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Stromal control of oncogenic traits expressed in response to the overexpression of GLI2, a pleiotropic oncogene.

Snijders AM, Huey B, Connelly ST, Roy R, Jordan RC, Schmidt BL, Albertson DG - Oncogene (2008)

Bottom Line: We show that GLI2 is a pleiotropic oncogene.The overexpression induces genomic instability and blocks differentiation, likely mediated in part by enhanced expression of the stem cell gene SOX2.GLI2 also induces transforming growth factor (TGF)B1-dependent transdifferentiation of foreskin and tongue, but not gingival fibroblasts into myofibroblasts, creating an environment permissive for invasion by keratinocytes, which are in various stages of differentiation having downregulated GLI2.

View Article: PubMed Central - PubMed

Affiliation: Cancer Research Institute, University of California San Francisco, San Francisco, CA 94143-0808, USA.

ABSTRACT
Hedgehog signaling is often activated in tumors, yet it remains unclear how GLI2, a transcription factor activated by this pathway, acts as an oncogene. We show that GLI2 is a pleiotropic oncogene. The overexpression induces genomic instability and blocks differentiation, likely mediated in part by enhanced expression of the stem cell gene SOX2. GLI2 also induces transforming growth factor (TGF)B1-dependent transdifferentiation of foreskin and tongue, but not gingival fibroblasts into myofibroblasts, creating an environment permissive for invasion by keratinocytes, which are in various stages of differentiation having downregulated GLI2. Thus, upregulated GLI2 expression is sufficient to induce a number of the acquired characteristics of tumor cells; however, the stroma, in a tissue-specific manner, determines whether certain GLI2 oncogenic traits are expressed.

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GLI2 expressing HaCaT cells do not migrate into collagen I gelsSpheroid cultures of eGFP expressing control HaCaT Tet cells (green), RFP expressing HaCaT GLI2 cells (red) and a 1:1 mixture of eGFP expressing HaCaT Tet cells (green) and RFP expressing HaCaT GLI2 cells (red) were embedded in a collagen I matrix and grown for 13 days with or without doxycycline to induce GLI2 expression.
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Figure 8: GLI2 expressing HaCaT cells do not migrate into collagen I gelsSpheroid cultures of eGFP expressing control HaCaT Tet cells (green), RFP expressing HaCaT GLI2 cells (red) and a 1:1 mixture of eGFP expressing HaCaT Tet cells (green) and RFP expressing HaCaT GLI2 cells (red) were embedded in a collagen I matrix and grown for 13 days with or without doxycycline to induce GLI2 expression.

Mentions: All keratinocytes invading into the collagen/fibroblast layer of GLI2 expressing HaCaT GLI2 tissue reconstructs appeared to be positive for pancytokeratin (Figure 2C) and were uniformly negative for E-cadherin (Figure 7C), while cells in the epithelial layer showed membranous staining for both E-cadherin and β-catenin (Figure 7D), suggesting that invasion is dependent on the loss of E-cadherin as is commonly observed in other systems. Enhanced expression of β-catenin was also noted in the myofibroblasts in GLI2 expressing HaCaT GLI2 reconstructs. It was notable that the invading cells down regulated expression of the GLI2 responsive gene BCL2 (Figures 7E and Supplementary Figure 9), as well as SOX2 and TITF1 (Figure 4), and some cells stained positively for differentiation markers (Figure 3) or markers of apoptosis (caspase 3 or TUNEL, Figure 7F and data not shown). We also observed a lack of sprouting from spheroids formed from GLI2 expressing HaCaT GLI2 cells embedded in collagen I matrices (Figure 8). These observations suggest that GLI2 expressing keratinocytes are non-invasive and that the capabilities to both invade and differentiate are acquired upon down regulation of GLI2. Nevertheless, invading cells appear to remain confined to the myofibroblast region. These observations together with the lack of invasion in tissue reconstructs lacking myofibroblasts (e.g. due to inhibition of TGFβ1 signaling) suggest that remodeling of the collagen I matrix by myofibroblasts is required for local invasion of HaCaT GLI2 cells that have down regulated GLI2 responsive genes.


