Linda Bojmar

Tumour exosome integrins determine organotropic metastasis.

Ever since Stephen Paget’s 1889 hypothesis, metastatic organotropism has remained one of cancer’s greatest mysteries. Here we demonstrate that exosomes from mouse and human lung-, liver- and brain-tropic tumour cells fuse preferentially with resident cells at their predicted destination, namely lung fibroblasts and epithelial cells, liver Kupffer cells and brain endothelial cells. We show that tumour-derived exosomes uptaken by organ-specific cells prepare the pre-metastatic niche. Treatment with exosomes from lung-tropic models redirected the metastasis of bone-tropic tumour cells. Exosome proteomics revealed distinct integrin expression patterns, in which the exosomal integrins α6β4 and α6β1 were associated with lung metastasis, while exosomal integrin αvβ5 was linked to liver metastasis. Targeting the integrins α6β4 and αvβ5 decreased exosome uptake, as well as lung and liver metastasis, respectively. We demonstrate that exosome integrin uptake by resident cells activates Src phosphorylation and pro-inflammatory S100 gene expression. Finally, our clinical data indicate that exosomal integrins could be used to predict organ-specific metastasis.

STC1 Expression By Cancer-Associated Fibroblasts Drives Metastasis of Colorectal Cancer

Platelet-derived growth factor (PDGF) receptor signaling is a major functional determinant of cancer-associated fibroblasts (CAF). Elevated expression of PDGF receptors on stromal CAFs is associated with metastasis and poor prognosis, but mechanism(s) that underlie these connections are not understood. Here, we report the identification of the secreted glycoprotein stanniocalcin-1 (STC1) as a mediator of metastasis by PDGF receptor function in the setting of colorectal cancer. PDGF-stimulated fibroblasts increased migration and invasion of cocultured colorectal cancer cells in an STC1-dependent manner. Analyses of human colorectal cancers revealed significant associations between stromal PDGF receptor and STC1 expression. In an orthotopic mouse model of colorectal cancer, tumors formed in the presence of STC1-deficient fibroblasts displayed reduced intravasation of tumor cells along with fewer and smaller distant metastases formed. Our results reveal a mechanistic basis for understanding the contribution of PDGF-activated CAFs to cancer metastasis.

The role of microRNA-200 in progression of human colorectal and breast cancer.

The role of the epithelial-mesenchymal transition (EMT) in cancer has been studied extensively in vitro, but involvement of the EMT in tumorigenesis in vivo is largely unknown. We investigated the potential of microRNAs as clinical markers and analyzed participation of the EMT-associated microRNA-200–ZEB–E-cadherin pathway in cancer progression. Expression of the microRNA-200 family was quantified by real-time RT-PCR analysis of fresh-frozen and microdissected formalin-fixed paraffin-embedded primary colorectal tumors, normal colon mucosa, and matched liver metastases. MicroRNA expression was validated by in situ hybridization and after in vitro culture of the malignant cells. To assess EMT as a predictive marker, factors considered relevant in colorectal cancer were investigated in 98 primary breast tumors from a treatment-randomized study. Associations between the studied EMT-markers were found in primary breast tumors and in colorectal liver metastases. MicroRNA-200 expression in epithelial cells was lower in malignant mucosa than in normal mucosa, and was also decreased in metastatic compared to non-metastatic colorectal cancer. Low microRNA-200 expression in colorectal liver metastases was associated with bad prognosis. In breast cancer, low levels of microRNA-200 were related to reduced survival and high expression of microRNA-200 was predictive of benefit from radiotheraphy. MicroRNA-200 was associated with ER positive status, and inversely correlated to HER2 and overactivation of the PI3K/AKT pathway, that was associated with high ZEB1 mRNA expression. Our findings suggest that the stability of microRNAs makes them suitable as clinical markers and that the EMT-related microRNA-200 – ZEB – E-cadherin signaling pathway is connected to established clinical characteristics and can give useful prognostic and treatment-predictive information in progressive breast and colorectal cancers.

