Expression and clinicopathological significance of lipin-1 in human breast cancer and its association with p53 tumor suppressor gene

Breast cancer (BC) is an important cause of female cancer-related death. It has recently been demonstrated that metabolic disorders including lipid metabolism are a hallmark of cancer cells. Lipin-1 is an enzyme that displays phosphatidate phosphatase activity and regulates the rate-limiting step in the pathway of triglycerides and phospholipids synthesis. The objective of this study was to evaluate lipin-1 expression, its prognostic significance, and its correlation with p53 tumor suppressor in patients with BC. In this study, 55 pairs of fresh samples of BC and adjacent noncancerous tissue were used to analyze lipin-1, using quantitative real-time polymerase chain reaction and immunohistochemistry (IHC) staining. The expression of other clinicopathological variables and p53 was also examined using IHC technique. The cell migration was studied in MCF-7 and MDA-MB231 cells following the inhibition of lipin-1 by propranolol. Our results show that the relative expression of lipin-1 messenger RNA was significantly higher in BC tissues compared with the adjacent normal tissue and its inhibition reduced cell migration in cancer cells. This upregulation was negatively correlated with histological grade of tumor and p53 status (p = .001 and p = .034) respectively and positively correlated with the tumor size (p = .006). Our results also seem to indicate that the high lipin-1 expression is related to a good prognosis in patients with BC. The expression of lipin-1 may be considered as a novel independent prognostic factor. The inhibition of lipin-1 may also have therapeutic significance for patients with BC. The correlation between lipin-1 and p53 confirms the role of p53 in the regulation of lipid metabolism in cancer cells.     

Generation of two modified mouse alleles of the Hic1 tumor suppressor gene

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene located on chromosome 17p13.3, a region frequently hypermethylated or deleted in human neoplasias. In mouse, Hic1 is essential for embryonic development and exerts an antitumor role in adult animals. Since Hic1-deficient mice die perinatally, we generated a conditional Hic1 null allele by flanking the Hic1-coding region by loxP sites. When crossed to animals expressing Cre recombinase in a cell-specific manner, the Hic1 conditional mice will provide new insights into the function of Hic1 in developing and mature tissues. Additionally, we used gene targeting to replace sequence-encoding amino acids 186-893 of Hic1 by citrine fluorescent protein cDNA. We demonstrate that the distribution of Hic1-citrine fusion polypeptide corresponds to the expression pattern of wild-type Hic1. Consequently, Hic1-citrine "reporter" mice can be used to monitor the activity of the Hic1 locus using citrine fluorescence.     

The tumor suppressor LKB1 induces p21 expression in collaboration with LMO4, GATA-6, and Ldb1

The LKB1/STK11 serine/threonine kinase is mutated in Peutz-Jeghers syndrome and various sporadic cancers such as lung adenocarcinoma. We show here that LKB1 forms a complex with LMO4, GATA-6, and Ldb1, and enhances GATA-mediated transactivation in a kinase-dependent manner. We further demonstrate that LKB1 has the potential to induce p21 expression in collaboration with LMO4, GATA-6, and Ldb1 through the p53-independent mechanism. Our findings suggest that LKB1 regulates GATA-mediated gene expression and that this activity of LKB1 may be important for its tumor suppressor function.     

Next generation sequencing demonstrates association between tumor suppressor gene aberrations and poor outcome in patients with cancer

Next generation sequencing is transforming patient care by allowing physicians to customize and match treatment to their patients’ tumor alterations. Our goal was to study the association between key molecular alterations and outcome parameters. We evaluated the characteristics and outcomes (overall survival (OS), time to metastasis/recurrence, and best progression-free survival (PFS)) of 392 patients for whom next generation sequencing (182 or 236 genes) had been performed. The Kaplan-Meier method and Cox regression models were used for our analysis, and results were subjected to internal validation using a resampling method (bootstrap analysis). In a multivariable analysis (Cox regression model), the parameters that were statistically associated with a poorer overall survival were the presence of metastases at diagnosis (P = 0.014), gastrointestinal histology (P < 0.0001), PTEN (P < 0.0001), and CDKN2A alterations (P = 0.0001). The variables associated with a shorter time to metastases/recurrence were gastrointestinal histology (P = 0.004), APC (P = 0.008), PTEN (P = 0.026) and TP53 (P = 0.044) alterations. TP53 (P = 0.003) and PTEN (P = 0.034) alterations were independent predictors of a shorter best PFS. A personalized treatment approach (matching the molecular aberration with a cognate targeted drug) also correlated with a longer best PFS (P = 0.046). Our study demonstrated that, across diverse cancers, anomalies in specific tumor suppressor genes (PTEN, CDKN2A, APC, and/or TP53) were independently associated with a worse outcome, as reflected by time to metastases/recurrence, best PFS on treatment, and/or overall survival. These observations suggest that molecular diagnostic tests may provide important prognostic information in patients with cancer.     

