Activation of p21(CIP1/WAF1) in mammary epithelium accelerates mammary tumorigenesis and promotes lung metastasis

Suppression of the long non-coding RNA LINC01279 triggers autophagy and apoptosis in lung cancer by regulating FAK and SIN3A

Long non-coding RNAs play critical roles in the development of lung cancer by functioning as tumor suppressors or oncogenes. Changes in the expression of LINC01279 have been associated with cell differentiation and human diseases. However, the mechanism underlying LINC01279 activity in tumorigenesis is not clear. Here, we analyzed the function of LINC01279 in lung adenocarcinoma using clinical samples, xenografts, and non-small-cell lung cancer cell lines. We found that LINC01279 is highly expressed in lung adenocarcinoma and may be considered as a predictive factor for this cancer. Knockdown of LINC01279 prevents tumor growth in xenografts and in cancer cell lines by activating autophagy and apoptosis. Molecularly, we revealed that LINC01279 regulates the expression of focal adhesion kinase and extracellular-regulated kinase signaling. In addition, it complexes with and stabilizes the transcriptional co-repressor SIN3A protein. Suppression of focal adhesion kinase and SIN3A also induces apoptosis and prevents tumor progression, suggesting that they may at least in part mediate the oncogenic activity of LINC01279. These results identify LINC01279 as a possible oncogene that plays an important role in the development of lung cancer. Our findings provide insights into the mechanism underlying LINC01279-mediated oncogenesis of lung adenocarcinoma. They may help to discover potential therapeutic targets for cancer diagnosis and prognosis.

Thyroid hormone enhances estrogen-mediated proliferation and cell cycle regulatory pathways in steroid receptor-positive breast Cancer

Estrogen receptor (ER) α expression and associated signaling is a major driver of over two-thirds of all breast cancers (BC). ER targeting strategies are typically used as a first-line therapy in patients with steroid receptor positive (SR+) disease. Secondary resistance to anti-estrogenic agents may occur with clonal expansion and disease progression. Mechanisms underlying hormone resistance are an expanding field of significant translational importance. Cross-talk with other nuclear hormones, receptors, and signaling pathways, including thyroid hormones (TH) and their receptors (THRs), have been shown to promote endocrine therapy resistance in some studies. We have shown that TH replacement therapy (THRT) was independently and significantly associated with higher rates of relapse and mortality in SR positive (+), node-negative (LN-) BC patients, whereas it showed no association with outcomes in SR negative (-) patients. LN-, SR+ patients receiving THRT and tamoxifen had the worst outcomes, suggesting a pro-carcinogenic interaction that significantly and independently shortened survival and increased mortality. Using in vivo and in vitro models, we previously showed hormonal cross-talk, altered gene signaling, target gene activation, and resistance to tamoxifen in the presence of TH. In this report, we show TH ± E2 ± tamoxifen inhibits cell cycle control signaling, reduces apoptosis, and enhances cell proliferation, tumor growth, tamoxifen resistance, and clonal expansion. Mechanistically these changes involve numerous genes and pathways, including critical cell cycle regulatory proteins and genes identified using various molecular methods. These studies facilitate a greater mechanistic understanding of the biological and molecular impact of TH on SR+ BC.

Sirtuin 4 Inhibits Prostate Cancer Progression and Metastasis by Modulating p21 Nuclear Translocation and Glutamate Dehydrogenase 1 ADP-Ribosylation

Protein posttranslational modification regulates several biological mechanisms, including tumor progression. In this study, we show that the mitochondrial Sirtuin 4 (SIRT4), which has ADP-ribosylation activity, plays a role in prostate cancer (PCa) progression. Firstly, SIRT4 expression was verified in PCa tissues and cell lines by quantitative real-time PCR (qRT-PCR) and western blotting. Subsequently, we established stable PC-3 and 22rv1 cells that overexpressed SIRT4 and knocked down SIRT4, respectively. The functions of SIRT4 in PCa were explored through various phenotype experiments. The mechanism underlying the functions of SIRT4 was investigated through western blotting, immunoprecipitation, immunofluorescence, and nuclear and cytoplasmic extraction assays. We revealed that SIRT4 inhibited cell progression both in vivo and in vitro. Mechanistically, on the one hand, SIRT4 promoted the ADP-ribosylation of glutamate dehydrogenase 1 to inhibit the glutamine metabolism pathways. On the other hand, SIRT4 inhibited the phosphorylation of AKT, thereby affecting p21 phosphorylation and its cellular localization for cell cycle arrest. In conclusion, our study indicates that SIRT4 is directly associated with PCa progression and could be a novel target for PCa therapy.

