The tumor suppressor p16(INK4a) gene is a regulator of apoptosis induced by ultraviolet light and cisplatin

Immunohistochemical Study of Airways Fibrous Remodeling in Smoking Mice

The fibrotic remodeling in chronic obstructive pulmonary disease (COPD) is held responsible for narrowing of small airways and thus for disease progression. Oxidant damage and cell senescence factors are recently involved in airways fibrotic remodeling. Unfortunately, we have no indications on their sequential expression at anatomical sites in which fibrotic remodeling develops in smoking subjects. Using immunohistochemical techniques, we investigated in two strains of mice after cigarette smoke (CS) exposure what happens at various times in airway areas where fibrotic remodeling occurs, and if there also exists correspondence among DNA damage induced by oxidants, cellular senescence, the presence of senescence-secreted factors involved in processes that affect transcription, metabolism as well as apoptosis, and the onset of fibrous remodeling that appears at later times in mice exposed to CS. A clear positivity for fibrogenic cytokines TGF-β, PDGF-B, and CTGF, and for proliferation marker PCNA around airways that will be remodeled is observed in both strains. Increased expression of p16ink4A senescence marker and MyoD is also seen in the same areas. p16ink4A and MyoD can promote cell cycle arrest, terminal differentiation of myofibroblasts, and can oppose their dedifferentiation. Of interest, an early progressive attenuation of SIRT-1 is observed after CS exposure. This intracellular regulatory protein can reduce premature cell senescence. These findings suggest that novel agents, which promote myofibroblast dedifferentiation and/or the apoptosis of senescent cells, may dampen progression of airway changes in smoking COPD subjects.

Cellular senescence induction leads to progressive cell death via the INK4a-RB pathway in naked mole-rats

Naked mole-rats (NMRs) have exceptional longevity and are resistant to age-related physiological decline and diseases. Given the role of cellular senescence in aging, we postulated that NMRs possess unidentified species-specific mechanisms to prevent senescent cell accumulation. Here, we show that upon induction of cellular senescence, NMR fibroblasts underwent delayed and progressive cell death that required activation of the INK4a-retinoblastoma protein (RB) pathway (termed "INK4a-RB cell death"), a phenomenon not observed in mouse fibroblasts. Naked mole-rat fibroblasts uniquely accumulated serotonin and were inherently vulnerable to hydrogen peroxide (H2 O2 ). After activation of the INK4a-RB pathway, NMR fibroblasts increased monoamine oxidase levels, leading to serotonin oxidization and H2 O2 production, which resulted in increased intracellular oxidative damage and cell death activation. In the NMR lung, induction of cellular senescence caused delayed, progressive cell death mediated by monoamine oxidase activation, thereby preventing senescent cell accumulation, consistent with in vitro results. The present findings indicate that INK4a-RB cell death likely functions as a natural senolytic mechanism in NMRs, providing an evolutionary rationale for senescent cell removal as a strategy to resist aging.

Cellular Senescence: Mechanisms and Therapeutic Potential

Cellular senescence is a complex and multistep biological process which cells can undergo in response to different stresses. Referring to a highly stable cell cycle arrest, cellular senescence can influence a multitude of biological processes-both physiologically and pathologically. While phenotypically diverse, characteristics of senescence include the expression of the senescence-associated secretory phenotype, cell cycle arrest factors, senescence-associated β-galactosidase, morphogenesis, and chromatin remodelling. Persistent senescence is associated with pathologies such as aging, while transient senescence is associated with beneficial programmes, such as limb patterning. With these implications, senescence-based translational studies, namely senotherapy and pro-senescence therapy, are well underway to find the cure to complicated diseases such as cancer and atherosclerosis. Being a subject of major interest only in the recent decades, much remains to be studied, such as regarding the identification of unique biomarkers of senescent cells. This review attempts to provide a comprehensive understanding of the diverse literature on senescence, and discuss the knowledge we have on senescence thus far.

Deletion of Nrip1 delays skin aging by reducing adipose-derived mesenchymal stem cells (ADMSCs) senescence, and maintaining ADMSCs quiescence

Our previous studies found that deletion of nuclear receptor interacting protein 1 (Nrip1) extended longevity in female mice and delayed cell senescence. The current study investigates the role of NRIP1 in regulating functions of adipose-derived mesenchymal stem cells (ADMSCs) and explores the mechanisms of NRIP1 in skin aging. We first verified the skin aging phenotypes in young (6 months) and old (20 months) C57BL/6J (B6) mice and found deletion of Nrip1 can delay skin aging phenotypes, including reduced thickness of dermis and subcutaneous white adipose tissue (sWAT), as well as the accumulation of senescent cells in sWAT. In ADMSCs isolated from sWAT, we found that deletion of Nrip1 could decrease cell proliferation, prevent cell apoptosis, and suppress adipogenesis. Interestingly, deletion of Nrip1 also reduced cell senescence and maintain cell quiescence of ADMSCs. Moreover, the expressions of genes associated with senescence (p21, and p53), inflammation (p65, IL6, and IL1a), and growth factor (mTOR, Igf1) were reduced in Nrip1 knockout ADMSCs, as well as in siNrip1-treated ADMSCs. Suppression of Nrip1 by siNrip1 also decreased the expressions of mTOR, p-mTOR, p65, and p-p65 in ADMSCs. Reduced expressions of p65 and p-p65 were also confirmed in the skin of Nrip1 knockout mice. These findings suggest that NRIP1 plays an important role in delaying skin aging by reducing ADMSCs senescence and maintaining ADMSCs quiescence.

Role of Long Non-Coding RNA Polymorphisms in Cancer Chemotherapeutic Response

Genetic polymorphisms are defined as the presence of two or more different alleles in the same locus, with a frequency higher than 1% in the population. Since the discovery of long non-coding RNAs (lncRNAs), which refer to a non-coding RNA with a length of more than 200 nucleotides, their biological roles have been increasingly revealed in recent years. They regulate many cellular processes, from pluripotency to cancer. Interestingly, abnormal expression or dysfunction of lncRNAs is closely related to the occurrence of human diseases, including cancer and degenerative neurological diseases. Particularly, their polymorphisms have been found to be associated with altered drug response and/or drug toxicity in cancer treatment. However, molecular mechanisms are not yet fully elucidated, which are expected to be discovered by detailed studies of RNA–protein, RNA–DNA, and RNA–lipid interactions. In conclusion, lncRNAs polymorphisms may become biomarkers for predicting the response to chemotherapy in cancer patients. Here we review and discuss how gene polymorphisms of lncRNAs affect cancer chemotherapeutic response. This knowledge may pave the way to personalized oncology treatments.

CDK4/6 Inhibitors in Melanoma: A Comprehensive Review

Historically, metastatic melanoma was considered a highly lethal disease. However, recent advances in drug development have allowed a significative improvement in prognosis. In particular, BRAF/MEK inhibitors and anti-PD1 antibodies have completely revolutionized the management of this disease. Nonetheless, not all patients derive a benefit or a durable benefit from these therapies. To overtake this challenges, new clinically active compounds are being tested in the context of clinical trials. CDK4/6 inhibitors are drugs already available in clinical practice and preliminary evidence showed a promising activity also in melanoma. Herein we review the available literature to depict a comprehensive landscape about CDK4/6 inhibitors in melanoma. We present the molecular and genetic background that might justify the usage of these drugs, the preclinical evidence, the clinical available data, and the most promising ongoing clinical trials.

