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

Tchaicha JH, Mobley AK, Hossain MG, Aldape KD, McCarty JH - Oncogene (2010)

Bottom Line: Although many factors that promote angiogenesis have been characterized, the identities and mechanisms of action of endogenous inhibitors of angiogenesis remain unclear.Diminished integrin expression in astrocytoma cells leads to reduced activation of latent TGFbetas, resulting in impaired TGFbeta receptor signaling in tumor-associated endothelial cells.Finally, these results show that an adhesion and signaling axis normally involved in developmental brain angiogenesis is pathologically exploited in adult brain tumors.

View Article: PubMed Central - PubMed

Affiliation: Department of Cancer Biology, University of Texas MD Anderson Cancer Center, Houston, TX, USA.

ABSTRACT
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 alphavbeta8 integrin. Diminished integrin expression in astrocytoma cells leads to reduced activation of latent TGFbetas, resulting in impaired TGFbeta receptor signaling in tumor-associated endothelial cells. These data reveal that astrocytoma cells manipulate their angiogenic balance by selectively suppressing alphavbeta8 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.

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Reduced αvβ8 integrin protein expression following oncogene-mediated astroglial cell transformation(A); Detergent-soluble lysates from wild type or β8−/− primary (prim.) and transformed (trans.) astroglial progenitors were immunoblotted with antibodies directed against αv, β1, and β8 integrins. In comparison to primary cells, note the progressive reduction in αv and β8 integrin protein expression in transformed cells. The lower molecular weight band in the αv integrin immunoblots (transformed samples) is likely non-glycosylated integrin protein. (B); Primary cells (upper panels) and transformed cells (lower panels) were analyzed by fluorescent activated cell sorting using an anti-αv integrin antibody conjugated to phycoerythrein (αv-PE). Percentages of primary and transformed cells expressing cell surface αv integrin protein are indicated in red font. (C); Wild type transformed astroglial progenitor cells were propagated over 12 passages. Detergent-soluble lysates (P2 to P12) were then immunoblotted with anti-αv and anti-β8 antibodies. In comparison to unpassaged primary cells (primary), note the progressive reduction in αvβ8 integrin protein expression as transformed cells are passaged.
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Figure 4: Reduced αvβ8 integrin protein expression following oncogene-mediated astroglial cell transformation(A); Detergent-soluble lysates from wild type or β8−/− primary (prim.) and transformed (trans.) astroglial progenitors were immunoblotted with antibodies directed against αv, β1, and β8 integrins. In comparison to primary cells, note the progressive reduction in αv and β8 integrin protein expression in transformed cells. The lower molecular weight band in the αv integrin immunoblots (transformed samples) is likely non-glycosylated integrin protein. (B); Primary cells (upper panels) and transformed cells (lower panels) were analyzed by fluorescent activated cell sorting using an anti-αv integrin antibody conjugated to phycoerythrein (αv-PE). Percentages of primary and transformed cells expressing cell surface αv integrin protein are indicated in red font. (C); Wild type transformed astroglial progenitor cells were propagated over 12 passages. Detergent-soluble lysates (P2 to P12) were then immunoblotted with anti-αv and anti-β8 antibodies. In comparison to unpassaged primary cells (primary), note the progressive reduction in αvβ8 integrin protein expression as transformed cells are passaged.

Mentions: Transformed wild type cells showed significantly reduced levels of αv and β8 integrin proteins, although the levels of β1 integrin protein were not altered in wild type or β8−/− transformed cells (Figure 4A). Due to a dearth of β8 integrin antibodies available for fluorescent activated cell sorting, integrin expression was quantified in primary versus transformed cells using an anti-αv antibody. As shown in Figure 4B, approximately 90% of wild type and β8−/− primary cells expressed detectable levels of cell surface αv integrin protein. In contrast, oncogene-mediated transformation resulted in an approximately 50% reduction in αv integrin protein expression (Figure 4B). Since β8 integrin heterodimerizes exclusively with the αv subunit (Milner et al., 2001), the reduction in β8 protein levels in wild type transformed cells is likely due to reduced levels of αv integrin protein; indeed, αv protein levels are reduced in oncogene-transformed β8−/− cells (Figure 4B). We have also detected reduced levels of β5 integrin, which also heterodimerizes exclusively with αv integrin, in wild type and β8−/− transformed astroglial cells (data not shown). Levels of αvβ8 integrin protein expression progressively diminished following sequential passaging of wild type transformed astroglial cells (Figure 4C). The diminished αvβ8 integrin protein expression in highly passaged transformed cells was not a secondary consequence of long-term growth in vitro, since we did not detect diminished integrin expression in sequentially passaged primary mouse neurospheres isolated from the post-natal subventricular zone (Supplemental Figure 2).


