Tumor microenvironment and breast cancer progression: a complex scenario

It is now widely accepted that the development and progression of a tumor toward the malignant phenotype is highly dependent on interactions between tumor cells and the tumor microenvironment. Different components of the tumor microenvironment may have stimulatory or inhibitory effects on tumor progression by regulating the gene expression repertoire in tumor cells and stromal cells. This review analyzes novel research findings on breast cancer progression, discussing acquisition of the metastatic phenotype in breast disease in relation to different aspects of cross-talk among components of the tumor microenvironment. Knowledge of the interaction of all of these factors would contribute to elucidating the mechanisms that disrupt regulatory/signaling cascades and downstream effects in breast cancer.     

Differentiation of EL4 lymphoma cells by tumoral environment is associated with inappropriate expression of the large chondroitin sulfate proteoglycan PG-M and the tumor-associated antigen HTgp-175

Progression to malignancy of transformed cells involves complex genetic alterations and aberrant gene expression patterns. While aberrant gene expression is often caused by alterations in individual genes, the contribution of the tumoral environment to the triggering of this gene expression is less well established. The stable but heterogeneous expression in cultured EL4/13 cells of a novel tumor-associated antigen, designated as HTgp-175, was chosen for the investigation of gene expression during tumor formation. Homogeneously HTgp-175-negative EL4/13 cells, isolated by cell sorting or obtained by subcloning, acquired HTgp-175 expression as a result of tumor formation. The tumorigenicity of HTgp-175-negative vs. HTgp-175-positive EL4 variants was identical, indicating that induction but not selection accounted for the phenotypic switch from HTgp-175-negative to HTgp-175-positive. Although mutagenesis experiments showed that the protein was not essential for tumor establishment, tumor-derived cells showed increased malignancy, linking HTgp-175 expression with genetic changes accompanying tumor progression. This novel gene expression was not an isolated event, since it was accompanied by ectopic expression of the large chondroitin sulfate proteoglycan PG-M and of normal differentiation antigens. We conclude that signals derived from the tumoral microenvironment contribute significantly to the aberrant gene expression pattern of malignant cells, apparently by fortuitous activation of differentiation processes and cause expression of novel differentiation antigens as well as of inappropriate tumor-associated and ectopic antigens. Int. J. Cancer 78:503–510, 1998.© 1998 Wiley-Liss, Inc.     

Gene expression profiling of the tumor microenvironment during breast cancer progression

Introduction  

The importance of the tumor microenvironment in breast cancer has been increasingly recognized. Critical molecular changes in the tumor stroma accompanying cancer progression, however, remain largely unknown. We conducted a comparative analysis of global gene expression changes in the stromal and epithelial compartments during breast cancer progression from normal to preinvasive to invasive ductal carcinoma.     

Metabolic microenvironment of tumor cells: a key factor in malignant progression

The hostile metabolic microenvironment of solid tumors, which is quite heterogeneous both spatially and temporally (? 4-D-heterogeneity ?), can trigger malignant progression. Above all, acute and fluctuating hypoxia elicits multiple cellular response pathways that alter gene expression and phenotype (at moderate hypoxia with oxygen concentrations below 1%). Upon severe hypoxia (oxygen concentrations below 0.1%), genomic instability can lead to cell variants with adaptations favorable to survival. These cell variants have growth advantages in the hostile tumor microenvironment and finally expand through clonal selection thus promoting tumor aggressiveness. In addition to hypoxia, high lactate concentrations (above approximately 8 mM) may promote malignant progression. The interpretation of the role of tumor pH in tumor progression is complicated by the frequently occurring coexistence of tumor hypoxia and acidosis.     

Cooperative autocrine and paracrine functions of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor in the progression of skin carcinoma cells

