DNA Damage Induces a Secretory Program in the Quiescent TME that Fosters Adverse Cancer Phenotypes

Carcinomas develop in complex environments that include a diverse spectrum of cell types that influence tumor cell behavior. These microenvironments represent dynamic systems that contribute to pathologic processes. Damage to DNA is a notable inducer of both transient and permanent alterations in cellular phenotypes. Induction of a DNA damage secretory program is known to promote adverse tumor cell behaviors such as proliferation, invasion, metastasis, and treatment resistance. However, prior studies designed to identify genotoxic stress-induced factors evaluated actively proliferating in vitro cultures of cells such as fibroblasts as experimental models. Conversely, the vast majority of benign cells in a typical tumor microenvironment (TME) are not proliferating but rather exist in quiescent (i.e., G₀) or in terminally differentiated states. In this study, the diversity and magnitude of transcriptional responses to genotoxic damage in quiescent prostate fibroblasts were assessed using gene expression profiling. The secretory damage response in quiescent cells was highly concordant with that of actively dividing cells. Quiescent human prostate stroma exposed to genotoxic agents (e.g., mitoxantrone) in vivo resulted in significant upregulation (2.7- to 5.7-fold; P ≤ 0.01) of growth factors and cytokines including IL1β, MMP3, IL6, and IL8. The paracrine effects of damaged quiescent cells consistently increased the proliferation and invasion of prostate cancer cells and promoted cell survival and resistance to apoptosis following exposure to chemotherapy.Implications: Benign quiescent cells in the TME respond to genotoxic stress by inducing a secretory program capable of promoting therapy resistance. Developing approaches to suppress the secretory program may improve treatment responses. Mol Cancer Res; 15(7); 842-51. ©2017 AACR.