Identification of distinct nanoparticles and subsets of extracellular vesicles by asymmetric flow field-flow fractionation

The heterogeneity of exosomal populations has hindered our understanding of their biogenesis, molecular composition, biodistribution and functions. By employing asymmetric flow field-flow fractionation (AF4), we identified two exosome subpopulations (large exosome vesicles, Exo-L, 90–120 nm; small exosome vesicles, Exo-S, 60–80 nm) and discovered an abundant population of non-membranous nanoparticles termed ‘exomeres’ (~35 nm). Exomere proteomic profiling revealed an enrichment in metabolic enzymes and hypoxia, microtubule and coagulation proteins as well as specific pathways, such as glycolysis and mTOR signalling. Exo-S and Exo-L contained proteins involved in endosomal function and secretion pathways, and mitotic spindle and IL-2/STAT5 signalling pathways, respectively. Exo-S, Exo-L and exomeres each had unique N-glycosylation, protein, lipid, DNA and RNA profiles and biophysical properties. These three nanoparticle subsets demonstrated diverse organ biodistribution patterns, suggesting distinct biological functions. This study demonstrates that AF4 can serve as an improved analytical tool for isolating extracellular vesicles and addressing the complexities of heterogeneous nanoparticle subpopulations.Lyden and colleagues use asymmetric flow field-flow fractionation to classify nanoparticles derived from cell lines and human samples, including previously uncharacterized large, Exo-L and small, Exo-S, exosome subsets.

MicroRNA-199a and -214 as potential therapeutic targets in pancreatic stellate cells in pancreatic tumor

Pancreatic stellate cells (PSCs) are the key precursor cells for cancer-associated fibroblasts (CAFs) in pancreatic tumor stroma. In this study, we explored miRNA as therapeutic targets in tumor stroma and found miR-199a-3p and miR-214-3p induced in patient-derived pancreatic CAFs and TGF-β-activated human PSCs (hPSCs). Inhibition of miR-199a/-214 using hairpin inhibitors significantly inhibited TGFβ-induced differentiation markers (e.g. α-SMA, collagen, PDGFβR), migration and proliferation. Furthermore, heterospheroids of Panc-1 and hPSCs attained smaller size with hPSCs transfected with anti-miR-199a/-214 compared to control anti-miR. The conditioned medium obtained from TGFβ-activated hPSCs induced tumor cell growth and endothelial cell tube formation. Interestingly, these inductions were abrogated in hPSCs transfected with anti-miR-199a or miR-214. Moreover, IPA analyses revealed signaling pathways related to miR-199a (TP53, mTOR, Smad1) and miR-214 (PTEN, Bax, ING4). Taken together, this study reveals miR-199a-3p and miR-214-3p as major regulators of PSC activation and PSC-induced pro-tumoral effects, representing them as key therapeutic targets in pancreatic cancer.

IL-1α Expression in Pancreatic Ductal Adenocarcinoma Affects the Tumor Cell Migration and Is Regulated by the p38MAPK Signaling Pathway

The interplay between the tumor cells and the surrounding stroma creates inflammation, which promotes tumor growth and spread. The inflammation is a hallmark for pancreatic adenocarcinoma (PDAC) and is to high extent driven by IL-1α. IL-1α is expressed and secreted by the tumor cells and exerting its effect on the stroma, i.e. cancer associated fibroblasts (CAF), which in turn produce massive amount of inflammatory and immune regulatory factors. IL-1 induces activation of transcription factors such as nuclear factor-κβ (NF-κβ), but also activator protein 1 (AP-1) via the small G-protein Ras. Dysregulation of Ras pathways are common in cancer as this oncogene is the most frequently mutated in many cancers. In contrast, the signaling events leading up to the expression of IL-1α by tumor cells are not well elucidated. Our aim was to examine the signaling cascade involved in the induction of IL-1α expression in PDAC. We found p38MAPK, activated by the K-Ras signaling pathway, to be involved in the expression of IL-1α by PDAC as blocking this pathway decreased both the gene and protein expression of IL-1α. Blockage of the P38MAPK signaling in PDAC also dampened the ability of the tumor cell to induce inflammation in CAFs. In addition, the IL-1α autocrine signaling regulated the migratory capacity of PDAC cells. Taken together, the blockage of signaling pathways leading to IL-1α expression and/or neutralization of IL-1α in the PDAC microenvironment should be taken into consideration as possible treatment or complement to existing treatment of this cancer.

