1. Oncogene Induced Senescence and secreted Cytokines

2. Senescence Senescent cells undergo an apparently irreversible growth arrest but remain metabolically active and display characteristic changes in cell morphology, physiology, and gene expression the erosion of the telomeres, other forms of DNA damage and cellular stress, whether caused by the presence of an activated oncogene, unscheduled DNA replication, oxidative stress, or suboptimal culture conditions can all provoke a senescence phenotype oncogene-induced senescence (OIS), replicative senescence, DNA- damage induced senescence a first-line defense against potentially dangerous mutations, so progression to malignancy would correlate with escape from or impairment of senescence.

3. characteristic changes in gene expression in senescent cells - activation of p53 or the upregulation of the cyclin-dependent kinase (CDK) inhibitors, p16 INK4a and p21 CIP1, relate directly to the establishment and maintenance of growth arrest; -producing increased amounts of secreted proteins, including extracellular proteases and matrix components, growth factors, cytokines, and chemokines Senescent cells can alter the tissue microenviroment and affect neighboring cells through paracrine signaling. For example, senescent fibroblasts can stimulate angiogenesis, alter differentiation. and promote growth and tumorigenesis of epithelial cells plasminogen activator inhibitor-1 (PAI-1), a secreted protein that has been regarded as a marker for senescence, is a transcriptional target of p53 that directly contributes to the establishment of senescence The multiple chemokines released by senescent cells. proinflammatory chemokine IL-8/CXCL8 (endothelial cell migration and angiogenesis, tumorigenesis, and metastasis ) Ras-dependent secretion of IL-8 enhances tumor progression by promoting vascularization through paracrine signaling Question: Despite steady progress in probing the roles of the p53 and Rb pathways, little is known about other mechanisms that might contribute to the senescent phenotype.

4. Downregulation of CXCR2 Expression Extends Cellular Life Span The CXCR2 receptor binds to angiogenic CXC chemokine family members, containing a glutamic acid-leucine-arginine motif (ELR+). Thus, in addition to IL-8, CXCR2 binds CXCL1, 2, and 3 (GROα, β, and γ), CXCL5 (ENA-78), CXCL6 (GCP2), and CXCL7 (NAP2), whereas CXCR1 binds only to GCP2, NAP2, and IL-8.

5. CXCR2 Depletion Diminishes OIS and the DNA-Damage Response IMR-90/MEK:ER cells: Increased expression of active MEK by 4-OH- induces senescence

6. Premature Senescence Induced by Expression of CXCR1 or CXCR2

7. Premature Senescence Induced by Expression of CXCR1 or CXCR2 Is Dependent on p53

8. Upregulation of CXCR2 during Senescence

9. Upregulation of CXCR2 Ligands during Senescence

10. NF-kB and C/EBP beta Regulate the Expression of CXCR2 Ligands during OIS SP600125 (JNK inhibitor), PD98059 (MEK inhibitor), SB202190 (p38 inhibitor), BAY 11- 7082 (IKK inhibitor, 10 μM), LY294002 (PI3K inhibitor), or SB225002 (CXCR2 inhibitor). The binding sites for NF-kB and C/EBP are present in neighboring positions in The IL-8, GRO  promoter

11. CXCR2 Is Activated in Senescence: endosomal localization by IL-8 GROα-neutralizing antibody (Neutr. Abs), SB225002 (SB); CXCR2 inhibitr, PD98059 (PD): MEK inhibitor

12. CXCR2 Expression Is Elevated in Premalignant Lesions normal skin (NS) or DMBA- TPA-induced mouse papillomas PIN, prostate intraepithelial neoplasia; A/N glands, atrophic/normal glands

13. A CXCR2 Mutation Present in Lung Adenocarcinoma Alleviates Senescence the COSMIC database; (http://www.sanger.ac.uk/genetics/CGP/cosmic/). An analysis of 40 cancer cell lines identified a point mutation in CXCR2 (G354W) in the lung adenocarcinoma cell line NCI-H1395.

