Biomarkers for Identification of the Dormancy Phenotypes Senescence and Quiescence in Malignancy
Vogt, Meagan M.
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There is widespread interest in the relationship between aging and cancer, and the involvement of senescence in both processes. A growing body of evidence indicates that senescent cells impart elevated risk of age-associated disease, including cancer; however, a continuing challenge in the field is the lack of senescence-specific biomarkers. Chemotherapy is a potent inducer of senescence, and the secretions of senescent cells have been hypothesized to propel tumor evolution and metastatic dissemination. In this work, comprehensive snapshots of the membrane-associated and secreted proteomes of senescent non-small cell lung cancer (NSCLC) cells were captured. A signature of 31 membrane-associated proteins unique to the chemotherapy-induced senescence (CIS) phenotype was elucidated, some of which were amenable to detection in human NSCLC tissue. A cohort of 65 proteins were unique to the secretome of CIS NSCLC cells, and the genes corresponding to some were found to be co-altered with driver genes in human NSCLC. In addition, both secreted candidate biomarker genes and NSCLC driver genes were localized within known amplification hot spots observed in a variety of human malignancies. Thus, the secretome of CIS NSCLC cells may serve as a genomic fingerprint of tumor evolution in NSCLC. Importantly, both the membrane-associated and secretome proteomic studies showed significant overlap between quiescence and senescence. Developing a better understanding of similarities and differences among these two forms of dormancy is imperative in order to accurately evaluate contributions of either phenotype to human disease. To evaluate how senescent cells may evade immune clearance, senescent NSCLC and triple negative breast cancer (TNBC) cell lines were analyzed for expression of co-inhibitory B7 family members. CIS NSCLC cells showed enrichment for B7-H3 and PD-L1, as did two TNBC cell lines. A series of reported SASP components are known to influence macrophages, and the SASP may promote their acquisition of a tumor-promoting phenotype. Primary human macrophages were cultured in conditioned medium from CIS NSCLC cells and analyzed for B7 family member expression. Macrophages cultured in senescent CM harbored FSC/SSC properties similar to M2 control macrophages, the most distinct observation being emergence of a larger population that was consistently positive for B7-H4.