Slow transcription of the 99a/let-7c/125b-2 cluster results in differential miRNA expression and promotes melanoma phenotypic plasticity

Almost half of human miRNAs are encoded in clusters. Although transcribed as a single unit, the levels of individual mature miRNAs often differ. The mechanisms underlying differential biogenesis of clustered miRNAs and the resulting physiological implications are mostly unknown. Here, we report that the melanoma master transcription regulator MITF regulates the differential expression of the 99a/let-7c/125b-2 cluster by altering the distribution of RNA polymerase II (Pol-II) along the cluster. We discovered that MITF interacts with TRIM28, a known inhibitor of Pol-II transcription elongation, at the let-7c region resulting in Pol-II pausing and causing its elevated expression, whereas low levels of Pol-II occupation over miR-99a and miR-125b-2 regions decreases their biogenesis. Furthermore, we showed that this differential expression affects the phenotypic state of melanoma cells. RNA-seq analysis of proliferative melanoma cells that express miR-99a and miR-125b mimics revealed a transcriptomic shift toward an invasive phenotype. Conversely, expression of a let-7c mimic in invasive melanoma cells induced a shift to a more proliferative state. We confirmed direct target genes of these miRNAs: FGFR3, BAP1, Bcl2, TGFBR1, and CDKN1A. Our study demonstrates a MITF-governed biogenesis mechanism that results in differential expression of clustered 99a/let-7c/125b-2 miRNAs that control melanoma progression.

The novel roles of virus infection-associated gene CDKN1A in chemoresistance and immune infiltration of glioblastoma

Chemoresistance is a common limitation for successful treatment of glioblastoma multiforme (GBM). Recently, virus infections have been demonstrated to be associated with tumorigenesis and chemoresistance in tumors. However, the role of infection-related genes in GBM haven’t been clearly demonstrated. Here, we explored the roles and mechanisms of human T-lymphotropic virus type-1 (HTLV-1) infections in tumorigenesis and chemoresistance in GBM. Four candidate genes, CDKN1A, MSX1, MYC and CHEK2, were identified to be the codifferentially expressed genes between three temozolomide (TMZ) chemotherapy datasets and one HTLV-1 infection gene set. Next, comprehensive bioinformatics data from several databases indicated that only CDKN1A was significantly upregulated in both GBM tissues and cells and showed the greatest prognostic value in GBM patients. Clinical data identified the correlations between CDKN1A expression and clinicopathological parameters of GBM patients. Moreover, CDKN1A was found to be involved in AKT-mediated TMZ resistance of glioma cells. In addition, KEGG analysis of CDKN1A-associated coexpression genes showed that CDKN1A was potentially involved in complement and coagulation cascades pathways in GBM. Finally, TISIDB database was used to investigate the role of CDKN1A in tumor-immune system interactions in GBM. These findings enhanced our understanding of the roles of CDKN1A in tumorigenesis and therapy response in GBM.

ROC-1, P21 and CAIX as markers of tumor aggressiveness in bladder carcinoma in Egyptian patients

BACKGROUND

Bladder cancer (BC) is one of the most common malignancies in Egypt, representing about 8.7% of cancers in both sexes with more predominance in males, making identification of valuable predictive and prognostic markers, mandatory. Cullin-RING ligases (CRL) play an important role in the ubiquitination of cell cycle-related proteins or other proteins (e.g., DNA replication protein, signal transduction protein). Regulator of Cullins-1 (ROC-1) is a key subunit of CRL. P21 belongs to the family of cyclin dependent kinase inhibitors (CKIs) which regulates cell cycle by inactivating Cyclin- Dependent Kinases key regulators of the cell cycle. CAIX a highly active member of the family of carbonic anhydrases has gained much interest as a hypoxic marker. Hypoxia is a consequence of the rapid growth of many tumors, including bladder cancer, and is an important regulator of gene expression and resistance to chemotherapy and radiotherapy. Therefore the purpose of this study is to evaluate the role of ROC-1, CAIX and P21 and its relationship with the clinico-pathological features of bladder cancer in Egyptian patients.

