ABSTRACT
Insulin and insulin-like growth factor-1 signaling have fundamental roles in energy metabolism, growth and development. Recent research suggests hyperactive insulin receptor (IR) and hyperinsulinemia are cancer risk factors. However, the mechanisms that account for the link between the hyperactive insulin signaling and cancer risk are not well understood. Here we show that an insulin-like signaling inhibits the DAF-18/(phosphatase and tensin homolog) PTEN tumour suppressor in Caenorhabditis elegans and that this regulation is conserved in human breast cancer cells. We show that inhibiting the IR increases PTEN protein levels, while increasing insulin signaling decreases PTEN protein levels. Our results show that the kinase region of IRß subunit physically binds to PTEN and phosphorylates on Y27 and Y174. Our genetic results also show that DAF-2/IR negatively regulates DAF-18/PTEN during C. elegans axon guidance. As PTEN is an important tumour suppressor, our results therefore suggest a possible mechanism for increased cancer risk observed in hyperinsulinemia and hyperactive IR individuals.
Subject(s)
Insulin/metabolism , PTEN Phosphohydrolase/metabolism , Receptor, Insulin/metabolism , Animals , Animals, Genetically Modified , Axons/metabolism , Caenorhabditis elegans/genetics , Caenorhabditis elegans/metabolism , Caenorhabditis elegans Proteins/agonists , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Cell Line , Gene Expression , Humans , Insulin/pharmacology , Insulins , Intestinal Mucosa/metabolism , Models, Biological , Mutation , Neurons/metabolism , PTEN Phosphohydrolase/genetics , Protein Binding , Receptor, Insulin/agonists , Receptor, Insulin/geneticsABSTRACT
Programmed cell death eliminates unwanted cells during normal development and physiological homeostasis. While cell interactions can influence apoptosis as they do other types of cell fate, outside of the adaptive immune system little is known about the intercellular cues that actively promote cell death in healthy cells. We used the Caenorhabditis elegans germline as a model to investigate the extrinsic regulators of physiological apoptosis. Using genetic and cell biological methods, we show that somatic gonad sheath cells, which also act as phagocytes of dying germ cells, promote death in the C. elegans germline through VAB-1/Eph receptor signaling. We report that the germline apoptosis function of VAB-1 impacts specific cell death pathways, and may act in parallel to extracellular signal-regulated kinase MAPK signaling. This work defines a non-autonomous, pro-apoptotic signaling for efficient physiological cell death, and highlights the dynamic nature of intercellular communication between dying cells and the phagocytes that remove them.
Subject(s)
Apoptosis , Caenorhabditis elegans Proteins/metabolism , Cell Cycle Proteins/metabolism , Gonads/metabolism , Receptor Protein-Tyrosine Kinases/metabolism , Animals , Caenorhabditis elegans/metabolism , Caenorhabditis elegans Proteins/antagonists & inhibitors , Caenorhabditis elegans Proteins/genetics , Cell Cycle Proteins/antagonists & inhibitors , Cell Cycle Proteins/genetics , Germ Cells/cytology , Germ Cells/metabolism , Gonads/cytology , Mitogen-Activated Protein Kinase Kinases/metabolism , Mutation , RNA Interference , Receptor Protein-Tyrosine Kinases/antagonists & inhibitors , Receptor Protein-Tyrosine Kinases/genetics , Signal TransductionABSTRACT
The development of the epidermis of the nematode worm Caenorhabditis elegans illustrates many common processes of epithelial morphogenesis. In the worm, these morphogenetic movements have been described with single-cell resolution, and the roles of individual cells have been probed in laser killing experiments. Genetic dissection is yielding insights into the molecular mechanisms of these complex morphogenetic processes.
Subject(s)
Caenorhabditis elegans/genetics , Animals , Caenorhabditis elegans/growth & development , MorphogenesisABSTRACT
The Eph receptor VAB-1 is required in neurons for epidermal morphogenesis during C. elegans embryogenesis. Two models were proposed for the non-autonomous role of VAB-1: neuronal VAB-1 might signal directly to epidermis, or VAB-1 signaling between neurons might be required for epidermal development. We show that the ephrin VAB-2 (also known as EFN-1) is a ligand for VAB-1 and can function in neurons to regulate epidermal morphogenesis. In the absence of VAB-1 signaling, ephrin-expressing neurons are disorganized. vab-2/efn-1 mutations synergize with vab-1 kinase alleles, suggesting that VAB-2/EFN-1 may partly function in a kinase-independent VAB-1 pathway. Our data indicate that ephrin signaling between neurons is required nonautonomously for epidermal morphogenesis in C. elegans.
Subject(s)
Caenorhabditis elegans Proteins , Caenorhabditis elegans/metabolism , Cell Cycle Proteins/metabolism , Ephrins , Epidermis/embryology , Helminth Proteins/metabolism , Neurons/metabolism , Receptor Protein-Tyrosine Kinases , Amino Acid Sequence , Animals , Caenorhabditis elegans/embryology , Caenorhabditis elegans/genetics , Cell Cycle Proteins/genetics , Cells, Cultured , Cloning, Molecular , Embryo, Nonmammalian , Helminth Proteins/genetics , Immunohistochemistry , Larva , Microscopy, Confocal , Molecular Sequence Data , Morphogenesis , Signal TransductionABSTRACT
Male sexual development in the nematode Caenorhabditis elegans requires the genes fem-1, fem-2, and fem-3. The current model of sex determination portrays the FEM proteins as components of a novel signal transduction pathway, but the mechanisms involved in signaling through the pathway are not understood. We report the isolation of fem-2 cDNAs in a yeast two-hybrid screen for clones encoding proteins that interact with FEM-3. Association of FEM-3 and FEM-2 in two independent in vitro binding assays substantiates the interaction detected in the two-hybrid system. FEM-2 is related in sequence to protein serine/threonine phosphatases of Type 2C (PP2C). We demonstrate that FEM-2 exhibits magnesium-dependent casein phosphatase activity, typical of PP2C, in vitro. Point mutations that abolish the casein phosphatase activity of FEM-2 without affecting its FEM-3-binding activity reduce severely its ability to rescue male development in fem-2 mutant nematodes. These results suggest that protein phosphorylation regulates sex determination in C. elegans.