miR-204 functions as a tumor suppressor by regulating SIX1 in NSCLC

The involvement of miR-204 in lung cancer development is unclear. In our study, we analyzed the expression of miR-204 in tumor- and adjacent-tissue samples from 141 patients with non-small cell lung cancer (NSCLC). MiR-204 expression was decreased in tumor samples compared with non-cancerous tissue-derived controls. Moreover, miR-204 expression negatively correlated with homeobox protein SIX1 expression, tumor size and metastasis. MiR-204 silencing in miR-204-positive NSCLC cell lines promoted cell invasion and proliferation. Concomitantly, MiR-204 overexpression resulted in reduced cell proliferation and invasion, upregulated E-cadherin and downregulated N-cadherin and Vimentin expression. SIX1 was identified as a potential target of miR-204, and SIX1 silencing partially compromised the invasive and proliferative capacity of miR-204-deficient cells. Thus, miR-204 may be involved in the NSCLC development.     

Yes-associated protein (YAP) functions as a tumor suppressor in breast

Yes-associated protein (YAP) has been shown to positively regulate p53 family members and to be negatively regulated by the AKT proto-oncogene product in promoting apoptosis. On the basis of this function and its location at 11q22.2, a site of frequent loss of heterozygosity (LOH) in breast cancer, we investigated whether YAP is a tumor suppressor in breast. Examination of tumors by immunohistochemistry demonstrated significant loss of YAP protein. LOH analysis revealed that protein loss correlates with specific deletion of the YAP gene locus. Functionally, short hairpin RNA knockdown of YAP in breast cell lines suppressed anoikis, increased migration and invasiveness, inhibited the response to taxol and enhanced tumor growth in nude mice. This is the first report indicating YAP as a tumor suppressor, revealing its decreased expression in breast cancer as well as demonstrating the functional implications of YAP loss in several aspects of cancer signaling.     

The growth and tumor suppressor NORE1A is a cytoskeletal protein that suppresses growth by inhibition of the ERK pathway

NORE1A is a growth and tumor suppressor that is inactivated in a variety of cancers. NORE1A has been shown to bind to the active Ras oncogene product. However, the mechanism of NORE1A-induced growth arrest and tumor suppression remains unknown. Using anchorage-independent growth assays, we mapped the NORE1A effector domain (the minimal region of the protein responsible for its growth-suppressive effects) to the fragment containing the central and Ras association domains of NORE1A (amino acids 191-363). Expression of the NORE1A effector domain in A549 lung adenocarcinoma cells resulted in the selective inhibition of signal transduction through the ERK pathway. The full-length NORE1A (416 amino acids) and its fragments capable of growth suppression were localized to centrosomes and microtubules in normal and transformed human cells in a Ras-independent manner. A mutant that was deficient in binding to centrosomes and microtubules was also deficient in inducing cell cycle arrest. This suggests that cytoskeletal localization is required for growth-suppressive effects of NORE1A. Ras binding function was required for growth-suppressive effects of the full-length NORE1A but not for the growth-suppressive effects of the effector domain. Our studies suggest that association of NORE1A with cytoskeletal elements is essential for NORE1A-induced growth suppression and that the ERK pathway is a target for NORE1A growth-suppressive activities.     

Zinc depletion suppresses tumor growth in mice

The hypothesis that in tumor-bearing animals an increase of host hepatic zinc metallothionein (Zn-MT) causes a restriction of zinc in the tumor tissue was studied. Three types of tumors were induced in laboratory mice by cell transplant. Tumor growth appears to be inhibited under zinc-deficient conditions, even in cases where zinc deficiency was started after tumor cell transplant. The survival times of tumor-bearing mice were prolonged by administration of cadmium chloride, which induces the synthesis of a combined zinc-cadmium metallothionein derivative in the host liver, but not in the tumor tissue, leading to an increase of hepatic zinc in the treated animals. The uptake of⁶⁵Zn by the liver of Cd-treated, tumor bearing mice was significantly higher than that of controls whereas uptake of⁶⁵Zn by tumor cells was significantly higher in controls than in the treated animals. These results suggest that restriction of zinc intake suppresses tumor growth.     