METHODS

Using the standard immunohistochemical technique, ROC-1, CAIX and P21 expression in 80 primary bladder carcinomas and 15 normal bladder specimens as control group were assessed. The bladder carcinoma cases included 50 cases with muscle invasive bladder cancer and 30 cases with non-muscle invasive bladder cancer.

RESULTS

Over expression of ROC-1, CAIX and P21 in BC were significantly associated with muscularis propria invasion and high grade BC. ROC-1, CAIX and P21, showed significant inverse relationship in primary BC cases. CAIX expression was significantly higher in BC compared with controls. Regarding the survival analysis, expression of ROC-1, CAIX and P21 didn't affect the survival of BC patients.

CONCLUSIONS

High expression of ROC-1, CAIX and P21 could be promising potential biomarkers for identifying patients with poor prognostic factors in bladder cancer serving as potential targets for cancer therapy.

The Multifaceted p21 (Cip1/Waf1/CDKN1A) in Cell Differentiation, Migration and Cancer Therapy

Loss of cell cycle control is characteristic of tumorigenesis. The protein p21 is the founding member of cyclin-dependent kinase inhibitors and an important versatile cell cycle protein. p21 is transcriptionally controlled by p53 and p53-independent pathways. Its expression is increased in response to various intra- and extracellular stimuli to arrest the cell cycle ensuring genomic stability. Apart from its roles in cell cycle regulation including mitosis, p21 is involved in differentiation, cell migration, cytoskeletal dynamics, apoptosis, transcription, DNA repair, reprogramming of induced pluripotent stem cells, autophagy and the onset of senescence. p21 acts either as a tumor suppressor or as an oncogene depending largely on the cellular context, its subcellular localization and posttranslational modifications. In the present review, we briefly mention the general functions of p21 and summarize its roles in differentiation, migration and invasion in detail. Finally, regarding its dual role as tumor suppressor and oncogene, we highlight the potential, difficulties and risks of using p21 as a biomarker as well as a therapeutic target.

Prognostic values of GMPS, PR, CD40, and p21 in ovarian cancer

Early detection and prediction of prognosis and treatment responses are all the keys in improving survival of ovarian cancer patients. This study profiled an ovarian cancer progression model to identify prognostic biomarkers for ovarian cancer patients. Mouse ovarian surface epithelial cells (MOSECs) can undergo spontaneous malignant transformation in vitro cell culture. These were used as a model of ovarian cancer progression for alterations in gene expression and signaling detected using the Illumina HiSeq2000 Next-Generation Sequencing platform and bioinformatical analyses. The differential expression of four selected genes was identified using the gene expression profiling interaction analysis (http://gepia.cancer-pku.cn/) and then associated with survival in ovarian cancer patients using the Cancer Genome Atlas dataset and the online Kaplan–Meier Plotter (http://www.kmplot.com) data. The data showed 263 aberrantly expressed genes, including 182 up-regulated and 81 down-regulated genes between the early and late stages of tumor progression in MOSECs. The bioinformatic data revealed four genes (i.e., guanosine 5′-monophosphate synthase (GMPS), progesterone receptor (PR), CD40, and p21 (cyclin-dependent kinase inhibitor 1A)) to play an important role in ovarian cancer progression. Furthermore, the Cancer Genome Atlas dataset validated the differential expression of these four genes, which were associated with prognosis in ovarian cancer patients. In conclusion, this study profiled differentially expressed genes using the ovarian cancer progression model and identified four (i.e., GMPS, PR, CD40, and p21) as prognostic markers for ovarian cancer patients. Future studies of prospective patients could further verify the clinical usefulness of this four-gene signature.

