Rajwinder Lehal

Stem cells living with a Notch

Notch signaling has been shown over the past few decades to play fundamental roles in a plethora of developmental processes in an evolutionarily conserved fashion. Notch-mediated cell-to-cell signaling is involved in many aspects of embryonic development and control of tissue homeostasis in a variety of adult tissues, and regulates stem cell maintenance, cell differentiation and cellular homeostasis. The focus of this Review is the role of Notch signaling in stem cells, comparing insights from flies, fish and mice to highlight similarities, as well as differences, between species, tissues and stem cell compartments.

Alzheimer’s disease mutations in APP but not γ-secretase modulators affect epsilon-cleavage-dependent AICD production

Pathological amino-acid substitutions in the amyloid precursor protein (APP) and chemical γ-secretase modulators affect the processing of APP by the γ-secretase complex and the production of the amyloid-beta peptide Aβ42, the accumulation of which is considered causative of Alzheimers disease. Here we demonstrate that mutations in the transmembrane domain of APP causing aggressive early-onset familial Alzheimers disease affect both γ- and ε-cleavage sites, by raising the Aβ42/40 ratio and inhibiting the production of AICD50-99, one of the two physiological APP intracellular domains (ICDs). This is in sharp contrast to γ-secretase modulators, which shift Aβ42 production towards the shorter Aβ38, but unequivocally spare the ε-site and APP- and Notch-ICDs production. Molecular simulations suggest that familial Alzheimers disease mutations modulate the flexibility of the APP transmembrane domain and the presentation of its γ-site, modifying at the same time, the solvation of the ε-site.

Very High Throughput Electrical Cell Lysis and Extraction of Intracellular Compounds Using 3D Carbon Electrodes in Lab-on-a-Chip Devices

Here we present an electrical lysis throughput of 600 microliters per minute at high cell density (108 yeast cells per ml) with 90% efficiency, thus improving the current common throughput of one microliter per minute. We also demonstrate the extraction of intracellular luciferase from mammalian cells with efficiency comparable to off-chip bulk chemical lysis. The goal of this work is to develop a sample preparation module that can act as a stand-alone device or be integrated to other functions already demonstrated in miniaturized devices, including sorting and analysis, towards a true lab-on-a-chip.

Generation and characterization of a Notch1 signaling-specific reporter mouse line

Signaling through the Notch1 receptor is essential for the control of numerous developmental processes during embryonic life as well as in adult tissue homeostasis and disease. Since the outcome of Notch1 signaling is highly context‐dependent, and its precise physiological and pathological role in many organs is unclear, it is of great interest to localize and identify the cells that receive active Notch1 signals in vivo. Here, we report the generation and characterization of a BAC‐transgenic mouse line, N1‐Gal4VP16, that when crossed to a Gal4‐responsive reporter mouse line allowed the identification of cells undergoing active Notch1 signaling in vivo. Analysis of embryonic and adult N1‐Gal4VP16 mice demonstrated that the activation pattern of the transgene coincides with previously observed activation patterns of the endogenous Notch1 receptor. Thus, this novel reporter mouse line provides a unique tool to specifically investigate the spatial and temporal aspects of Notch1 signaling in vivo. genesis 50:700–710, 2012.

Abstract IA10: Notch signaling and cancer

Cancer can be seen as disease of perturbed self-renewal. In the last decades it became clear that many of the signaling pathways known to be important during embryonic development also play important roles in regulating self-renewing tissues. Deregulation of the self-renewal process results in sustained proliferation, evasion of cell death, loss of differentiation capacity, invasion and metastasis all of which are hallmarks of cancer. The major question is how do these deregulated signaling cascades mechanistically contribute to cancer and are they suitable for targeting therapy? The Notch pathway is one such cascade required for normal stem cell maintenance and development of different organs. Over activation of this pathway due to mutations in the Notch receptor are found in more than 50% of human T-cell leukemia and deregulated Notch signaling has been shown to promote tumor progression of various organs. The oncogenic mediators of aberrant Notch function in T-ALL and other Notch-driven cancers appear to be manifold and complex. The modulatory function of individual miRNAs in Notch driven T-ALLs has recently been established. However, whether Dicer1-processed miRNAs are essential for Notch-driven T-ALL is currently unknown. We used conditional and inducible genetic loss of function approaches to show that development and maintenance of Notch-driven T-ALL is dependent on Dicer1 function. Lineage tracing experiments revealed that Dicer1 deficiency led to the induction of apoptosis in T-ALL cells whereas cell cycle progression remained unaltered. Through microarray-based miRNA profiling, we identified miR-21 as a previously unrecognized miRNA deregulated in both mouse and human T-ALL. Herein, we demonstrate that miR-21 regulates T-ALL cell survival via repression of the tumor suppressor Pdcd4. Moreover, we will report on the identification of a novel small molecule inhibitor (CB103) that blocks Notch signaling by interfering with the transcriptional activation complex. The compound CB103 has shown remarkable ability to block Notch signaling in human cancer cell lines as well as primary human T-ALL cells, thus abrogating their proliferative properties. In addition, compound CB103 exhibit in vivo activity as demonstrated by its ability to impinge upon Notch dependent developmental processes and by impeding tumor growth in xenograft models of human leukemia and breast cancer. Citation Format: Fabian Junker, Rajwinder Lehal, Viktoras Frimantas, Beat C. Bornhauser, Jean-Pierre Bourquin, Ute Koch, Freddy Radtke. Notch signaling and cancer. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr IA10.