Expression and role of p16 and GLUT1 in malignant diseases and lung cancer: A review

Non‐small cell lung cancer (NSCLC) is the leading cause of cancer death and in most cases it is often diagnosed at an advanced stage. Many genetic and microenvironmental factors are able to modify the cell cycle inducing carcinogenesis and tumor growth. Among the metabolic and genetic factors that come into play in carcinogenesis and tumor cell differentiation and growth there are two different proteins that should be considered which are glucose transporters (GLUTs) and p16^INK4 The first are glucose transporters which are strongly involved in tumor metabolism, notably accelerating cancer cell metabolism both in aerobic and anaerobic conditions. There are different subtypes of GLUT family factors of which GLUT 1 is the most important and widely expressed. By contrast, p16 is mainly a tumor‐suppressor protein that acts on cyclin‐dependent kinase favoring cell cycle arrest in the G1 phase. Our search focused on the action of the aforementioned factors.

The Zn(S-pr-thiosal)2 complex attenuates murine breast cancer growth by inducing apoptosis and G1/S cell cycle arrest

Aim: We investigated the antitumor effects of zinc(II) complex with S-propyl thiosalicylic acid [Zn(S-pr-thiosal)₂] in 4T1 murine breast cancer model. Results: The Zn(S-pr-thiosal)₂ complex reduced primary tumor growth in vivo and induced tumor cell apoptosis. The Zn(S-pr-thiosal)₂ complex disrupted the balance between pro- and antiapoptotic Bcl-2 family members in 4T1 cells and induced G1/S cell cycle arrest. The Zn(S-pr-thiosal)₂ complex increased the percentage of p16, p21 and p27 positive 4T1 cells. There was a significantly decrease in expression of STAT3 and its targets c-Myc and cyclin D3 in 4T1 cells treated with the Zn(S-pr-thiosal)₂ complex thus contributing to G1/S cell cycle arrest and/or apoptosis. Conclusion: Our data suggest that the Zn(S-pr-thiosal)₂ complex restricted tumor growth through induction of mitochondrial-driven apoptosis and suppression of cell cycle progression.

Boolean model of growth signaling, cell cycle and apoptosis predicts the molecular mechanism of aberrant cell cycle progression driven by hyperactive PI3K

The PI3K/AKT signaling pathway plays a role in most cellular functions linked to cancer progression, including cell growth, proliferation, cell survival, tissue invasion and angiogenesis. It is generally recognized that hyperactive PI3K/AKT1 are oncogenic due to their boost to cell survival, cell cycle entry and growth-promoting metabolism. That said, the dynamics of PI3K and AKT1 during cell cycle progression are highly nonlinear. In addition to negative feedback that curtails their activity, protein expression of PI3K subunits has been shown to oscillate in dividing cells. The low-PI3K/low-AKT1 phase of these oscillations is required for cytokinesis, indicating that oncogenic PI3K may directly contribute to genome duplication. To explore this, we construct a Boolean model of growth factor signaling that can reproduce PI3K oscillations and link them to cell cycle progression and apoptosis. The resulting modular model reproduces hyperactive PI3K-driven cytokinesis failure and genome duplication and predicts the molecular drivers responsible for these failures by linking hyperactive PI3K to mis-regulation of Polo-like kinase 1 (Plk1) expression late in G2. To do this, our model captures the role of Plk1 in cell cycle progression and accurately reproduces multiple effects of its loss: G2 arrest, mitotic catastrophe, chromosome mis-segregation / aneuploidy due to premature anaphase, and cytokinesis failure leading to genome duplication, depending on the timing of Plk1 inhibition along the cell cycle. Finally, we offer testable predictions on the molecular drivers of PI3K oscillations, the timing of these oscillations with respect to division, and the role of altered Plk1 and FoxO activity in genome-level defects caused by hyperactive PI3K. Our model is an important starting point for the predictive modeling of cell fate decisions that include AKT1-driven senescence, as well as the non-intuitive effects of drugs that interfere with mitosis.

The deficiency of CX3CL1/CX3CR1 system ameliorates high fructose diet-induced kidney injury by regulating NF-κB pathways in CX3CR1-knock out mice

Fructose, the most important functional food additive from the last century, has been widely used in industry, agriculture, light industry, food and medicine. With the improvement of people's living standard and economic level, excess intake of fructose results in metabolic symptoms, including hyperleptinemia, insulin resistance and neuroinflammation is causing high risk of chronic kidney disease development in humans and animals. However, the underlying molecular mechanism of renal injury is still not fully understood, and the development of effective drugs and treatments are delayed. Hence, we investigated the role of crosstalk of CX3CL1-CX3CR1 axis and nuclear factor-κB (NF-κB) signaling pathway in the development of renal injury. CX3CL1-knock-out C57BL/6 mice were constructed and used to analyze the influence of CX3CL1-related signaling pathways on kidney injury of wild-type (WT) mice and CXECR1 deficiency mice, which were administrated with 30% fructose water. Western blotting, quantitative RT-PCR (qRT-PCR), immunohistochemistry, ELISA, flow cytometry and biochemical indicator analysis were used to determine the levels of renal injury and key signaling pathway associated with renal damage. The results indicated that administration of high fructose intake can cause typical renal inflammatory responses in serum and tissues. Fructose enhances the CX3CL1-CX3CR1 axis and NF-κB activation, and promotes crosstalk of CX3CL1-CX3CR1 and NF-κB pathways. The phosphorylated AKT could be significantly activated in fructose-induced renal injury via CX3CL1-CX3CR1 axis. CX3CR1 expression between WT and CX3CR1^−/− mice were evaluated to establish their relationship with injury. Our results indicated that CX3CR1 may be the central and major indicator in the process of renal injury, which mediate AKT pathway and further enhance the NF-κB activation. These findings demonstrated that crosstalk of CX3CL1-CX3CR1 axis and NF-κB signaling pathway play a direct role in fructose-induced kidney injury. Inhibition of CX3CL1-CX3CR1 pathway may suppress renal-related diseases. It may be a potential treatment choice for the clinical diagnoses and treatment in the future.

C-terminal binding protein-2 promotes cell proliferation and migration in breast cancer via suppression of p16INK4A

C-terminal binding protein-2 (CtBP2) enhances cancer proliferation and metastasis. The role and mechanism of CtBP2 in breast cancer remains to be elucidated. Western blot and immunochemistry were employed to evaluate the level of CtBP2 and p16^INK4A in breast cancer. Genetic manipulation was used to study the expression of p16^INK4A and its downstream genes regulated by CtBP2. Functional assays, including colony formation, wound healing, transwell invasion, anchorage-independent growth assay and a xenograft tumor model were used to determine the oncogenic role of CtBP2 in breast cancer progression. The expression of CtBP2 was increased in breast cancer tissues and cell lines. The expression of p16^INK4A were inversely correlated CtBP2 (r² = 0.43, P < 0.01). The expression of both CtBP2 and p16^INK4A were significantly related to histological differentiation (P < 0.01 and P = 0.004, respectively) and metastasis (P = 0.046 and 0.047, respectively). The overall survival rate was lower in patients with increased CtBP2 expression and lower p16^INK4A expression. Knockdown of CtBP2 resulted in the activation of p16^INK4A and down–regulation of cell cycle regulators cyclin D, cyclin E and cyclin-dependent kinase 2 and 4. This down-regulation also led to a decreased transition of the G1-S phase in breast cancer cells. Moreover, gain-of-function experiments showed that CtBP2 suppressed p16^INK4A and matrix metalloproteinase-2, subsequently enhancing the migration in breast cancer. However, the silence of CtBP2 abrogated this effect. Collectively, these findings provide insight into the role CtBP2 plays in promoting proliferation and migration in breast cancer by the inhibition of p16^INK4A.

