Differentiation antigens of hemoblastoses and epithelial tumors: relations to the mechanisms of transformation and progression

The role of mechanisms underlying differentiation is considered in malignant transformation of hemoblastoses and epithelial tumors. In hemoblastoses, differentiation is intimately related to malignant transformation and they are underlain by the same mechanisms. Immunophenotyping of hemoblastoses is fully based on successive stages of their differentiation with characteristic expression of differentiation antigens. Unlike hemoblastoses, epithelial tumors gradually, in the course of progression, lose their differentiation due to the degradation of the connections with the microenvironment, which controls the direction and level of epithelial differentiation. Therefore, carcinomas are characterized by varying degrees of "antigenic simplification", including the epithelial-mesenchymal transition.     

Differentiation mechanisms and malignancy

This review considers the relationship between differentiation mechanisms and the genesis and maintenance of tumor phenotype. To a certain extent, carcinomas preserve differentiation markers of normal tissue, and hemoblastoses precisely reflect the direction and differentiation level of their precursor cells. Both tumor types retain the ability to differentiate. Mechanisms of T and B cell differentiation are reviewed considering the activation of protooncogenes by translocation to the region of tissue-specific genes including the immunoglobulin (Ig) and T cell receptor (TCR) genes. Apart from the classical oncogenes (MYC, PRAD, BCL-2), heterologous differentiation of trans-factors can be activated in a similar manner. Their activation at inappropriate time and place induces oncogenic transformation in a number of hemoblastoses. Chimeric genes and fused proteins are analyzed, including their genesis by specific translocation resulting in transformation and their role in differentiation and maintenance of the tumor phenotype. Induction of terminal differentiation in leukemia can have significant therapeutic effect. These hemoblastoses include hairy cell leukemia, promyelocytic leukemia, and in part chronic myeloid leukemia. Specific attention is given to the role of intercellular interactions in the control of tumor growth and maintenance of a differentiated state of the cells. It is suggested that alterations in these interactions during tumor progression simultaneously stimulate malignant growth and decrease differentiation level, thus inducing re-expression of embryonic antigens in the tumors.     

Tumor-stroma interactions directing phenotype and progression of epithelial skin tumor cells

Tumor-stroma interactions play a significant role in tumor development and progression. Alterations in the stromal microenvironment, including enhanced vasculature (angiogenesis), modified extracellular matrix composition, inflammatory cells, and dys-balanced protease activity, are essential regulatory factors of tumor growth and invasion. Differential modulation of stromal characteristics is induced by epithelial skin tumor cells depending on their transformation stage when grown as surface transplants in vivo. Tumor cells can regulate the development of a "tumor-stroma" via the aberrant expression of growth factors or induction of growth factor receptors in the stromal compartment. In this context, secretion of the hematopoietic growth factors G-CSF and GM-CSF, constituitively expressed in enhanced malignant tumors, may be good candidates for induction of a tumor stroma through their effect on inflammatory cells. Upon its induction, the tumor stroma will reciprocally influence the differentiation status of tumor cells resulting in a normalization of benign tumor epithelia and the maintenance of a malignant phenotype, respectively. In the HaCaT model for squamous cell carcinoma of the skin, stromal activation and angiogenesis are transient in pre-malignant transplants, however they remain persistent in malignant transplants where progressive angiogenesis is closely correlated with tumor invasion. While continued expression of VEGF and PDGF are associated with benign tumor phenotypes, activation of VEGFR-2 is a hallmark of malignant tumors and accompanies ongoing angiogenesis and tumor invasion. As a consequence the inhibition of ongoing angiogenesis by blocking VEGFR-2 signalling resulted in dramatically impaired malignant tumor expansion and invasion. Comparably, tumor vascularization and invasion was blocked by disturbing the balance of matrix protease activity caused by a lack of PAI-1 in the stromal cells of the knockout mouse hosts. A similar inhibition of tumor vascularization was caused by TSP-1 over-expression in skin carcinoma cells, which also blocked tumor invasion and expansion. On the other hand, when granulation tissue and angiogenesis were only transiently activated as a result of stable transfection of PDGF into non-tumorigenic HaCaT cells, the target cells formed benign, but not malignant, tumors. Collectively, these data show that tumor vascularization, providing intimate association of blood vessels with tumor cells, is a prerequisite for tumor invasion. A potential mechanism for this interrelationship may be the differential regulation of MMP-expression in tumors of different grades of malignancy. In vitro MMP expression did not discriminate between benign and malignant tumor cells unless they were co-cultured with stromal fibroblasts. However, in vivo regulation of MMP expression was clearly dependent on tumor phenotype. While MMP-1 and MMP-13 were down-regulated in benign transplants, they were persistently up-regulated in malignant ones. A tight balance between proteases and their inhibitors is crucial for both the formation and infiltration of blood vessels and for tumor cell invasion, thus again emphasizing the importance of the stromal compartment for the development and progression of carcinomas.     

