Matthias Schulz

Microglia promote colonization of brain tissue by breast cancer cells in a Wnt-dependent way.

Although there is increasing evidence that blood‐derived macrophages support tumor progression, it is still unclear whether specialized resident macrophages, such as brain microglia, also play a prominent role in metastasis formation. Here, we show that microglia enhance invasion and colonization of brain tissue by breast cancer cells, serving both as active transporters and guiding rails. This is antagonized by inactivation of microglia as well as by the Wnt inhibitor Dickkopf‐2. Proinvasive microglia demonstrate altered morphology, but neither upregulation of M2‐like cytokines nor differential gene expression. Bacterial lipopolysacharide shifts tumor‐educated microglia into a classical M1 phenotype, reduces their proinvasive function, and unmasks inflammatory and Wnt signaling as the most strongly regulated pathways. Histological findings in human brain metastases underline the significance of these results. In conclusion, microglia are critical for the successful colonization of the brain by epithelial cancer cells, suggesting inhibition of proinvasive microglia as a promising antimetastatic strategy.

β-catenin-independent WNT signaling in basal-like breast cancer and brain metastasis.

A role of WNT signaling for primary breast cancers of the basal-like subtype and as a predictor of brain metastasis has been described. However, a responsible WNT ligand has not been identified. To further clarify this question, we comparatively investigated 22 human breast cancer brain metastases as well as the highly invasive human breast cancer cell line MDA-MB-231 and the weakly motile MCF-7 as models for the basal-like and the luminal A subtype. WNT5A and B were found overexpressed in MDA-MB-231 cells as compared with MCF-7. This corresponded to reduction of MDA-MB-231 invasiveness by WNT inhibitors, whereas MCF-7 invasion was enhanced by recombinant WNT5B and abolished by WNT and Jun-N-terminal kinase antagonists. Expression and subcellular distribution of β-catenin remained uninfluenced. Consistently, β-catenin was not localized in the nuclei of brain metastases while there was strong nuclear c-Jun staining. Similar to MDA-MB-231, metastases showed expression of WNT5A/B and the alternative WNT receptors ROR1 and 2. These findings were validated using external gene expression datasets (Gene Expression Omnibus) of different breast cancer subtypes and brain metastases. Hierarchical cluster analysis yielded a close relation between basal-like cancers and brain metastases. Gene set enrichment analyses confirmed WNT pathway enrichment not only in basal-like primaries but also in cerebral metastases of all subtypes. In conclusion, WNT signaling seems highly relevant for basal-like and other subtypes of breast cancers metastasizing into the brain. β-catenin-independent WNT signaling, presumably via ROR1-2, plays a major role in this context.

mRNA expression of matrix metalloproteases and their inhibitors differs in subtypes of renal cell carcinomas

Altered expression of matrix metalloproteases (MMPs) and their inhibitors, the tissue inhibitors of matrix metalloproteases (TIMPs), has been demonstrated in various tumour tissues. mRNA expression patterns of MMP-1, MMP-2, MMP-3, MMP-9, MMP-11, MMP-12, MMP-14 and TIMP-1, TIMP-2, TIMP-3 and TIMP-4 were evaluated by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in 30 renal cell carcinomas (RCC), as well as in the surrounding tissues. Expression of the MMPs was significantly stronger in the carcinomas than in non-malignant tissues. High levels were demonstrated particularly in clear cell RCCs (CC-RCC). Except for MMP-1, MMP expression in the papillary RCCs (P-RCC) was, for most MMPs, significantly lower. Expression of the TIMPs in malignant cells of both subtypes was weak, with the exception of TIMP-4 which was strongly expressed in the P-RCCs and downregulated in the CC-RCCs. The latter was correlated with chromosomal loss of 3p, harbouring the TIMP-4 gene locus. In conclusion, deregulated expression of the MMPs and TIMPs in RCCs differs according to histology, grade, size and cytogenetic characteristics, suggesting that MMP and TIMP expression patterns play an important role for the typical histomorphological features of RCC subtypes and their respective biological behaviour.