Inhibition of coiled coil domain containing protein 69 enhances platinum-induced apoptosis in ovarian cancer cells

Cisplatin is a platinum-based drug that is used for the treatment of human gynecological cancers. However, molecular mechanisms of chemo-resistance in ovarian cancer are poorly understood. The aim of the study is to examine the role of coiled coil domain containing protein 69 (CCDC69) in the underlying mechanism of chemoresistance. Heavy CpG methylation (73.1% and 74.3%) was found in A2780 and A2780cis cells assessing by bisulfite sequencing. Restoration in the expression of CCDC69 was found in A2780 and A2780cis cells after 5-Aza-dC treatment. In fact, the expression levels of CCDC69 were about 3-4 fold higher in cisplatin-resistant A2780cis cells than its parental cisplatin-sensitive A2780 cells. When knockout CCDC69 in cisplatin-resistant A2780cis and SKOV3 cells by CRISPR/Cas9, the CCDC69 knockout cisplatin-resistant A2780cis and CCDC69 knockout SKOV3 cells were also shown increased sensitive to cisplatin treatment. Moreover, treating CCDC69 knockout A2780cis cells with cisplatin, abrogated G1 and G2/M arrest, increased of cleaved caspase 3&8, greater ΔΨm loss and higher levels of Bax were observed. When restoring CCDC69 expression in CCDC69 knockout A2780cis cells by transient transfection, it attenuated sensitivity to cisplatin. By immunoblotting, we found that depletion of CCDC69 increased p53 acetylation at K382 site and Bax mitochondrial redistribution. Additionally, inhibition of c-Myc enhanced cisplatin sensitivities in CCDC69 knockout A2780cis cells, overexpression of c-Myc reduced apoptosis in CCDC69 knockout SKOV3 cells. Our results showed that CCDC69 inhibition might interfere with the effectiveness of combination therapy with platinum drugs.

Disruption of PCNA-lamins A/C interactions by prelamin A induces DNA replication fork stalling

The accumulation of prelamin A is linked to disruption of cellular homeostasis, tissue degeneration and aging. Its expression is implicated in compromised genome stability and increased levels of DNA damage, but to date there is no complete explanation for how prelamin A exerts its toxic effects. As the nuclear lamina is important for DNA replication we wanted to investigate the relationship between prelamin A expression and DNA replication fork stability. In this study we report that the expression of prelamin A in U2OS cells induced both mono-ubiquitination of proliferating cell nuclear antigen (PCNA) and subsequent induction of Pol η, two hallmarks of DNA replication fork stalling. Immunofluorescence microscopy revealed that cells expressing prelamin A presented with high levels of colocalisation between PCNA and γH2AX, indicating collapse of stalled DNA replication forks into DNA double-strand breaks. Subsequent protein-protein interaction assays showed prelamin A interacted with PCNA and that its presence mitigated interactions between PCNA and the mature nuclear lamina. Thus, we propose that the cytotoxicity of prelamin A arises in part, from it actively competing against mature lamin A to bind PCNA and that this destabilises DNA replication to induce fork stalling which in turn contributes to genomic instability.

Association between well-characterized lung cancer lncRNA polymorphisms and platinum-based chemotherapy toxicity in Chinese patients with lung cancer

Platinum-based chemotherapy is the standard first-line treatment for most lung cancer patients. However, the toxicity induced by platinum-based chemotherapy greatly impedes its clinical use. Previous studies showed that long non-coding RNAs (lncRNAs) with over 200 nucleotides in length affect drug response and toxicity. In the present study, we investigated the association of well-characterized lung cancer lncRNA polymorphisms with platinum-based chemotherapy toxicity in Chinese patients with lung cancer. A total of 467 lung cancer patients treated with platinum-based chemotherapy for at least two cycles were recruited. We primarily focused on gastrointestinal and hematological toxicities. A total of 14 potentially functional polymorphisms within 8 lncRNAs (HOTTIP, HOTAIT, H19, ANRIL, CCAT2, MALAT1, MEG3, and POLR2E) were genotyped. Unconditional logistical regression analysis was conducted to assess the associations. Gene-gene and gene-environment interactions were identified using the software generalized multifactor dimensionality reduction (GMDR). ANRIL rs1333049 was associated with severe overall toxicity in an additive model (adjusted OR=0.723, 95% CI=0.541-0.965, P=0.028). ANRIL rs1333049 was also associated with severe gastrointestinal toxicity in both the additive (adjusted OR=0.690, 95% CI=0.489-0.974, P=0.035) and dominant (adjusted OR=0.558, 95% CI=0.335-0.931, P=0.025) models. MEG3 rs116907618 was associated with severe gastrointestinal toxicity in an additive model (adjusted OR=1.717, 95% CI=1.007-2.927, P=0.047). GMDR identified the three-factor interaction model of POLR2E rs3787016-HOTTIP rs3807598-chemotherapy regimen as the best predictive model for hematological toxicity. In conclusion, ANRIL and MEG3 genetic polymorphisms are associated with severe platinum toxicity and could be considered as biomarkers for pretreatment evaluation in Chinese patients with lung cancer.

p16INK4A enhances the transcriptional and the apoptotic functions of p53 through DNA-dependent interaction

p16^INK4A and p53 are two important tumor suppressor proteins that play essential roles during cell proliferation and aging through regulating the expression of several genes. Here, we report that p16^INK4A and p53 co-regulate a plethora of transcripts. Furthermore, both proteins colocalize in the nucleus of human primary skin fibroblasts and breast luminal cells, and form a heteromer whose level increases in response to genotoxic stress as well as aging of human fibroblasts and various mouse organs. CDK4 is also present in this heteromeric complex, which is formed only in the presence of DNA both in vitro using pure recombinant proteins and in vivo. We have also shown that p16^INK4A enhances the binding efficiency of p53 to its cognate sequence presents in the CDKN1A promoter in vitro, and both proteins are present at the promoters of CDKN1A and BAX in vivo. Importantly, the fourth ankyrin repeat of p16^INK4A and the C-terminal domain of p53 were necessary for the physical association between these two proteins. The physiologic importance of this association was revealed by the inability of cancer-associated p16^INK4A mutants to interact with p53 and to transactivate the expression of its major targets CDKN1A and BAX in the p16-defective U2OS cells expressing either wild-type or mutated p16^INK4A . Furthermore, the association between p16^INK4A and p53 was capital for their nuclear colocalization, the X-ray-dependent induction of p21 and Bax proteins as well as the induction of apoptosis in various types of cells. Together, these results show DNA-dependent physical interaction between p16^INK4A and p53.