Conventional, but not remote ischemic preconditioning, reduces iNOS transcription in liver ischemia/reperfusion

AIM To study the effects of preconditioning on inducible nitric oxide synthase (iNOS) and interleukin 1 (IL-1) receptor transcription in rat liver ischemia/reperfusion injury (IRI). METHODS Seventy-two male rats were randomized into 3 groups: the one-hour segmental ischemia (IRI, n = 24) group, the ischemic preconditioning (IPC, n = 24) group or the remote ischemic preconditioning (R-IPC, n = 24) group. The IPC and R-IPC were performed as 10 min of ischemia and 10 min of reperfusion. The iNOS and the IL-1 receptor mRNA in the liver tissue was analyzed with real time PCR. The total Nitrite and Nitrate (NOx) in continuously sampled microdialysate (MD) from the liver was analyzed. In addition, the NOx levels in the serum were analyzed. RESULTS After 4 h of reperfusion, the iNOS mRNA was significantly higher in the R-IPC (ΔCt: 3.44 ± 0.57) group than in the IPC (ΔCt: 5.86 ± 0.82) group (P = 0.025). The IL-1 receptor transcription activity was reduced in the IPC group (ΔCt: 1.88 ± 0.53 to 4.81 ± 0.21), but not in the R-IPC group, during reperfusion (P = 0.027). In the MD, a significant drop in the NOx levels was noted in the R-IPC group (12.3 ± 2.2 to 4.7 ± 1.2 μmol/L) at the end of ischemia compared with the levels in early ischemia (P = 0.008). A similar trend was observed in the IPC group (11.8 ± 2.1 to 6.4 ± 1.5 μmol/L), although this difference was not statistically significant. The levels of NOx rose quickly during reperfusion in both groups. CONCLUSION IPC, but not R-IPC, reduces iNOS and IL-1 receptor transcription during early reperfusion, indicating a lower inflammatory reaction. NOx is consumed in the ischemic liver lobe.

Remote or Conventional Ischemic Preconditioning -Local Liver Metabolism in Rats Studied with Microdialysis

BACKGROUND Ischemic preconditioning (IPC) of the liver decreases liver injury secondary to ischemia and reperfusion. An attractive alternative to IPC is remote ischemic preconditioning (R-IPC), but these two methods have not previously been compared. MATERIAL AND METHODS Eighty-seven rats were randomized into four groups: sham operated (n = 15), 1 h segmental ischemia (IRI, n = 24), preceded by IPC (n = 24), or R-IPC (n = 24) (to the left hindleg). IPC and R-IPC were performed with 10 min ischemia and 10 min of reperfusion. Analyses of liver microdialysate (MD), serum transaminase levels, and liver histology were made. RESULTS Rats treated with IPC and R-IPC had significantly lower AST, 71.5 (19.6) IU/L respective 96.6 (12.4) at 4 h reperfusion than those subjected to IRI alone, 155 (20.9), P = 0.0004 and P = 0.04 respectively. IPC also had lower ALT levels, 41.6 (11.3) IU/L than had IRI 107.4 (15.5), P = 0.003. The MD glycerol was significantly higher during ischemia in the R-IPC [759 (84) μM] and the IRI [732 (67)] groups than in the IPC 514 (70) group, P = 0.022 and P = 0.046 respectively. The MD glucose after ischemia was lower in the IPC group 7.1 (1.2) than in the IRI group 12.7 (1.6), P = 0.005. Preconditioning to the liver caused an direct increase in lactate, glucose and glycerol in the ischemic segment compared with the control segment an effect not seen in the R-IPC and IRI groups. CONCLUSIONS IPC affects glucose metabolism in the rat liver, observed with MD. IPC reduces liver cell injury during ischemic and reperfusion in rats. R-IPC performed over the same length of time as IPC does not have the same effect as the latter on ALT levels and MD glycerol; this may suggest that R-IPC does not offer the same protection as IPC in this setting of rat liver IRI.

