Neoplastic transformation and defective control of cell proliferation and differentiation

The control of proliferation of nontransformed 3T3 t-proadipocytes in vitro can be mediated at three states in the G1 phase of the cell cycle. These states are induced by the commitment of cells to differentiate (GD); by growth factor deprivation at low density or "contact inhibition" at high density (Gs); and by nutrient deprivation (GN). To determine if neoplastic transformation of proadipocytes is associated with a selective defect in one or more of these G1 growth arrest processes, we developed and studied eight cloned and several noncloned tumorigenic proadipocyte cell lines. We report that all transformed proadipocyte cell lines are tumorigenic and all lack the ability to arrest at GD and differentiate. By contrast, or approximately 90% of transformed proadipocyte cell lines retain their ability to growth arrest at Gs at low density when deprived of growth factors, and or approximately 90% growth arrest at GN when deprived of nutrients. These observations suggest that neoplastic transformation of proadipocytes is primarily associated with abrogation of growth control mediated at GD. However, whereas most transformed proadipocytes arrest at Gs at low density when deprived of serum, all transformed proadipocyte cell lines do not efficiently arrest at Gs at high density due to "contact inhibition." This suggests that neoplastic transformation of proadipocytes results from a primary defect in growth control mediated at GD and from an additional defect at Gs. These results are discussed with respect to their possible significance for the biological mechanisms of the initiation and promotion of carcinogenesis.     

Melatonin decreases cell proliferation and transformation in a melatonin receptor-dependent manner

There are conflicting claims for the role of melatonin in oncogenesis. In addition, the mechanism(s) underlying melatonin's effects in oncogenic processes is (are) unknown. In this study, the effects of melatonin exposure on cell proliferation and transformation were assessed in NIH3T3 cells transfected with either the human mt(1) (NIH-mt1) or MT(2) (NIH-MT2) melatonin receptors. The effects of melatonin exposure on proliferation was assessed by direct cell counts and [(3)H]thymidine uptake assays. The effect of chronic melatonin pretreatment on transformation was assessed by focus assays. In both NIH-mt1 and NIH-MT2 cells, melatonin pretreatment decreased cell proliferation and transformation. Control (NIH-neo) cells did not show this effect. However, as revealed by the [(3)H]thymidine uptake assays, an increase in DNA synthesis occurred in NIH-mt1 cells, whereas no increase occurred in the NIH-MT2 or NIH-neo cells. Upon examination of melatonin receptors, a decrease in the function of both mt(1) and MT(2) receptors occurred. These data suggest that perhaps an attenuation of receptor-mediated processes are involved in the anti-proliferative and anti-transformation capabilities of melatonin in NIH3T3 cells. In addition, based on the [(3)H]thymidine assays, receptor mediated signal transduction mechanisms may slow the growth of cells via actions on the cell cycle. The results from this study shed new insight on the putative mechanisms underlying melatonin's effects on cell proliferation and transformation and lends support for a protective role of melatonin in oncogenesis.     

The shed ectodomain of Nr-CAM stimulates cell proliferation and motility, and confers cell transformation

Nr-CAM, a cell-cell adhesion molecule of the immunoglobulin-like cell adhesion molecule family, known for its function in neuronal outgrowth and guidance, was recently identified as a target gene of beta-catenin signaling in human melanoma and colon carcinoma cells and tissue. Retrovirally mediated transduction of Nr-CAM into fibroblasts induces cell motility and tumorigenesis. We investigated the mechanisms by which Nr-CAM can confer properties related to tumor cell behavior and found that Nr-CAM expression in NIH3T3 cells protects cells from apoptosis in the absence of serum by constitutively activating the extracellular signal-regulated kinase and AKT signaling pathways. We detected a metalloprotease-mediated shedding of Nr-CAM into the culture medium of cells transfected with Nr-CAM, and of endogenous Nr-CAM in B16 melanoma cells. Conditioned medium and purified Nr-CAM-Fc fusion protein both enhanced cell motility, proliferation, and extracellular signal-regulated kinase and AKT activation. Moreover, Nr-CAM was found in complex with alpha4beta1 integrins in melanoma cells, indicating that it can mediate, in addition to homophilic cell-cell adhesion, heterophilic adhesion with extracellular matrix receptors. Suppression of Nr-CAM levels by small interfering RNA in B16 melanoma inhibited the adhesive and tumorigenic capacities of these cells. Stable expression of the Nr-CAM ectodomain in NIH3T3 cells conferred cell transformation and tumorigenesis in mice, suggesting that the metalloprotease-mediated shedding of Nr-CAM is a principal route for promoting oncogenesis by Nr-CAM.     