Association of well-characterized lung cancer lncRNA polymorphisms with lung cancer susceptibility and platinum-based chemotherapy response

Long non-coding RNAs (lncRNAs) play important roles in carcinogenesis and drug efficacy. Platinum-based chemotherapy is first-line treatment for lung cancer chemotherapy. In this study, we aimed to investigate the association of well-characterized lung cancer lncRNA genetic polymorphisms with the lung cancer susceptibility and platinum-based chemotherapy response. A total of 498 lung cancer patients and 213 healthy controls were recruited in the study. Among them, 467 patients received at least two cycles of platinum-based chemotherapy. Thirteen polymorphisms in HOXA distal transcript antisense RNA (HOTTIP), HOX transcript antisense intergenic RNA (HOTAIR), H19, CDKN2B antisense RNA 1 (ANRIL), colon cancer-associated transcript 2 (CCAT2), metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), and maternally expressed gene 3 (MEG3) genes were genotyped by allele-specific MALDI-TOF mass spectrometry. We found that patients with HOTTIP rs5883064 C allele or rs1859168 A allele had increased lung cancer risk (P = 0.01, P = 0.01, respectively). CCAT2 rs6983267 (P = 0.02, adenocarcinoma) and H19 rs2107425 (P = 0.02, age under 50 years) showed strong relationship with lung cancer susceptibility. CCAT2 rs6983267, H19 rs2839698, MALAT1 rs619586, and HOTAIR rs7958904 were associated with platinum-based chemotherapy response in dominant model ((P = 0.02, P = 0.04, P = 0.04, P = 0.01, respectively). ANRIL rs10120688 (P = 0.02, adenocarcinoma) and rs1333049 (P = 0.04, small-cell lung cancer), H19 rs2107425 (P = 0.02, small-cell lung cancer) and HOTAIR rs1899663 (P = 0.03, male; P = 0.03, smoker) were associated with response to platinum-based chemotherapy. HOTTIP, CCAT2, H19, HOTAIR, MALATI, ANRIL genetic polymorphisms were significantly associated with lung cancer susceptibility or platinum-based chemotherapy response. They may be potential clinical biomarkers to predict lung cancer risk and platinum-based chemotherapy response.

p16 expression predicts neoadjuvant tumor necrosis in osteosarcomas: reappraisal with a larger series using whole sections

The presence of greater than or equal to 90% necrosis after neoadjuvant chemotherapy is a favorable prognostic factor in osteosarcomas. A recent study using tissue microarrays of 40 conventional osteosarcomas showed that p16 expression independently predicted the necrotic response to neoadjuvant chemotherapy. In this study, we investigated this finding using whole sections in a larger group of osteosarcomas. Cases of 83 patients who had pretreatment biopsies and received neoadjuvant chemotherapy and surgical resection were collected from 3 reference hospital archives. Age, sex, tumor size, tumor subtype, location, and percentage of tumor necrosis were recorded; 4-μm sections from pretreatment biopsies were stained for p16. More than 30% strong nuclear staining was regarded as positive. The median age was 17 years (5-68 years), and male/female ratio was 2.3. The mean tumor diameter was 9.9 cm (2-30 cm). Tumors were most commonly of the osteoblastic type (60%) and located at the femur (47%). p16 positivity was seen in 66% of the patients. The median pathologic necrosis was 65%, and 39% of the patients responded favorably (≥%90 necrosis) to neoadjuvant therapy. In univariate analysis, p16 expression significantly correlated with greater than or equal to 90% response (P = .022). On multivariate analysis, p16 expression (odds ratio [OR], 7.71; P = .008), female sex (OR, 8.62; P = .006), and smaller tumor size (OR, 0.86; P = .023) were independent predictors of favorable response to neoadjuvant chemotherapy. We confirmed the finding that p16 expression predicts postchemotherapy necrotic response in conventional osteosarcomas.

p16 Protein and gigaxonin are associated with the ubiquitination of NFκB in cisplatin-induced senescence of cancer cells

The molecular mechanism of p16-mediated senescence in cisplatin-treated cancer cells is not fully understood. Here we show that cisplatin treatment of head and neck cancer cells results in nuclear transport of p16 leading to a molecular modification of NFκB. Chromatin immunoprecipitation assays show that this modification is associated with the inhibition of NFκB interacting with its DNA binding sequences, leading to decreased expression of NFκB-transcribed proteins. LCMS proteomic analysis of LAP-TAP-purified proteins from HeLa cells containing a tetracycline-inducible GFP-S peptide-NFκB expression system identified gigaxonin, an ubiquitin E3 ligase adaptor, as an NFκB-interacting protein. Immunoblotting and siRNA studies confirmed the NFκB-gigaxonin interaction and the dependence of this binding on p16-NFκB binding. Using gel shift assays, we have confirmed p16-NFκB and gigaxonin-NFκB interactions. Furthermore, we have observed increased NFκB ubiquitination with cisplatin treatment that is abolished in the absence of p16 and gigaxonin expression. Analysis of 103 primary tumors has shown that increased nuclear p16 expression correlates with enhanced survival of head and neck cancer patients (p < 0.0000542), indicating the importance of nuclear p16 expression in prognosis. Finally, p16 expression is associated with reduced cytokine expression and the presence of human papilloma virus in chemoradiation-sensitive basaloid tumors. However, the absence of p16 expression is associated with enhanced cytokine expression and the absence of human papilloma virus in aggressive tumors. These results clearly demonstrate that nuclear p16 and gigaxonin play an important role in chemosensitivity of head and neck cancers through ubiquitination of NFκB.

CtBP2 contributes to malignant development of human esophageal squamous cell carcinoma by regulation of p16INK4A

C-terminal binding protein-2 (CtBP2), as a transcriptional co-repressor, has been shown to mediate the repression of p16(INK4A) , a tumor suppressor gene product, in primary human cells. Here we aimed to investigate how the correlation between CtBP2 and p16(INK4A) influenced the development of esophageal squamous cell carcinoma (ESCC). Immunohistochemistry of ESCC tissue sections indicated that the CtBP2 and p16(INK4A) expressions were inversely correlated to each other with a linear regression coefficient of -0.747 (P < 0.05), and Western blot analysis revealed that CtBP2 was higher expressed in tumorous tissues than in adjacent non-tumorous tissues. Either CtBP2 or p16(INK4A) expression was significantly related to histological differentiation (P = 0.016 or 0.001) and to the expression of Ki-67, a proliferating marker (P = 0.006 or 0.02), and patients with higher CtBP2 and lower p16(INK4A) expressions had shorter overall survival. We also observed that CtBP2 modulated the cell proliferation and cell cycle in ECA109 cells, an ESCC cell line, by inhibiting p16(INK4A) . Overexpression or knockdown of CtBP2 in ECA109 cells was found to inhibit or activate the mRNA or protein expression of p16(INK4A) , which in turn altered the cell proliferation and cell cycle in ECA109 cells, as measured by flow cytometry and cell count assay. Additionally, after ECA109 cells silenced for CtBP2 were treated with cisplatin (an anti-ESCC agent), the p16(INK4A) expression was up-regulated, and the cell apoptosis was promoted, thus confirming the repression of p16(INK4A) by CtBP2. Collectively, all results suggested that CtBP2 might contribute to the progression of ESCC through a negative transcriptional regulation of p16(INK4A).

Combination of SAHA and bortezomib up-regulates CDKN2A and CDKN1A and induces apoptosis of Epstein-Barr virus-positive Wp-restricted Burkitt lymphoma and lymphoblastoid cell lines

Epstein-Barr virus (EBV) latent proteins exert anti-apoptotic effects on EBV-transformed lymphoid cells by down-regulating BCL2L11 (BIM), CDKN2A (p16(INK4A) ) and CDKN1A (p21(WAF1) ). However, the potential therapeutic effects of targeting these anti-apoptotic mechanisms remain unexplored. Here, we tested both in vitro and in vivo effects of the combination of histone deacetylase (HDAC) and proteasome inhibitors on the apoptosis of six endemic Burkitt lymphoma (BL) lines of different latency patterns (types I and III and Wp-restricted) and three lymphoblastoid cell lines (LCLs). We found that the combination of HDAC and proteasome inhibitors (e.g. SAHA/bortezomib) synergistically induced the killing of Wp-restricted and latency III BL and LCLs but not latency I BL cells. The synergistic killing was due to apoptosis, as evidenced by the high percentage of annexin V positivity and strong cleavage of PARP1 (PARP) and CASP3 (caspase-3). Concomitantly, SAHA/bortezomib up-regulated the expression of CDKN2A and CDKN1A but did not affect the level of BCL2L11 or BHRF1 (viral homologue of BCL2). The apoptotic effects were dependent on reactive oxygen species generation. Furthermore, SAHA/bortezomib suppressed the growth of Wp-restricted BL xenografts in nude mice. This study provides the rationale to test the novel application of SAHA/bortezomib on the treatment of EBV-associated Wp-restricted BL and post-transplant lymphoproliferative disorder.