p21Waf1/Cip1: its paradoxical effect in the regulation of breast cancer

p21^Waf1/Cip1, the cyclin-dependent kinase (CDK) inhibitor belonging to the KIP/CIP family, was initially regarded as a tumor suppressor protein because it was recognized as the chief mediator of p53-dependent cell cycle arrest elicited by DNA damage. Conversely, it has been proposed that p21^Waf1/Cip1 may also function as an oncogene because it can inhibit apoptosis. Thus, p21^Waf1/Cip1 is regarded as a protein with a dual behavior, as its expression might cause potential benefits or dangerous effects in breast cancer. Consequently, careful planning is required in targeting p21^Waf1/Cip1 expression for therapy of breast cancer patients. This review illustrates the discovery and mechanisms of induction of p21^Waf1/Cip1. Then, we focus on elucidating the paradoxical effect of p21^Waf1/Cip1 expression on human breast carcinogenesis and explaining how the subcellular localization (nuclear or cytoplasmic) of p21^Waf1/Cip1 has an impact on both determining its fate as either cell-growth inhibitor or antiapoptotic molecule and, its effect on clinicopathological factors and prognosis of breast cancer patients. Moreover, we explore how the pattern of the p21^Waf1/Cip1 could affect the responsiveness of human breast cancer to chemotherapy. Furthermore, the pharmacological approaches to target p21^Waf1/Cip1 expression for therapy of breast cancer are clarified.

LincIN, a novel NF90-binding long non-coding RNA, is overexpressed in advanced breast tumors and involved in metastasis

BACKGROUND

Recent genome-wide profiling by sequencing and distinctive chromatin signatures has identified thousands of long non-coding RNA (lncRNA) species (>200 nt). LncRNAs have emerged as important regulators of gene expression, involving in both developmental and pathological processes. While altered expression of lncRNAs has been observed in breast cancer development, their roles in breast cancer progression and metastasis are still poorly understood.

METHODS

To identify novel breast cancer-associated lncRNA candidates, we employed a high-density SNP array-based approach to uncover intergenic lncRNA genes that are aberrantly expressed in breast cancer. We first evaluated the potential value as a breast cancer prognostic biomarker for one breast cancer-associated lncRNA, LincIN, using a breast cancer cohort retrieved from The Cancer Genome Atlas (TCGA) Data Portal. Then we characterized the role of LincIN in breast cancer progression and metastasis by in vitro invasion assay and a mouse tail vein injection metastasis model. To study the action of LincIN, we identified LincIN-interacting protein partner(s) by RNA pull-down experiments followed with protein identification by mass spectrometry.

RESULTS

High levels of LincIN expression are frequently observed in tumors compared to adjacent normal tissues, and are strongly associated with aggressive breast cancer. Importantly, analysis of TCGA data further suggest that high expression of LincIN is associated with poor overall survival in patients with breast cancer (P = 0.044 and P = 0.011 after adjustment for age). The functional experiments demonstrate that knockdown of LincIN inhibits tumor cell migration and invasion in vitro, which is supported by the results of transcriptome analysis in the LincIN-knockdown cells. Furthermore, knockdown of LincIN diminishes lung metastasis in a mouse tail vein injection model. We also identified a LincIN-binding protein, NF90, through which overexpression of LincIN may repress p21 protein expression by inhibiting its translation, and upregulation of p21 by LincIN knockdown may be associated with less aggressive metastasis phenotypes.

CONCLUSIONS

Our studies provide clear evidence to support LincIN as a new regulator of tumor progression-metastasis at both transcriptional and translational levels and as a promising prognostic biomarker for breast cancer.

Oncogenic role of p21 in hepatocarcinogenesis suggests a new treatment strategy

A well-known tumor suppressor, p21, acts paradoxically by promoting tumor growth in some cellular conditions. These conflicting functions have been demonstrated in association with the HBx gene and in hepatocarcinogenesis. The molecular behavior of p21 depends on its subcellular localization. Nuclear p21 may inhibit cell proliferation and be proapoptotic, while cytoplasmic p21 may have oncogenic and anti-apoptotic functions. Because most typical tumor suppressive proteins also have different effects according to subcellular localization, elucidating the regulatory mechanisms underlying nucleo-cytoplasmic transport of these proteins would be significant and may lead to a new strategy for anti-hepatocellular carcinoma (HCC) therapy. Chromosome region maintenance 1 (CRM1) is a major nuclear export receptor involved in transport of tumor suppressors from nucleus to cytoplasm. Expression of CRM1 is enhanced in a variety of malignancies and in vitro studies have shown the efficacy of specific inhibition of CRM1 against cancer cell lines. Interestingly, interferon may keep p21 in the nucleus; this is one of the mechanisms of its anti-hepatocarcinogenic function. Here we review the oncogenic property of p21, which depends on its subcellular localization, and discuss the rationale underlying a new strategy for HCC treatment and prevention.

