Differentiation and cancer: the conditional autonomy of phenotype

Prognostic significance of cytoplasmic SOX9 in invasive ductal carcinoma and metastatic breast cancer

SOX9, a high mobility group (HMG) box transcription factor, is required for development, differentiation and lineage commitment. It is known to exert its effects through nuclear translocation, such as cell cycle changes in response to retinoic acid treatment in breast cancer cells. However, it is not known whether SOX9 has prognostic significance in human breast cancer. Over-expression and cytoplasmic sequestration of nuclear proteins are implicated in tumor progression. To determine whether SOX9 has any prognostic significance in human breast cancer, its expression and subcellular localization were analyzed in more than 200 human breast carcinomas (BCs). SOX9 mRNA expression data for human BCs were computed from microarray studies available in public databases and correlated with known poor prognostic parameters of BCs. SOX9 protein expression and its correlation with Ki-67 staining in human BCs were assessed using immunohistochemistry. Higher SOX9 mRNA levels were significantly associated with estrogen receptor negative (P ≤ 0.001) and higher grade (P ≤ 0.01) human breast tumors. Patients with higher SOX9 mRNA level had significantly shorter overall survival (P ≤ 0.0001). SOX9 protein, which is normally nuclear, was instead localized in the cytoplasm of 25-30% invasive ductal carcinomas (IDCs) and lymph node metastases. Its cytoplasmic accumulation significantly correlated with enhanced proliferation in breast tumors (Kendall's tau = 0.337 with a P value < 0.0001). Cytoplasmic SOX9 can serve as a valuable prognostic marker for IDCs and metastatic breast cancer. Its significant correlation with breast tumor cell proliferation implies that SOX9 directly contributes to the poor clinical outcomes associated with invasive breast cancer.

Loss of GATA4 and GATA6 expression specifies ovarian cancer histological subtypes and precedes neoplastic transformation of ovarian surface epithelia

BACKGROUND

The family of zinc finger-containing GATA transcription factors plays critical roles in cell lineage specification during early embryonic development and organ formation. GATA4 and GATA6 were found to be frequently lost in ovarian cancer, and the loss is proposed to account for dedifferentiation of the cancer cells.

METHODOLOGY/PRINCIPAL FINDINGS

We further investigated the expression of GATA4 and GATA6 in ovarian surface epithelial lesions and histological subtypes of ovarian carcinomas by immunostaining. GATA4 and GATA6 were found to be absent in high percentages (80 to 90%) of serous, clear cell, and endometrioid ovarian cancer examined. In contrast, both were found positive in 11 out of 12 cases of mucinous carcinomas, suggesting the expression of the GATA factors can distinguish mucinous cancer from other histological subtypes. GATA4 was frequently lost in preneoplastic lesions such as morphologically normal inclusion cysts and epithelial hyperplasia adjacent to malignant cells. The loss of GATA6 correlates closely with neoplastic morphological transformation of ovarian surface epithelia. In culture, GATA4 expression was progressively reduced upon passaging primary ovarian surface epithelial cells, which correlated with changes in histone modification of the GATA4 locus. A reduced GATA6 gene dosage as in GATA6 (+/-) mice led to an increased pre-neoplastic changes and inclusion cysts in the ovaries, suggesting the loss of GATA6 contributes to ovarian cancer development.

CONCLUSIONS/SIGNIFICANCE

This study suggests that the expression status of GATA4 and GATA6 may dictate distinct pathologic pathways leading to serous or mucinous ovarian carcinomas. The readily loss of GATA4 expression through changes in chromatin conformation suggests a potential non-phenotypic initiating event, leading to subsequent loss of GATA6, morphological transformation, and ultimate tumorigenesis.

Repression of HIP/RPL29 expression induces differentiation in colon cancer cells

We had previously shown that the expression of heparin/heparan sulfate interacting protein/ribosomal protein L29 (HIP/RPL29) was upregulated in colon cancer tissues. The present study investigated the role of HIP/RPL29 in differentiation in colon cancer cells. Inducing cellular differentiation in HT-29 cells by both sodium butyrate and glucose deprivation resulted in a significant downregulation of HIP/RPL29 expression. The beta-catenin/Tcf-4 pathway is the most important pathway controlling the switch between cellular differentiation and proliferation in intestinal epithelial cells. Inducing differentiation by dominant-negative inhibition of the beta-catenin/Tcf-4 complexes in LS174T cells also resulted in downregulation of HIP/RPL29. To determine whether a lower expression of HIP/RPL29 could induce differentiation in cancer cells, small interfering RNA (siRNA) targeting HIP/RPL29 was transfected into LS174T cells. The resultant knockdown of HIP/RPL29 expression induced cellular differentiation, as shown by the increased expression of two known markers of differentiation in LS174T cells, galectin-4 and mucin-2. In addition, the differentiation process induced by repression of HIP/RPL29 expression was accompanied by the upregulation of p21 and p53. In conclusion, HIP/RPL29 plays a role in the cellular differentiation process in colon cancer cells. The differentiation process is at least partially mediated by the upregulation of p21 and p53 pathways.

