Abstract
BackgroundThe transcription factor PAX6 is expressed in various cancers. In anaplastic astrocytic glioma, PAX6 expression is inversely related to tumor grade, resulting in low PAX6 expression in Glioblastoma, the highest-grade astrocytic glioma. The aim of the present study was to develop a PAX6 knock out cell line as a tool for molecular studies of the roles PAX6 have in attenuating glioblastoma tumor progression.MethodsThe CRISPR-Cas9 technique was used to knock out PAX6 in U251 N cells. Viral transduction of a doxycycline inducible EGFP-PAX6 expression vector was used to re-introduce (rescue) PAX6 expression in the PAX6 knock out cells. The knock out and rescued cells were rigorously characterized by analyzing morphology, proliferation, colony forming abilities and responses to oxidative stress and chemotherapeutic agents.ResultsThe knock out cells had increased proliferation and colony forming abilities compared to wild type cells, consistent with clinical observations indicating that PAX6 functions as a tumor-suppressor. Cell cycle distribution and sensitivity to H2O2 induced oxidative stress were further studied, as well as the effect of different chemotherapeutic agents. For the PAX6 knock out cells, the percentage of cells in G2/M phase increased compared to PAX6 control cells, indicating that PAX6 keeps U251 N cells in the G1 phase of the cell cycle. Interestingly, PAX6 knock out cells were more resilient to H2O2 induced oxidative stress than wild type cells. Chemotherapy treatment is known to generate oxidative stress, hence the effect of several chemotherapeutic agents were tested. We discovered interesting differences in the sensitivity to chemotherapeutic drugs (Temozolomide, Withaferin A and Sulforaphane) between the PAX6 expressing and non-expressing cells.ConclusionsThe U251 N PAX6 knock out cell lines generated can be used as a tool to study the molecular functions and mechanisms of PAX6 as a tumor suppressor with regard to tumor progression and treatment of glioblastoma.
Highlights
The transcription factor PAX6 is expressed in various cancers
Some of the single cell clones had a marked reduction in PAX6 expression compared to wild type (WT) U251 N cells, indicative of heterozygous knockout of PAX6
Sequencing of PAX6 knock out (KO) cells showed that cell lines originating from single cell clones had a variety of mutations creating stop codons downstream of the transcription start site (TSS) (Additional file 2: Figure S2), it will not be correct to label them as clones and they will hereby be referred to as cell lines or cells
Summary
PAX6 expression is inversely related to tumor grade, resulting in low PAX6 expression in Glioblastoma, the highest-grade astrocytic glioma. The aim of the present study was to develop a PAX6 knock out cell line as a tool for molecular studies of the roles PAX6 have in attenuating glioblastoma tumor progression. The most common and aggressive brain tumor in adults is Glioblastoma (GBM), consisting of cells with astrocytic features. GBM can arise either as a primary tumor, or from anaplastic astrocytoma (AA). 10% of patients getting surgical treatment combined with radiotherapy and chemotherapy survive 5 years after diagnosis [4, 5]. Chemotherapeutic treatment options are few and efficacy poor for glioma patients. Patient survival is approximately 12 months from diagnosis [7, 8]. Increased knowledge about the genetics of GBM is crucial for developing new, targeted therapy
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