Deletion of p18(INK4c) aggravates cisplatin-induced acute kidney injury

Protection of cyclin-dependent kinase inhibitors (CDKIs) has been demonstrated in acute kidney injury (AKI). However, previous studies on CDKIs have mainly focused on CIP/KIP family members, with INK4 family members rarely being investigated. This study investigated the behaviors of p18(INK4c) (p18) in cisplatin-induced AKI using p18 gene knockout mice (p18-/-). AKI was induced in p18-/- and wild-type (p18+/+) mice after a single cisplatin (12.5 mg/kg) intraperitoneal injection. Protection by p18 was identified by a comparison of survival, renal function and morphological injuries between p18-/- and p18+/+ mice. Further investigation of endoplasmic reticulum stress (ERS) was performed by western blot analysis in p18-/- and p18+/+ kidneys at day 3 after cisplatin injection. The results revealed that after cisplatin injection, the survival of p18-/- mice was significantly shorter than that of p18+/+ mice, accompanied by aggravated renal function and more severe morphological injuries. Deletion of p18 also significantly aggravated ERS in cisplatin-induced AKI. In conclusion, p18 exerts protective effects on cisplatin‑induced AKI, which may be associated with the effect of p18 on cell death pathways, such as the ERS pathway.

The cyclin-dependent kinase inhibitor p16INK4a physically interacts with transcription factor Sp1 and cyclin-dependent kinase 4 to transactivate microRNA-141 and microRNA-146b-5p spontaneously and in response to ultraviolet light-induced DNA damage

p16(INK4a) is a tumor suppressor protein involved in several stress-related cellular responses, including apoptosis. Recent lines of evidence indicate that p16(INK4a) is also a modulator of gene expression. However, the molecular mechanisms underlying this novel function are still obscure. Here, we present clear evidence that p16(INK4a) modulates the levels of various microRNAs, with marked positive effect on miR-141 and miR-146b-5p. This effect is mediated through the formation of the p16-CDK4-Sp1 heterocomplex, which binds to Sp1 consensus-binding motifs present in the promoters of miR-141 and miR-146b-5p, and it enables their transcription. In addition, we have shown that p16(INK4a) interacts with Sp1 through the fourth ankyrin repeat, which is crucial for Sp1 binding to the miR-141 and miR-146b-5p promoters and their transcriptional activation. The physiological importance of this association was revealed by the inability of cancer-related p16(INK4a) mutants to interact with Sp1. Moreover, we have shown p16-CDK4-Sp1-dependent up-regulation of miR-141 and miR-146b-5p following UV light-induced DNA damage and the role of these two microRNAs in mediating p16-related induction of apoptosis in response to this genotoxic stress. Together, these results indicate that p16(INK4a) associates with CDK4 not only to inhibit the cell cycle but also to enable the transcription of two important onco-microRNAs, which act as downstream effectors.

p16(INK4A) positively regulates p21(WAF1) expression by suppressing AUF1-dependent mRNA decay

Background

p16^INK4a and p21^WAF1 are two independent cyclin-dependent kinase inhibitors encoded by the CDKN2A and CDKN1A genes, respectively. p16^INK4a and p21^WAF1 are similarly involved in various anti-cancer processes, including the regulation of the critical G1 to S phase transition of the cell cycle, senescence and apoptosis. Therefore, we sought to elucidate the molecular mechanisms underlying the link between these two important tumor suppressor proteins.

Methodology/Principal Findings

We have shown here that the p16^INK4a protein positively controls the expression of p21^WAF1 in both human and mouse cells. p16^INK4a stabilizes the CDKN1A mRNA through negative regulation of the mRNA decay-promoting AUF1 protein. Immunoprecipitation of AUF1-associated RNAs followed by quantitative RT-PCR indicated that endogenous AUF1 binds to the CDKN1A mRNA in a p16^INK4A-dependent manner. Furthermore, while AUF1 down-regulation increased the expression level of the CDKN1A mRNA, the concurrent knockdown of AUF1 and CDKN2A, using specific silencing RNAs, restored the normal expression of the gene. Moreover, we used EGFP reporter fused to the CDKN2A AU-rich element (ARE) to demonstrate that p16^INK4A regulation of the CDKN1A mRNA is AUF1- and ARE-dependent. Furthermore, ectopic expression of p16^INK4A in p16^INK4A-deficient breast epithelial MCF-10A cells significantly increased the level of p21^WAF1, with no effect on cell proliferation. In addition, we have shown direct correlation between p16^INK4a and p21^WAF1 levels in various cancer cell lines.

Conclusion/Significance

These findings show that p16^INK4a stabilizes the CDKN1A mRNA in an AUF1-dependent manner, and further confirm the presence of a direct link between the 2 important cancer-related pathways, pRB/p16^INK4A and p14^ARF/p53/p21^WAF1.

INK4a/ARF limits the expansion of cells suffering from replication stress

Replication stress (RS) is a source of DNA damage that has been linked to cancer and aging, which is suppressed by the ATR kinase. In mice, reduced ATR levels in a model of the ATR-Seckel syndrome lead to RS and accelerated aging. Similarly, ATR-Seckel embryonic fibroblasts (MEF) accumulate RS and undergo cellular senescence. We previously showed that senescence of ATR-Seckel MEF cannot be rescued by p53-deletion. Here, we show that the genetic ablation of the INK4a/Arf locus fully rescues senescence on ATR mutant MEF, but also that induced by other conditions that generate RS such as low doses of hydroxyurea or ATR inhibitors. In addition, we show that a persistent exposure to RS leads to increased levels of INK4a/Arf products, revealing that INK4a/ARF behaves as a bona fide RS checkpoint. Our data reveal an unknown role for INK4a/ARF in limiting the expansion of cells suffering from persistent replication stress, linking this well-known tumor suppressor to the maintenance of genomic integrity.

p16INK4A represses breast stromal fibroblasts migration/invasion and their VEGF-A-dependent promotion of angiogenesis through Akt inhibition

Stromal fibroblasts, the most abundant and probably the most active cellular component of breast cancer-associated stroma, become active and promote angiogenesis through paracrine effects. However, it still unclear how these processes are regulated. Here, we have shown that down-regulation of the tumor suppressor p16(INK4A) protein enhances the migration/invasion abilities of breast stromal fibroblasts, which form dendritic network of extensions into matrigel. Furthermore, we present clear evidence that p16(INK4A) represses the expression/secretion of the proangiogenesis protein vascular endothelial growth factor A (VEGF-A). Consequently, p16(INK4A)-deficient breast stromal fibroblasts and mouse embryonic fibroblasts enhanced endothelial cell differentiation into capillary-like structures in a paracrine manner. This effect was suppressed by adding bevacizumab, a specific VEGF-A inhibitor. Additionally, p16(INK4A)-defective mouse embryonic fibroblasts enhanced angiogenesis in breast cancer xenografts in mice. Furthermore, we have shown that p16(INK4A) suppresses the Akt/mammalian target of rapamycin (mTOR) signaling pathway and its downstream effector hypoxia-inducible factor 1-alpha (HIF-1α), which transactivates VEGF-A. Consequently, Akt inactivation suppressed both the p16(INK4A)-dependent autocrine effect on fibroblast migration/invasion and the paracrine effect on angiogenesis, showing the important role of this protein kinase in mediating the various effects related to p16(INK4A) deficiency. These results indicate that p16(INK4A) is an efficient inhibitor of the migration/invasion abilities of breast stromal fibroblasts and also their paracrine proangiogenic effects, through inhibition of Akt. Therefore, pharmacologic restoration of p16(INK4A) level in stromal fibroblasts may be exploited as therapeutic strategy to help eradicate tumor cells and/or prevent their recurrence, through suppressing cell non-autonomous procarcinogenic mediators.

