The PI 3-kinase and mTOR signaling pathways are important modulators of epithelial tubule formation

An Update on Molecular Pathways Regulating Vasculogenic Mimicry in Human Osteosarcoma and Their Role in Canine Oncology

Canine tumors are valuable comparative models for human counterparts, especially to explore novel biomarkers and to understand pathways and processes involved in metastasis. Vasculogenic mimicry (VM) is a unique property of malignant cancer cells which promote metastasis. Thus, it represents an opportunity to investigate both the molecular mechanisms and the therapeutic targets of a crucial phenotypic malignant switch. Although this biological process has been largely investigated in different human cancer types, including osteosarcoma, it is still largely unknown in veterinary pathology, where it has been mainly explored in canine mammary tumors. The presence of VM in human osteosarcoma is associated with poor clinical outcome, reduced patient survival, and increased risk of metastasis and it shares the main pathways involved in other type of human tumors. This review illustrates the main findings concerning the VM process in human osteosarcoma, search for the related current knowledge in canine pathology and oncology, and potential involvement of multiple pathways in VM formation, in order to provide a basis for future investigations on VM in canine tumors.

Phosphorylated mTOR Expression Profiles in Human Normal and Carcinoma Tissues

Mammalian target of rapamycin (mTOR) is a key controller of cell growth and proliferation in normal tissues and solid tumors. In the present study, an immunohistochemical analysis of the expression pattern of phosphorylated mTOR (p-mTOR) was performed in human normal fetal and adult tissues and various carcinoma tissues. p-mTOR expression showed tissue and cell type specificity in normal and cancer tissues. In normal fetal and adult tissues, p-mTOR staining was observed in the intestinal crypt, intrahepatic bile ductule, pancreatic duct, distal nephron of the kidney, umbrella cell of urothelium, mesothelial cell, and choroid plexus. In cancer tissues, p-mTOR expression was higher in adenocarcinoma than in other types of cancers, in metastatic cancer than in primary cancer, and in the forefront of the infiltrating cancer cells. These results suggest that p-mTOR is implicated not only in cell proliferation but also in tubular morphogenesis in normal and cancer tissues. In addition, mTOR activation appears to be associated with cancer cell invasion and migration in solid tumors.

Neoatherosclerosis after Drug-Eluting Stent Implantation: Roles and Mechanisms

In-stent neoatherosclerosis (NA), characterized by a relatively thin fibrous cap and large volume of yellow-lipid accumulation after drug-eluting stents (DES) implantation, has attracted much attention owing to its close relationship with late complications, such as revascularization and late stent thrombosis (ST). Accumulating evidence has demonstrated that more than one-third of patients with first-generation DES present with NA. Even in the advent of second-generation DES, NA still occurs. It is indicated that endothelial dysfunction induced by DES plays a critical role in neoatherosclerotic development. Upregulation of reactive oxygen species (ROS) induced by DES implantation significantly affects endothelial cells healing and functioning, therefore rendering NA formation. In light of the role of ROS in suppression of endothelial healing, combining antioxidant therapies with stenting technology may facilitate reestablishing a functioning endothelium to improve clinical outcome for patients with stenting.

An mTOR anti-sense oligonucleotide decreases polycystic kidney disease in mice with a targeted mutation in Pkd2