14. Summary Summary: - the chemokine receptor CXCR2 and many of its ligands are upregulated during senescence. NFKb-CREB-alpa mediated regulation. -They form part of a chemokine network reinforcing growth arrest in a p53-dependent manner. -different preneoplastic lesions show enhanced expression of CXCR2 -downregulation or mutation may be necessary for progression of some cancer types. Distinct roles of CXCR2/ligands as a ant-oncogenic or pro-oncogenetic -The roles of cytokines (IL-8 etc) acts to reinforce senescence via CXCR2 -How about paracrine and autocrine effects of these ligands: enothelial migration, metastasis or recruit immune cell for clearing damaged cells ? -overstimulation of CXCR2 activity induced by upstream oncogenic signals, elicits a senescence phenotype in primary cells. -However, autocrine CXCR2 signaling becomes pro-oncogenic in cells in which the senescence machinery is compromised, such as p53−/− MEFs) or immortal NIH 3T3 cells

15. Oncogene Induced Senescence and secreted Cytokines

16. Introduction The cell-cycle arrest observed in nongrowing benign lesions like melanocytic nevi shares a number of key characteristics with cellular senescence. oncogene-induced cellular senescence (OIS), which is induced prematurely a vital cause of arrest of benign neoplasms. oncoproteins like BRAFE600 or RASV12 or by the loss of tumor suppressor proteins, like PTEN or NF1 activated OIS OIS is often accompanied by the upregulation of the CDK inhibitors p15INK4B, p16INK4A, and p21CIP1, senescence-associated β- galactosidase (SA-β-Gal) activity Inactivation of Rb or p53 genes reverse senescence A further hallmark is the formation of senescence-associated heterochromatic foci (SAHF), subnuclear structures containing heterochromatin proteins

17. OIS Is Associated with Activation of an Inflammatory Transcriptome Including IL-6 Induction (M > 2 and p < 0.001) Specific Upregulation of IL-6/8 during OIS but it is independent on p16

18. A Critical Role for IL-6 in Mediating OIS

19. IL-6 Inhibits Proliferation in the Context of Oncogenic Stress IL-6 Acts in a Cell-Autonomous Fashion in OIS

20. C/EBPb Is a Critical Regulator of IL-6 in OIS

21. IL-6 Depletion Correlates with Reduced Formation of SAHF and Deregulation of p15INK4B Expression

22. . IL-6 Is a Central Regulator of an Inflammatory Network Mediating OIS These results argue that the mechanism by which IL-6 controls the cellular response to oncogenic signaling involves a positive feedback loop with C/EBPb, which acts to sustain and amplify the activation of the inflammatory network. IL-8,whose expression levels is reulated in a strictly IL-6- dependent manner

23. IL-8 Plays a Role in OIS

24. IL-8 Colocalizes with p16INK4A in Growth-Arrested, Human Colon Adenoma Cells

25. A Role for Interleukins In Vivo and a Model Reconciling the Antagonistic Functions of Interleukins in OIS and Cancer Summary OIS is linked specifically to the activation of an inflammatory transcriptome. Induced genes included the pleiotropic cytokine interleukin-6 (IL-6), which upon secretion by senescent cells acted mitogenically in a paracrine fashion. Unexpectedly, IL-6 was also required for the execution of OIS, but in a cell-autonomous mode. Its depletion caused the inflammatory network to collapse and abolished senescence entry and maintenance. the transcription factor C/EBPβ cooperates with IL-6 to amplify the activation of the inflammatory network, including IL-8. In human colon adenomas, IL-8 specifically colocalized with arrested, p16INK4A-positive epithelium. Model: the context-dependent cytostatic and promitogenic functions of specific interleukins contribute to connect senescence with an inflammatory phenotype and cancer

26. Senescence Associated Secretory Phenotype (SASP) depends on persistent DNA damage signaling (Fumagalli M. and d’Adda di Fagagna F., Nat Cell Biol., 2009) -Persistent DNA damage causes cells to undergo senescence. When cells do so, they secrete cytokines that boost the senescence response for themselves, and at the same time, promote tumor growth and invasion. -I believe these cytokine secretion helps to maintain organ homeostasis by enabling compensatory cell activation upon loss of certain cells.