Quantitative proteomic profiling of tumor cell response to telomere dysfunction using isotope-coded protein labeling (ICPL) reveals interaction network of candidate senescence markers.

Telomerase inhibition causes progressive telomere shortening and cellular senescence, which constitutes a universal barrier to tumor growth and therefore an attractive target for tumor therapy. To expand our previous studies, we investigated the global effects of telomere dysfunction on the proteome of tumor cells in order to find novel senescence biomarkers. Telomerase-deficient HCT-116 cell clones were analyzed by a quantitative proteomic approach using isotope-coded protein labeling (ICPL) and nanoflow-HPLC-MS/MS. Stringent reduction of the extensive proteomic data from this tumor cell model revealed a list of 59 markers including proteins identified in our former studies and a number of novel proteins involved in tumorigenesis and metastasis such as SFN, S100A4, ANXA2, and LGALS1. A loss of the chromatin protein HMGB2 was demonstrated not only in various telomerase-inhibited clones of different tumor cell lines, but also in normal human fibroblasts undergoing replicative senescence and in aging telomerase knockout mice. Impressively, a coherent and dense network of protein-protein interactions for the bulk of the markers and their implementation in signaling pathways involving key regulators for tumorigenesis were revealed. These results have an impact on the understanding of telomere- and senescence-related signal transduction in tumor cells in consideration of the general lack of senescence markers. Induction of cellular senescence constitutes a potent concept for tumor therapy which interferes with immortalization and additional hallmarks of cancer. The application of a powerful quantitative proteomic approach using isotope-coded protein labeling to an approved model for senescence represented by telomerase inhibited tumor cells led to the identification of novel candidate biomarkers for telomere dysfunction and replicative senescence. Thereby, the identified markers not only fit in the context of the investigated processes with a relevance for additional hallmarks of cancer but are also involved in a strong interaction network and integrated in canonical pathways centered around key cancer-relevant proteins. These potential markers alone or in combination will significantly extend the view on telomere-associated signal transduction in tumor cells and contribute to the field of cellular senescence and aging in consideration of the general lack of biomarkers in this regard.