Immortalization and transformation of primary cells mediated by engineered ecDNAs

Focal gene amplifications are among the most common cancer-associated mutations, but their evolution and contribution to tumorigenesis have proven challenging to recapitulate in primary cells and model organisms. Here we describe a general approach to engineer large (>1 Mbp) focal amplifications mediated by extrachromosomal circular DNAs (ecDNAs, also known as "double minutes") in a spatiotemporally controlled manner in cancer cell lines and in primary cells derived from genetically engineered mice. With this strategy, ecDNA formation can be coupled with expression of fluorescent reporters or other selectable markers to enable the identification and tracking of ecDNA-containing cells. We demonstrate the feasibility of this approach by engineering MDM2-containing ecDNAs in near-diploid human cells, showing that GFP expression can be used to track ecDNA dynamics under physiological conditions or in the presence of specific selective pressures. We also apply this approach to generate mice harboring inducible Myc - and Mdm2 -containing ecDNAs analogous to those spontaneously occurring in human cancers. We show that the engineered ecDNAs rapidly accumulate in primary cells derived from these animals, promoting proliferation, immortalization, and transformation.

ERα-LBD, an isoform of estrogen receptor alpha, promotes breast cancer proliferation and endocrine resistance

Estrogen receptor alpha (ERα) drives mammary gland development and breast cancer (BC) growth through an evolutionarily conserved linkage of DNA binding and hormone activation functions. Therapeutic targeting of the hormone binding pocket is a widely utilized and successful strategy for breast cancer prevention and treatment. However, resistance to this endocrine therapy is frequently encountered and may occur through bypass or reactivation of ER-regulated transcriptional programs. We now identify the induction of an ERα isoform, ERα-LBD, that is encoded by an alternative ESR1 transcript and lacks the activation function and DNA binding domains. Despite lacking the transcriptional activity, ERα-LBD is found to promote breast cancer growth and resistance to the ERα antagonist fulvestrant. ERα-LBD is predominantly localized to the cytoplasm and mitochondria of BC cells and leads to enhanced glycolysis, respiration and stem-like features. Intriguingly, ERα-LBD expression and function does not appear to be restricted to cancers that express full length ERα but also promotes growth of triple-negative breast cancers and ERα-LBD transcript (ESR1-LBD) is also present in BC samples from both ERα(+) and ERα(-) human tumors. These findings point to ERα-LBD as a potential mediator of breast cancer progression and therapy resistance.

Inducible and reversible inhibition of miRNA-mediated gene repression in vivo

Although virtually all gene networks are predicted to be controlled by miRNAs, the contribution of this important layer of gene regulation to tissue homeostasis in adult animals remains unclear. Gain and loss-of-function experiments have provided key insights into the specific function of individual miRNAs, but effective genetic tools to study the functional consequences of global inhibition of miRNA activity in vivo are lacking. Here we report the generation and characterization of a genetically engineered mouse strain in which miRNA-mediated gene repression can be reversibly inhibited without affecting miRNA biogenesis or abundance. We demonstrate the usefulness of this strategy by investigating the consequences of acute inhibition of miRNA function in adult animals. We find that different tissues and organs respond differently to global loss of miRNA function. While miRNA-mediated gene repression is essential for the homeostasis of the heart and the skeletal muscle, it is largely dispensable in the majority of other organs. Even in tissues where it is not required for homeostasis, such as the intestine and hematopoietic system, miRNA activity can become essential during regeneration following acute injury. These data support a model where many metazoan tissues primarily rely on miRNA function to respond to potentially pathogenic events.

High-Resolution In Vivo Identification of miRNA Targets by Halo-Enhanced Ago2 Pull-Down

The identification of microRNA (miRNA) targets by Ago2 crosslinking-immunoprecipitation (CLIP) methods has provided major insights into the biology of this important class of non-coding RNAs. However, these methods are technically challenging and not easily applicable to an in vivo setting. To overcome these limitations and facilitate the investigation of miRNA functions in vivo, we have developed a method based on a genetically engineered mouse harboring a conditional Halo-Ago2 allele expressed from the endogenous Ago2 locus. By using a resin conjugated to the HaloTag ligand, Ago2-miRNA-mRNA complexes can be purified from cells and tissues expressing the endogenous Halo-Ago2 allele. We demonstrate the reproducibility and sensitivity of this method in mouse embryonic stem cells, developing embryos, adult tissues, and autochthonous mouse models of human brain and lung cancers. This method and the datasets we have generated will facilitate the characterization of miRNA-mRNA networks in vivo under physiological and pathological conditions.

