Project description:In this study, we use the epidermis as a model system to elucidate the cellular effects and signaling feedback sequelae of mTORC1 loss-of-function in epithelial tissue. In mice with conditional epidermal loss of mTORC1 components Rheb or Rptor, we find that mTORC1 loss-of-function unexpectedly results in a profound skin barrier defect with epidermal abrasions, blistering and early postnatal lethality, due to a thinned epidermis with decreased desmosome expression and incomplete biochemical differentiation. Impaired cell-cell adhesion in the context of mTORC1 loss-of-function is caused by constitutive activation of Rho kinase (ROCK) signaling with increased cytoskeletal tension, and inhibition or silencing of ROCK1 is sufficient to rescue keratinocyte adhesion and biochemical differentiation. mTORC1 loss-of-function results in marked feedback up-regulation of upstream TGF-β signaling, triggering ROCK activity and its downstream effects on desmosomal gene expression. These findings elucidate a novel role for mTORC1 in the regulation of epithelial barrier formation, cytoskeletal tension and cell adhesion and underscore the complexity of signaling feedback after mTORC1 inhibition
Project description:MiT/TFE transcriptional activity controls lysosomal biogenesis and is negatively regulated by the nutrient sensor mTORC1. Some tumors bypass this regulatory circuit via genetic alterations that drive MiT/TFE expression and activity; however, the mechanisms by which cells with intact or constitutive mTORC1 signaling maintain lysosomal catabolism remain to be elucidated. Using the murine epidermis as a model system, we find that epidermal Tsc1 deletion results in a wavy hair phenotype due to increased EGFR degradation. Unexpectedly, constitutive mTORC1 activation increases lysosomal content via up-regulated expression and activity of MiT/TFEs, while genetic or prolonged pharmacologic mTORC1 inactivation has the reverse effect. This paradoxical up-regulation of lysosomal biogenesis by mTORC1 is mediated by feedback inhibition of AKT, and a resulting suppression of AKT-induced MiT/TFE proteasomal degradation. These data suggest that oncogenic feedback loops work to restrain or maintain cellular lysosomal content during chronically inhibited or constitutively active mTORC1 signaling respectively, and reveal a mechanism by which mTORC1 regulates upstream receptor tyrosine kinase signaling.
Project description:<p>Kidney injury initiates epithelial dedifferentiation and myofibroblast activation during the progression of chronic kidney disease (CKD). Herein, we found that the expression of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) was significantly increased in the kidney tissues of both CKD patients and CKD mice induced by unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion (UIR) injury. In vivo, knockout of DNA-PKcs or treatment with its specific inhibitor NU7441 hampered the development of CKD in mice. In vitro, DNA-PKcs deficiency preserved epithelial cell phenotype and inhibited fibroblast activation induced by transforming growth factor-beta 1 (TGF-beta-1). Additionally, our results showed that TBP-associated factor 7 (TAF7), as a possible substrate of DNA-PKcs, enhanced mTORC1 activation by upregulating RAPTOR expression, which subsequently promoted metabolic reprogramming in injured epithelial cells and myofibroblasts. Taken together, DNA-PKcs can be inhibited to correct metabolic reprogramming via the TAF7/mTORC1 signaling in CKD, and serve as a new target for treating CKD.</p>
Project description:Here we report the characterization of a novel role for the retinoblastoma protein (pRb) as a regulator of osteoblast adhesion. Abrogation of pRb in osteoblasts resulted in aberrant cadherin expression and loss of adherens junctions. This produced defects suggestive of a transformed phenotype such as impaired cell-to-cell adhesion, loss of contact-dependent growth arrest, and the capacity to evade anoikis. This also resulted in profound abnormalities in bone structure. Consistent with this, microarray analyses showed that pRb regulates a wide repertoire of osteoblast cell adhesion genes. In addition, pRb loss also resulted in altered expression and function of several known regulators of cellular adhesion and adherens junction assembly, such as the Rho GTPase Rac1 and the merlin tumor suppressor. Taken together, our results show that pRb controls cell adhesion by regulating the expression and adherens junction components and by regulating the function of molecules involved in adherens junction assembly and stability. Microarray results helped us to portrait the overall influence on cell adhesion via both individual genes and pathway analysis. Experiment Overall Design: MC3T3 cells were obtained from immortalizing primary cultured mouse osteoblast cells by using 3T3 protocol. There are 3 biological replicates for each group, 6 samples in total were analyzed.
Project description:Signals emanating from Rho GTPases play pivotal roles in epidermal stem cell homeostasis. However, the agents regulating Rho GTPase output within the epidermal stem cell niche are poorly known. Here, we report that the Rho exchange factor Vav2 regulates the epidermal stem cell transcriptome in an age-dependent manner.
Project description:Rho GTPases integrate control of cell structure and adhesion with downstream signaling events. In keratinocytes, RhoA is activated at early times of differentiation and plays an essential function in establishment of cellcell adhesion. We report here that, surprisingly, Rho signaling suppresses downstream gene expression events associated with differentiation. Similar inhibitory effects are exerted by a specific Rho effector, CRIK (Citron kinase), which is selectively down-modulated with differentiation, thereby allowing the normal process to occur. The suppressing function of Rho/CRIK on differentiation is associated with induction of KyoT1/2, a LIM domain protein gene implicated in integrin-mediated processes and/or Notch signaling. Like activated Rho and CRIK, elevated KyoT1/2 expression suppresses differentiation. Thus, Rho signaling exerts an unexpectedly complex role in keratinocyte differentiation, which is coupled with induction of KyoT1/2, a LIM domain protein gene with a potentially important role in control of cell self renewal. Experiment Overall Design: Total RNA from primary mouse keratinocytes infected with adeno-GFP, adeno-RhoV14, or adeno-CRIK-SK for 48 h was used for biotin-labeled cRNA probe preparation and hybridization to Affymetrix U74A gene chips. cRNA probes from each condition were tested in duplicate.
Project description:Rho GTPases integrate control of cell structure and adhesion with downstream signaling events. In keratinocytes, RhoA is activated at early times of differentiation and plays an essential function in establishment of cell-cell adhesion. We report here that, surprisingly, Rho signaling suppresses downstream gene expression events associated with differentiation. Similar inhibitory effects are exerted by a specific Rho effector, CRIK (Citron kinase), which is selectively down-modulated with differentiation, thereby allowing the normal process to occur. The suppressing function of Rho/CRIK on differentiation is associated with induction of KyoT1/2, a LIM domain protein gene implicated in integrin-mediated processes and/or Notch signaling. Like activated Rho and CRIK, elevated KyoT1/2 expression suppresses differentiation. Thus, Rho signaling exerts an unexpectedly complex role in keratinocyte differentiation, which is coupled with induction of KyoT1/2, a LIM domain protein gene with a potentially important role in control of cell self renewal. Keywords: epithelial cell differentiation | gene expression | Rho signaling | stem cell