Argonaute 2 and nasopharyngeal carcinoma: a genetic association study and functional analysis

Background

Argonaute 2 (AGO2), a central component of RNA-induced silencing complex, plays critical roles in cancer. We examined whether the single nucleotide polymorphisms (SNPs) of AGO2 were related to the risk of nasopharyngeal carcinoma (NPC).

Methods

Twenty-five tag SNPs within AGO2 were genotyped in Guangxi population consisting of 855 NPC patients and 1036 controls. The SNPs significantly associated with NPC were further replicated in Guangdong population consisting of 996 NPC patients and 972 controls. Functional experiments were conducted to examine the biologic roles of AGO2 in NPC.

Results

A significantly increased risk of advanced lymph node metastasis of NPC was identified for the AGO2 rs3928672 GA + AA genotype compared with GG genotype in both the Guangxi and Guangdong populations (combined odd ratio = 2.08, 95 % confidence interval = 1.44-3.01, P = 8.60 × 10⁻⁵). Moreover, the AGO2 protein expression levels of rs3928672 GA + AA genotype carriers were higher than the GG genotype carriers in the NPC tissues (P = 0.041), and AGO2 was significantly over-expressed in NPC tissues compared with non-cancerous nasopharyngeal tissues (P = 0.011). In addition, AGO2 knockdown reduced cell proliferation, induced apoptosis, and inhibited migration of NPC cells. Furthermore, gene expression microarray showed that genes altered following AGO2 knockdown were clustered in tumorigenesis and metastasis relevant pathways.

Conclusions

Our findings suggest that the genetic polymorphism in AGO2 may be a risk factor for the advanced lymph node metastasis of NPC in Chinese populations, and AGO2 acts as an oncogene in the development of NPC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1895-4) contains supplementary material, which is available to authorized users.

Expression of CDKN1A/p21 and TGFBR2 in breast cancer and their prognostic significance

BACKGROUND

A new diagnostic and prognostic biomarker may be of value in cancer diseases. Our study aimed to evaluate the CDKN1A/p21 and TGFBR2 level measurable in a cohort of patients with breast cancer after mastectomy, and to confirm their suitability to serve as prognostic biomarkers of the cancer.

METHODS

The expression levels of CDKN1A/p21 and TGFBR2 were detected by reverse transcription-PCR (RT-PCR), western blot assay and immunohistochemical staining for 65 primary tumor samples and paired adjacent noncancerous breast tissues. Their relations to clinicopathologic parameters and to the prognosis of patients with breast cancer were analyzed.

RESULTS

We found the mRNA and protein expression levels of CDKN1A/p21 were significantly upregulated in breast cancer tissues compared with adjacent nontumorous breast tissues. Increased CDKN1A/p21 expression showed a significant correlation with larger tumor size (P=0.014), higher tumor dedifferentiation grade (P=0.021), lymph node metastasis (P=0.019) and a shorter disease-free survival (P=0.044). Contrarily, the expression levels of TGFBR2 mRNA and protein were significantly decreased in breast cancer tissues compared with adjacent nontumorous breast tissues. Underexpression of TGFBR2 in breast cancer was correlated with larger tumor size (P=0.034), lymph node metastasis (P=0.039) and a shorter disease-free survival (P=0.035). Statistical analysis suggested that there was no significant association between CDKN1A/p21 and TGFBR2 expression.

CONCLUSIONS

in summary, our results suggested that high CDKN1A/p21 and low TGFBR2 expression was closely correlated with adverse pathological parameters and poor prognosis in breast cancer. Both CDKN1A/p21 and TGFBR2 are presented as possible candidates for breast cancer biomarkers.

Role of cannabinoid receptor CB2 in HER2 pro-oncogenic signaling in breast cancer

BACKGROUND

Pharmacological activation of cannabinoid receptors elicits antitumoral responses in different cancer models. However, the biological role of these receptors in tumor physio-pathology is still unknown.

METHODS

We analyzed CB2 cannabinoid receptor protein expression in two series of 166 and 483 breast tumor samples operated in the University Hospitals of Kiel, Tübingen, and Freiburg between 1997 and 2010 and CB2 mRNA expression in previously published DNA microarray datasets. The role of CB2 in oncogenesis was studied by generating a mouse line that expresses the human V-Erb-B2 Avian Erythroblastic Leukemia Viral Oncogene Homolog 2 (HER2) rat ortholog (neu) and lacks CB2 and by a variety of biochemical and cell biology approaches in human breast cancer cells in culture and in vivo, upon modulation of CB2 expression by si/shRNAs and overexpression plasmids. CB2-HER2 molecular interaction was studied by colocalization, coimmunoprecipitation, and proximity ligation assays. Statistical tests were two-sided.

