Characterization of oncogene-induced senescence and the role of the senescence-associated secretory phenotype in pilocytic astrocytoma

Introduction:

Variations in proliferation caused by oncogene-induced senescence (OIS) are proposed to cause the benign but unpredictable growth behaviour of pilocytic astrocytoma (PA). In PA OIS is induced by aberrant MAPK pathway activation. The senescence-associated secretory phenotype (SASP), a set of cytokines, growth factors and proteases, regulates the OIS state. We here characterize the key SASP factors in PA and investigate their functional significance as growth regulators and potential targets.

Methods:

DKFZ-BT66, a genetically engineered primary PA cell culture model, was used to study OIS in PA. Via inducible expression of the SV40 Large T Antigen and subsequent suppression of p53/RB signaling, switching between senescence and proliferation is possible. Both conditions were characterized using gene-expression profiling (GEP), Western Blot, real-time qPCR, ELISA, cell counts and viability by automated trypan blue exclusion staining.

Results:

During OIS a significant increase of the SASP was detected when comparing the GEP of senescent versus proliferating PA cells. The representative SASP factors IL-6 and IL-1B were upregulated on mRNA and protein level. Their receptor proteins were expressed, and both pathways were active in the OIS state. Proliferating cells showed impaired growth after stimulation of selected SASP pathways.

Conclusion:

The patient-derived PA tumor cell line DKFZ-BT66 is a suitable model to investigate the relevance of OIS in PA and demonstrates activity of the OIS-characteristic SASP. Ongoing studies will show whether the OIS-induced growth arrest is reversible and whether it is the source of the unpredictable regrowth of PAs observed in patients. These findings could furthermore be relevant for treatment decisions concerning anti-inflammatory or immunosuppressive drugs in PA patients.