Tumor growth and progression are critically controlled by alterations in the microenvironment often caused by an aberrant expression of growth factors and receptors. We demonstrated previously that tumor progression in patients and in the experimental HaCaT tumor model for skin squamous cell carcinomas is associated with a constitutive neoexpression of the hematopoietic growth factors granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), causing an autocrine stimulation of tumor cell proliferation and migration in vitro. To analyze the critical contribution of both factors to tumor progression, G-CSF or GM-CSF was stably transfected in factor-negative benign tumor cells. Forced expression of GM-CSF resulted in invasive growth and enhanced tumor cell proliferation in a three-dimensional culture model in vitro, yet tumor growth in vivo remained only transient. Constitutive expression of G-CSF, however, caused a shift from benign to malignant and strongly angiogenic tumors. Moreover, cells recultured from G-CSF-transfected tumors exhibited enhanced tumor aggressiveness upon reinjection, i.e., earlier onset and faster tumor expansion. Remarkably, this further step in tumor progression was again associated with the constitutive expression of GM-CSF strongly indicating a synergistic action of both factors. Additionally, expression of GM-CSF in the transfected tumors mediated an earlier recruitment of granulocytes and macrophages to the tumor site, and expression of G-CSF induced an enhanced and persistent angiogenesis and increased the number of granulocytes and macrophages in the tumor vicinity. Thus both factors directly stimulate tumor cell growth and, by modulating the tumor stroma, induce a microenvironment that promotes tumor progression.     

The hypoxic tumor microenvironment and gene expression

Solid tumors are not static entities but are constantly responding to environmental signals as they grow and develop. One mechanism by which they respond to the adverse conditions of the tumor microenvironment is through coordinated changes in gene expression. The synchronized turning of genes on and off leads to biologic adaption to the adverse oxygen-poor environment. Because tumor hypoxia can be found in almost every solid tumor, it represents one of the most pervasive microenvironmental stresses that can impact malignant progression and therapeutic response. Interestingly, tumors that exhibit robust induction of hypoxia-responsive gene expression networks show a clinically more aggressive natural history. The contribution of hypoxia-responsive gene networks to malignant response is currently under investigation. An understanding of the coordinated functions of hypoxia induced and repressed genes can lead to a better understanding of the clinical significance of the hypoxic tumor phenotype.     

c-Ski activates cancer-associated fibroblasts to regulate breast cancer cell invasion

Aberrant expression of c-Ski oncoprotein in some tumor cells has been shown to be associated with cancer development. However, the role of c-Ski in cancer-associated fibroblasts (CAFs) of tumor microenvironment has not been characterized. In the current study, we found that c-Ski is highly expressed in CAFs derived from breast carcinoma microenvironment and this CAF-associated c-Ski expression is associated with invasion and metastasis of human breast tumors. We showed that c-Ski overexpression in immortalized breast normal fibroblasts (NFs) induces conversion to breast CAFs by repressing p53 and thereby upregulating SDF-1 in NFs. SDF-1 treatment or p53 knockdown in NFs had similar effects on the activation of NFs as c-Ski overexpression. The c-Ski-activated CAFs show increased proliferation, migration, invasion and contraction compared with NFs. Furthermore, c-Ski-activated CAFs facilitated the migration and invasion of MDA-MB-231 breast cancer cells. Our data suggest that c-Ski is an important regulator in the activation of CAFs and may serve as a potential therapeutic target to block breast cancer progression.     

Tumor associated CD70 expression is involved in promoting tumor migration and macrophage infiltration in GBM

Tumor migration/metastasis and immunosuppression are major obstacles in effective cancer therapy. Incidentally, these 2 hurdles usually coexist inside tumors, therefore making therapy significantly more complicated, as both oncogenic mechanisms must be addressed for successful therapeutic intervention. Our recent report highlights that the tumor expression of a TNF family member, CD70, is correlated with poor survival for primary gliomas. In this study, we investigated how CD70 expression by GBM affects the characteristics of tumor cells and the tumor microenvironment. We found that the ablation of CD70 in primary GBM decreased CD44 and SOX2 gene expression, and inhibited tumor migration, growth and the ability to attract monocyte‐derived M2 macrophages in vitro. In the tumor microenvironment, CD70 was associated with immune cell infiltrates, such as T cells; myeloid‐derived suppressor cells; and monocytes/macrophages based on the RNA‐sequencing profile. The CD163+ macrophages were far more abundant than T cells were. This overwhelming level of macrophages was identified only in GBM and not in low‐grade gliomas and normal brain specimens, implying their tumor association. CD70 was detected only on tumor cells, not on macrophages, and was highly correlated with CD163 gene expression in primary GBM. Additionally, the co‐expression of the CD70 and CD163 genes was found to correlate with decreased survival for patients with primary GBM. Together, these data suggest that CD70 expression is involved in promoting tumor aggressiveness and immunosuppression via tumor‐associated macrophage recruitment/activation. Our current efforts to target this molecule using chimeric antigen receptor T cells hold great potential for treating patients with GBM.     

