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KLF-8: A novel integrin signalling molecule, which enhances malignant proliferation in gliomas and is expressed grade dependent
Objective: The downstream mechanisms used by integrins to promote proliferation of malignant cells in brain tumors are widely unknown. In the present study we investigate for the first time pivotal factors of a newly found integrin proliferation pathway including the potent transcription factor KLF-8 that stimulates cyclin D1 and subsequently G1/S-progression of the cell cycle in gliomas of different WHO grades.
Methods: Sections and single tumor cells from primary diagnosed glioblastomas (WHO grade IV, n=5), anaplastic astrocytomas (WHO grade III, n=5), low grade astrocytomas (WHO grade II, n=5) as well as normal brain tissue (cells) were subjected to immunohistochemical and immunocytochemical staining for integrin alpha v beta 3 and downstream signalling molecules: the phosphorylated focal adhesion kinase (pFAK) and cyclin D1. Isolated tumor cells were stained for coexpression of integrin alpha v beta 3 as well as pFAK, the transcription factor KLF-8, and cyclin D1. To determine whether these molecules are expressed in a WHO grade dependent manner we also performed Western blot analysis in the same entities (n=5 each).
Results: Besides alpha v beta 3, pFAK and cyclin D1, the transcription factor KLF-8 could be detected in low and high grade gliomas. Western blot analysis and immunhistochemistry revealed a WHO grade-dependent overexpression of KLF-8, pFAK, and cyclin D1 in high and low grade gliomas compared to normal brain. On the single cell level, alpha v beta 3-integrin and the pFAK kinase were found to be co-localized on cell membranes, whereas cyclin D1 and KLF-8 were detected preferentially in the nucleus of isolated cells.
Conclusion: Our data provide the first description of the potent transcription factor KLF-8 and evidence for a significant grade-dependent expression of downstream integrin signalling molecules in human gliomas. Furthermore, first functional data support the strong proliferation enhancing role of KLF-8. Thus, inhibiting downstream integrin signalling by blocking KLF-8 may represent a novel antiproliferative treatment strategy for malignant brain tumors.