RESULTS

We show an association between elevated CB2 expression in HER2+ breast tumors and poor patient prognosis (decreased overall survival, hazard ratio [HR] = 0.29, 95% confidence interval [CI] = 0.09 to 0.71, P = .009) and higher probability to suffer local recurrence (HR = 0.09, 95% CI = 0.049 to 0.54, P = .003) and to develop distant metastases (HR = 0.33, 95% CI = 0.13 to 0.75, P = .009). We also demonstrate that genetic inactivation of CB2 impairs tumor generation and progression in MMTV-neu mice. Moreover, we show that HER2 upregulates CB2 expression by activating the transcription factor ELK1 via the ERK cascade and that an increased CB2 expression activates the HER2 pro-oncogenic signaling at the level of the tyrosine kinase c-SRC. Finally, we show HER2 and CB2 form heteromers in cancer cells.

CONCLUSIONS

Our findings reveal an unprecedented role of CB2 as a pivotal regulator of HER2 pro-oncogenic signaling in breast cancer, and they suggest that CB2 may be a biomarker with prognostic value in these tumors.

Loss of p21Cip1/CDKN1A renders cancer cells susceptible to Polo-like kinase 1 inhibition

The deregulation of Polo-like kinase 1 is inversely linked to the prognosis of patients with diverse human tumors. Targeting Polo-like kinase 1 has been widely considered as one of the most promising strategies for molecular anticancer therapy. While the preclinical results are encouraging, the clinical outcomes are rather less inspiring by showing limited anticancer activity. It is thus of importance to identify molecules and mechanisms responsible for the sensitivity of Polo-like kinase 1 inhibition. We have recently shown that p21Cip1/CDKN1A is involved in the regulation of mitosis and its loss prolongs the mitotic duration accompanied by defects in chromosome segregation and cytokinesis in various tumor cells. In the present study, we demonstrate that p21 affects the efficacy of Polo-like kinase 1 inhibitors, especially Poloxin, a specific inhibitor of the unique Polo-box domain. Intriguingly, upon treatment with Polo-like kinase 1 inhibitors, p21 is increased in the cytoplasm, associated with anti-apoptosis, DNA repair and cell survival. By contrast, deficiency of p21 renders tumor cells more susceptible to Polo-like kinase 1 inhibition by showing a pronounced mitotic arrest, DNA damage and apoptosis. Furthermore, long-term treatment with Plk1 inhibitors induced fiercely the senescent state of tumor cells with functional p21. We suggest that the p21 status may be a useful biomarker for predicting the efficacy of Plk1 inhibition.

Synergistic anti-tumour effects of tetrandrine and chloroquine combination therapy in human cancer: a potential antagonistic role for p21

BACKGROUND AND PURPOSE

Tetrandrine, a bisbenzylisoquinoline alkaloid isolated from the Chinese medicinal herb Stephaniae tetrandrae, has a long history in Chinese clinical applications to treat diverse diseases. Tetrandrine induced apoptosis or, at low concentrations, autophagy of human hepatocellular carcinoma cells. Here we have tested the effects of inhibitors of autophagy such as chloroquine, on the response to low concentrations of tetrandrine in cancer cells.

EXPERIMENTAL APPROACH

Cultures of several cancer cell lines, including Huh7, U251, HCT116 and A549 cells, were exposed to tetrandrine, chloroquine or a combination of these compounds. Cell viability and content of reactive oxygen species (ROS) were measured and synergy assessed by calculation of the combination index. Western blot and RT-PCR assays were also used along with fluorescence microscopy and histochemical techniques.

KEY RESULTS

Combinations of tetrandrine and chloroquine were more cytotoxic than the same concentrations used separately and these effects showed synergy. Such effects involved increased ROS generation and were dependent on caspase-3 but independent of Akt activity. Blockade of tetrandrine-induced autophagy with 3-methyladenine or bafilomycin-A1 induced apoptosis in cancer cells. Lack of p21 protein (p21(-/-) HCT116 cells) increased sensitivity to the apoptotic effects of the combination of tetrandrine and chloroquine. In a tumour xenograft model in mice, combined treatment with tetrandrine and chloroquine induced ROS accumulation and cell apoptosis, and decreased tumour growth.

