are receptors for many extracellular matrix (ECM) protein ligands, including latent transforming growth factor betas (TGFβs). Various studies in mice have shown that ablation of genes encoding αv integrin or TGFβ signaling pathway components leads to spontaneous squamous cell carcinomas (SCCs) in the conjunctiva and periocular skin. Here, we have analyzed patterns of αv integrin protein expression and TGFβ signaling in human eyelid and periorbital SCC samples.

A Mosaic Mouse Model of Astrocytoma Identifies αvβ8 Integrin as an Essential Regulator of Tumor-Induced Angiogenesis

Angiogenesis involves a complex set of cell–cell and cell–extracellular matrix (ECM) interactions that coordinately promote and inhibit blood vessel growth and sprouting. Although many factors that promote angiogenesis have been characterized, the identities and mechanisms of action of endogenous inhibitors of angiogenesis remain unclear. Furthermore, little is known about how cancer cells selectively circumvent the actions of these inhibitors to promote pathological angiogenesis, a requisite event for tumor progression. Using mosaic mouse models of the malignant brain cancer, astrocytoma, we report that tumor cells induce pathological angiogenesis by suppressing expression of the ECM protein receptor αvβ8 integrin. Diminished integrin expression in astrocytoma cells leads to reduced activation of latent TGFβs, resulting in impaired TGFβ receptor signaling in tumor-associated endothelial cells. These data reveal that astrocytoma cells manipulate their angiogenic balance by selectively suppressing αvβ8 integrin expression and function. Finally, these results show that an adhesion and signaling axis normally involved in developmental brain angiogenesis is pathologically exploited in adult brain tumors.