Terminally differentiating epithelial tissues in primary explant culture: A model of growth and development

Summary Many epithelial tissues are characterized by the presence of basal cells which serve the dual roles of self-renewal and of progression through terminal differentiation, to a functional state. Such tissues, when grownin vitro as primary explants, exhibit a characteristic pattern of outgrowth and development which includes both renewal and efforts toward normal differentiation. The degree of differentiation achieved depends upon conditions of culture and may be modulated in a variety of ways. The human prostate constitutes such a system and offers numerous possibilities for investigating basic control mechanisms in growth and development. Information on a variety of epithelial tissues is reviewed and experimental results using human prostate tissue are presented. The work was supported by grant R26 CA 2365, National Cancer Institute.     

Differentiation Antigens: Dependence on Carcinogenesis Mechanisms and Tumor Progression (A Hypothesis)

The data considered in the paper indicate that a tumor clone resulting from cell transformation, in order to develop into an overt neoplasm, should overcome a microenvironmental constraint. This destroys intercellular contacts and cell interactions with extracellular matrix required for induction and maintenance of epithelium differentiation. The possible reasons for this lie in mutations of genes that control cell adhesion molecules and integrins, as well as proteases secreted by a tumor. These events lead to partial loss of differentiation antigens by a cell or to their incorrect localization in a cell. Simultaneously, the expression of embryo-specific genes is unblocked, leading to overexpression of embryonic antigens and their abnormal secretion into blood, which results in appearance of oncofetal serum markers. Discussed from this point of view are alpha-fetoprotein, the carcinoembryonic antigen, and the prostate-specific antigen, which are used as tumor markers.     

Biology of human papillomavirus (HPV) infections and their role in squamous cell carcinogenesis

Current data implicating the role of human papillomavirus (HPV) infections in squamous cell carcinogenesis may be summarised as follows: animal models have shown that PVs can induce malignant transformation; HPV involvement in both benign and malignant human squamous cell tumours has been demonstrated by morphological, immunohistochemical and DNA hybridisation techniques; HPV infections in the genital tract are venereally transmitted and are associated with the same risk factors as cervical carcinoma; the natural history of cervical HPV lesions is similar to that of CIN, namely, they have the potential to develop into carcinoma in situ; malignant transformation of PV-induced lesions seems to depend on virus type and the physical state of its DNA, e.g., whether or not it is integrated in the host cell DNA; malignant transformation most probably requires synergistic actions between the PVs and chemical or physical carcinogens, or other infectious agents; genetic disposition (at least in animals) significantly contributes to malignant transformation; immunological defence mechanisms of the host are probably capable of modifying the course of PV infections (efficacy in man remains to be elucidated). Many details of the molecular mechanisms, however, still remain to be clarified. Although BPV1 is capable of transforming fibroblasts, the way that papillomaviruses transform epithelial cells is unclear. Which gene is capable of inducing the limited cell proliferation in benign lesions? No model systems exist to provide the answer nor to elucidate the progression to malignant cells and then to invasive cancer. Improved tissue culture systems for in vitro differentiation of keratinocytes should help in elucidating the biology of papillomaviruses and their interaction with cell division and differentiation.     

Characterization of extended primary and secondary cultures of hamster tracheal epithelial cells

Summary Studies on the regulation of differentiation in airway epithelial cells have been hampered by the lack of cell culture systems that differentiate in vitro. One such system that does exhibit differentiation is hamster tracheal epithelial cells (HTE). A major problem with this system, however, is that at the time cells differentiate, they lyze the collagen gel upon which they grow, resulting in termination of the culture. Here we report that by growing the HTE cells at 32° instead of 37°C we can totally prevent lysis of the collagen gel. Cells grown at this lower temperature maintain their differentiated phenotype as evidenced by abundant mucus granules and the secretion of authentic mucus glycoproteins into the culture media. We have also developed a method for subculturing the primary cells which allows growth and differentiation in secondary culture. The HTE cells were capable of being passaged at least three times and did not become transformed as judged by their inability to grow in soft agar and to produce tumors in syngeneic animals. This improved HTE cell culture system will allow detailed studies on the mechanisms which regulate growth, differentiation, and mucus secretion in surface airway epithelial cells. This work was supported in part by grants HL-19717 and HL-36854 from the National Institutes of Health, Bethesda, MD.     