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

Tchaicha JH, Mobley AK, Hossain MG, Aldape KD, McCarty JH - Oncogene (2010)

Reduced αvβ8 integrin protein expression following oncogene-mediated astroglial cell transformation(A); Detergent-soluble lysates from wild type or β8−/− primary (prim.) and transformed (trans.) astroglial progenitors were immunoblotted with antibodies directed against αv, β1, and β8 integrins. In comparison to primary cells, note the progressive reduction in αv and β8 integrin protein expression in transformed cells. The lower molecular weight band in the αv integrin immunoblots (transformed samples) is likely non-glycosylated integrin protein. (B); Primary cells (upper panels) and transformed cells (lower panels) were analyzed by fluorescent activated cell sorting using an anti-αv integrin antibody conjugated to phycoerythrein (αv-PE). Percentages of primary and transformed cells expressing cell surface αv integrin protein are indicated in red font. (C); Wild type transformed astroglial progenitor cells were propagated over 12 passages. Detergent-soluble lysates (P2 to P12) were then immunoblotted with anti-αv and anti-β8 antibodies. In comparison to unpassaged primary cells (primary), note the progressive reduction in αvβ8 integrin protein expression as transformed cells are passaged.
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Related In: Results  -  Collection

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Figure 4: Reduced αvβ8 integrin protein expression following oncogene-mediated astroglial cell transformation(A); Detergent-soluble lysates from wild type or β8−/− primary (prim.) and transformed (trans.) astroglial progenitors were immunoblotted with antibodies directed against αv, β1, and β8 integrins. In comparison to primary cells, note the progressive reduction in αv and β8 integrin protein expression in transformed cells. The lower molecular weight band in the αv integrin immunoblots (transformed samples) is likely non-glycosylated integrin protein. (B); Primary cells (upper panels) and transformed cells (lower panels) were analyzed by fluorescent activated cell sorting using an anti-αv integrin antibody conjugated to phycoerythrein (αv-PE). Percentages of primary and transformed cells expressing cell surface αv integrin protein are indicated in red font. (C); Wild type transformed astroglial progenitor cells were propagated over 12 passages. Detergent-soluble lysates (P2 to P12) were then immunoblotted with anti-αv and anti-β8 antibodies. In comparison to unpassaged primary cells (primary), note the progressive reduction in αvβ8 integrin protein expression as transformed cells are passaged.
Mentions: Transformed wild type cells showed significantly reduced levels of αv and β8 integrin proteins, although the levels of β1 integrin protein were not altered in wild type or β8−/− transformed cells (Figure 4A). Due to a dearth of β8 integrin antibodies available for fluorescent activated cell sorting, integrin expression was quantified in primary versus transformed cells using an anti-αv antibody. As shown in Figure 4B, approximately 90% of wild type and β8−/− primary cells expressed detectable levels of cell surface αv integrin protein. In contrast, oncogene-mediated transformation resulted in an approximately 50% reduction in αv integrin protein expression (Figure 4B). Since β8 integrin heterodimerizes exclusively with the αv subunit (Milner et al., 2001), the reduction in β8 protein levels in wild type transformed cells is likely due to reduced levels of αv integrin protein; indeed, αv protein levels are reduced in oncogene-transformed β8−/− cells (Figure 4B). We have also detected reduced levels of β5 integrin, which also heterodimerizes exclusively with αv integrin, in wild type and β8−/− transformed astroglial cells (data not shown). Levels of αvβ8 integrin protein expression progressively diminished following sequential passaging of wild type transformed astroglial cells (Figure 4C). The diminished αvβ8 integrin protein expression in highly passaged transformed cells was not a secondary consequence of long-term growth in vitro, since we did not detect diminished integrin expression in sequentially passaged primary mouse neurospheres isolated from the post-natal subventricular zone (Supplemental Figure 2).

Bottom Line: Although many factors that promote angiogenesis have been characterized, the identities and mechanisms of action of endogenous inhibitors of angiogenesis remain unclear.Diminished integrin expression in astrocytoma cells leads to reduced activation of latent TGFbetas, resulting in impaired TGFbeta receptor signaling in tumor-associated endothelial cells.Finally, these results show that an adhesion and signaling axis normally involved in developmental brain angiogenesis is pathologically exploited in adult brain tumors.

View Article: PubMed Central - PubMed

Affiliation: Department of Cancer Biology, University of Texas MD Anderson Cancer Center, Houston, TX, USA.

ABSTRACT
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 alphavbeta8 integrin. Diminished integrin expression in astrocytoma cells leads to reduced activation of latent TGFbetas, resulting in impaired TGFbeta receptor signaling in tumor-associated endothelial cells. These data reveal that astrocytoma cells manipulate their angiogenic balance by selectively suppressing alphavbeta8 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.

Show MeSH
Related in: MedlinePlus