Carcinoma cells misuse the host tissue damage response to invade the brain

The metastatic colonization of the brain by carcinoma cells is still barely understood, in particular when considering interactions with the host tissue. The colonization comes with a substantial destruction of the surrounding host tissue. This leads to activation of damage responses by resident innate immune cells to protect, repair, and organize the wound healing, but may distract from tumoricidal actions. We recently demonstrated that microglia, innate immune cells of the CNS, assist carcinoma cell invasion. Here we report that this is a fatal side effect of a physiological damage response of the brain tissue. In a brain slice coculture model, contact with both benign and malignant epithelial cells induced a response by microglia and astrocytes comparable to that seen at the interface of human cerebral metastases. While the glial damage response intended to protect the brain from intrusion of benign epithelial cells by inducing apoptosis, it proved ineffective against various malignant cell types. They did not undergo apoptosis and actually exploited the local tissue reaction to invade instead. Gene expression and functional analyses revealed that the C‐X‐C chemokine receptor type 4 (CXCR4) and WNT signaling were involved in this process. Furthermore, CXCR4‐regulated microglia were recruited to sites of brain injury in a zebrafish model and CXCR4 was expressed in human stroke patients, suggesting a conserved role in damage responses to various types of brain injuries. Together, our findings point to a detrimental misuse of the glial damage response program by carcinoma cells resistant to glia‐induced apoptosis. GLIA 2013;61:1331–1346

Stromal endothelin B receptor-deficiency inhibits breast cancer growth and metastasis

The endothelin (ET) axis, often deregulated in cancers, is a promising target for anticancer strategies. Whereas previous investigations have focused mostly on ET action in malignant cells, we chose a model allowing separate assessment of the effects of ETs and their receptors ETAR and ETBR in the tumor cells and the stromal compartment, which is increasingly recognized as a key player in cancer progression. In homozygous spotting lethal rats (sl/sl), a model of constitutive ETBR deficiency, we showed significant reduction of growth and metastasis of MAT B III rat mammary adenocarcinoma cells overexpressing ETAR and ET-1 but negative for ETBR. Lack of stromal ETBR expression did not influence angiogenesis. However, it was correlated with diminished infiltration by tumor-associated macrophages and with reduced production of tumor necrosis factor-α, both known as powerful promoters of tumor progression. These effects were almost completely abolished in transgenic sl/sl rats, wherein ETBR function is restored by expression of an intact ETBR transgene. This shows that tumor growth and metastasis are critically dependent on ETBR function in cells of the microenvironment and suggests that successful ETR antagonist therapy should also target the stromal component of ET signaling.[Mol Cancer Ther 2009;8(8):2452–60]

Neutral sphingomyelinases control extracellular vesicles budding from the plasma membrane

ABSTRACT Extracellular vesicles (EVs) are membrane particles secreted from cells into all body fluids. Several EV populations exist differing in size and cellular origin. Using differential centrifugation EVs pelleting at 14,000 g (“microvesicles” (MV)) and 100,000 g (“exosomes”) are distinguishable by protein markers. Neutral sphingomyelinase (nSMase) inhibition has been shown to inhibit exosome release from cells and has since been used to study their functional implications. How nSMases (also known as SMPD2 and SMPD3) affect the basal secretion of MVs is unclear. Here we investigated how SMPD2/3 impact both EV populations. SMPD2/3 inhibition by GW4869 or RNAi decreases secretion of exosomes, but also increases secretion of MVs from the plasma membrane. Both populations differ significantly in metabolite composition and Wnt proteins are specifically loaded onto MVs under these conditions. Taken together, our data reveal a novel regulatory function of SMPD2/3 in vesicle budding from the plasma membrane and clearly suggest that – despite the different vesicle biogenesis – the routes of vesicular export are adaptable.