Conditional loss of PTEN leads to precocious development and neoplasia in the mammary gland

PTEN tumor suppressor is frequently mutated in human cancers, including breast cancers. Female patients with inherited PTEN mutations suffer from virginal hypertrophy of the breast with high risk of malignant transformation. However, the exact mechanisms of PTEN in controlling mammary gland development and tumorigenesis are unclear. In this study, we generated mice with a mammary-specific deletion of the Pten gene. Mutant mammary tissue displayed precocious lobulo-alveolar development, excessive ductal branching, delayed involution and severely reduced apoptosis. Pten null mammary epithelial cells were disregulated and hyperproliferative. Mutant females developed mammary tumors early in life. Similar phenotypes were observed in Pten-null mammary epithelia that had been transplanted into wild-type stroma, suggesting that PTEN plays an essential and cell-autonomous role in controlling the proliferation, differentiation and apoptosis of mammary epithelial cells.     

MicroRNAs: critical regulators of epithelial to mesenchymal (EMT) and mesenchymal to epithelial transition (MET) in cancer progression

MicroRNAs (miRNAs) are a class of small highly conserved RNAs that provide widespread expressional control through the translational repression of mRNA. MiRNAs have fundamental roles in the regulation of intracellular processes, and their importance during malignant transformation and metastasis is becoming increasingly well recognized. An important event in the metastatic cascade is epithelial to mesenchymal transition (EMT), a reversible phenotypic switch over, which endows malignant epithelial cells with the capacity to break free from one another and invade the surrounding stroma. Our understanding of EMT has been significantly improved by the characterization of miRNAs that influence the signalling pathways and downstream events that define EMT on a molecular level. Here, we detail the role of miRNAs in EMT, and in doing so demonstrate their importance in the early stages of the metastatic cascade; we discuss a significant body of data that suggest new opportunities for drug development, and we highlight critical knowledge gaps that remain to be addressed.     

Matrix metalloproteinases as stromal effectors of human carcinoma progression: Therapeutic implications

The matrix metalloproteinases (MMPs) are extracellular zinc-enzymes implicated in a number of physiological and pathological tissue remodeling processes, including cancer progression. For a long time they have been thought to be produced by malignant cells and to specifically contribute to tumor invasion, through their ability to degrade extracellular matrix components. However, studies performed over the last few years have demonstrated that extracellular proteinases implicated in the progression of human carcinomas, including most MMPs, are in fact predominantly expressed by stromal and not by cancer cells. Furthermore, membrane receptors, activators and/or binding sites for some of these proteinases are also predominantly found to be associated with stromal cells. These findings, together with the observation that MMPs can cleave some molecules implicated in controlling growth factor activities, suggest that the role of MMPs during cancer progression is not limited to facilitating malignant cell invasion alone but is also likely to participate in other aspects of the malignant phenotype. MMPs should in fact be regarded as pan-regulators of tissue neoformation characteristic of malignant tumors, which includes both epithelial cell expansion and stroma formation. In this context, synthetic MMP inhibitors which are presently designed should lead to the development of a new generation of anticancer agents which additional beneficial properties compared to the existing cytotoxic agents used in the treatment of human malignancies.     

Nucleostemin和HDAC1在卵巢肿瘤中的表达及意义

目的:研究核干细胞因子(Nucleostemin, NS)和组蛋白去乙酰化酶1(HDAC1)在卵巢肿瘤及正常卵巢组织中的表达,并分析其表达与临床指标的关系及两者间的表达相关性。方法:选择2010年至2017年我院卵巢石蜡标本60例,其中卵巢肿瘤50例,正常卵巢组织10例。应用免疫组化法检测NS与HDAC1的表达,并分析它们与年龄、肿瘤分期等临床指标的相关性。结果:在30例卵巢恶性肿瘤、10例卵巢交界性肿瘤、10例卵巢良性肿瘤组织中,NS表达的阳性率分别为93.3%、40%、20%,HDAC1的阳性率分别为90%、60%、20%。在正常卵巢组织中未见NS及HDAC1表达。在卵巢恶性肿瘤组中,NS和HDAC1的阳性表达率显著高于其他三组(P0.05),两者表达呈正相关(r=0.56, P0.05),且均与分化程度呈负相关(r=-0.76, P0.001; r=-0.53, P0.01),而与患者年龄、术前血清CA125水平、临床分期和病理类型无关。结论:NS和HDAC1倾向于卵巢恶性肿瘤中表达,且与卵巢恶性肿瘤的分化程度负相关。     