CONCLUSIONS AND IMPLICATIONS

The combinations of tetrandrine and chloroquine exhibited synergistic anti-tumour activity, in vitro and in vivo. Our results suggest a novel therapeutic strategy for tumour treatment.

The opposite prognostic significance of nuclear and cytoplasmic p21 expression in resectable gastric cancer patients

BACKGROUND

Protein p21(Cip1/Waf1) is a cyclin-dependent kinase inhibitor, which plays important roles in cell cycle arrest, senescence, and apoptosis. Interestingly, the nuclear and cytoplasmic p21 executes various functions in the cell. In this study, we investigated the prognostic impact of subcellular p21 expression in gastric cancer (GC).

METHODS

Expressions of subcellular p21 was assessed by immunohistochemistry using a tissue microarray in a training cohort and it went into a second testing cohort and finally to a validating cohort. Prognostic and predictive role of subcellular p21 expression status was evaluated. We also studied the roles of subcellular p21 in GC cell migration and invasion.

RESULTS

Nuclear and cytoplasmic p21 protein levels were significantly reduced and increased in GC lesions compared with adjacent non-cancerous tissues, respectively. Low nuclear p21 or high cytoplasmic p21 expression significantly correlated with shorter overall survival (OS), as well as with clinicopathologic characteristics in patients. Multivariate regression analysis showed that low nuclear and high cytoplasmic p21 expression, separately and together, were independent negative markers of OS. Finally, we found that nuclear p21 inhibits but cytoplasmic p21 promotes cell migration and invasion abilities.

CONCLUSIONS

These findings suggest that nuclear and cytoplasmic p21 protein expression in tumor are novel candidate prognostic markers in resectable human gastric carcinoma, and they exert distinct roles in cell migration and invasion.

A conditional mouse mutant in the tumor suppressor SdhD gene unveils a link between p21(WAF1/Cip1) induction and mitochondrial dysfunction

Mutations in mitochondrial complex II (MCII; succinate dehydrogenase, Sdh) genes cause familiar pheochromocytoma/paraganglioma tumors. Several mechanisms have been proposed to account for Sdh-mutation-induced tumorigenesis, the most accepted of which is based on the constitutive expression of the hypoxia-inducible factor 1α (Hif1α) at normal oxygen tension, a theory referred to as “pseudo-hypoxic drive”. Other molecular processes, such as oxidative stress, apoptosis, or chromatin remodeling have been also proposed to play a causative role. Nevertheless, the actual contribution of each of these mechanisms has not been definitively established. Moreover, the biological factors that determine the tissue-specificity of these tumors have not been identified. In this work, we made use of the inducible SDHD-ESR mouse, a conditional mutant in the SdhD gene, which encodes the small subunit of MCII, and that acts as a tumor suppressor gene in humans. The analysis of the Hif1α pathway in SDHD-ESR tissues and in two newly derived cell lines after complete SdhD loss -a requirement for hereditary paraganglioma type-1 tumor formation in humans- partially recapitulated the “pseudo-hypoxic” response and rendered inconsistent results. Therefore, we performed microarray analysis of adrenal medulla and kidney in order to identify other early gene expression changes elicited by SdhD deletion. Our results revealed that each mutant tissue displayed different variations in their gene expression profiles affecting to different biological processes. However, we found that the Cdkn1a gene was up-regulated in both tissues. This gene encodes the cyclin-dependent kinase inhibitor p21^WAF1/Cip1, a factor implicated in cell cycle, senescence, and cancer. The two SDHD-ESR cell lines also showed accumulation of this protein. This new and unprecedented evidence for a link between SdhD dysfunction and p21^WAF1/Cip1 will open new avenues for the study of the mechanisms that cause tumors in Sdh mutants. Finally, we discuss the actual role of Hif1α in tumorigenesis.

