ACTH-induced caveolin-1 tyrosine phosphorylation is related to podosome assembly in Y1 adrenal cells
ABSTRACT Y1 adrenocortical cells respond to ACTH with a characteristic rounding-up that facilitates cAMP signaling, critical for transport of cholesterol to the mitochondria and increase in steroid secretion. We here demonstrate that caveolin-1 participates in coupling activation of protein kinase A (PKA) to the control of cell shape. ACTH/8-Br-cAMP induced reorganization of caveolin-1-positive structures in correlation with the cellular rounding-up. Concomitant with this change, there was an increase in the phosphorylation of caveolin-1 (Tyr-14) localized at focal adhesions (FA) with reorganization of FA to rounded, ringlike structures. Colocalization with phalloidin showed that phosphocaveolin is present at the edge of actin filaments and that after ACTH stimulation F-actin dots at the cell periphery become surrounded by phosphocaveolin-1. These observations along with electron microscopy studies revealed these structures as podosomes. Podosome assembly was dependent on both PKA and tyrosine kinase activities because their formation was impaired after treatment with specific inhibitors [myristoylated PKI (mPKI) or PP2, respectively] previous to ACTH/8-Br-cAMP stimulation. These results show for the first time that ACTH induces caveolin-1 phosphorylation and podosome assembly in Y1 cells and support the view that the morphological and functional responses to PKA activation in steroidogenic cells are related to cytoskeleton dynamics.
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ABSTRACT: Pollen tube growth is localized at the apex and displays oscillatory dynamics. It is thought that a balance between intracellular turgor pressure (hydrostatic pressure, reflected by the cell volume) and cell wall loosening is a critical factor driving pollen tube growth. We previously demonstrated that water flows freely into and out of the pollen tube apical region dependent on the extracellular osmotic potential, that cell volume changes reflect changes in the intracellular pressure, and that cell volume changes differentially induce increases or decreases in specific phospholipid signals. This article shows that manipulation of the extracellular osmotic potential rapidly induces modulations in pollen tube growth rate frequencies, demonstrating that changes in the intracellular pressure are sufficient to reset the pollen tube growth oscillator. This indicates a direct link between intracellular hydrostatic pressure and pollen tube growth. Altering hydrodynamic flow through the pollen tube by replacing extracellular H2O with 2H2O adversely affects both cell volume and growth rate oscillations and induces aberrant morphologies. Normal growth and cell morphology are rescued by replacing 2H2O with H2O. Further studies revealed that the cell volume oscillates in the pollen tube apical region. These cell volume oscillations were not from changes in cell shape at the tip and were detectable up to 30 mum distal to the tip (the longest length measured). Cell volume in the apical region oscillates with the same frequency as growth rate oscillations but surprisingly the cycles are phase-shifted by 180 degrees . Raman microscopy yields evidence that hydrodynamic flow out of the apex may be part of the biomechanics that drive cellular expansion. The combined results suggest that hydrodynamic loading/unloading in the apical region induces cell volume oscillations and has a role in driving cell elongation and pollen tube growth.Cell Biochemistry and Biophysics 02/2006; 46(3):209-32. DOI:10.1385/CBB:46:3:209 · 2.38 Impact Factor
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ABSTRACT: Studies in modeled microgravity or during orbital space flights have clearly demonstrated that endothelial cell physiology is strongly affected by the reduction of gravity. Nevertheless, the molecular mechanisms by which endothelial cells may sense gravity force remain unclear. We previously hypothesized that endothelial cell caveolae could be a mechanosensing system involved in hypergravity adaptation of human endothelial cells. In this study, we analyzed the effect on the physiology of human umbilical vein endothelial cell monolayers of short exposure to modeled microgravity (24-48 h) obtained by clinorotation. For this purpose, we evaluated the levels of compounds, such as nitric oxide and prostacyclin, involved in vascular tone regulation and synthesized starting from caveolae-related enzymes. Furthermore, we examined posttranslational modifications of Caveolin (Cav)-1 induced by simulated microgravity. The results we collected clearly indicated that short microgravity exposure strongly affected endothelial nitric oxide synthase activity associated with Cav-1 (Tyr 14) phosphorylation, without modifying the angiogenic response of human umbilical vein endothelial cells. We propose here that one of the early molecular mechanisms responsible for gravity sensing of endothelium involves endothelial cell caveolae and Cav-1 phosphorylation.Cell Biochemistry and Biophysics 02/2006; 46(2):155-64. DOI:10.1385/CBB:46:2:155 · 2.38 Impact Factor
Article: Adhesions that mediate invasion.[Show abstract] [Hide abstract]
ABSTRACT: Infiltration of new tissue areas requires that a mammalian cell overcomes the physical and biochemical barrier of the surrounding extracellular matrix. Cell migration during embryonic development, and growth, invasion and dispersal of metastatic tumor cells depend to a large extent on the controlled degradation of extracellular matrix components. Localized degradation of the surrounding matrix is seen at defined adhesive (podosomes) and/or protrusive (invadopodia) locations in a variety of normal cells and aggressive carcinoma cells, suggesting that these membrane-associated cellular devices have a central role in mediating polarized migration in cells that cross-tissue boundaries. Here, we will discuss the recent advances and developments in this field, and provide our provisional outlook into the future understanding of the principles of focal extracellular matrix degradation by podosomes and invadopodia.The International Journal of Biochemistry & Cell Biology 02/2006; 38(11):1875-92. DOI:10.1016/j.biocel.2006.05.003 · 4.24 Impact Factor