Role of stroma in carcinogenesis of the prostate

Prostatic development is induced by androgens acting via mesenchymal-epithelial interactions. Androgens elicit their morphogenetic effects by acting through androgen receptors (ARs) in urogenital sinus mesenchyme (UGM), which induces prostatic epithelial development. In adulthood reciprocal homeostatic stromal-epithelial interactions maintain functional differentiation and growth-quiescence. Testosterone plus estradiol (T+E2) have been shown to induce prostatic carcinogenesis in animal models. Thus, tissue recombinant studies were undertaken to explore the mechanisms of prostatic carcinogenesis in BPH-1 cells in which ARs and estrogen receptors (ERs) are undetectable. For this purpose, BPH-1 cells were combined with UGM, and the UGM+BPH-1 recombinants were grafted to adult male hosts. Solid branched epithelial cords and ductal structures formed in untreated UGM+BPH-1 recombinants. Growth was modest, and tumors did not develop. UGM+BPH-1 recombinants treated with T+E2 formed invasive carcinomas. BPH-1 cells lack ARs and ERs, whereas rat UGM expresses both of these receptors. These data show that immortalized nontumorigenic human prostatic epithelial cells can undergo hormonal carcinogenesis in response to T+E2 stimulation via paracrine mechanisms and demonstrate that the stromal environment plays an important role in mediating hormonal carcinogenesis. During prostatic carcinogenesis the stroma undergoes progressive loss of smooth muscle with the appearance of carcinoma-associated fibroblasts (CAF). This altered stroma was tested for its ability to promote carcinogenesis of nontumorigenic but immortalized human prostatic epithelial cells (BPH-1). CAF+BPH-1 tissue recombinants formed large carcinomas. In contrast, recombinants composed of normal prostatic stroma+BPH-1 cells exhibited minimal growth. This stroma-induced malignant transformation was associated with additional genetic alterations and changes in gene expression. Thus, alteration in the stromal microenvironment was sufficient to promote malignant transformation of human prostatic epithelial cells.     

Overexpression of EphB4 in the mammary epithelium shifts the differentiation pathway of progenitor cells and promotes branching activity and vascularization

Postnatally, the mammary gland undergoes continuous morphogenesis and thereby is especially prone to malignant transformation. Thus, the maintenance of the epithelium depends on a tight control of stem cell recruitment. We have previously shown that epithelial overexpression of the EphB4 receptor results in defective mammary epithelial development and conferred a metastasizing tumor phenotype on experimental mouse mammary tumors accompanied by a preponderance of progenitor cells. To analyze the effect of EphB4 overexpression on mammary epithelial cell fate, we have used Fluorescence Activated Cell Sorting (FACS) analyses to quantify epithelial sub‐populations and repopulation assays of cleared fat pads to investigate their regenerative potential. These experiments revealed that deregulated EphB4 expression leads to an augmentation of bi‐potent progenitor cells and to a shift of the differentiation pathway towards the luminal lineage. The analyses of the ductal outgrowths indicated that EphB4 overexpression leads to enforced branching activity, impedes ductal differentiation and stimulates angiogenesis. To elucidate the mechanisms forwarding EphB4 signals, we have compared the expression profile of defined cell populations between EphB4 transgene and wild type mammary glands concentrating on the wnt signaling pathway and on genes implicated in cell migration. With respect to wnt signaling, the progenitor cell population was the most affected, whereas the stem cell‐enriched population showed the most pronounced deregulation of migration‐associated genes. Thus, the luminal epithelial EphB4 signaling contributes, most likely via wnt signaling, to the regulation of migration and cell fate of early progenitors and is involved in the determination of branching points along the ductal tree.     

肝干细胞的可塑性和分化机理的研究进展

对肝干细胞的可塑性、多向分化潜能、分化机理及其与肝癌发病机制的关系等方面进行综述.肝干细胞是一类具有自我更新能力和多向分化潜能的细胞. 在不同的条件下,肝干细胞可分化为肝细胞、胆上皮细胞、胰腺细胞和肠上皮细胞. 肝干细胞的分化涉及微环境、细胞因子和细胞外基质等多种调控因素. 肝干细胞分化为成熟肝细胞受多种转录因子和信号通路的调节,其分化异常有可能诱发形成肝细胞癌.     

Diversification and progression of malignant tumors

Tumor-cell diversification mechanisms insure that malignant neoplasms contain diversified tumor-cell subpopulations. Because of the instability of tumor cell phenotypes, some malignant cells will evolve with the most favorable properties for their progression to highly metastatic cells. The rates of cellular phenotypic diversification vary greatly among different tumors, and they are probably modulated, in part, by genetic and chromosome defects and by epigenetic events that may vary widely depending upon the nature of the tumor cells and their microenvironments. As tumor diversification and selection proceed, the most malignant cell subpopulations may eventually become dominant and gradually lose their microenvironmental responsiveness. Tumor-cell diversification mechanisms may be similar or identical to normal, developmentally regulated diversification mechanisms that are used during embryonic cell diversification and differentiation.