Chronic expression of p16INK4a in the epidermis induces Wnt-mediated hyperplasia and promotes tumor initiation (2)
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ABSTRACT: In this study we examine the outcomes of p16INK4a activation in the adult epidermis. We found that prolonged expression of p16INK4a induces epidermal hyperplasia and dysplasia. We also found that continued p16INK4a expression increased the number of epidermal papillomas that developed after carcinogen treatment. Profling of p16INK4a- expressing cells showed elevated levels of Wnt-pathway ligands and targets, and pharmacologic or genetic Wnt inhibition suppressed p16-induced hyperplasia. In human actinic keratosis, a precursor of squamous cell carcinoma, p16-expressing cells are typically found adjacent to dividing cells, consistent with paracrine interaction. These findings reveal that in addition to its cell-autonomous role in blocking cell proliferation, p16 can induce hyperplasia through paracrine stimulation, suggesting that its activity contributes to the formation of early premalignant epidermal lesions.
Project description:In this study we examine the outcomes of p16INK4a activation in the adult epidermis. We found that prolonged expression of p16INK4a induces epidermal hyperplasia and dysplasia. We also found that continued p16INK4a expression increased the number of epidermal papillomas that developed after carcinogen treatment. Profling of p16INK4a- expressing cells showed elevated levels of Wnt-pathway ligands and targets, and pharmacologic or genetic Wnt inhibition suppressed p16-induced hyperplasia. In human actinic keratosis, a precursor of squamous cell carcinoma, p16-expressing cells are typically found adjacent to dividing cells, consistent with paracrine interaction. These findings reveal that in addition to its cell-autonomous role in blocking cell proliferation, p16 can induce hyperplasia through paracrine stimulation, suggesting that its activity contributes to the formation of early premalignant epidermal lesions.
Project description:The cyclin-dependent kinase inhibitor p16INK4a (CDKN2A) is an important tumor-suppressor gene frequently inactivated in human tumors. p16 suppresses the development of cancer by triggering an irreversible arrest of cell proliferation termed cellular senescence. Here, we describe another anti-oncogenic function of p16 in addition to its ability to halt cell cycle progression. We show that transient expression of p16 stably represses the hTERT gene, encoding the catalytic subunit of telomerase, in both normal and malignant breast epithelial cells. Short-term p16 expression increases the amount of histone H3 trimethylated on lysine 27 (H3K27) bound to the hTERT promoter, resulting in transcriptional silencing, likely mediated by polycomb complexes. Our results indicate that transient p16 exposure may prevent malignant progression in dividing cells by irreversible repression of genes, such as hTERT, whose activity is necessary for extensive self-renewal. 27 samples were analyzed to study three histone modifications (H3K4me3, H3K9me3, H3K27me3) in three different cell lines. Each combination of histone modification and cell line had three biological replicates (A,B,C).
Project description:The cyclin-dependent kinase inhibitor p16INK4a (CDKN2A) is an important tumor-suppressor gene frequently inactivated in human tumors. p16 suppresses the development of cancer by triggering an irreversible arrest of cell proliferation termed cellular senescence. Here, we describe another anti-oncogenic function of p16 in addition to its ability to halt cell cycle progression. We show that transient expression of p16 stably represses the hTERT gene, encoding the catalytic subunit of telomerase, in both normal and malignant breast epithelial cells. Short-term p16 expression increases the amount of histone H3 trimethylated on lysine 27 (H3K27) bound to the hTERT promoter, resulting in transcriptional silencing, likely mediated by polycomb complexes. Our results indicate that transient p16 exposure may prevent malignant progression in dividing cells by irreversible repression of genes, such as hTERT, whose activity is necessary for extensive self-renewal.
Project description:p16INK4A inhibits the CDK4/6 kinases and is therefore an important cell cycle regulator. Accumulation of p16INK4A in response to oncogenic transformation leads to cellular senescence and it is therefore frequently lost in cancer. p16INK4A is also known to accumulate under conditions of cellular oxidative stress and therefore could potentially be regulated by redox signaling, which is a form of signal transduction that is mediated by the reversible oxidation of cysteine-thiol side chains in proteins. We found that oxidation of the single cysteine residue in p16INK4A in human cells occurs under relatively mild oxidizing conditions and that this leads to disulfide dependent dimerization. p16INK4A is a well-characterized all alpha-helical protein, but we find that upon cysteine-dependent dimerization, p16INK4A undergoes a dramatic structural rearrangement and forms aggregates that have the typical features of amyloid fibrils, including binding of diagnostic dyes, presence of cross-β sheet structure, and typical dimensions found in electron microscopy. We find that p16INK4A amyloid formation abolishes its function as a CDK4/6 inhibitor in human cells. Taken together, these observations mechanistically link the cellular redox state to the inactivation of p16INK4A through the formation of amyloid fibrils.
Project description:The goal of this study is to identify the senescent cells expressing high level of p16Ink4a (p16Ink4a Hi) in GBMs and characterize their action on the tumor microenvironment at an early timepoint. We introduced the p16-3MR transgene in the GBM mouse model to selectively delete p16Ink4a Hi senescent cells upon ganciclovir (GCV) injection. We compared p16-3MR+GCV to WT+GCV control GBMs that were harvested 7 days after the last GCV injection.
Project description:Expression profiles of 17 melanoma cell lines were analysed to identify genes differentially expressed between cell lines harbouring wild-type or mutant p16INK4A. Relevant paper: Pavey et al. (2007). Note: all of these cell lines contained wild-type p14ARF, so that the transcriptional effects of p16INk4A could be determined without interference from p14ARF. Keywords: Affymetrix Hu133_Plus microarrays
Project description:P16Ink4a is a well-established marker of senescence. Although P16Ink4a is expressed in endothelial cells, little is known about its function in these cells. Using isolated liver endothelial cells with silencing or overexpression of P16Ink4a, we show here that dependent on P16Ink4a levels, different pathways and functions are affected. High levels of P16Ink4a reduce proliferation and induce senescence while low levels have the opposite effects. Only high P16Ink4a expression reduces in vitro angiogenesis. Expression profiling reveals an inflammatory phenotype upon silencing of P16Ink4a while P16Ink4a overexpression is associated with a profile associated to DNA damage, repair and senescence. Low levels of P16Ink4a induce reactive oxygen species (ROS) generation and increase endothelial cell leakage. Collectively, P16Ink4a represents an “antagonistic pleiotropy” gene, which is on the one hand required to prevent ROS generation and endothelial damage and on the other hand at high levels inhibits angiogenesis through induction of senescence.