Role of p16(INK4A) in Replicative Senescence and DNA Damage-Induced Premature Senescence in p53-Deficient Human Cells

The p16(INK4A) (hereafter p16) tumor suppressor is encoded by the INK4A/ARF locus which is among the most commonly dysregulated sequences in human cancer. By inhibiting cyclin-dependent kinases, p16 activates the G1-S checkpoint, and this response is often considered to be critical for establishing a senescence-like growth arrest. Not all studies support a universal role for p16 in senescence. Single-cell analysis of noncancerous human fibroblast cultures undergoing senescence as a function of culture age (replicative senescence) has revealed that p16 is not expressed in the majority (>90%) of cells that exhibit features of senescence (e.g., flattened and enlarged morphology coupled with senescence-associated β-galactosidase expression), ruling out a requirement for p16 in this process. In addition, ionizing radiation triggers premature senescence in human cancer cell lines that do not express p16. These observations are made with cells that express wild-type p53, a key mediator of the DNA damage response. In this paper, we examine the growing evidence suggesting a negative regulatory relationship between p16 and p53 and discuss recent reports that implicate a role for p16 in replicative senescence and ionizing radiation-induced premature senescence in human cells that lack wild-type p53 function.

Mechanism of cisplatin resistance in human urothelial carcinoma cells

An isogenic pair of cisplatin-susceptible (NTUB1) and -resistant (NTUB1/P) human urothelial carcinoma cell lines was used to elucidate the mechanism of cisplatin resistance. The significantly lower intracellular platinum (IP) concentration, which resulted from the decreased cisplatin uptake, was found in NTUB1/P cells. The enhancement of IP concentration did not increase the susceptibility of NTUB1/P cells to cisplatin treatment. The reduction of IP concentration as well was unable to enhance the cisplatin-resistance in susceptible NTUB1 cells. This indicated that reduction of IP concentration was not the account for the development of cisplatin resistance here. Instead, the over expression of anti-apoptotic Bcl-2, anti-oxidative heme oxygenase-1 (HO-1) and cell cycle regulator p16INK4 seemed to be more important for the gaining of cisplatin in these human urothelial carcinoma cell.

Overexpression of p18INK⁴C in LLC-PK1 cells increases resistance to cisplatin-induced apoptosis

Studies have demonstrated that cyclin-dependent kinase inhibitors (CDKI) that inhibit cell-cycle progression have a protective effect against acute kidney injury (AKI). Most studies have focused on the CIP/KIP family members of CDKI; only a few have explored the role of INK4 family members in AKI. Because INK4 family members block the G1-S transition, we postulated that they should have protective effects against AKI. The most conserved INK4 member is p18, so we selected it to explore its effects on cisplatin-induced renal cell injury. We overexpressed p18 in renal tubular epithelial cells (LLC-PK1) by transient transfection and investigated its effects on the cell cycle and proliferation. After transfection, cell injury was induced by cisplatin (100 μM) incubation for 24 h in a standard medium. The effect of p18 was assayed by assessing cell necrosis and apoptosis in transfected cells. The endoplasmic reticulum stress (ERS) pathway was evaluated to interpret the possible mechanism of p18 action in cisplatin-induced renal cell injury. Overexpression of p18 arrested cell cycle progression in the G1 phase and inhibited proliferation. Compared with vehicle transfection, p18 overexpression did not affect cisplatin-induced necrosis, but it reduced the percentage of apoptotic cells significantly. The severity of ERS induced by cisplatin was also decreased by p18 overexpression. P18 protects against cisplatin-induced renal cell injury. The mechanism of p18 protection may lie in its effect on the cell death pathway.

p16( INK4a) positively regulates cyclin D1 and E2F1 through negative control of AUF1

Background

The cyclin-D/CDK4,6/p16^INK4a/pRB/E2F pathway, a key regulator of the critical G1 to S phase transition of the cell cycle, is universally disrupted in human cancer. However, the precise function of the different members of this pathway and their functional interplay are still not well defined.

Methodology/Principal Findings

We have shown here that the tumor suppressor p16^INK4a protein positively controls the expression of cyclin D1 and E2F1 in both human and mouse cells. p16^INK4a stabilizes the mRNAs of the corresponding genes through negative regulation of the mRNA decay-promoting AUF1 protein. Immunoprecipitation of AUF1-associated RNAs followed by RT-PCR indicated that endogenous AUF1 binds to the cyclin D1 and E2F1 mRNAs. Furthermore, AUF1 down-regulation increased the expression levels of these genes, while concurrent silencing of AUF1 and p16^INK4a, using specific siRNAs, restored normal expression of both cyclinD1 and E2F1. Besides, we have shown the presence of functional AU-rich elements in the E2F1 3′UTR, which contributed to p16/AUF1-mediated regulation of E2F1 post-transcriptional events in vivo. Importantly, genome-wide gene expression microarray analysis revealed the presence of a large number of genes differentially expressed in a p16^INK4a -dependent manner, and several of these genes are also members of the AUF1 and E2F1 regulons. We also present evidence that E2F1 mediates p16-dependent regulation of several pro- and anti-apoptotic proteins, and the consequent induction of spontaneous as well as doxorubicin-induced apoptosis.

Conclusion/Significance

These findings show that the cyclin-dependent kinase inhibitor p16 ^INK4a is also a modulator of transcription and apoptosis through controlling the expression of two major transcription regulators, AUF1 and E2F1.

Intracellular clusterin negatively regulates ovarian chemoresistance: compromised expression sensitizes ovarian cancer cells to paclitaxel

Understanding the molecular events that lead to paclitaxel (TX) resistance is necessary to identify effective means to prevent chemoresistance. Previously, results from our lab revealed that secretory clusterin (CLU) form positively mediates TX response in ovarian cancer cells. Thus, we had interest to study the role of another non-secreted form (intracellular clusterin (i-CLU)) in chemo-response. Here, we provide evidences that i-CLU form localizes mainly in the nucleus and differentially expressed in the TX-responsive KF cells, versus TX-resistant, KF-TX, ovarian cancer cells and negatively regulate cellular chemo-response. I-CLU was cloned, by deleting the secretion-leading signaling peptide from full-length CLU cDNA, and transiently over-expressed in OVK-18 cells. Forced expression of truncated i-CLU was mainly detectable in the nuclei and significantly reduced cellular growth, accumulating cells in G1 phase which finally died through apoptosis. Importantly, compromised expression of i-CLU under an inducible promoter was tolerated and did not induce apoptosis but sensitized ovarian cancer cells to TX. We then demonstrated that this sensitization mechanism was cell cycle independent and relied on i-CLU/Ku70 binding probably due to controlling the free amount of Ku70 available for DNA repair in the nucleus. Results from CLU immunohistochemistry in ovarian tumor tissues verified the retardation of nuclear CLU staining in the recurrent tumor even though their primary counterparts showed nuclear CLU staining. Thus, the controversial data on CLU function in chemo-response/resistance may be explained by a shift in the pattern of CLU expression and intracellular localization as well when tumor acquires chemoresistance.