Characterisation of tumour-derived microvesicles in cancer patients’ blood and correlation with clinical outcome

ABSTRACT To evaluate whether tumour-derived microvesicles (T-MV), originating from the plasma membrane, represent suitable cancer biomarkers, we isolated MV from peripheral blood samples of cancer patients with locally advanced and/or metastatic solid tumours (n = 330, including 79 head & neck cancers, 74 lung cancers, 41 breast cancers, 28 colorectal cancers and 108 with other cancer forms) and controls (n = 103). Whole MV preparations were characterised using flow cytometry. While MV carrying the tumour-associated proteins MUC1, EGFR and EpCAM were found to be enhanced in a tumour-subtype-specific way in patients’ blood, expression of the matrix metalloproteinase inducer EMMPRIN was increased independent of tumour type. Higher levels of EMMPRIN+-MV correlated significantly with poor overall survival, whereas the other markers were prognostic only in specific tumour subgroups. By combining all four tumour-associated antigens, cancer patients were separated from healthy controls with an AUC of up to 0.85. Ex vivo, whole MV preparations from cancer patients, in contrast to those of controls, induced a tumour-supporting phenotype in macrophages and increased tumour cell invasion, which was dependent on the highly glycosylated isoform of EMMPRIN. In conclusion, the detection of T-MV in whole blood, even in minor amounts, is feasible with standard techniques, proves functionally relevant and correlates with clinical outcome.

Isolation and Characterization of Microvesicles from Peripheral Blood

The release of extracellular vesicles (EVs) including small endosomal-derived exosomes (Exos, diameter < 100 nm) and large plasma membrane-derived microvesicles (MVs, diameter > 100 nm) is a fundamental cellular process that occurs in all living cells. These vesicles transport proteins, lipids and nucleic acids specific for their cell of origin and in vitro studies have highlighted their importance as mediators of intercellular communication. EVs have been successfully isolated from various body fluids and especially EVs in blood have been identified as promising biomarkers for cancer or infectious diseases. In order to allow the study of MV subpopulations in blood, we present a protocol for the standardized isolation and characterization of MVs from peripheral blood samples. MVs are pelleted from EDTA-anticoagulated plasma samples by differential centrifugation and typically possess a diameter of 100 - 600 nm. Due to their larger size, they can easily be studied by flow cytometry, a technique that is routinely used in clinical diagnostics and available in most laboratories. Several examples for quality control assays of the isolated MVs will be given and markers that can be used for the discrimination of different MV subpopulations in blood will be presented.

Relaxins enhance growth of spontaneous murine breast cancers as well as metastatic colonization of the brain

Relaxins are known for their tissue remodeling capacity which is also a hallmark of cancer progression. However, their role in the latter context is still unclear, particularly in breast cancer. In a mouse model with spontaneously arising breast cancer due to erbB2-overexpression we show that exposure to porcine relaxin results in significantly enhanced tumour growth as compared to control animals. This is accompanied by increased serum concentrations of progesterone and estradiol as well as elevated expression of the respective receptors and the relaxin receptor RXFP1 in the tumour tissue. It is also associated with enhanced infiltration by tumour-associated macrophages which are known to promote tumour progression. Additionally, we show in an ex vivo model of metastatic brain colonization that porcine relaxin as well as human brain-specific relaxin-3 promotes invasion into the brain tissue and enhance interaction of breast cancer cells with the resident brain macrophages, the microglia. Relaxin signaling is mediated via RXFP1, since R 3/I5, a specific agonist of the relaxin-3 receptor RXFP3 in the brain, does not significantly enhance invasion. Taken together, these findings strongly support a role of relaxins in the progression of breast cancer where they foster primary tumour growth as well as metastatic colonization by direct and indirect means.

LEF1 reduces tumor progression and induces myodifferentiation in a subset of rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and show characteristics of skeletal muscle differentiation. The two major RMS subtypes in children are alveolar (ARMS) and embryonal RMS (ERMS). We demonstrate that approximately 50% of ARMS and ERMS overexpress the LEF1/TCF transcription factor LEF1 when compared to normal skeletal muscle and that LEF1 can restrain aggressiveness especially of ARMS cells. LEF1 knockdown experiments in cell lines reveal that depending on the cellular context, LEF1 can induce pro-apoptotic signals. LEF1 can also suppress proliferation, migration and invasiveness of RMS cells both in vitro and in vivo. Furthermore, LEF1 can induce myodifferentiation of the tumor cells. This may involve regulation of other LEF1/TCF factors i.e. TCF1, whereas β-catenin activity plays a subordinate role. Together these data suggest that LEF1 rather has tumor suppressive functions and attenuates aggressiveness in a subset of RMS.