Membrane-bound macrophage colony-stimulating factor mediated auto-juxtacrine downregulates matrix metalloproteinase-9 release on J6-1 leukemic cell

Earlier studies indicate that J6-1 human leukemic cells proliferate and propagate via the membrane-bound macrophage colony-stimulating factor (M-CSF)-mediated auto-juxtacrine mechanism. Matrix metalloproteinases (MMPs) can modulate the activity of cell membrane molecules and influence many cellular behaviors. Therefore, we hypothesized that MMP may also be involved in the membrane-bound M-CSF-mediated juxtacrine mechanism. First, we investigated whether blocking of membrane-bound M-CSF by neutralizing antibody to M-CSF or M-CSF receptor and adding of exogenous M-CSF are able to influence MMP-9 release. Next, we determined whether MMP-9 participated in J6-1 cells proliferation and influence the shedding of membrane-bound M-CSF and its receptor. Current studies show that blockade of the interaction between membrane-bound M-CSF and M-CSF receptor by antibody to M-CSF or M-CSF receptor promotes MMP-9 release. Moreover, we demonstrated that because of M-CSF mediated juxtacrine, lack of MMP-9 promotes J6-1 cell proliferation, in which a decrease in the shedding of cell-surface M-CSFR is involved. Hence, we suggest that membrane-bound M-CSF inhibit MMP-9 release and down-regulated MMP-9 contribute to juxtacrine stimulating in leukemic cell growth.

Morphological and molecular evidence of differentiation during etoposide-induced apoptosis in human lymphoblastoid cells

The relationship between apoptosis and cell differentiation has been a subject for continuous debate, with evidence showing leukaemic cell differentiation and drug-induced apoptosis have reciprocal, interdependent and a highly schedule-dependent relationship. We have addressed this relationship in terms of a widely-used model for apoptosis induced by cytotoxic drugs: namely the effect of etoposide on CEM cells. In respect of commitment toward differentiation, we assessed changes in expression of marker genes and the level of CD3 antigenicity. Changes in these parameters following exposure of CEM cells to etoposide was similar to that observed following treatment of the same cells with phorbol 12-myristate 13-acetate (PMA), though this latter treatment did not cause cell death. Similarities in response to etoposide and PMA also included generation of 50 kilobase fragmentation of DNA and convolution of nuclei as assessed by transmission electron microscopy. However, condensation of chromatin and externalization of phosphatidylserine were only recorded in response to the cytotoxic drug and not in response to PMA. The data are consistent with apoptosis in these lymphoblastoid cells being accompanied by activation of specific markers of T-cell differentiation, but ultimately involving processes unequivocally associated with cell death.

Differentiation and cancer in the mammary gland: shedding light on an old dichotomy

In this brief review, the development of breast cancer is discussed from the vantage of phenotypic differentiation, similar to what has been considered over the years for leukemias and melanomas, both of which express easily visible differentiation markers (Hart and Easty, 1991; Clarke et al., 1995; Lynch, 1995; Sachs, 1996; Sledge, 1996). The review is divided into a theoretical background for human breast differentiation and a discussion of recent experimental results in our laboratories with differentiation of breast epithelial cells. In the theoretical background, in situ markers of differentiation of normal breast and carcinomas are discussed with emphasis on their possible implications for tumor therapy. So far, most of the emphasis regarding differentiation therapy of tumors has been focused on the possible action of soluble factors, such as colony-stimulating factors in leukemias and retinoic acids in solid tumors (Lotan, 1996; Sachs, 1996). However, an emerging and promising new avenue in this area appears to point to additional factors, such as the cellular form and extracellular matrix (ECM) (Bissel et al., 1982; Bissel and Barcellos-Hoff, 1987; Ingber, 1992). The recent interest in these parameters has evolved along with an increasing understanding of the molecular composition of the ECM, and of the molecular basis of the classical findings that normal cell--in contrast to tumor cells--are anchorage dependent for survival and growth (Folkman and Moscona, 1978; Hannigan et al., 1996). We now know that this is the case for epithelial as well as fibroblastic cells, and that interaction with ECM is crucial for such regulation. Indeed, ECM and integrins are emerging as the central regulators of differentiation, apoptosis, and cancer (Boudreau et al., 1995; Boudreau and Bissel, 1996; Werb et al., 1996; Bissell, 1997; Weaver, et al., 1997). In the experimental part, we elaborate on our own recent experiments with functional culture models of the human breast, with particular emphasis on how "normal" and cancer cells could be defined within a reconstituted ECM. Special attention is given to integrins, the prominent ECM receptors. We further discuss a number of recent experimental results, all of which point to the same conclusion: namely that phenotypic reversion toward a more normal state for epithelial tumors is no longer an elusive goal. Thus "therapy by differentiation" could be broadened to include not only blood-borne tumors, but also solid tumors of epithelial origin.

