Abstract
The benign but unpredictable growth behaviour of pilocytic astrocytoma (PA) is thought to originate from variations in proliferation caused by oncogene-induced senescence (OIS). An increase in MAPK pathway activation, present in virtually all PAs, serves a stimulus driving the tumor into OIS. Upregulation of p16, p21 and several other OIS-related genes has been observed in primary PAs. The secretion of a set of cytokines, growth factors and proteases, referred to as the senescence-associated secretory phenotype (SASP), is a characteristic feature of senescent cells. The SASP is thought to be involved in the induction and maintenance of the OIS state. The key SASP factors in PA and their functional significance are unknown. To study OIS in PA, the genetically engineered primary PA cell culture model DKFZ-BT66 was used. The model allows switching between senescence and proliferation via inducible expression of the SV40 Large T Antigen suppressing p53/RB signaling. Readouts used were gene-expression profiling (GEP), Western Blot, real-time qPCR, ELISA, cell counts and viability by automated trypan blue exclusion staining. Comparison of the GEP of senescent versus proliferating cells showed a significant increase in the SASP during OIS. The upregulation of the representative SASP factors IL-6 and IL-1B was confirmed on mRNA and protein level. The respective receptor proteins were both expressed, and activation of both pathways was detected in the OIS state. Stimulation of selected SASP pathways led to reduced cell growth of proliferating cells. In summary, the first representative patient-derived PA tumor model DKFZ-BT66 confirms the presence of OIS in PA, and additionally reveals activity of the OIS-characteristic SASP. Ongoing studies will show whether the OIS-induced growth arrest is reversible and if it may explain the unpredictable regrowth of PAs observed in patients. These findings will be relevant for treatment decisions concerning anti-inflammatory or immunosuppressive drugs in PA patients.