Mature retinal ganglion cells (RGCs) cannot normally regenerate axons into the injured optic nerve but can do so after lens injury. Astrocyte-derived ciliary neurotrophic factor and leukemia inhibitory factor have been identified as essential key factors mediating this effect. However, the outcome of this regeneration is still limited by inhibitors associated with the CNS myelin and the glial scar. The current study demonstrates that Taxol markedly enhanced neurite extension of mature RGCs and PC12 cells by stabilization of microtubules and desensitized axons toward myelin and chondroitin sulfate proteoglycan (CSPG) inhibition in vitro without reducing RhoA activation. In vivo, the local application of Taxol at the injury site of the optic nerve of rats enabled axons to regenerate beyond the lesion site but did not affect the intrinsic regenerative state of RGCs. Furthermore, Taxol treatment markedly increased lens injury-mediated axon regeneration in vivo, delayed glial scar formation, suppressed CSPG expression, and transiently reduced the infiltration of macrophages at the injury site. Thus, microtubule-stabilizing compounds such as Taxol might be promising candidates as adjuvant drugs in the treatment of CNS injuries particularly when combined with interventions stimulating the intrinsic regenerative state of neurons.
Expression of the human CCR2 receptors, CCR2a and CCR2b, in mammalian cells results in ligand-dependent changes in the activity of multiple cellular signal transduction pathways, mediated in most cases by pertussis toxin-sensitive heterotrimeric G proteins of the Gi/o subfamily. In addition, CCR2a and CCR2b receptors have been shown to couple to Gq family members, triggering the canonical activation of phospholipase Cβ isoenzymes. Activation of pertussis toxin-insensitive Gq proteins by cell-surface receptors is not only coupled to activation of phospholipase isoenzymes but also to Rho guanine nucleotide exchange factors, which in turn mediate activation of the Rho GTPases. Activated Rho GTPases regulate numerous cellular functions, including the organization of the actin cytoskeleton and gene transcription, such as the transcription factor serum response factor. These findings prompted us to investigate whether CCR2a and/or CCR2b stimulate serum response factor activity. The results presented herein demonstrate that stimulation of human CCR2a- or CCR2b-expressing COS-7 cells caused a vigorous induction of serum response factor activity. This effect was specifically mediated by Gq and/or G14, as well as Rho A and/or a closely related Rho GTPase. Furthermore, the stimulatory effect of CCR2a and CCR2b and Gαq was sensitive to coexpression of the Gαq-interacting leukemia-associated Rho guanine nucleotide exchange factor. The findings of the work indicate a role for Gαq and/or Gα14 and in CCR2a/CCR2b-stimulated Rho A GTPase-mediated serum response factor activation and introduce a noncanonical pathway activated by CCR2 receptors by coupling to Gq proteins.
USP8 and the ESCRT pathway (endosomal sorting complex required for transport) are required for cellular homeostasis through key functions in shuttling ubiquitinated proteins towards lysosomal degradation, and through regulating the maturation of autophagosomal structures. In large-scale siRNA screens, the vast majority of cancer cell lines do not demonstrate dependency on USP8 or ESCRT pathway components for viability. However, we identified three cell lines (HCC70, HCC1954 and PFSK1) that are acutely dependent on USP8 and other ESCRT components (HGS, TSG101) for viability. Using a transcriptome-wide association approach, we found that these three USP8-dependent cell lines also had in common the expression of SerpinB3, also known as SCCA1 (Squamous Cell Carcinoma Antigen 1). After selecting additional Squamous Cell Carcinoma cell lines for further validation of USP8-dependency by siRNA screening, we found that Squamous Carcinoma cell lines, irrespective of their SerpinB3 expression status, were far more likely to be dependent on USP8 for viability (23%; N = 22) than cancer cell lines of non-Squamous epithelial origin (4.5%; N = 67). To unravel possible molecular mechanisms underpinning the requirement of USP8 for the viability of USP8-dependent Squamous Carcinoma cell lines (including SCABER, BICR22, CALU1 and EBC1), we conducted additional transcriptome association studies and genetic interaction screens to uncover genes that are synthetic lethal with USP8 knock-down. Citation Format: Wendy Zhong, Elissa Cosgrove, Elissa Swearingen, Mike Ollmann, Jayee Banerjee, Vivienne Watson, Peter Jaeckel, Mariana Pfreimer, Silvia Materna-Reichelt, Holger Beckmann, Paul Kassner, Astrid Ruefli-Brasse, Olivier Nolan-Stevaux. High throughput siRNA screens uncover a high rate of USP8 and ESCRT pathway dependency in squamous carcinoma cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4548.
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