Ectopic expression of methionine aminopeptidase-2 causes cell transformation and stimulates proliferation

Methionine aminopeptidase-2 (MetAP2) processes N-terminal methionine from nascent cellular proteins. Inhibition of MetAP2 has been shown to block angiogenesis and suppress tumor growth in preclinical tumor models. However, the biological role of MetAP2 in cancer is not well understood. We examined the effect of three distinct chemical classes of MetAP2 inhibitors on the growth of a panel of human cancer cells in vitro. All MetAP2 inhibitors caused inhibition of tumor cell growth in both anchorage-dependent and, particularly, in anchorage-independent manner. These data prompted us to examine the possible roles of MetAP2 in cancers. Ectopic expression of MetAP2 in NIH-3T3 cells caused transformation, evidenced by the formation of foci in monolayer culture and growth of large colonies in soft agar. Overexpression of MetAP2 in an immortalized bronchial epithelial cell line NL20 accelerated growth. These phenotypes induced by the overexpression of MetAP2 were reversed by the treatment with MetAP2 inhibitors, indicating that the catalytic function of MetAP2 was essential. Accordingly, overexpression of a catalytically inactive MetAP2 resulted in growth retardation of HT1080 tumor cells, suggesting a dominant-negative role of the inactive MetAP2 mutant. Finally, we analysed the expression of MetAP2 in patient cancer samples by immunohistochemistry. Moderate-to-high staining was identified in the majority of breast, colon, lung, ovarian and prostate carcinomas examined. These data suggest that MetAP2 plays an important role in tumor cell growth and may contribute to tumorigenesis.     

人支气管上皮细胞转化过程中凋亡与增殖的改变

目的 观察凋亡、增殖在人支气管上皮细胞转化中的改变,探讨其有关机理。方法 使用末端脱氧核苷酰转移酶标记凋亡法（ＴＤＴ）、Ｂｒｄｕ掺入法、Ｗｅｓｔｅｒｎ ｂｌｏｔｔｉｎｇ、荧光原位杂交等方法。结果 人永生化支气管上皮细胞Ｙ在无血清培养基连续转代过程中,晚代细胞软琼脂克隆形成率显著增高,并对血清分化产生明显抗性,对表皮生长因子（ＥＧＦ）依赖性有减弱倾向,细胞增殖速度明显加快,顺铂诱导的凋亡发生率显著低     

食管鳞癌组织AIB1与Ki-67表达相关性研究

目的:探讨食管鳞癌组织AIB1的表达水平及其与Ki-67的相关性.方法:用免疫组织化学SP方法,联合检测20例正常食管鳞状上皮组织和60例食管鳞癌组织中AIB1和Ki-67的表达,分析AIB1的表达与临床病理参数的关系以及与Ki-67的相关性.结果:20例正常食管鳞状上皮组织中呈微弱表达或不表达,60例食管鳞癌组织中有25例(41.6％)为AIB1高表达,P＜0.05.AIB1的表达水平与临床分期、淋巴结转移有明显相关性;在T3～T4期的表达水平高于T1～T2期(P＜0.05),在有淋巴结转移的组织中表达较高(P＜0.05),而其在不同性别、年龄、病理学分型中的表达差异无统计学意义,P＞0.05;Ki-67蛋白在食管鳞状细胞癌中的表达为65.0％(39/60),在39例Ki-67蛋白阳性表达的食管鳞癌组织中有29例同时表达AIB1,且其中25例AIB1过表达,AIB1与Ki-67的表达呈中度正相关,P＜0.01.结论:AIB1蛋白与食管鳞癌的临床分期和淋巴结转移有相关性,Ki-67可能也是AIB1蛋白非类固醇激素受体途径的相关蛋白之一.     

Induced type-B reticulum cell neoplasia in mice III. The importance of T-cell proliferation and cellular relocation in accessory cell transformation

After the transfer of spleen cells from old CBA/T6T6 mice (greater than 75 weeks) into young syngeneic CBA/Ca recipients there usually follows a selective expansion of the donor T-cell population and the emergence of type B reticulum cell neoplasms (RCN-B), also of donor origin though probably derived not from the T-cells but from lymphoid dendritic accessory cells. As few as one million injected cells led to significant donor T-cell hyperplasia and tumour induction. Injection of cells from young donors did not have such consequences. Similar tumours were induced by transferring syngeneic cells in both C57BL and DBA/2 mice, although in the latter strain there was no requirement for the injected cells to derive from old donors. It appeared that T-cell proliferation was independent of donor accessory cells or RCN-B induction, since injection of enriched T-cells led to few tumours, although the T-cell chimaerism was indistinguishable from that in recipients of unseparated spleen cells. Development of tumours, however, seemed to be dependent upon stimulated T-cells. Recipients of spleen cells from old T-cell-deprived mice did not develop tumours; conversely, tumours, mostly of donor origin, were induced in recipients of young syngeneic cells when an extrinsic stimulus to T-cell proliferation was provided by continued allostimulation. The apparent selectivity of tumorigenesis for donor cells has led to the proposal that cellular relocation, as a result of transfer, may be an important predisposing factor in malignant transformation in circumstances of T-cell stimulation provided by antigenic challenge or by transfer of T-cells from old donors.     