LKB1 tumor suppressor protein: PARtaker in cell polarity

The LKB1 (also called serine/threonine kinase 11) tumor suppressor gene was cloned in 1998 by linkage analysis of Peutz-Jeghers cancer syndrome patients. Mammalian LKB1 has been implicated as a regulator of multiple biological processes and signaling pathways, including the control of cell-cycle arrest, p53-mediated apoptosis, Wnt signaling, transforming growth factor (TGF)-beta signaling, ras-induced cell transformation, and energy metabolism. The Caenorhabditis elegans and Drosophila melanogaster LKB1 homologs, termed PAR4 and dLKB1, respectively, regulate cell polarity. Recently, mammalian LKB1 was found to be active only in a complex with two other proteins--STRAD and MO25--and to induce complete polarization of intestinal epithelial cells in a cell-autonomous fashion. In this article, we summarize the findings regarding LKB1 over the past six years. In addition, we discuss LKB1 in polarity in the context of both the other PAR proteins and its tumor suppressive activities.     

MiRNA-181b suppresses IGF-1R and functions as a tumor suppressor gene in gliomas

MicroRNAs (miRNAs) are single-stranded, 18- to 23-nt RNA molecules that function as regulators of gene expression. Previous studies have shown that microRNAs play important roles in human cancers, including gliomas. Here, we found that expression levels of miR-181b were decreased in gliomas, and we identified IGF-1R as a novel direct target of miR-181b. MiR-181b overexpression inhibited cell proliferation, migration, invasion, and tumorigenesis by targeting IGF-1R and its downstream signaling pathways, PI3K/AKT and MAPK/ERK1/2. Overexpression of IGF-1R rescued the inhibitory effects of miR-181b. In clinical specimens, IGF-1R was overexpressed, and its protein levels were inversely correlated with miR-181b expression. Taken together, our results indicate that miR-181b functions in gliomas to suppress growth by targeting the IGF-1R oncogene and that miR-181b may serve as a novel therapeutic target for gliomas.     

A novel role of hematopoietic CCL5 in promoting triple-negative mammary tumor progression by regulating generation of myeloid-derived suppressor cells

CCL5 is a member of the CC chemokine family expressed in a wide array of immune and non-immune cells in response to stress signals. CCL5 expression correlates with advanced human breast cancer. However, its functional significance and mode of action have not been established. Here, we show that CCL5-deficient mice are resistant to highly aggressive, triple-negative mammary tumor growth. Hematopoietic CCL5 is dominant in this phenotype. The absence of hematopoietic CCL5 causes aberrant generation of CD11b⁺/Gr-1⁺, myeloid-derived suppressor cells (MDSCs) in the bone marrow in response to tumor growth by accumulating Ly6C^hi and Ly6G⁺ MDSCs with impaired capacity to suppress cytotoxicity of CD8⁺ T cells. These properties of CCL5 are observed in both orthotopic and spontaneous mammary tumors. Antibody-mediated systemic blockade of CCL5 inhibits tumor progression and enhances the efficacy of therapeutic vaccination against non-immunogenic tumors. CCL5 also helps maintain the immunosuppressive capacity of human MDSCs. Our study uncovers a novel, chemokine-independent activity of the hematopoietically derived CCL5 that promotes mammary tumor progression via generating MDSCs in the bone marrow in cooperation with tumor-derived colony-stimulating factors. The study sheds considerable light on the interplay between the hematopoietic compartment and tumor niche. Because of the apparent dispensable nature of this molecule in normal physiology, CCL5 may represent an excellent therapeutic target in immunotherapy for breast cancer as well as a broad range of solid tumors that have significant amounts of MDSC infiltration.     

ATG1, an autophagy regulator, inhibits cell growth by negatively regulating S6 kinase

It has been proposed that cell growth and autophagy are coordinated in response to cellular nutrient status, but the relationship between them is not fully understood. Here, we have characterized the fly mutants of Autophagy-specific gene 1 (ATG1), an autophagy-regulating kinase, and found that ATG1 is a negative regulator of the target of rapamycin (TOR)/S6 kinase (S6K) pathway. Our Drosophila studies have shown that ATG1 inhibits TOR/S6K-dependent cell growth and development by interfering with S6K activation. Consistently, overexpression of ATG1 in mammalian cells also markedly inhibits S6K in a kinase activity-dependent manner, and short interfering RNA-mediated knockdown of ATG1 induces ectopic activation of S6K and S6 phosphorylation. Moreover, we demonstrated that ATG1 specifically inhibits S6K activity by blocking phosphorylation of S6K at Thr 389. Taken together, our genetic and biochemical results strongly indicate crosstalk between autophagy and cell growth regulation.     