Autosomal dominant polycystic kidney disease (ADPKD) is the most common life-threatening hereditary disease in the USA. In human ADPKD studies, sirolimus, a mammalian target of rapamycin complex 1 (mTORC1) inhibitor, had little therapeutic effect. While sirolimus robustly inhibits mTORC1, it has a minimal effect on mTOR complex 2 (mTORC2). Polycystic kidneys of Pkd2WS25/- mice, an orthologous model of human ADPKD caused by a mutation in the Pkd2 gene, had an early increase in pS6 (marker of mTORC1) and pAktSer(473) (marker of mTORC2). To investigate the effect of combined mTORC1 and 2 inhibition, Pkd2WS25/- mice were treated with an mTOR anti-sense oligonucleotide (ASO) that blocks mTOR expression thus inhibiting both mTORC1 and 2. The mTOR ASO resulted in a significant decrease in mTOR protein, pS6 and pAktSer(473). Pkd2WS25/- mice treated with the ASO had a normalization of kidney weights and kidney function and a marked decrease in cyst volume. The mTOR ASO resulted in a significant decrease in proliferation and apoptosis of tubular epithelial cells. To demonstrate the role of mTORC2 on cyst growth, Rictor, the functional component of mTORC2, was silenced in Madin-Darby canine kidney cell cysts grown in 3D cultures. Silencing Rictor significantly decreased cyst volume and expression of pAktSer(473). The decreased cyst size in the Rictor silenced cells was reversed by introduction of a constitutively active Akt1. In vitro, combined mTORC1 and 2 inhibition reduced cyst growth more than inhibition of mTORC1 or 2 alone. In conclusion, combined mTORC1 and 2 inhibition has therapeutic potential in ADPKD.

Constitutive activation of the mTOR signaling pathway within the normal glomerulus

Agents that target the activity of the mammalian target of rapamycin (mTOR) kinase in humans are associated with proteinuria. However, the mechanisms underlying mTOR activity and signaling within the kidney are poorly understood. In this study, we developed a sensitive immunofluorescence technique for the evaluation of activated pmTOR and its associated signals in situ. While we find that pmTOR is rarely expressed in normal non-renal tissues, we consistently find intense expression in glomeruli within normal mouse and human kidneys. Using double staining, we find that the expression of pmTOR co-localizes with nephrin in podocytes and expression appears minimal within other cell types in the glomerulus. In addition, we found that pmTOR was expressed on occasional renal tubular cells within mouse and human kidney specimens. We also evaluated mTOR signaling in magnetic bead-isolated glomeruli from normal mice and, by Western blot analysis, we confirmed function of the pathway in glomerular cells vs. interstitial cells. Furthermore, we found that the activity of the pathway as well as the expression of VEGF, a target of mTOR-induced signaling, were reduced within glomeruli of mice following treatment with rapamycin. Collectively, these findings demonstrate that the mTOR signaling pathway is constitutively hyperactive within podocytes. We suggest that pmTOR signaling functions to regulate glomerular homeostasis in part via the inducible expression of VEGF.

Liver progenitor cells fold up a cell monolayer into a double-layered structure during tubular morphogenesis

Bile ducts are hepatic tubular structures that are lined by cholangiocytes, a type of liver epithelial cell. Cholangiocytes first form a single layer of cells, termed the ductal plate, surrounding the portal vein, which eventually remodels into the branching tubular network of bile ducts. The process of bile duct morphogenesis is not yet clear: a conventional model where cholangiocytes proliferate to duplicate a single layer of the ductal plate before lumen formation seems inconsistent with the observation that proliferation is dramatically reduced when hepatoblasts, liver progenitor cells, differentiate into cholangiocytes. Here, we developed a new culture system in which a liver progenitor cell line, HPPL, reorganizes from a monolayer to tubular structures in response to being overlaid with a gel containing type I collagen and Matrigel. We found that some of the HPPL in the monolayer depolarized and migrated to fold up the monolayer into a double-cell layer. These morphogenetic processes occurred without cell proliferation and required phosphatidylinositol 3-kinase and Akt activity. Later in morphogenesis, luminal space was generated between the two cell layers. This process, in particular enlargement of the apical lumen, involved transcriptional activity of HNF1beta. Thus, using this sandwich culture system, we could segregate tubulogenesis of bile ducts into distinct steps and found that the PI3K/Akt pathway and HNF1beta regulated different steps of the morphogenesis. Although the process of tubulogenesis in culture specifically resembled early bile duct formation, involvement of these two key players suggests that the sandwich culture might help us to find common principles of tubulogenesis in general.