"Oh, Dear We Are in Tribble": An Overview of the Oncogenic Functions of Tribbles 1.

Pseudokinases are catalytically inactive proteins in the human genome that lack the ability to transfer phosphate from ATP to their substrates. The Tribbles family of pseudokinases contains three members: Tribbles 1, 2, and 3. Tribbles 1 has recently gained importance because of its involvement in various diseases, including cancer. It acts as a scaffolding protein that brings about the degradation of its substrate proteins, such as C/EBPα/ß, MLXIPL, and RAR/RXRα, among others, via the ubiquitin proteasome system. It also serves as an adapter protein, which sequesters different protein molecules and activates their downstream signaling, leading to processes, such as cell survival, cell proliferation, and lipid metabolism. It has been implicated in cancers such as AML, prostate cancer, breast cancer, CRC, HCC, and glioma, where it activates oncogenic signaling pathways such as PI3K-AKT and MAPK and inhibits the anti-tumor function of p53. TRIB1 also causes treatment resistance in cancers such as NSCLC, breast cancer, glioma, and promyelocytic leukemia. All these effects make TRIB1 a potential drug target. However, the lack of a catalytic domain renders TRIB1 "undruggable", but knowledge about its structure, conformational changes during substrate binding, and substrate binding sites provides an opportunity to design small-molecule inhibitors against specific TRIB1 interactions.

TRIB1 confers therapeutic resistance in GBM cells by activating the ERK and Akt pathways.

GBM (Glioblastoma) is the most lethal CNS (Central nervous system) tumor in adults, which inevitably develops resistance to standard treatments leading to recurrence and mortality. TRIB1 is a serine/threonine pseudokinase which functions as a scaffold platform that initiates degradation of its substrates like C/EBPα through the ubiquitin proteasome system and also activates MEK and Akt signaling. We found that increased TRIB1 gene expression associated with worse overall survival of GBM patients across multiple cohorts. Importantly, overexpression of TRIB1 decreased RT/TMZ (radiation therapy/temozolomide)-induced apoptosis in patient derived GBM cell lines in vitro. TRIB1 directly bound to MEK and Akt and increased ERK and Akt phosphorylation/activation. We also found that TRIB1 protein expression was maximal during G2/M transition of cell cycle in GBM cells. Furthermore, TRIB1 bound directly to HDAC1 and p53. Importantly, mice bearing TRIB1 overexpressing tumors had worse overall survival. Collectively, these data suggest that TRIB1 induces resistance of GBM cells to RT/TMZ treatments by activating the cell proliferation and survival pathways thus providing an opportunity for developing new targeted therapeutics.

Humanized Dsp ACM Mouse Model Displays Stress-Induced Cardiac Electrical and Structural Phenotypes.

Arrhythmogenic cardiomyopathy (ACM) is an inherited disorder characterized by fibro-fatty infiltration with an increased propensity for ventricular arrhythmias and sudden death. Genetic variants in desmosomal genes are associated with ACM. Incomplete penetrance is a common feature in ACM families, complicating the understanding of how external stressors contribute towards disease development. To analyze the dual role of genetics and external stressors on ACM progression, we developed one of the first mouse models of ACM that recapitulates a human variant by introducing the murine equivalent of the human R451G variant into endogenous desmoplakin (DspR451G/+). Mice homozygous for this variant displayed embryonic lethality. While DspR451G/+ mice were viable with reduced expression of DSP, no presentable arrhythmogenic or structural phenotypes were identified at baseline. However, increased afterload resulted in reduced cardiac performance, increased chamber dilation, and accelerated progression to heart failure. In addition, following catecholaminergic challenge, DspR451G/+ mice displayed frequent and prolonged arrhythmic events. Finally, aberrant localization of connexin-43 was noted in the DspR451G/+ mice at baseline, becoming more apparent following cardiac stress via pressure overload. In summary, cardiovascular stress is a key trigger for unmasking both electrical and structural phenotypes in one of the first humanized ACM mouse models.

Assessment of temporal functional changes and miRNA profiling of human iPSC-derived cardiomyocytes.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been developed for cardiac cell transplantation studies more than a decade ago. In order to establish the hiPSC-CM-based platform as an autologous source for cardiac repair and drug toxicity, it is vital to understand the functionality of cardiomyocytes. Therefore, the goal of this study was to assess functional physiology, ultrastructural morphology, gene expression, and microRNA (miRNA) profiling at Wk-1, Wk-2 & Wk-4 in hiPSC-CMs in vitro. Functional assessment of hiPSC-CMs was determined by multielectrode array (MEA), Ca2+ cycling and particle image velocimetry (PIV). Results demonstrated that Wk-4 cardiomyocytes showed enhanced synchronization and maturation as compared to Wk-1 & Wk-2. Furthermore, ultrastructural morphology of Wk-4 cardiomyocytes closely mimicked the non-failing (NF) adult human heart. Additionally, modulation of cardiac genes, cell cycle genes, and pluripotency markers were analyzed by real-time PCR and compared with NF human heart. Increasing expression of fatty acid oxidation enzymes at Wk-4 supported the switching to lipid metabolism. Differential regulation of 12 miRNAs was observed in Wk-1 vs Wk-4 cardiomyocytes. Overall, this study demonstrated that Wk-4 hiPSC-CMs showed improved functional, metabolic and ultrastructural maturation, which could play a crucial role in optimizing timing for cell transplantation studies and drug screening.

Obscure functions: the location-function relationship of obscurins.

The obscurin family of polypeptides is essential for normal striated muscle function and contributes to the pathogenesis of fatal diseases, including cardiomyopathies and cancers. The single mammalian obscurin gene, OBSCN, gives rise to giant (∼800 kDa) and smaller (∼40-500 kDa) proteins that are composed of tandem adhesion and signaling motifs. Mammalian obscurin proteins are expressed in a variety of cell types, including striated muscles, and localize to distinct subcellular compartments where they contribute to diverse cellular processes. Obscurin homologs in Caenorhabditis elegans and Drosophila possess a similar domain architecture and are also expressed in striated muscles. The long sought after question, "what does obscurin do?" is complex and cannot be addressed without taking into consideration the subcellular distribution of these proteins and local isoform concentration. Herein, we present an overview of the functions of obscurins and begin to define the intricate relationship between their subcellular distributions and functions in striated muscles.