The miR-15a/16-1 and miR-15b/16-2 clusters regulate early B cell development by limiting IL7R receptor expression

MicroRNAs are small non-coding RNAs that have emerged as post-transcriptional regulators involved in development and function of different types of immune cells, and aberrant miRNA expression has often been linked to cancer. One prominent miRNA family in the latter setting is the miR-15 family, consisting of the three clusters miR-15a/16-1, miR-15b/16-2 and miR-497/195, which is best known for its prominent tumor suppressive role in chronic lymphocytic leukemia (CLL). However, little is known about the physiological role of the miR-15 family. In this study, we provide a comprehensive in vivo analysis of the physiological functions of miR-15a/16-1 and miR-15b/16-2, both of which are highly expressed in immune cells, in early B cell development. In particular, we report a previously unrecognized physiological function of the miR-15 family in restraining progenitor B cell expansion, as loss of both clusters induces an increase of the pro-B as well as pre-B cell compartments. Mechanistically, we find that the miR-15 family mediates its function through repression of at least two different types of target genes: First, we confirm that the miR-15 family suppresses several prominent cell cycle regulators such as Ccne1, Ccnd3 and Cdc25a also in vivo, thereby limiting the proliferation of progenitor B cells. Second, this is complemented by direct repression of the Il7r gene, which encodes the alpha chain of the IL-7 receptor (IL7R), one of the most critical growth factor receptors for early B cell development. In consequence, deletion of the miR-15a/16-1 and miR-15b/16-2 clusters stabilizes Il7r transcripts, resulting in enhanced IL7R surface expression. Consistently, our data show an increased activation of PI3K/AKT, a key signaling pathway downstream of the IL7R, which likely drives the progenitor B cell expansion we describe here. Thus, by deregulating a target gene network of cell cycle and signaling mediators, loss of the miR-15 family establishes a pro-proliferative milieu that manifests in an enlarged progenitor B cell pool.

The miR-26 family regulates early B cell development and transformation

MiRNAs are small noncoding RNAs that promote the sequence-specific repression of their respective target genes, thereby regulating diverse physiological as well as pathological processes. Here, we identify a novel role of the miR-26 family in early B cell development. We show that enhanced expression of miR-26 family members potently blocks the pre-B to immature B cell transition, promotes pre-B cell expansion and eventually enables growth factor independency. Mechanistically, this is at least partially mediated by direct repression of the tumor-suppressor Pten, which consequently enhances PI3K-AKT signaling. Conversely, limiting miR-26 activity in a more physiological loss-of-function approach counteracts proliferation and enhances pre-B cell differentiation in vitro as well as in vivo. We therefore postulate a rheostat-like role for the miR-26 family in progenitor B cells, with an increase in mature miR-26 levels signaling cell expansion, and facilitating pre-B to the immature B cell progression when reduced.

Differential roles of miR-15a/16-1 and miR-497/195 clusters in immune cell development and homeostasis

MicroRNAs (miRNAs) post-transcriptionally repress almost all genes in mammals and thereby form an additional layer of gene regulation. As such, miRNAs impact on nearly every physiological process and have also been associated with cancer. Prominent examples of such miRNAs can be found in the miR-15 family, composed of the bicistronic clusters miR-15a/16-1, miR-15b/16-2, and miR-497/195. In particular, the miR-15a/16-1 cluster is deleted in almost two thirds of all chronic B lymphocytic leukemia (CLL) cases, a phenotype that is also recapitulated by miR-15a/16-1-deficient as well as miR-15b/16-2-deficient mice. Under physiological conditions, those two clusters have been implicated in T-cell function, and B-cell and natural killer (NK) cell development; however, it is unclear whether miR-497 and miR-195 confer similar roles in health and disease. Here, we have generated a conditional mouse model for tissue-specific deletion of miR-497 and miR-195. While mice lacking miR-15a/16-1 in the hematopoietic compartment developed clear signs of CLL over time, aging mice deficient for miR-497/195 did not show such a phenotype. Likewise, loss of miR-15a/16-1 impaired NK and early B-cell development, whereas miR-497/195 was dispensable for these processes. In fact, a detailed analysis of miR-497/195-deficient mice did not reveal any effect on steady-state hematopoiesis or immune cell function. Unexpectedly, even whole-body deletion of the cluster was well-tolerated and had no obvious impact on embryonic development or healthy life span. Therefore, we postulate that the miR-497/195 cluster is redundant to its paralog clusters or that its functional relevance is restricted to certain physiological and pathological conditions.

Skin dendritic cells in melanoma are key for successful checkpoint blockade therapy

BACKGROUND

Immunotherapy with checkpoint inhibitors has shown impressive results in patients with melanoma, but still many do not benefit from this line of treatment. A lack of tumor-infiltrating T cells is a common reason for therapy failure but also a loss of intratumoral dendritic cells (DCs) has been described.

