Endosomal signaling and oncogenesis

ERBB1- and ERBB2-Positive Medullary Thyroid Carcinoma: A Case Report

Medullary thyroid carcinomas (MTCs) are rare thyroid tumors occurring in both sporadic and hereditary forms, whose pathogenesis is related to RET proto-oncogene alterations. MTCs originate from parafollicular cells, which produce calcitonin that represents the biochemical activity of MTC. Total thyroidectomy is the main treatment for MTC and often cures patients with confined diseases. In the presence of metastasis, the therapeutic approach depends on the rate of disease progression. We report a case of a 54-year-old female with a single, incidentally discovered, thyroid nodule of 1 cm, classified as suspicious MTC after a stimulation test with intravenous (iv) calcium. After surgery, we examined the nodule using immunohistochemistry, immunofluorescence, and electron microscopy. In addition to calcitonin, we found that it expressed intracellular positivity for the tyrosine kinase RTK receptors ERBB1 and ERBB2. Consistently with MTC features, the ultrastructural examination of the tumor displayed heterogeneous spindle-shaped cells containing two groups of secretory granules. Because of the significant correlation found between high ERBB1/ERBB2 levels in MTCs and extrathyroidal growth, the detection of ERBB1 and ERBB2 expression suggests that the two oncoproteins may be involved in the tumor proliferative responses and/or in the differentiation of parafollicular C-cells. The biological, prognostic, and therapeutic significance of these patterns would merit further investigations.

GDC-0152-induced autophagy promotes apoptosis in HL-60 cells

GDC-0152 is a new type of chemical compound which can downregulate inhibitor of apoptosis protein. We previously reported that GDC-0152 induced apoptosis in HL-60 cells in a caspase-dependent manner. In this study, we have focused on GDC-0152-induced autophagy and the relationship between apoptosis and autophagy. We found that GDC-0152 can evoke autophagy flux as confirmed by the upregulation of LC3 and downregulation of p62. The conversion of LC3I to LC3II verified the existence of autophagy flux further. GDC-0152 induced autophagy through downregulating B cell lymphoma 2 and Bcl-2-interacting myosin-like coiled-coil protein, and upregulating WD-repeat domain phosphoinositide-interacting protein 1. Pretreating HL-60 cells with autophagy inhibitor Bafolimycin A1 reduced GDC-0152-induced apoptosis. However, pretreatment with caspase inhibitor Z-VAD-FMK had no effect on autophagy. Reactive oxygen species were released in GDC-0152-treated HL-60 cells but did not take part in the regulation of autophagy and apoptosis. In conclusion, our findings suggest that GDC-0152-induced autophagy can trigger apoptosis in HL-60 cells.

RAB7 counteracts PI3K-driven macropinocytosis activated at early stages of melanoma development

Derailed endolysosomal trafficking is emerging as a widespread feature of aggressive neoplasms. However, the oncogenic signals that alter membrane homeostasis and their specific contribution to cancer progression remain unclear. Understanding the upstream drivers and downstream regulators of aberrant vesicular trafficking is distinctly important in melanoma. This disease is notorious for its inter- and intra-tumoral heterogeneity. Nevertheless, melanomas uniformly overexpress a cluster of endolysosomal genes, being particularly addicted to the membrane traffic regulator RAB7. Still, the underlying mechanisms and temporal determinants of this dependency have yet to be defined. Here we addressed these questions by combining electron microscopy, real time imaging and mechanistic analyses of vesicular trafficking in normal and malignant human melanocytic cells. This strategy revealed Class I PI3K as the key trigger of a hyperactive influx of macropinosomes that melanoma cells counteract via RAB7-mediated lysosomal degradation. In addition, gain- and loss-of-function in vitro studies followed by histopathological validation in clinical biopsies and genetically-engineered mouse models, traced back the requirement of RAB7 to the suppression of premature cellular senescence traits elicited in melanocytes by PI3K-inducing oncogenes. Together, these results provide new insight into the regulators and modes of action of RAB7, broadening the impact of endosomal fitness on melanoma development.

WIPI proteins: essential PtdIns3P effectors at the nascent autophagosome

Autophagy is a pivotal cytoprotective process that secures cellular homeostasis, fulfills essential roles in development, immunity and defence against pathogens, and determines the lifespan of eukaryotic organisms. However, autophagy also crucially contributes to the development of age-related human pathologies, including cancer and neurodegeneration. Macroautophagy (hereafter referred to as autophagy) clears the cytoplasm by stochastic or specific cargo recognition and destruction, and is initiated and executed by autophagy related (ATG) proteins functioning in dynamical hierarchies to form autophagosomes. Autophagosomes sequester cytoplasmic cargo material, including proteins, lipids and organelles, and acquire acidic hydrolases from the lysosomal compartment for cargo degradation. Prerequisite and essential for autophagosome formation is the production of phosphatidylinositol 3-phosphate (PtdIns3P) by phosphatidylinositol 3-kinase class III (PI3KC3, also known as PIK3C3) in complex with beclin 1, p150 (also known as PIK3R4; Vps15 in yeast) and ATG14L. Members of the human WD-repeat protein interacting with phosphoinositides (WIPI) family play an important role in recognizing and decoding the PtdIns3P signal at the nascent autophagosome, and hence function as autophagy-specific PtdIns3P-binding effectors, similar to their ancestral yeast Atg18 homolog. The PtdIns3P effector function of human WIPI proteins appears to be compromised in cancer and neurodegeneration, and WIPI genes and proteins might present novel targets for rational therapies. Here, we summarize the current knowledge on the roles of the four human WIPI proteins, WIPI1-4, in autophagy. This article is part of a Focus on Autophagosome biogenesis. For further reading, please see related articles: 'ERES: sites for autophagosome biogenesis and maturation?' by Jana Sanchez-Wandelmer et al. (J. Cell Sci. 128, 185-192) and 'Membrane dynamics in autophagosome biogenesis' by Sven R. Carlsson and Anne Simonsen (J. Cell Sci. 128, 193-205).

Essential role of STX6 in esophageal squamous cell carcinoma growth and migration

Abnormalities in endosomes, or dysregulation in their trafficking, play an important role directly in many diseases including oncogenesis. Syntaxin-6 (STX6) is involved in diverse cellular functions in a variety of cell types and has been shown to regulate many intracellular membrane trafficking events such as endocytosis, recycling and anterograde and retrograde trafficking. However, its expression pattern and biological functions in esophageal squamous cell carcinoma (ESCC) remained unknown. Here, we have found that the expression of STX6 was up-regulated in ESCC samples, its expression was significantly correlated with tumor size, histological differentiation, lymph node metastasis and depth. On one hand, STX6 silencing inhibited ESCC cells viability and proliferation in a p53-dependent manner. On the other hand, STX6 effect integrin trafficking and regulate ESCC cells migration. Taken together, our study revealed the oncogenic roles of STX6 in the progression of ESCC, and it might be a valuable target for ESCC therapy.