Induction of senescence in human malignant glioma cells by p16INK4A
L Uhrbom1, M Nistér, B Westermark
1Department of Pathology, Uppsala University, University Hospital, Sweden.
Abstract:
p16INK4A is a G1-specific cell cycle inhibitor which maps to human chromosome 9p21, a region frequently mutated or deleted in cancer cell lines and primary tumors. In glioblastomas the frequency of homozygous deletions is 40-70% making it one of the most common mutations in this tumor type. We have analysed the significance of the loss of this gene in gliomas by introducing the cDNA for p16INK4A into the human glioma cell line U-1242 MG which has a deleted CDKN2 locus. We used the tetracycline repressible vector system and obtained two stably transfected clones that expressed p16INK4A upon induction. p16INK4A expression caused a G1 arrest and enlargement of the cells similar to that of senescent cells. When staining for Senescence-Associated beta-galactosidase activity, described to be specific for senescent cells, we could show that the enlarged cells specifically gave a positive staining reaction. This senescence phenotype was dependent on the continuous expression of p16INK4A since it was reversed upon reintroduction of tetracycline suppression. Thus, the induced expression of p16INK4A in these glioma cells reverted their immortal phenotype and caused an immediate cellular senescence.
Insights
Introducing p16INK4A into glioma cells halted cell division and induced senescence, reversing their immortal phenotype. This demonstrates p16INK4A’s role in cellular senescence and potential therapeutic applications for glioblastoma.
Area of Science:
- Oncology
- Cell Biology
- Molecular Biology
Background:
- The p16INK4A gene, a G1 cell cycle inhibitor, is frequently lost in cancers, particularly glioblastomas (40-70% homozygous deletions).
- Loss of p16INK4A contributes to the uncontrolled proliferation characteristic of glioblastoma multiforme.
Purpose of the Study:
- To investigate the functional significance of p16INK4A loss in gliomas.
- To determine if reintroducing p16INK4A can reverse the immortal phenotype of glioma cells and induce senescence.
Main Methods:
- Human glioma cell line U-1242 MG with a deleted CDKN2 locus was used.
- A tetracycline-inducible system was employed to stably express p16INK4A cDNA.
- Senescence was assessed via cell enlargement and Senescence-Associated beta-galactosidase staining.
Main Results:
- Stable expression of p16INK4A induced a G1 cell cycle arrest and significant cell enlargement.
- Enlarged cells exhibited positive staining for Senescence-Associated beta-galactosidase, indicating cellular senescence.
- The induced senescence phenotype was reversible upon tetracycline suppression, confirming p16INK4A dependency.
Conclusions:
- Induced expression of p16INK4A effectively reverts the immortal phenotype of U-1242 MG glioma cells.
- p16INK4A expression triggers immediate cellular senescence in these glioma cells.
- Restoring p16INK4A function represents a potential strategy for glioblastoma therapy.
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