Progestin drives breast cancer growth by inducing p21(CIP1) expression through the assembly of a transcriptional complex among Stat3, progesterone receptor and ErbB-2

Cell cycle regulator p21(CIP1) has controversial biological effects in breast cancer since in spite of its role as cell cycle inhibitor and promoter of cellular senescence, it also induces cell proliferation and chemoteraphy resistance. We here explored the molecular mechanisms involved in progestin regulation of p21(CIP1) expression. We also investigated the biological effects of p21(CIP1) in breast cancer cells. We found that the synthetic progestin medroxyprogesterone acetate (MPA) upregulates p21(CIP1) protein expression via c-Src, signal transducer and activator of transcription 3 (Stat3) and ErbB-2 phosphorylation. Notably, we also found that ErbB-2 nuclear function plays a key role in MPA-induction of p21(CIP1) expression. Interestingly, we determined that progestin drives p21(CIP1) transcriptional activation via a novel nonclassical transcriptional mechanism in which progesterone receptor is recruited along with Stat3 and ErbB-2 to a Stat3 binding site at p21(CIP1) promoter. Our findings revealed that ErbB-2 functions as a coactivator of Stat3 in progestin induction of p21(CIP1) transcriptional activation. Furthermore, we demonstrated that blockage of p21(CIP1) expression strongly inhibited in vitro and in vivo progestin-induced breast cancer cell proliferation. These results further support the hypothesis that according to cell context and type of stimulus, p21(CIP1) is capable of inducing cell cycle progression. Moreover, we provided evidence that Stat3 and nuclear ErbB-2 are key players in progestin-induced p21(CIP1) regulation.

Cyclin-dependent kinase inhibitor p21(Waf1): contemporary view on its role in senescence and oncogenesis

p21(Waf1) was identified as a protein suppressing cyclin E/A-CDK2 activity and was originally considered as a negative regulator of the cell cycle and a tumor suppressor. It is now considered that p21(Waf1) has alternative functions, and the view of its role in cellular processes has begun to change. At present, p21(Waf1) is known to be involved in regulation of fundamental cellular programs: cell proliferation, differentiation, migration, senescence, and apoptosis. In fact, it not only exhibits antioncogenic, but also oncogenic properties. This review provides a contemporary understanding of the functions of p21(Waf1) depending on its intracellular localization. On one hand, when in the nucleus, it serves as a negative cell cycle regulator and tumor suppressor, in particular by participating in the launch of a senescence program. On the other hand, when p21(Waf1) is localized in the cytoplasm, it acts as an oncogene by regulating migration, apoptosis, and proliferation.

p21CIP1 mediates reciprocal switching between proliferation and invasion during metastasis

Cell proliferation and invasion are critical for malignant progression, yet how these processes relate to each other and whether they regulate one another during metastasis is unknown. We show that invasiveness of breast cancer cells is associated with growth arrest due to p21CIP1 upregulation. Knockdown of p21CIP1 increases cell proliferation and suppresses invasion. Since p21CIP1 acts to inhibit cyclin E during cell-cycle progression, we demonstrated that a constitutively active form of cyclin E had similar effects to p21CIP1 inhibition resulting in enhanced cell growth and suppressed invasiveness. We tested these findings in vivo in the Polyoma middle T mammary tumor model in which p21CIP1 was deleted. p21CIP1 knockout mice exhibited dramatic suppression of metastasis, independent of tumor growth, which was rescued by p21CIP1. Metastasis suppression by p21CIP1 ablation was associated with striking cytoskeletal reorganization leading to a non-invasive and highly proliferative state. Thus, p21CIP1 regulates metastasis by mediating reciprocal switching between invasion and proliferation.

Protein localization in disease and therapy

The eukaryotic cell is organized into membrane-covered compartments that are characterized by specific sets of proteins and biochemically distinct cellular processes. The appropriate subcellular localization of proteins is crucial because it provides the physiological context for their function. In this Commentary, we give a brief overview of the different mechanisms that are involved in protein trafficking and describe how aberrant localization of proteins contributes to the pathogenesis of many human diseases, such as metabolic, cardiovascular and neurodegenerative diseases, as well as cancer. Accordingly, modifying the disease-related subcellular mislocalization of proteins might be an attractive means of therapeutic intervention. In particular, cellular processes that link protein folding and cell signaling, as well as nuclear import and export, to the subcellular localization of proteins have been proposed as targets for therapeutic intervention. We discuss the concepts involved in the therapeutic restoration of disrupted physiological protein localization and therapeutic mislocalization as a strategy to inactivate disease-causing proteins.