Abstract B63: Differences between replicative senescence- versus radiation- associated secretory phenotype
Authors: Schlegel Julian , Domhan Sophie , Debus Jürgen , Abdollahi Amir 
Published: May 2015

Abstract
Background: A growing body of data indicates an important role for induction of senescence associated programs in tumor-stroma communication. In addition to the replicative senecence, limiting uncontrolled cell proliferation in non-malignant cells, oncogenes and radiotherapy are postulated to induce cellular senescence. The senescence-associated secretory phenotype (SASP) describes the expression and secretion of series of key cytokines involved in inflammatory response. We sought to investigate the molecular mechanisms governing SASP after classical replicative senescence vs. radiation induced intercellular communication.
Methods: Primary isolated human renal proximal tubules epithelial cells (RPTEC) were grown in culture until they undergo replicative senescence. Early passage RPTEC were in parallel irradiated with different doses (0-6Gy). Senescence cells were detected by color-producing substrate-conversion by senescence-associated ß-Galactosidase (SA-ßGal). Induction of senescence associated relevant regulators of cell cycle such as p21 were longitudinally investigated. For investigation of the cytokine response real time quantitative RT-PCR and ELISA was performed in a panel of key known SASP-cytokines. To confirm the data generated in RPTEC, primary isolated human umbilical vein endothelial cells, pulmonary microvascular endothelial cells and fibroblasts were used as alternative models.
Results: RPTEC growth was limited to 11-13 passages after which the majority of cells undergo replicative senescence demonstrating a strong SA-ß-Gal signal. In parallel, a subpopulation of RPTECs demonstrated elevated SA-ßGal signal followed by irradiation. Both radiation induced growth arrest and replicative exhaustion was associated with upregulation of p21 (CDKN1A). Interleukin-1? and ? (IL-1?/?) transcript levels were increased 246±21.9% and 185±24.8%-fold after irradiation, respectively. Likewise, a 478±40.2% and 869±70.7%-fold increase of IL-1?/? was found in senescent RPTECs. In line with these observations, IL-8 levels were strongly increased under both conditions. Surprisingly, a panel of key cytokines in tumor-stroma communication were induced by irradiation but decreased after replicative senescence in RPTECs. For example, transcript levels of IL-6 were increased by irradiation (3.2±0.1-fold) while decreased by 68±1.4% in senescent (p12) vs. earlier passages RPTECs (p5). This inverse regulation pattern was also observed for other chemokines such as C-X-C-Ligand 1 (CXCL1) being downregulated in senescent RPTECs (71.1±2.2%) whereas upregulated by 105±4.3% in case of irradiation.
Conclusion: We report here differential, in part inverse, regulation pattern of key cytokines involved in tumor-stroma communication after replicative senescence (SASP) vs. radiotherapy in primary human RPTEC. These data indicate that potentially distinct mechanisms govern radiation-induced SASP like cytokine profiles.
Citation Format: Julian Schlegel, Sophie Domhan, Jürgen Debus, Amir Abdollahi. Differences between replicative senescence- versus radiation- associated secretory phenotype. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr B63. doi:10.1158/1538-7445.CHTME14-B63