Retinoblastoma tumor suppressor functions shared by stem cell and cancer cell strategies

Carcinogenic transformation of somatic cells resembles nuclear reprogramming toward the generation of pluripotent stem cells.These events share eternal escape from cellular senescence,continuous self-renewal in limited but certain population of cells,and refractoriness to terminal differentiation while maintaining the potential to differentiate into cells of one or multiple lineages.As represented by several oncogenes those appeared to be first keys to pluripotency,carcinogenesis and nuclear reprogramming seem to share a number of core mechanisms.The retinoblastoma tumor suppressor product retinoblastoma(RB)seems to be critically involved in both events in highly complicated manners.However,disentangling such complicated interactions has enabled us to better understand how stem cell strategies are shared by cancer cells.This review covers recent findings on RB functions related to stem cells and stem cell-like behaviors of cancer cells.     

ATP/P2X7 axis modulates myeloid-derived suppressor cell functions in neuroblastoma microenvironment

Tumor microenvironment of solid tumors is characterized by a strikingly high concentration of adenosine and ATP. Physiological significance of this biochemical feature is unknown, but it has been suggested that it may affect infiltrating immune cell responses and tumor progression. There is increasing awareness that many of the effects of extracellular ATP on tumor and inflammatory cells are mediated by the P2X7 receptor (P2X7R). Aim of this study was to investigate whether: (i) extracellular ATP is a component of neuroblastoma (NB) microenvironment, (ii) myeloid-derived suppressor cells (MDSCs) express functional P2X7R and (iii) the ATP/P2X7R axis modulates MDSC functions. Our results show that extracellular ATP was detected in NB microenvironment in amounts that increased in parallel with tumor progression. The percentage of CD11b⁺/Gr-1⁺ cells was higher in NB-bearing mice compared with healthy animals. Within the CD11b/Gr-1⁺ population, monocytic MDSCs (M-MDSCs) produced higher levels of reactive oxygen species (ROS), arginase-1 (ARG-1), transforming growth factor-β1 (TGF-β1) and stimulated more potently in vivo tumor growth, as compared with granulocytic MDSCs (G-MDSCs). P2X7R of M-MDSCs was localized at the plasma membrane, coupled to increased functionality, upregulation of ARG-1, TGF-β1 and ROS. Quite surprisingly, the P2X7R in primary MDSCs as well as in the MSC-1 and MSC-2 lines was uncoupled from cytotoxicity. This study describes a novel scenario in which MDSC immunosuppressive functions are modulated by the ATP-enriched tumor microenvironment.     

抑制小鼠乳腺肿瘤转移 microRNA 的筛选

目的：鉴定25种microRNA的功能及其在乳腺癌中发挥的作用,以筛选新的抑制乳腺癌转移的microRNA分子。方法利用脂质体2000将25种鼠源microRNA表达载体转染至4TO7细胞,经G418筛选结合流式细胞仪分选获绿色荧光细胞得稳定表达鼠源microRNA 的细胞株。将细胞2＆#215;105个/只尾静脉注射接种于BALB/C小鼠,14 d后解剖分离肺组织,统计小鼠肺组织结节数目。结果和接种阴性对照细胞小鼠相比,接种mir-449a稳转细胞的小鼠肿瘤肺转移减少。而接种 mir-1935稳转细胞的小鼠肿瘤肺转移增多。其它23种microRNA稳转细胞接种小鼠肿瘤肺转移既不增加也不减少。结论从25种鼠源microRNA中筛选到2种与乳腺癌肿瘤转移相关的microRNA：mir-449a抑制乳腺癌细胞肺转移,mir-1935则促进癌细胞肺转移。     