METHODS

We used the transgenic tg(Grm1)EPv melanoma mouse strain that develops spontaneous, slow-growing tumors to perform immunological analysis during tumor progression. With flow cytometry, the frequencies of DCs and T cells at different tumor stages and the expression of the inhibitory molecules programmed cell death protein-1 (PD-1) and T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) on T cells were analyzed. This was complemented with RNA-sequencing (RNA-seq) and real-time quantitative PCR (RT-qPCR) analysis to investigate the immune status of the tumors. To boost DC numbers and function, we administered Fms-related tyrosine 3 ligand (Flt3L) plus an adjuvant mix of polyI:C and anti-CD40. To enhance T cell function, we tested several checkpoint blockade antibodies. Immunological alterations were characterized in tumor and tumor-draining lymph nodes (LNs) by flow cytometry, CyTOF, microarray and RT-qPCR to understand how immune cells can control tumor growth. The specific role of migratory skin DCs was investigated by coculture of sorted DC subsets with melanoma-specific CD8+ T cells.

RESULTS

Our study revealed that tumor progression is characterized by upregulation of checkpoint molecules and a gradual loss of the dermal conventional DC (cDC) 2 subset. Monotherapy with checkpoint blockade could not restore antitumor immunity, whereas boosting DC numbers and activation increased tumor immunogenicity. This was reflected by higher numbers of activated cDC1 and cDC2 as well as CD4+ and CD8+ T cells in treated tumors. At the same time, the DC boost approach reinforced migratory dermal DC subsets to prime gp100-specific CD8+ T cells in tumor-draining LNs that expressed PD-1/TIM-3 and produced interferon γ (IFNγ)/tumor necrosis factor α (TNFα). As a consequence, the combination of the DC boost with antibodies against PD-1 and TIM-3 released the brake from T cells, leading to improved function within the tumors and delayed tumor growth.

CONCLUSIONS

Our results set forth the importance of skin DC in cancer immunotherapy, and demonstrates that restoring DC function is key to enhancing tumor immunogenicity and subsequently responsiveness to checkpoint blockade therapy.

SAFB2 Enables the Processing of Suboptimal Stem-Loop Structures in Clustered Primary miRNA Transcripts

Many microRNAs (miRNAs) are generated from primary transcripts containing multiple clustered stem-loop structures that are thought to be recognized and cleaved by the Microprocessor complex as independent units. Here, we uncover an unexpected mode of processing of the bicistronic miR-15a-16-1 cluster. We find that the primary miR-15a stem-loop is not processed on its own but that the presence of the neighboring primary miR-16-1 stem-loop on the same transcript can compensate for this deficiency in cis. Using a CRISPR/Cas9 screen, we identify SAFB2 (scaffold attachment factor B2) as an essential co-factor in this miR-16-1-assisted pri-miR-15 cleavage and describe SAFB2 as an accessory protein of the Microprocessor. Notably, SAFB2-mediated cleavage expands to other clustered pri-miRNAs, indicating a general mechanism. Together, our study reveals an unrecognized function of SAFB2 in miRNA processing and suggests a scenario in which SAFB2 enables the binding and processing of suboptimal Microprocessor substrates in clustered primary miRNA transcripts.

Abstract A102: Rescue of lost skin dendritic cells in melanoma is key for the resuscitation of antitumor T-cell responses

One major characteristic of skin-related cancers is the loss of skin-resident dendritic cell populations. In the tg(Grm1)EPv mouse model, ectopic expression of the metabotropic glutamate receptor-1 in melanocytes leads to a highly proliferative and antiapoptotic phenotype, resulting in melanoma formation within the dermis. The slow progression of these tumors allows for the in depth analysis of the immune infiltrate in growing tumors. We here show that total DCs (CD11c+ cells) are gradually lost as the tumor progresses. Mainly the dermal CD11b+ DCs are affected, whereas epidermal Langerhans cells remain unchanged. We hypothesized that extrinsic cell death of the DCs may be induced within the growing tumor. Indeed, the tumor tissue upregulated the expression of Fas ligand (FasL) that can induce extrinsic apoptosis in immature DCs that express Fas (CD95). Fas-mediated apoptosis depends on the activation of caspase-8 and mice in which the autoproteolytic cleavage site D387 is mutated to alanine (casp8D387A/casp8D387A) show strong resistance to Fas-mediated death. We compared the apoptosis induction in the different DC subsets in casp8WT/casp8WT and in casp8D387A/casp8D387A upon intradermal administration of an agonistic anti-CD95 antibody and we found that, indeed, CD11b+ DCs in WT mice are susceptible to apoptosis via CD95. In order to retrieve the intratumoral DCs, we treated tg(Grm1)EPv mice carrying tumor lesions with Flt3L and the percentages of the CD11b+ subset could be restored back to the levels of tumor-free mice. At the same time, T-cells from both the tumor and the tumor-draining lymph node were able to produce more cytotoxic cytokines. Our data thus indicate that the loss of DCs in melanoma depends on induction of apoptosis within the tumor; rescue of skin DCs may be a promising strategy in order to enhance the efficacy of existing immunotherapeutic strategies against skin-related cancers.