Experimental co-expression of vimentin and keratin intermediate filaments in human breast cancer cells results in phenotypic interconversion and increased invasive behavior

The expression of intermediate filament proteins is remarkably tissue specific, which suggests that the intermediate filament type(s) present in cells is somehow related to their biological function. However, in some cancers, particularly malignant breast carcinoma, there is a strong indication that vimentin is co-expressed with keratins, thus presenting as a dedifferentiated or interconverted (between epithelial and mesenchymal) phenotype. In the present study, we recapitulated the interconverted phenotype by developing stable transfectants of MCF-7 human breast cancer cells, termed MoVi clones, to express both vimentin and keratins. Overexpression of vimentin in these cells led to augmentation of motility and invasiveness in vitra. These activities could be transiently down-regulated by vimentin antisense oligonucleotides in MoVi clones and MDA-MB-231 cells (which constitutively co-express keratins and vimentin). Furthermore, in the MoVi experimental transfectants expressing the highest percentage of vimentin-positive cells, their proliferative capacity, clonogenic potential, and tumorigenicity increased. However, the metastatic ability of the MoVi transfectants remained unchanged compared with MCF-7neo controls. The MDA-MB-231 cells metastasized to axillary lymph nodes in a SCID mouse model. Finally, we explored the possibility that potential changes could occur with respect to cell surface integrins. These studies revealed a decrease in the alpha 2- and alpha 3-containing promiscuous integrins, in addition to beta 1 containing integrins, concomitant with an increase in the alpha 6-containing laminin receptor integrin. Further functional analysis of the alpha 6 observation showed an increase in the baptotactic migration of MoVi transfectants toward a laminin substrate. From these data, it is postulated that the ability to co-express vimentin and keratins confers a selective advantage to breast cancer cells in their interpretation of signaling cues from the extracellular matrix; however the addition of vimentin intermediate filaments alone is not sufficient to confer the metastatic phenotype.

Role of intermediate filaments in migration, invasion and metastasis

The expression of intermediate filament proteins is remarkably tissue-specific which suggests that the intermediate filament (IF) type(s) present in cells is somehow related to their biological function. However, in some cancers-particularly malignant melanoma and breast carcinoma, there is a strong indication that vimentin and keratin IFs are coexpressed, thus presenting as a dedifferentiated or interconverted (between epithelial and mesenchymal) phenotype. In this review, two in vitro models are presented which recapitulate the interconverted phenotype in human melanoma and breast carcinoma, and allow, for the first time, unique observations to be made with respect to the role of IFs in cancer progression. These studies have provided direct evidence linking overexpression of keratin IFs in human melanoma with increased migratory and invasive activity in vitro, which can be down-regulated by substituting dominant-negative keratin mutants. Overexpression of vimentin IFs in the breast carcinoma model leads to augmentation of motility and invasiveness in vitro, which can be transiently down-regulated by treatment with antisense oligonucleotides to vimentin. Additional experimental evidence suggests that the mechanism(s) responsible for the differential expression of metastatic properties associated with the interconverted phenotype rest(s) in the unique interaction, either direct or indirect, of IFs with specific integrins interacting with the extracellular matrix. In this review, we discuss the observations derived from the human melanoma and breast carcinoma models to address the hypothesis that the ability to coexpress vimentin and keratins confers a selective advantage to tumor cells in their interpretation of and response to signaling cues from the extracellular matrix. The ramifications of these observations are discussed with respect to the patholophysiology of the respective in situ tumors.

Dissecting the individuality of cancer cells: the morphological and molecular dynamics of single human glioma cells

A glioma produces some of the most heterogeneously growing, angiogenic, and invasive primary brain tumor cells known. To dissect cellular individuality, and therefore tumor heterogeneity, multiple morphological and molecular processes in single living human glioma cells were measured using multimode light microscopy. Feature extraction of time-lapse image series of spreading, locomoting, and interacting cells either in the presence or absence of physiological modulators was performed by defining five parameters that described cell shape, movement, and cell-cell contacts. Concurrent visualization of all five parameters with a scatterplot matrix revealed temporal as well as time-independent relationships between the parameters that were sufficient to define the individuality of normal and transformed glial cells. Because the actin-cytoskeleton plays a role in regulating the cellular processes described above, the dynamics of a fluorescent analog of non-muscle actin within motile glioma cells were measured in addition to the morphological parameters. The actin-cytoskeleton within the thin sweeping lamellipodia of a glioma exhibited a paucity of large stress fibers, a rich collection of microvillar structures containing actin, and dynamics that were distinct from those of normal motile cells. This approach can therefore potentially be used to dissect the molecular origins of transformation using a small number of representative tumor cells.

A role for the Drosophila bag-of-marbles protein in the differentiation of cystoblasts from germline stem cells

Cell differentiation commonly dictates a change in the cell cycle of mitotic daughters. Previous investigations have suggested that the Drosophila bag of marbles (bam) gene is required for the differentiation of germline stem cell daughters (cystoblasts) from the mother stem cells, perhaps by altering the cell cycle. In this paper, we report the preparation of antibodies to the Bam protein and the use of those reagents to investigate how Bam is required for germ cell development. We find that Bam exists as both a fusome component and as cytoplasmic protein and that cytoplasmic and fusome Bam might have separable activities. We also show that bam mutant germ cells are blocked in differentiation and are trapped as mitotically active cells like stem cells. A model for how Bam might regulate cystocyte differentiation is presented.