Evidence of oncogene-induced senescence in thyroid carcinogenesis.

Oncogene-induced senescence (OIS) is a growth arrest triggered by the enforced expression of cancer-promoting genes and acts as a barrier against malignant transformation in vivo. In this study, by a combination of in vitro and in vivo approaches, we investigate the role of OIS in tumours originating from the thyroid epithelium. We found that expression of different thyroid tumour-associated oncogenes in primary human thyrocytes triggers senescence, as demonstrated by the presence of OIS hallmarks: changes in cell morphology, accumulation of SA-β-Gal and senescence-associated heterochromatic foci, and upregulation of transcription of the cyclin-dependent kinase inhibitors p16(INK4a) and p21(CIP1). Furthermore, immunohistochemical analysis of a panel of thyroid tumours characterised by different aggressiveness showed that the expression of OIS markers such as p16(INK4a), p21(CIP1) and IGFBP7 is upregulated at early stages, and lost during thyroid tumour progression. Taken together, our results suggest a role of OIS in thyroid carcinogenesis.