P42 Ebp1 functions as a tumor suppressor in non-small cell lung cancer

Although the short isoform of ErbB3-binding protein 1 (Ebp1), p42 has been considered to be a potent tumor suppressor in a number of human cancers, whether p42 suppresses tumorigenesis of lung cancer cells has never been clarified. In the current study we investigated the tumor suppressor role of p42 in non-small cell lung cancer cells. Our data suggest that the expression level of p42 is inversely correlated with the cancerous properties of NSCLC cells and that ectopic expression of p42 is sufficient to inhibit cell proliferation, anchorage-independent growth, and invasion as well as tumor growth in vivo. Interestingly, p42 suppresses Akt activation and overexpression of a constitutively active form of Akt restores the tumorigenic activity of A549 cells that is ablated by exogenous p42 expression. Thus, we propose that p42 Ebp1 functions as a potent tumor suppressor of NSCLC through interruption of Akt signaling. [BMB Reports 2015; 48(3): 159-165]     

Novel mechanism for negatively regulating Rho-kinase (ROCK) signaling through Coronin1B protein in neuregulin 1 (NRG-1)-induced tumor cell motility

Although many mechanisms that activate ROCK are known, corresponding negative regulatory mechanisms required for cytoskeletal plasticity are poorly understood. We have discovered that Coronin1B is a novel attenuator of ROCK signaling. We initially identified Coronin1A in a proteomics screen for ROCK2-binding proteins, and here we demonstrate that Coronin1A/B bind directly to ROCK2 through its PH (Pleckstrin Homology) domain. The consequence of the ROCK2-Coronin1B interaction was tested and revealed that increased expression of Coronin1B inhibited, whereas knockdown of Coronin1B stimulated, phosphorylation of the ROCK substrate myosin light chain phosphatase and subsequently, myosin light chain. Thus, Coronin1B is a previously unrecognized inhibitor of ROCK signaling to myosin. Furthermore, we found that the phosphatase Slingshot IL (SSH1L) was required for Coronin1B to inhibit ROCK signaling. To test the significance of this novel mechanism in tumor cell motility, we investigated its role in neuregulin 1 (NRG-1)-induced cell scattering. Importantly, we found that attenuation of the ROCK signaling by Coronin1B was required for NRG-1 stimulated scattering. Our data support a model in which Coronin1B fine-tunes ROCK signaling to modulate myosin activity, which is important for tumor cell motility.     

MiR-142-3p functions as a tumor suppressor by targeting RAC1/PAK1 pathway in breast cancer

MicroRNA-142-3p (miR-142-3p) was previously investigated in various cancers, whereas, it's role in breast cancer (BC) remains far from understood. In this study, we found that miR-142-3p was markedly decreased both in cell lines and BC tumor tissues. Elevated miR-142-3p expression suppressed growth and metastasis of BC cell lines via gain-of-function assay in vitro and in vivo. Mechanistically, miR-142-3p could regulate the ras-related C3 botulinum toxin substrate 1 (RAC1) expression in protein level, which simultaneously suppressed the epithelial-to-mesenchymal transition related protein levels and the activity of PAK1 phosphorylation, respectively. In addition, rescue experiments revealed RAC1 overexpression could reverse tumor-suppressive role of miR-142-3p. Our results showed miR-142-3p could function as a tumor suppressor via targeting RAC1/PAK1 pathway in BC, suggesting a potent therapeutic target for BC treatment.     

53BP1 cooperates with p53 and functions as a haploinsufficient tumor suppressor in mice

p53 binding protein 1 (53BP1) is a putative DNA damage sensor that accumulates at sites of double-strand breaks (DSBs) in a manner dependent on histone H2AX. Here we show that the loss of one or both copies of 53BP1 greatly accelerates lymphomagenesis in a p53-null background, suggesting that 53BP1 and p53 cooperate in tumor suppression. A subset of 53BP1-/- p53-/- lymphomas, like those in H2AX-/- p53-/- mice, were diploid and harbored clonal translocations involving antigen receptor loci, indicating misrepair of DSBs during V(D)J recombination as one cause of oncogenic transformation. Loss of a single 53BP1 allele compromised genomic stability and DSB repair, which could explain the susceptibility of 53BP1+/- mice to tumorigenesis. In addition to structural aberrations, there were high rates of chromosomal missegregation and accumulation of aneuploid cells in 53BP1-/- p53+/+ and 53BP1-/- p53-/- tumors as well as in primary 53BP1-/- splenocytes. We conclude that 53BP1 functions as a dosage-dependent caretaker that promotes genomic stability by a mechanism that preserves chromosome structure and number.