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Integrin-linked kinase: Dispensable for radiation survival of three-dimensionally cultured fibroblasts

OncoRay - Center for Radiation Research in Oncology, Dresden University of Technology, Fetscherstrasse, Germany.
Radiotherapy and Oncology (Impact Factor: 4.86). 04/2008; 86(3):329-35. DOI: 10.1016/j.radonc.2007.09.007
Source: PubMed

ABSTRACT Cancer treatment by conventional radiotherapy is limited by normal tissue side-effects. Fibroblasts as "non-target" stromal cell type are considered as strong promoter of tumor growth and for developing a therapy resistant phenotype. Regarding application of novel molecular therapeutics combined with radiotherapy, evaluation of a specific targeted molecule in both tumor and normal cells is mandatory for efficacy and tolerability assessment. Previous work showed integrin-linked kinase (ILK), a mediator of beta-integrin signals and putative phosphorylator of AKT, as potent anti-survival regulator in human cancer cell lines.
To evaluate the role of ILK in normal fibroblast survival, ILK-wild-type (ILK(fl/fl)), ILK(-/-) and ILK(N-terminal) and ILK(C-terminal) domain expressing fibroblasts were irradiated with X-rays on different substrata or in three-dimensional laminin-rich extracellular matrix (lrECM).
On control substrata, ILK-deficient and ILK-mutant fibroblasts showed significant increase in radiation survival relative to ILK-wild-type cells. This effect was compensated by growth on ECM proteins and in 3D lrECM. ILK regulated AKT activity in a phosphatidylinositol-3 kinase (PI3K)-dependent manner. Upon PI3K inhibition, only ILK-wild-type fibroblasts showed significant radiosensitization.
These findings obtained in 3D cell cultures suggest ILK to be dispensable for the radiation survival response of normal fibroblasts. However, targeting the PI3K/AKT signaling axis pharmacologically might be critical for survival of normal fibroblasts exposed to ionizing radiation.

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    • "Studies using ex vivo cell cultures show the loss of morphological and functional properties in an artificial environment such as cell culture plastic as compared to ECM scaffolds [38, 69, 71]. Interesting studies in diverse tumor cell lines and normal cells showed that 3D growth in a matrix modifies gene and protein expression, cell survival, proliferation, differentiation, and metabolism in comparison to conventional 2D monolayer cell cultures [40, 42, 43, 46, 48, 116]. In line with these findings, osteosarcoma cells are protected against doxorubicin treatment [125] and head and neck and non-small-cell lung cancer cells display a reduced radiation sensitivity when grown in a 3D matrix in contrast to 2D [11, 40]. "
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    • "In addition to the use of 3D cell culture models in tissue engineering [19], [20], [21] and studies on embryonic development and physiology [18], 3D cell cultures are increasingly employed in cancer research [7], [8], [9], [12], [16], [22]. In the vast majority of cases, tumor cell lines of different origin show an enhanced resistance to radio- and chemotherapy in a 3D environment indicative by increased clonogenicity and decreased apoptosis [12], [13], [14], [16], [17], [23], [24], [25], [26], [27]. Apart from a significant impact of integrin-mediated cell-ECM interactions [28], a complex interplay of biochemical signaling pathways and biophysical/mechanotransduction-related factors is thought to confer this enhanced tumor cell resistance whose underlying mechanisms remain to be determined both on the gene and on the protein level [2]. "
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    • "Consequently, the usage of a 3D lrECM model, as performed here, pinpoints the complexity of signaling events and protein–protein interactions and the consideration that such models provide valuable and more realistic insights into molecular mechanisms [21] [33]. "
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