CD74 is dispensable for development of chronic lymphocytic leukemia in Eµ-TCL1 transgenic mice.

CD74 is a surface protein expressed on immune cells, which acts as receptor for the chemokine macrophage migration inhibitory factor (MIF). Signaling via the MIF/CD74-axis has been reported to be important for the pathogenesis of chronic lymphocytic leukemia (CLL). We wanted to clarify the role of CD74 in MIF-induced signaling/leukemic development. In Eµ-TCL1 transgenic mice, occurrence of the leukemic phenotype was associated with increased surface CD74 expression. Eµ-TCL1+/+Cd74-/- mice showed similar kinetics and clinical features of CLL development as Eµ-TCL1+/+ mice. MIF stimulation of leukemic splenocytes led to AKT activation in a CD74-dependent manner. AKT activation was reduced in Cd74-deficient splenocytes in the presence of the oncogenic TCL1-transgene. Tumor cell apoptosis/proliferation were unaffected in Eµ-TCL1+/+Cd74-/- mice. Our data suggest that the need for active CD74 signaling is overcome in the leukemic context of TCL1-driven CLL, and that CD74 may have a dispensable role for CLL pathogenesis in this model.

Elevation in type I interferons inhibits HCN1 and slows cortical neuronal oscillations.

Central nervous system (CNS) inflammation involves the generation of inducible cytokines such as interferons (IFNs) and alterations in brain activity, yet the interplay of both is not well understood. Here, we show that in vivo elevation of IFNs by viral brain infection reduced hyperpolarization-activated currents (Ih) in cortical pyramidal neurons. In rodent brain slices directly exposed to type I IFNs, the hyperpolarization-activated cyclic nucleotide (HCN)-gated channel subunit HCN1 was specifically affected. The effect required an intact type I receptor (IFNAR) signaling cascade. Consistent with Ih inhibition, IFNs hyperpolarized the resting membrane potential, shifted the resonance frequency, and increased the membrane impedance. In vivo application of IFN-ß to the rat and to the mouse cerebral cortex reduced the power of higher frequencies in the cortical electroencephalographic activity only in the presence of HCN1. In summary, these findings identify HCN1 channels as a novel neural target for type I IFNs providing the possibility to tune neural responses during the complex event of a CNS inflammation.

Plasticity-related gene 3 promotes neurite shaft protrusion.

BACKGROUND: Recently, we and others proposed plasticity-related gene 3 (PRG3) as a novel molecule in neuritogenesis based on PRG3 overexpression experiments in neuronal and non-neuronal cell lines. However, direct information on PRG3 effects in neuronal development and, in particular, its putative spatio-temporal distribution and conditions of action, is sparse. RESULTS: We demonstrate here that PRG3 induces filopodia formation in HEK293 cells depending on its N-glycosylation status. The PRG3 protein was strongly expressed during mouse brain development in vivo from embryonic day 16 to postnatal day 5 (E16 - P5). From P5 on, expression declined. Furthermore, in early, not yet polarized hippocampal cultured neurons, PRG3 was expressed along the neurite shaft. Knock-down of PRG3 in these neurons led to a decreased number of neurites. This phenotype is rescued by expression of an shRNA-resistant PRG3 construct in PRG3 knock-down neurons. After polarization, endogenous PRG3 expression shifted mainly to axons, specifically to the plasma membrane along the neurite shaft. These PRG3 pattern changes appeared temporally and spatially related to ongoing synaptogenesis. Therefore we tested (i) whether dendritic PRG3 re-enhancement influences synaptic currents and (ii) whether synaptic inputs contribute to the PRG3 shift. Our results rendered both scenarios unlikely: (i) PRG3 over-expression had no influence on miniature excitatory postsynaptic currents (mEPSC) and (ii) blocking of incoming signals did not alter PRG3 distribution dynamics. In addition, PRG3 levels did not interfere with intrinsic neuronal properties. CONCLUSION: Taken together, our data indicate that endogenous PRG3 promotes neurite shaft protrusion and therefore contributes to regulating filopodia formation in immature neurons. PRG3 expression in more mature neurons, however, is predominantly localized in the axon. Changes in PRG3 levels did not influence intrinsic or synaptic neuronal properties.

Delayed development of chronic lymphocytic leukemia in the absence of macrophage migration inhibitory factor.

UNLABELLED: Survival of chronic lymphocytic leukemia (CLL) cells depends on stimuli provided by a suitable microenvironment. The factors and mechanisms providing this growth support for CLL cells are not fully understood. We found that plasma levels of macrophage migration inhibitory factor (MIF), a proinflammatory and immunoregulatory chemokine, were elevated in CLL patients. Therefore, we characterized the functional role of MIF in a CLL mouse model. For this purpose, we crossed Eµ-TCL1 mice with MIF knockout (MIF-/-) mice. The resulting TCL1+/wtMIF/ mice showed a delayed onset of leukemia, reduced splenomegaly and hepatomegaly, and a longer survival than TCL1+/wtMIFwt/wt controls. Immunohistochemical examination of the lymphoid organs showed that the numbers of macrophages were significantly reduced in the spleen and bone marrow of TCL1+/wtMIF/ mice compared with TCL1+/wtMIFwt/wt controls. Mechanistic studies in vitro revealed that the absence of MIF rendered CLL cells more susceptible to apoptosis. Accordingly, incubation with an anti-MIF antibody reduced the survival of CLL cells on a macrophage feeder layer. In addition, the migratory activity of TCL1+/wtMIF/ macrophages was decreased compared with TCL1+/wtMIFwt/wt macrophages. Taken together, our results provide evidence that MIF supports the development of CLL by enhancing the interaction of CLL cells with macrophages. KEY POINTS: Targeted deletion of the gene for macrophage migration inhibitory factor (MIF) delays development of chronic lymphocytic leukemia and prolongs survival in mice. MIF recruits leukemia-associated macrophages to spleen or liver.

I(h) "run-up" in rat neocortical neurons and transiently rat or human HCN1-expressing HEK293 cells.

Hyperpolarization-activated cyclic nucleotide-gated ion channels (HCN) are key determinants of CNS functions. Here we describe an increase in hyperpolarization-activated current (I(h)) at the beginning of whole-cell recordings in rat layer 5 cortical neurons. For a closer investigation of this I(h) increase, we overexpressed the predominant layer 5 rat subunit HCN1 in HEK293 cells. We characterized the resulting I(h) in the cell-attached and whole-cell configurations. Breaking into whole-cell configuration led to about a 30% enhancement of rat HCN1-mediated I(h) accompanied by a depolarizing shift in voltage dependence and an accelerated time course of activation. This current enhancement is not species specific; for human HCN1, the current similarly increases in amount and kinetics. Although the changes were bound to cytosolic solution exchange, they were independent of cAMP, ATP, GTP, and the phosphate group donor phosphocreatine. Together, these data provide a characterization of heterologous expression of rat HCN1 and suggest that cytosolic contents suppress I(h). Such a mechanism might constitute a reserve in h-channel function in vivo.