Regulatory mechanisms of tumor suppressor P16(INK4A) and their relevance to cancer

P16(INK4A) (also known as P16 and MTS1), a protein consisting exclusively of four ankyrin repeats, is recognized as a tumor suppressor mainly because of the prevalence of genetic inactivation of the p16(INK4A) (or CDKN2A) gene in virtually all types of human cancers. However, it has also been shown that an elevated level of expression (upregulation) of P16 is involved in cellular senescence, aging, and cancer progression, indicating that the regulation of P16 is critical for its function. Here, we discuss the regulatory mechanisms of P16 function at the DNA level, the transcription level, and the posttranscriptional level, as well as their implications for the structure-function relationship of P16 and for human cancers.

Hepatitis B virus X protein impedes the DNA repair via its association with transcription factor, TFIIH

Background

Hepatitis B virus (HBV) infections play an important role in the development of hepatocellular carcinoma (HCC). HBV X protein (HBx) is a multifunctional protein that can modulate various cellular processes and plays a crucial role in the pathogenesis of HCC. HBx is known to interact with DNA helicase components of TFIIH, a basal transcriptional factor and an integral component of DNA excision repair.

Results

In this study, the functional relevance of this association was further investigated in the context to DNA repair. By site-directed mutagenesis HBx's critical residues for interaction with TFIIH were identified. Similarly, TFIIH mutants lacking ATPase domain and the conserved carboxyl-terminal domain failed to interact with HBx. Yeast and mammalian cells expressing HBx^wt conferred hypersensitivity to UV irradiation, which is interpreted as a basic deficiency in nucleotide excision repair. HBx^mut120 (Glu to Val) was defective in binding to TFIIH and failed to respond to UV.

Conclusions

We conclude that HBx may act as the promoting factor by inhibiting DNA repair causing DNA damage and accumulation of errors, thereby contributing to HCC development.

Prolonged mechanical ventilation induces cell cycle arrest in newborn rat lung

RATIONALE

The molecular mechanism(s) by which mechanical ventilation disrupts alveolar development, a hallmark of bronchopulmonary dysplasia, is unknown.

OBJECTIVE

To determine the effect of 24 h of mechanical ventilation on lung cell cycle regulators, cell proliferation and alveolar formation in newborn rats.

METHODS

Seven-day old rats were ventilated with room air for 8, 12 and 24 h using relatively moderate tidal volumes (8.5 mL.kg⁻¹).

MEASUREMENT AND MAIN RESULTS

Ventilation for 24 h (h) decreased the number of elastin-positive secondary crests and increased the mean linear intercept, indicating arrest of alveolar development. Proliferation (assessed by BrdU incorporation) was halved after 12 h of ventilation and completely arrested after 24 h. Cyclin D1 and E1 mRNA and protein levels were decreased after 8-24 h of ventilation, while that of p27(Kip1) was significantly increased. Mechanical ventilation for 24 h also increased levels of p57(Kip2), decreased that of p16(INK4a), while the levels of p21(Waf/Cip1) and p15(INK4b) were unchanged. Increased p27(Kip1) expression coincided with reduced phosphorylation of p27(Kip1) at Thr¹⁵⁷, Thr¹⁸⁷ and Thr¹⁹⁸ (p<0.05), thereby promoting its nuclear localization. Similar -but more rapid- changes in cell cycle regulators were noted when 7-day rats were ventilated with high tidal volume (40 mL.kg⁻¹) and when fetal lung epithelial cells were subjected to a continuous (17% elongation) cyclic stretch.

CONCLUSION

This is the first demonstration that prolonged (24 h) of mechanical ventilation causes cell cycle arrest in newborn rat lungs; the arrest occurs in G₁ and is caused by increased expression and nuclear localization of Cdk inhibitor proteins (p27(Kip1), p57(Kip2)) from the Kip family.

Single-cell analysis of p16(INK4a) and p21(WAF1) expression suggests distinct mechanisms of senescence in normal human and Li-Fraumeni Syndrome fibroblasts

Herein we used single-cell observation methods to gain insight into the roles of p16(INK4A) and p21(WAF1) (hereafter p16 and p21) in replicative senescence and ionizing radiation-induced accelerated senescence in human [normal, ataxia telangiectasia (AT) and Li-Fraumeni syndrome (LFS)] fibroblast strains. Cultures of all strains entered a state of replicative senescence at late passages, as evident from inhibition of growth, acquisition of flattened and enlarged cell morphology, and positive staining for senescence-associated beta-galactosidase. In addition, proliferating early-passage cultures of these strains exhibited accelerated senescence in response to ionizing radiation. Immunofluorescence microscopy revealed the heterogeneous expression of p16 in normal and AT fibroblast strains, with the majority of the cells exhibiting undetectable levels of p16 irrespective of in vitro culture age. Importantly, replicative senescence as well as accelerated senescence triggered by ionizing radiation were accompanied by sustained nuclear accumulation of p21, but did not correlate with p16 expression in p53-proficient (normal and AT) fibroblasts. In p53-deficient (LFS) fibroblasts, on the other hand, replicative senescence and ionizing radiation-triggered accelerated senescence strongly correlated with expression of p16 but not of p21. Furthermore, senescence in LFS fibroblasts was associated with genomic instability encompassing polyploidy. Our findings are compatible with a model in which p16 serves as a backup regulator of senescence, triggering this response preferentially in the absence of wild-type p53 activity. The possibility that one of the tumor-suppressor functions of p16 may be associated with genomic instability, preventing the emergence of malignant progeny from polyploid giant cells, is also supported by these results.

Breast carcinoma-associated fibroblasts and their counterparts display neoplastic-specific changes

It has become clear that the initiation and progression of carcinomas depend not only on alterations in epithelial cells, but also on changes in their microenvironment. To identify these changes, we have undertaken cellular and molecular characterization of carcinoma-associated fibroblasts (CAF) and their tumor counterpart fibroblasts (TCF) isolated from 12 breast cancer patients. Normal breast fibroblasts (NBF) from plastic surgery were used as normal control. We present evidence that both CAFs and TCFs are myofibroblasts and show tumor-associated features. Indeed, the p53/p21 response pathway to gamma-rays was defective in 70% CAFs, whereas it was normal in all the TCF and NBF cells. In addition, the basal levels of the p53 and p21 proteins were significantly low in 83% of CAFs and modulated in the majority of TCFs compared with NBFs. Interestingly, both TCFs and CAFs expressed high levels of the cancer marker survivin and consequently exhibited high resistance to cisplatin and UV light. Moreover, most CAFs were positive for the proliferation marker Ki-67 and exhibited high proliferation rate compared with NBFs and TCFs. However, proliferating cell nuclear antigen was highly expressed in both CAFs and TCFs. Using the two-dimensional gel electrophoresis technique, we have also shown that CAF, TCF, and NBF cells present different proteome profiles, with many proteins differentially expressed between these cells. Taken together these results indicate that different genetic alterations can occur in breast CAFs and their corresponding adjacent counterparts, showing the important role that stroma could play in breast carcinogenesis and treatment.