转谷氨酰胺酶与肿瘤

转谷氨酰胺酶是一组催化调控蛋白质多肽分子交联过程的酶系,目前已知的人类转谷氨酰胺酶系包括9种异构酶,分别分布于人体的不同组织,发挥不同的生理作用。转谷氨酰胺酶在各组织中表达水平及活性的高低的改变,可能影响到细胞周期、细胞分化、细胞凋亡、信号传导、细胞黏附以及肿瘤生长和转移等诸多肿瘤病理学机制的运行。     

Enforced expression of RASAL1 suppresses cell proliferation and the transformation ability of gastric cancer cells

RAS protein activator like 1 (RASAL1) is a member of the RAS GTPase-activating protein (GAP) family, and it is an important molecule in the regulation of RAS activation. In the present study, we investigated the role of RASAL1 in gastric carcinogenesis. Decreased expression pattern of RASAL1 in gastric cancer tissues and cell lines was found in protein and RNA levels, although there was no statistically significant relationship between RASAL1 and clinicopathological features. Restored expression of RASAL1 induced by DNA methylation inhibitor 5-aza-2'-deoxycytidine (5'-AZA) and HDAC inhibitor trichostatin A (TSA) implied that RASAL1 expression is regulated by epigenetic mechanisms. The biological role of RASAL1 in gastric carcinogenesis was determined by in?vitro tumorigenicity assays. Overexpression of RASAL1 showed suppression of cell proliferation due to cell apoptosis. Subsequently, enforced expression of RASAL1 repressed significantly the gastric cancer cell transformation ability. These findings demonstrated that decreased RASAL1 expression is a characteristic of gastric cancer and regulated by epigenetic mechanisms. RASAL1 may be a functional tumor suppressor involved in gastric cancer. This study provides novel insights into the biological role of RASAL1 in gastric carcinogenesis.     

Synthesis,maturation and extracellular release of procathepsin D as influenced by cell proliferation or transformation

The relationship between cell growth and intra- and extracellular accumulation of cathepsin D (CD), a lysosomal endopepti-dase involved in cell protein breakdown, was examined in cultures of normal and transformed BALB/c mouse 3T3 fibro-blasts grown at various cell densities. In crowded cultures of normal 3T3 cells (doubling time, Td, 53 hr) intracellular CD activity was 2–fold higher than in sparse, rapidly-growing (Td, 27 hr) cultures. In uncrowded (Td, 18 hr) and crowded (Td, 32 hr) cultures of benzo[a]pyrene-transformed cells intracellular CD levels were one third and two thirds, respectively, of those measured in hyperconfluent 3T3 cultures. Regardless of cell density, SV-40–virus-transformed cells (Td, 12 hr) contained one third of CD levels found in hyperconfluent 3T3 cells. Both transformed cell lines released into the medium a higher proportion of CD, compared with their untransformed counterpart, yet the amount secreted was not sufficient to account for the reduced intracellular level of the enzyme. Serum withdrawal induced a marked increase of both intra- and extracellular levels of CD activity. In both normal and virally or chemically transformed 3T3 cells CD comprised a precursor (52 kDa) and processed mature polypeptides; the latter were mostly represented by a 48–kDa peptide, but a minor part was in a double-chain form (31 and 16 kDa respectively). The proportion of mature enzyme vs. precursor was much higher in confluent, slowly-growing cells than in fast-growing cells, whether normal or transformed. In the latter, conversion of mature 48–kDa peptide into the double-chain form occurred more efficiently. © 1995 Wiley-Liss, Inc.     

CDK2调控ALDH1A3介导原神经-间质转化促进胶质瘤干细胞增殖的机制研究

目的:研究细胞周期蛋白依赖性激酶2(CDK2)促进胶质瘤干细胞(GSCs)增殖和诱导原神经-间质转化的作用机制.方法:利用生物信息学方法对GSCs中CDK2的表达水平进行分析,并利用shRNA沉默CDK2的表达以探究其促进GSCs增殖的作用;建立GSCs原神经-间质转换(PMT)模型,并对CDK2介导PMT的下游靶点和机制进行预测和验证.结果:CDK2在GSCs中高表达,而特异性沉默CDK2能够显著抑制GSCs生长(P＜0.01).当GSCs接受放射处理后CDK2和ALDH1 A3表达显著上调,而CDK2沉默能够显著下调ALDH1A3的表达.E2F1是和CDK2表达关联性最高的ALDH1A3启动子区域结合蛋白,而利用shRNA沉默CDK2能够下调GSCs中E2F1和ALDH1A3的表达水平.结论:CDK2能够通过调节E2F1的表达激活ALDH1 A3的启动子活性并调控其表达和功能,进而调控GSCs的生长并诱导GSCs发生PMT.     

