Detection of Oncogene-Induced Senescence In Vivo

Oncogene-induced senescence or OIS is defined as a permanent state of proliferative arrest resulting from an activating oncogenic-lesion. OIS has been suggested to function as a cancer cell intrinsic mechanism to restrain tumor growth and has been implicated as a key mechanism preventing the progression of certain premalignant lesions in genetically engineered mouse models of cancer. The senescent phenotype can be defined by two criteria that include cell cycle arrest and resistance to mitogens and oncogenic transformation. While the phenotype and properties of senescent cells in vitro are well described, the morphological characteristics defining senescence in vivo have been controversial with no specific marker that definitively proves a senescent state. Indeed, many of the published in vivo markers to identify and characterize senescence in an organism are unreliable and often times have been found to be nonspecific. However, the use of multiple markers is accepted as confirmation of senescence in vivo. Here, we describe protocols for some of the most commonly used indicators of senescence in oncogenic Kras-induced lung adenomas including the detection of senescence-associated beta-galactosidase, expression of the tumor suppressor p19^ARF, the presence of senescence-associated heterochromatin foci, and in vivo BrdU uptake to confirm cell cycle arrest.