Evolution of Cancer Stem-like Cells in Endocrine-Resistant Metastatic Breast Cancers Is Mediated by Stromal Microvesicles

The hypothesis that microvesicle-mediated miRNA transfer converts noncancer stem cells into cancer stem cells (CSC) leading to therapy resistance remains poorly investigated. Here we provide direct evidence supporting this hypothesis, by demonstrating how microvesicles derived from cancer-associated fibroblasts (CAF) transfer miR-221 to promote hormonal therapy resistance (HTR) in models of luminal breast cancer. We determined that CAF-derived microvesicles horizontally transferred miR-221 to tumor cells and, in combination with hormone therapy, activated an ER^lo/Notch^hi feed-forward loop responsible for the generation of CD133^hi CSCs. Importantly, microvesicles from patients with HTR metastatic disease expressed high levels of miR-221. We further determined that the IL6-pStat3 pathway promoted the biogenesis of onco-miR-221^hi CAF microvesicles and established stromal CSC niches in experimental and patient-derived breast cancer models. Coinjection of patient-derived CAFs from bone metastases led to de novo HTR tumors, which was reversed with IL6R blockade. Finally, we generated patient-derived xenograft (PDX) models from patient-derived HTR bone metastases and analyzed tumor cells, stroma, and microvesicles. Murine and human CAFs were enriched in HTR tumors expressing high levels of CD133^hi cells. Depletion of murine CAFs from PDX restored sensitivity to HT, with a concurrent reduction of CD133^hi CSCs. Conversely, in models of CD133^neg, HT-sensitive cancer cells, both murine and human CAFs promoted de novo HT resistance via the generation of CD133^hi CSCs that expressed low levels of estrogen receptor alpha. Overall, our results illuminate how microvesicle-mediated horizontal transfer of genetic material from host stromal cells to cancer cells triggers the evolution of therapy-resistant metastases, with potentially broad implications for their control. Cancer Res; 77(8); 1927-41. ©2017 AACR.

Antagonism of the cannabinoid CB-1 receptor protects rat liver against ischaemia-reperfusion injury complicated by endotoxaemia

BACKGROUND/AIM

Endotoxaemia can complicate hepatic ischaemia-reperfusion (IR) injury. Endocannabinoids appear to modulate the haemodynamic alterations and cytokine response induced by lipopolysaccharide (LPS). Thus, we aimed to determine the effect of the endocannabinoid CB1-receptor antagonist Rimonabant in a model of hepatic IR injury complicated by endotoxaemia.

METHODS

Sprague-Dawley rats pre-treated with Rimonabant 3 or 10 mg/kg or vehicle underwent partial hepatic IR and lipopolysaccharide (LPS) injection at reperfusion. Liver injury was evaluated by serum alanine aminotransferase (ALT) and necrotic-cell count. The inflammatory response was investigated by assessing hepatic neutrophil infiltration, tumour necrosis factor alpha (TNFalpha), interferon gamma (IFNgamma), interleukin 6 (IL6), and suppressor of cytokine signalling (SOCS) 1 and SOCS3 gene expression by real-time polymerase chain reaction (RT-PCR). Systolic blood pressure and hepatic blood flow were measured as haemodynamic parameters. Finally, lipid peroxidation, glutathione status, and immunoreactive CB1 receptor expression in the liver were also determined.

RESULTS

Liver injury and neutrophil infiltration occurring in the late-phase of LPS-enhanced IR were significantly reduced by CB1-receptor antagonism. Rimonabant-treated rats showed significantly higher gene expression of IFNgamma, IL6, SOCS1 and SOCS3 in "early" reperfusion, while that of TNFalpha was reduced. These findings were associated with increased STAT3 phosphorylation. Furthermore, CB1-receptor antagonism significantly improved the oxidative injury and haemodynamic alterations occurring during reperfusion in untreated rats. Finally, CB1-receptor immunoreactivity was upregulated early after reperfusion.

CONCLUSIONS

This study demonstrates that CB1-receptor antagonism protects the liver against LPS-enhanced IR injury by interfering with the inflammatory response that causes the late, neutrophil-dependent phase of reperfusion injury, although the prevention of the transient endotoxin-related hypotension occurring early during reperfusion may be also involved.