Endocytic crosstalk: cavins, caveolins, and caveolae regulate clathrin-independent endocytosis

PLoS Biol. 2014 Apr 8;12(4):e1001832. doi: 10.1371/journal.pbio.1001832. eCollection 2014 Apr.

Abstract

Several studies have suggested crosstalk between different clathrin-independent endocytic pathways. However, the molecular mechanisms and functional relevance of these interactions are unclear. Caveolins and cavins are crucial components of caveolae, specialized microdomains that also constitute an endocytic route. Here we show that specific caveolar proteins are independently acting negative regulators of clathrin-independent endocytosis. Cavin-1 and Cavin-3, but not Cavin-2 or Cavin-4, are potent inhibitors of the clathrin-independent carriers/GPI-AP enriched early endosomal compartment (CLIC/GEEC) endocytic pathway, in a process independent of caveola formation. Caveolin-1 (CAV1) and CAV3 also inhibit the CLIC/GEEC pathway upon over-expression. Expression of caveolar protein leads to reduction in formation of early CLIC/GEEC carriers, as detected by quantitative electron microscopy analysis. Furthermore, the CLIC/GEEC pathway is upregulated in cells lacking CAV1/Cavin-1 or with reduced expression of Cavin-1 and Cavin-3. Inhibition by caveolins can be mimicked by the isolated caveolin scaffolding domain and is associated with perturbed diffusion of lipid microdomain components, as revealed by fluorescence recovery after photobleaching (FRAP) studies. In the absence of cavins (and caveolae) CAV1 is itself endocytosed preferentially through the CLIC/GEEC pathway, but the pathway loses polarization and sorting attributes with consequences for membrane dynamics and endocytic polarization in migrating cells and adult muscle tissue. We also found that noncaveolar Cavin-1 can act as a modulator for the activity of the key regulator of the CLIC/GEEC pathway, Cdc42. This work provides new insights into the regulation of noncaveolar clathrin-independent endocytosis by specific caveolar proteins, illustrating multiple levels of crosstalk between these pathways. We show for the first time a role for specific cavins in regulating the CLIC/GEEC pathway, provide a new tool to study this pathway, identify caveola-independent functions of the cavins and propose a novel mechanism for inhibition of the CLIC/GEEC pathway by caveolin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Animals
  • COS Cells
  • Caveolae / metabolism*
  • Caveolin 1 / metabolism*
  • Cell Movement
  • Cell Physiological Phenomena
  • Chlorocebus aethiops
  • Cholesterol / metabolism
  • Clathrin
  • Endocytosis / genetics
  • Endocytosis / physiology*
  • Enzyme Activation
  • GPI-Linked Proteins / metabolism
  • Hyaluronan Receptors / metabolism
  • Membrane Microdomains / metabolism*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • RNA Interference
  • RNA, Small Interfering
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • cdc42 GTP-Binding Protein / metabolism

Substances

  • Caveolin 1
  • Cavin1 protein, mouse
  • Cd44 protein, mouse
  • Cdc42 protein, mouse
  • Clathrin
  • GPI-Linked Proteins
  • Hyaluronan Receptors
  • Membrane Proteins
  • RNA, Small Interfering
  • RNA-Binding Proteins
  • Cholesterol
  • cdc42 GTP-Binding Protein

Grant support

This work was supported by the National Health and Medical Research Council of Australia, fellowships and grants to R.G. Parton (grant numbers APP569542, APP1045092); to A.S. Yap (grant number APP1044041); to R.G. Parton, K. Gaus, and A.S. Yap (grant number APP1037320), and the Kids Cancer Project of the Oncology Research Foundation. Confocal microscopy was performed at the Australian Cancer Research Foundation (ACRF)/Institute for Molecular Bioscience (IMB) Dynamic Imaging Facility for Cancer Biology, established with funding from the ACRF. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.