Prosaposin,tumor‐secreted protein,promotes pancreatic cancer progression by decreasing tumor‐infiltrating lymphocytes

Glycoproteins produced by tumor cells are involved in cancer progression, metastasis, and the immune response, and serve as possible therapeutic targets. Considering the dismal outcomes of pancreatic ductal adenocarcinoma (PDAC) due to its unique tumor microenvironment, which is characterized by low antitumor T‐cell infiltration, we hypothesized that tumor‐derived glycoproteins may serve as regulating the tumor microenvironment. We used glycoproteomics with tandem mass tag labeling to investigate the culture media of three human PDAC cell lines, and attempted to identify the key secreted proteins from PDAC cells. Among the identified glycoproteins, prosaposin (PSAP) was investigated for its functional contribution to PDAC progression. PSAP is highly expressed in various PDAC cell lines; however, knockdown of intrinsic PSAP expression did not affect the proliferation and migration capacities. Based on the immunohistochemistry of resected human PDAC tissues, high PSAP expression was associated with poor prognosis in patients with PDAC. Notably, tumors with high PSAP expression showed significantly lower CD8⁺ T‐cell infiltration than those with low PSAP expression. Furthermore, PSAP stimulation decreased the proportion of CD8⁺ T cells in peripheral blood monocytes. Finally, in an orthotopic transplantation model, the number of CD8⁺ T cells in the PSAP shRNA groups was significantly increased, resulting in a decreased tumor volume compared with that in the control shRNA group. PSAP suppresses CD8⁺ T‐cell infiltration, leading to the promotion of PDAC progression. However, further studies are warranted to determine whether this study contributes to the development of a novel immunomodulating therapy for PDAC.     

Molecular co-expression of the c-Met oncogene and hepatocyte growth factor in primary colon cancer predicts tumor stage and clinical outcome

INTRODUCTION/HYPOTHESIS: Over-expression of the c-Met receptor tyrosine kinase has been described in a variety of cancers and implicated in tumor progression. Unlike some solid tumors, current evidence indicates that c-Met activation in colon cancer is unrelated to gene mutation, is ligand dependent, and occurs via a paracrine fashion. We hypothesize that over-expression of the c-Met receptor and its ligand, hepatocyte growth factor (HGF) in the tumor microenvironment is associated with tumor progression and metastases. METHODS: Primary tumor c-Met and HGF mRNA expression was analyzed in 60 colon adenocarcinomas. Receptor and ligand expression was analyzed for correlation and association with clinicopathologic features and outcome. RESULTS: Compared to adjacent normal mucosa, 69% and 48% of tumors showed a greater than 2- and greater than 10-fold elevation in c-Met mRNA, respectively. Elevated HGF mRNA was noted in 47% of tumors with 19% having a greater than 10-fold increase. Tumor c-Met expression was correlated with HGF expression, and a cohort of 33 patients could be defined with both low c-Met and HGF expression. Compared with the 27 tumors with either high c-Met or HGF, the cohort with low c-Met and HGF expression had fewer nodal and distant metastases as well as improved overall survival (HR=2.3, p<0.05). CONCLUSION: Evaluation of the c-Met receptor in context of ligand, HGF, allows identification of a metastatic phenotype that correlates with advanced stage and poor survival. c-Met and HGF co-expression in the tumor microenvironment could be useful in the molecular staging of colon cancer and viable therapeutic targets.     

Molecular Crosstalk between Chromatin Remodeling and Tumor Microenvironment in Multiple Myeloma

Multiple myeloma (MM) is a complex disease driven by numerous genetic and epigenetic alterations that are acquired over time. Despite recent progress in the understanding of MM pathobiology and the availability of innovative drugs, which have pronounced clinical outcome, this malignancy eventually progresses to a drug-resistant lethal stage and, thus, novel therapeutic drugs/models always play an important role in effective management of MM. Modulation of tumor microenvironment is one of the hallmarks of cancer biology, including MM, which affects the myeloma genomic architecture and disease progression subtly through chromatin modifications. The bone marrow niche has a prime role in progression, survival, and drug resistance of multiple myeloma cells. Therefore, it is important to develop means for targeting the ecosystem between multiple myeloma bone marrow microenvironment and chromatin remodeling. Extensive gene expression profile analysis has indeed provided the framework for new risk stratification of MM patients and identifying novel molecular targets and therapeutics. However, key tumor microenvironment factors/immune cells and their interactions with chromatin remodeling complex proteins that drive MM cell growth and progression remain grossly undefined.