Tumor suppressor and aging biomarker p16(INK4a) induces cellular senescence without the associated inflammatory secretory phenotype

Cellular senescence suppresses cancer by preventing the proliferation of cells that experience potentially oncogenic stimuli. Senescent cells often express p16(INK4a), a cyclin-dependent kinase inhibitor, tumor suppressor, and biomarker of aging, which renders the senescence growth arrest irreversible. Senescent cells also acquire a complex phenotype that includes the secretion of many cytokines, growth factors, and proteases, termed a senescence-associated secretory phenotype (SASP). The SASP is proposed to underlie age-related pathologies, including, ironically, late life cancer. Here, we show that ectopic expression of p16(INK4a) and another cyclin-dependent kinase inhibitor, p21(CIP1/WAF1), induces senescence without a SASP, even though they induced other features of senescence, including a stable growth arrest. Additionally, human fibroblasts induced to senesce by ionizing radiation or oncogenic RAS developed a SASP regardless of whether they expressed p16(INK4a). Cells induced to senesce by ectopic p16(INK4a) expression lacked paracrine activity on epithelial cells, consistent with the absence of a functional SASP. Nonetheless, expression of p16(INK4a) by cells undergoing replicative senescence limited the accumulation of DNA damage and premature cytokine secretion, suggesting an indirect role for p16(INK4a) in suppressing the SASP. These findings suggest that p16(INK4a)-positive cells may not always harbor a SASP in vivo and, furthermore, that the SASP is not a consequence of p16(INK4a) activation or senescence per se, but rather is a damage response that is separable from the growth arrest.     

p53 Activates the Long Noncoding RNA Pvt1b to Inhibit Myc and Suppress Tumorigenesis

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Simultaneous haploinsufficiency of Pten and Trp53 tumor suppressor genes accelerates tumorigenesis in a mouse model of prostate cancer

Tumor suppressor gene PTEN is important in the initiation and progression of human prostate carcinoma, whereas the role of TP53 remains controversial. Since Pten/Trp53 double conditional knockout mice show earlier onset and fast progression of prostate cancer when compared to Pten knockout mice, we asked whether heterozygosity of these two tumor suppressor genes was sufficient to accelerate prostatic tumorigenesis. To answer this question we examined prostatic lesion progression of Pten/Trp53 double heterozygous mice and a series of controls such as Pten heterozygous, Pten conditional knockout, Trp53 heterozygous and Trp53 knockout mice. Tissue recombination of adult prostatic epithelium coupled with embryonic rat seminal vesicle mesenchyme was used as a tool to stimulate prostatic epithelial proliferation. In our study, high-grade prostatic intraepithelial neoplasia (PIN) was found with high frequency at 8 weeks post-tissue recombination transplantation. PIN lesions in Pten/Trp53 double heterozygous mice were more severe than those seen in Pten heterozygous alone. Furthermore, morphologic features attributable to Pten or Trp53 loss appeared to be enhanced in double heterozygous tissues. LOH analysis of Pten and Trp53 in genomic DNA collected from high-grade PIN lesions in Pten heterozygous and Pten/Trp53 double heterozygous mice showed an intact wild-type allele for both genes in all samples examined. In conclusion, simultaneous heterozygosity of Pten and Trp53 accelerates prostatic tumorigenesis in this mouse model of prostate cancer independently of loss of heterozygosity of either gene.     

Structural characterization of inhibitor complexes with checkpoint kinase 2 (Chk2), a drug target for cancer therapy

Chk2 (checkpoint kinase 2) is a serine/threonine kinase that participates in a series of signaling networks responsible for maintaining genomic integrity and responding to DNA damage. The development of selective Chk2 inhibitors has recently attracted much interest as a means of sensitizing cancer cells to current DNA-damaging agents used in the treatment of cancer. Additionally, selective Chk2 inhibitors may reduce p53-mediated apoptosis in normal tissues, thereby helping to mitigate adverse side effects from chemotherapy and radiation. Thus far, relatively few selective inhibitors of Chk2 have been described and none have yet progressed into clinical trials. Here, we report crystal structures of the catalytic domain of Chk2 in complex with a novel series of potent and selective small molecule inhibitors. These compounds exhibit nanomolar potencies and are selective for Chk2 over Chk1. The structures reported here elucidate the binding modes of these inhibitors to Chk2 and provide information that can be exploited for the structure-assisted design of novel chemotherapeutics.