The effect of sodium selenite on cell proliferation and transformation of primary rat tracheal epithelial cells.

The effects of sodium selenite (Na2SeO3) on cell proliferation and the development of preneoplastic transformed variants were studied in primary cultures of rat tracheal epithelial cells. Results revealed a biphasic effect of Na2SeO3 on cell proliferation: at concentrations between 6 x 10(-8) and 6 x 10(-6) M, it stimulated and at concentrations of approximately 2 x 10(-5) and above it inhibited cell proliferation (presumably due to toxicity). Nontoxic concentrations of Na2SeO3 (6 x 10(-8) -6 x 10(-7) M) significantly reduced the spontaneous transformation frequency. Transformation induced by the tobacco-specific nitrosamine 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was effectively inhibited by nontoxic as well as toxic concentrations of Na2SeO3. Treatment of cultures with Na2SeO3 after cessation of NNK exposure, i.e. during the selection period, also significantly reduced the transformation frequency. These experiments show that the inhibition of transformation by Na2SeO3 is not the result of an antiproliferative effect. They further indicate that the inhibitory effect occurs even when the chemical treatment occurs during the 'postinitiation' phase. Thus the inhibition of transformation by Na2SeO3 cannot solely be explained by its effects on drug metabolism.     

Transglutaminase 2 in cancer

The significant influence of tumor microenvironment on malignant cells has been investigated with enthusiasm in this era of targeted therapy. Transglutaminase 2 (TG2, EC 2.3.2.13), a multi-functional enzyme that catalyzes the formation of intermolecular isopeptide bonds between glutamine and lysine side-chains, has been reported to exert important pathophysiological functions. The aim of this review was to investigate the correlation between TG2 and malignant behaviors, which could provide the rationale for novel approaches in anti-cancer therapy. We performed a systematic and electronic search on Medline, Scopus, and Web of Science for relevant publications from inception to April 2015. The bibliographic references of retrieved articles were further reviewed for additional relevant studies. TG2 exerts important physiological functions and plays vital roles in inflammation mainly through its modulation on the structure and stability of extracellular matrix (ECM). It also regulates EMT of diverse malignant cells through various intracellular and extracellular pathways. TG2 also plays an important role in tumor progression and may serve as a novel prognostic biomarker and therapeutic target in various cancer types. TG2 promotes malignant cell mobility, invasion, and metastasis, and induces chemo-resistance of cancer cells, mainly through its pro-crosslink and signaling transduction mediation propensities. In conclusion, TG2 plays vital roles in malignancy progression, and may have important prognostic and therapeutic significances.     

Notch and Schwann cell transformation

Benign plexiform neurofibromas in NF1 patients can transform spontaneously into malignant peripheral nerve sheath tumors (MPNSTs). Although mutations in the p53 gene have been found in a subset of MPNSTs and mouse models support a role for p53 mutations in malignant conversion, we found that each of three Schwann cell lines derived from human MPNSTs possessed active p53. One of the lines expressed the Notch intracellular domain (NICD), indicative of ongoing Notch signaling. Consistent with a role in malignancy, NICD was able to transform primary rat Schwann cells. Transformation was robust--NICD-transduced cells generated tumors in nude rats--and was associated with the loss of markers associated with Schwann cell differentiation. These data suggest that aberrant Notch signaling may contribute to the conversion of benign neurofibromas to MPNSTs.     

Clonal proliferation index and its changes in malignant transformation of tissues

The microspectrometric investigation used 5- and 8 microns-thick histological specimens, stained after Feulgen, and the following equipment: scanning integrating microspectrophotometer (1,080); TV-image analyzer (70). Interphase nuclei of normal growth tissue, mild and moderate dysplasia, atypical proliferation and carcinoma were investigated using bioptical material from the larynx, cervix uteri, endometrium, stomach, large bowel, prostate and breast. The weighted mean index of DNA accumulation in nuclei as well as the "index of clonal proliferation" (ICP)--ratio of average DNA index for carcinogenesis stage in question and normal tissue index--suggested by the author, were measured. Malignant transformation was characterized by the following ICP values: mild and moderate dysplasia--less than 1.4; intraepithelial neoplasia--2.2 and carcinoma and adenocarcinoma--3.3 and higher. Microspectrophotometric analysis of Feulgen-DNA yields reliable data on ICP in malignant tissue which can be used for clinical purposes in treatment and prognosis of malignant disease.