Citation Format: Anastasia Prokopi, Christoph H. Tripp, Bart Tummers, Kerstin Komenda, Katharina Hutter, Giuseppe Cappellano, Lydia Bellmann, Mirjana Efremova, Zlatko Trajanoski, Suzie Chen, Bjorn E. Clausen, Douglas R. Green, Patrizia Stoitzner. Rescue of lost skin dendritic cells in melanoma is key for the resuscitation of antitumor T-cell responses [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A102.

A Physical–biological Coupled Model for Algal Dynamics in Lakes

A coupled model is presented for simulating physical and biological dynamics in fresh water lakes. The physical model rests upon the assumption that the turbulent kinetic energy in a water column of the lake is fully contained in a mixed layer of variable depth. Below this layer the mechanical energy content is assumed to vanish. Additionally, the horizontal currents are ignored. This one-dimensional two-layered model describes the internal conversion of the mechanical and thermal energy input from the atmosphere into an evolution of the mixed layer depth by entrainment and detrainment mechanisms. It is supposed to form the physical domain in which the simulation of the biological processes takes place. The biological model describes mathematically the typical properties of phyto- and zooplankton, their interactions and their response to the physical environment. This description then allows the study of the behaviour of Lagrangian clusters of virtual plankton that are subjected to such environments. The essence of the model is the dynamical simulation of an arbitrary number of nutrient limited phytoplankton species and one species of zooplankton. The members of the food web above and below affect the model only statically. The model is able to reproduce the typical progression of a predator-prey interaction between phyto- and zooplankton as well as the exploitative competition for nutrients between two phytoplankton species under grazing pressure of Daphnia. It suggests that the influence of the biological system on the physical system results in a weak increase of the surface temperature for coupled simulations, but a considerably higher seasonal thermocline in spring and a lower one in autumn.

[Acute myocardial infarction mortality in a hospital department during the last decades]

Authors surveyed the data of 2677 patients with acute myocardial infarction treated in cardiological department between 1970 and 1993. Activity of Coronary Care Unit (has been working from 1974) reduced the earlier hospital mortality in general internal medicine possibilities with 50%. Main cause of this reduction was the temporal electrotherapy of cardiac arrhythmias. Since the middle of last decade the goal of has been generally introduced combined therapy (beta-blockers, intravenous nitrates, acetyl-salicic acid, thrombolytics) is to reduce the mass of damaged myocardium and hereby increasing the ratio of survival. They reduced the hospital mortality around 10% with consistent application of this therapy. According to the authors application of thrombolytic therapy has basic importance in management of myocardial infarction, but they could not treat a lot of patients with streptokinase in consequence of too long prehospital time period and not properly controlled hypertension. The proportion of systemic thrombolytic therapy on their patients is almost a quarter of them. It would be very important to increase this beneficial ratio with reducing the time of patients decision to turn to health care and applying systemic thrombolytic therapy more than six hours after the onset of symptoms of myocardial infarction.

Further characterization of acquired-resistance to Cisplatin in a rat ovarian tumor-cell line

The proliferation of a rat ovarian tumor cell line (O-342) was completely inhibited by a 2 h exposure to 20 muM cisplatin (DDP) in vitro up to 120 h after its removal, while in its DDP resistant subline (O-342/DDP), the same treatment only caused a transient growth inhibition within the first 24 h post the exposure, followed by the recovery of proliferation at a similar rate as the control cells. DNA interstrand cross links (ISCL) were maximally formed 12 h post DDP treatment in either O-342 or O-342/DDP cells, with a 2.8-fold increase in the sensitive cells at this time (262 vs. 95 rad eq.). After further 12 h incubation, however, 75% of DNA-ISCL was removed in O-342/DDP cells, while only 22% of them were repaired in O-342 cells. DNA single strand breaks (SSB) were produced to a similar extent in both lines but reached a maximum at 12 and 24 h in the resistant and the sensitive cells, respectively. ADP-ribosyl transferase (ADPRT) activity, a DNA repair-associated enzyme, was 2.6-fold higher in O-342/DDP cells compared to the sensitive subline. Following DDP treatment, the activity was stimulated in the sensitive cells with a maximum of about 1.5-fold at 24 h, whereas the inhibitory effect was observed in the resistant cells, although at 12 h it recovered almost to the control level. Flow cytometric analysis showed that there were at least two sub-populations (2n and 4n) in O-342 cells, while only 2n population was observed in O-342/DDP cells. Following DDP exposure, O-342/DDP cells progressed through the cell cycle with only a small and transient accumulation of cells in S-phase at 12 h and 24 h, while in the sensitive cells, it was impossible to distinguish cell-cycle distribution at 12 h due to severe damage, at 24 h most of the cells became arrested in G2-phases, which persisted until the end of the observation (48 h). Our results suggest that both reduced interaction of cellular DNA with DDP and increased DNA repair are contributing factors for development of DDP resistance, which might be directly or indirectly subsequent to alterations of poly (ADP-ribose) metabolism in the resistant cells.