Cell cycle inhibitor, p19INK4d, promotes cell survival and decreases chromosomal aberrations after genotoxic insult due to enhanced DNA repair

Genome integrity and cell proliferation and survival are regulated by an intricate network of pathways that includes cell cycle checkpoints, DNA repair and recombination, and programmed cell death. It makes sense that there should be a coordinated regulation of these different processes, but the components of such mechanisms remain unknown. In this report, we demonstrate that p19INK4d expression enhances cell survival under genotoxic conditions. By using p19INK4d-overexpressing clones, we demonstrated that p19INK4d expression correlates with the cellular resistance to UV treatment with increased DNA repair activity against UV-induced lesions. On the contrary, cells transfected with p19INK4d antisense cDNA show reduced ability to repair DNA damage and increased sensitivity to genotoxic insult when compared with their p19INK4d-overexpressing counterparts. Consistent with these findings, our studies also show that p19INK4d-overexpressing cells present not only a minor accumulation of UV-induced chromosomal aberrations but a lower frequency of spontaneous chromosome abnormalities than p19INK4d-antisense cells. Lastly, we suggest that p19INK4d effects are dissociated from its role as CDK4/6 inhibitor. The results presented herein support a crucial role for p19INK4d in regulating genomic stability and overall cell viability under conditions of genotoxic stress. We propose that p19INK4d would belong to a protein network that would integrate DNA repair, apoptotic and checkpoint mechanisms in order to maintain the genomic integrity.

The p16INK4a tumor suppressor controls p21WAF1 induction in response to ultraviolet light

p16INK4a and p21WAF1, two major cyclin-dependent kinase inhibitors, are the products of two tumor suppressor genes that play important roles in various cellular metabolic pathways. p21WAF1 is up-regulated in response to different DNA damaging agents. While the activation of p21WAF1 is p53-dependent following -rays, the effect of ultraviolet (UV) light on p21WAF1 protein level is still unclear. In the present report, we show that the level of the p21WAF1 protein augments in response to low UVC fluences in different mammalian cells. This up-regulation is mediated through the stabilization of p21WAF1 mRNA in a p16INK4a-dependent manner in both human and mouse cells. Furthermore, using p16-siRNA treated human skin fibroblast; we have shown that p16 controls the UV-dependent cytoplasmic accumulation of the mRNA binding HuR protein. In addition, HuR immunoprecipitations showed that UV-dependent binding of HuR to p21 mRNA is p16-related. This suggests that p16 induces p21 by enabling the relocalization of HuR from the nucleus to the cytoplasm. Accordingly, we have also shown that p16 is necessary for efficient UV-dependent p53 up-regulation, which also requires HuR. These results indicate that, in addition to its role in cell proliferation, p16INK4a is also an important regulator of the cellular response to UV damage.

The tumor suppressor p16Ink4a regulates T lymphocyte survival

In contrast to other cell cycle inhibitors, the tumor suppressor p16Ink4a is not detectable or expressed at very low levels in embryonic and adult mouse tissues, and therefore it has often been considered as a specialized checkpoint protein that does not participate in the control of normal cell cycle progression. However, Ink4a-/- mice possess increased thymus size and cellularity, thus suggesting the involvement of p16(Ink4a) in the control of thymocyte proliferation. In this study, we found increased numbers of CD8 and CD4 T lymphocytes in thymus and spleen from Ink4a-/- mice. Unexpectedly, this was not related to an increase in T-cell division rates, which were similar in lymphoid organs of Ink4a-/- and wild-type mice. In contrast, T-cell apoptosis rates were significantly decreased in thymus and spleen from Ink4a-/- mice. Moreover, whereas p16Ink4a-deficient and wild-type T cells were equally sensitive to Fas or TCR-mediated apoptosis, the former were clearly more resistant to apoptosis induced by oxidative stress or gamma irradiation. Our results indicate that p16Ink4a function is associated with T-cell apoptosis, and subsequently contributes to the control of T-cell population size in lymphoid organs.

Induction of p19INK4d in response to ultraviolet light improves DNA repair and confers resistance to apoptosis in neuroblastoma cells

The genetic instability driving tumorigenesis is fueled by DNA damage and by errors made by the DNA replication. Upon DNA damage the cell organizes an integrated response not only by the classical DNA repair mechanisms but also involving mechanisms of replication, transcription, chromatin structure dynamics, cell cycle progression, and apoptosis. In the present study, we investigated the role of p19INK4d in the response driven by neuroblastoma cells against DNA injury caused by UV irradiation. We show that p19INK4d is the only INK4 protein whose expression is induced by UV light in neuroblastoma cells. Furthermore, p19INK4d translocation from cytoplasm to nucleus is observed after UV irradiation. Ectopic expression of p19INK4d clearly reduces the UV-induced apoptosis as well as enhances the cellular ability to repair the damaged DNA. It is clearly shown that DNA repair is the main target of p19INK4d effect and that diminished apoptosis is a downstream event. Importantly, experiments performed with CDK4 mutants suggest that these p19INK4d effects would be independent of its role as a cell cycle checkpoint gene. The results presented herein uncover a new role of p19INK4d as regulator of DNA-damage-induced apoptosis and suggest that it protects cells from undergoing apoptosis by allowing a more efficient DNA repair. We propose that, in addition to its role as cell cycle inhibitor, p19INK4d is involved in maintenance of DNA integrity and, therefore, would contribute to cancer prevention.

Mechanisms of platinum drug resistance

Platinum-based drugs are among the most active anticancer agents available and are used widely for the treatment of a variety of human solid tumors. Although patients show high response rates to platinum drugs, most patients develop resistance to these drugs during treatment. Because the acquisition of resistance is a major obstacle to the clinical use of platinum drugs, the processes by which cells develop such resistance are of great interest and efforts have been made to overcome this problem. Both mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) cascades are involved in resistance to these drugs, and clinical trials of some small-molecule inhibitors of the MAPK and PI3K-Akt cascades to overcome resistance to platinum drugs are ongoing.

Cdk1 and Cdk2 complexes (cyclin dependent kinases) in apoptosis: a role beyond the cell cycle

The family of cyclin-dependent kinase complexes (Cdks) are well known for their role in the cell division cycle. What is less well known, however, is that Cdks also participate in a subset of apoptosis programs. Evidence for the role of Cdks in apoptosis comes from a variety of experimental approaches, including studies using genetic mutants, protein inhibitors, and chemical inhibitors of protein kinase activity. The precise role of Cdks in apoptosis remains to be defined, although one promising approach to clarify this question is to identify Cdk protein substrates during apoptosis. Currently a number of Cdk inhibitors are being tested in clinical trials. By understanding how Cdks function during apoptosis it may be possible to optimise the use of these inhibitors in treating human tumours by blocking proliferation but permitting apoptosis.

Effects of loss of p53 and p16 function on life span and survival of human urothelial cells

Human urothelial cell carcinoma evolves via the accumulation of numerous genetic alterations, with loss of p53 and p16 function representing important stages in the development of superficial lesions and their progression to malignant disease. To investigate the effects of disabling either or both proteins in otherwise normal human urothelial cells, we performed retroviral transductions with a dominant negative p53 miniprotein and/or mutant cyclin-dependent kinase 4 (CDK4R24C) in 3 independent cell lines. Although cells with disabled p53 function showed a higher proliferation rate, inactivation of neither p53 nor p16 function resulted in any extension of life span and the double-transductants failed to flourish, demonstrating that further genetic alterations are required to attain an immortalised phenotype. However, CDK4R24C transductants showed a marked increase in apoptotic susceptibility to membrane-presented CD40 ligand, being intermediate between normal cells (nonsusceptible) and transformed cells (highly susceptible). By contrast, loss of p53 function alone only slightly increased the apoptotic susceptibility of urothelial cells. These results demonstrate that loss of p16 function, while insufficient to immortalise urothelial cells, nevertheless renders the cells more vulnerable to apoptosis induced by CD40 ligation.