Stromal control of oncogenic traits expressed in response to the overexpression of GLI2, a pleiotropic oncogene.

Snijders AM, Huey B, Connelly ST, Roy R, Jordan RC, Schmidt BL, Albertson DG - Oncogene (2008)

GLI2 expressing HaCaT cells do not migrate into collagen I gelsSpheroid cultures of eGFP expressing control HaCaT Tet cells (green), RFP expressing HaCaT GLI2 cells (red) and a 1:1 mixture of eGFP expressing HaCaT Tet cells (green) and RFP expressing HaCaT GLI2 cells (red) were embedded in a collagen I matrix and grown for 13 days with or without doxycycline to induce GLI2 expression.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2643346&req=5

Figure 8: GLI2 expressing HaCaT cells do not migrate into collagen I gelsSpheroid cultures of eGFP expressing control HaCaT Tet cells (green), RFP expressing HaCaT GLI2 cells (red) and a 1:1 mixture of eGFP expressing HaCaT Tet cells (green) and RFP expressing HaCaT GLI2 cells (red) were embedded in a collagen I matrix and grown for 13 days with or without doxycycline to induce GLI2 expression.
Mentions: All keratinocytes invading into the collagen/fibroblast layer of GLI2 expressing HaCaT GLI2 tissue reconstructs appeared to be positive for pancytokeratin (Figure 2C) and were uniformly negative for E-cadherin (Figure 7C), while cells in the epithelial layer showed membranous staining for both E-cadherin and β-catenin (Figure 7D), suggesting that invasion is dependent on the loss of E-cadherin as is commonly observed in other systems. Enhanced expression of β-catenin was also noted in the myofibroblasts in GLI2 expressing HaCaT GLI2 reconstructs. It was notable that the invading cells down regulated expression of the GLI2 responsive gene BCL2 (Figures 7E and Supplementary Figure 9), as well as SOX2 and TITF1 (Figure 4), and some cells stained positively for differentiation markers (Figure 3) or markers of apoptosis (caspase 3 or TUNEL, Figure 7F and data not shown). We also observed a lack of sprouting from spheroids formed from GLI2 expressing HaCaT GLI2 cells embedded in collagen I matrices (Figure 8). These observations suggest that GLI2 expressing keratinocytes are non-invasive and that the capabilities to both invade and differentiate are acquired upon down regulation of GLI2. Nevertheless, invading cells appear to remain confined to the myofibroblast region. These observations together with the lack of invasion in tissue reconstructs lacking myofibroblasts (e.g. due to inhibition of TGFβ1 signaling) suggest that remodeling of the collagen I matrix by myofibroblasts is required for local invasion of HaCaT GLI2 cells that have down regulated GLI2 responsive genes.

Bottom Line: We show that GLI2 is a pleiotropic oncogene.The overexpression induces genomic instability and blocks differentiation, likely mediated in part by enhanced expression of the stem cell gene SOX2.GLI2 also induces transforming growth factor (TGF)B1-dependent transdifferentiation of foreskin and tongue, but not gingival fibroblasts into myofibroblasts, creating an environment permissive for invasion by keratinocytes, which are in various stages of differentiation having downregulated GLI2.

View Article: PubMed Central - PubMed

Affiliation: Cancer Research Institute, University of California San Francisco, San Francisco, CA 94143-0808, USA.

ABSTRACT
Hedgehog signaling is often activated in tumors, yet it remains unclear how GLI2, a transcription factor activated by this pathway, acts as an oncogene. We show that GLI2 is a pleiotropic oncogene. The overexpression induces genomic instability and blocks differentiation, likely mediated in part by enhanced expression of the stem cell gene SOX2. GLI2 also induces transforming growth factor (TGF)B1-dependent transdifferentiation of foreskin and tongue, but not gingival fibroblasts into myofibroblasts, creating an environment permissive for invasion by keratinocytes, which are in various stages of differentiation having downregulated GLI2. Thus, upregulated GLI2 expression is sufficient to induce a number of the acquired characteristics of tumor cells; however, the stroma, in a tissue-specific manner, determines whether certain GLI2 oncogenic traits are expressed.

Show MeSH
Related in: MedlinePlus