Variant ribosomal RNA alleles are conserved and exhibit tissue-specific expression

Ribosomal RNA sequence variants are conserved, exhibit tissue-specific expression, and are found in actively translating ribosomes. The ribosome, the integration point for protein synthesis in the cell, is conventionally considered a homogeneous molecular assembly that only passively contributes to gene expression. Yet, epigenetic features of the ribosomal DNA (rDNA) operon and changes in the ribosome’s molecular composition have been associated with disease phenotypes, suggesting that the ribosome itself may possess inherent regulatory capacity. Analyzing whole-genome sequencing data from the 1000 Genomes Project and the Mouse Genomes Project, we find that rDNA copy number varies widely across individuals, and we identify pervasive intra- and interindividual nucleotide variation in the 5S, 5.8S, 18S, and 28S ribosomal RNA (rRNA) genes of both human and mouse. Conserved rRNA sequence heterogeneities map to functional centers of the assembled ribosome, variant rRNA alleles exhibit tissue-specific expression, and ribosomes bearing variant rRNA alleles are present in the actively translating ribosome pool. These findings provide a critical framework for exploring the possibility that the expression of genomically encoded variant rRNA alleles gives rise to physically and functionally heterogeneous ribosomes that contribute to mammalian physiology and human disease.

Nitrite, a novel method to decrease ischemia/reperfusion injury in the rat liver.

AIM To investigate whether nitrite administered prior to ischemia/reperfusion (I/R) reduces liver injury. METHODS Thirty-six male Sprague-Dawley rats were randomized to 3 groups, including sham operated (n = 8), 45-min segmental ischemia of the left liver lobe (IR, n = 14) and ischemia/reperfusion (I/R) preceded by the administration of 480 nmol of nitrite (n = 14). Serum transaminases were measured after 4 h of reperfusion. Liver microdialysate (MD) was sampled in 30-min intervals and analyzed for glucose, lactate, pyruvate and glycerol as well as the total nitrite and nitrate (NOx). The NOx was measured in serum. RESULTS Aspartate aminotransferase (AST) at the end of reperfusion was higher in the IR group than in the nitrite group (40 ± 6.8 μkat/L vs 22 ± 2.6 μkat/L, P = 0.022). Similarly, alanine aminotransferase (ALT) was also higher in the I/R group than in the nitrite group (34 ± 6 μkat vs 14 ± 1.5 μkat, P = 0.0045). The NOx in MD was significantly higher in the nitrite group than in the I/R group (10.1 ± 2.9 μmol/L vs 3.2 ± 0.9 μmol/L, P = 0.031) after the administration of nitrite. During ischemia, the levels decreased in both groups and then increased again during reperfusion. At the end of reperfusion, there was a tendency towards a higher NOx in the I/R group than in the nitrite group (11.6 ± 0.7 μmol/L vs 9.2 ± 1.1 μmol/L, P = 0.067). Lactate in MD was significantly higher in the IR group than in the nitrite group (3.37 ± 0.18 mmol/L vs 2.8 ± 0.12 mmol/L, P = 0.01) during ischemia and the first 30 min of reperfusion. During the same period, glycerol was also higher in the IRI group than in the nitrite group (464 ± 38 μmol/L vs 367 ± 31 μmol/L, P = 0.049). With respect to histology, there were more signs of tissue damage in the I/R group than in the nitrite group, and 29% of the animals in the I/R group exhibited necrosis compared with none in the nitrite group. Inducible nitric oxide synthase transcription increased between early ischemia (t = 15) and the end of reperfusion in both groups. CONCLUSION Nitrite administered before liver ischemia in the rat liver reduces anaerobic metabolism and cell necrosis, which could be important in the clinical setting.