The rab11 effector protein FIP1 regulates adiponectin trafficking and secretion

PLoS One. 2013 Sep 11;8(9):e74687. doi: 10.1371/journal.pone.0074687. eCollection 2013.

Abstract

Adiponectin is an adipokine secreted by white adipocytes involved in regulating insulin sensitivity in peripheral tissues. Secretion of adiponectin in adipocytes relies on the endosomal system, however, the intracellular machinery involved in mediating adiponectin release is unknown. We have previously reported that intracellular adiponectin partially compartmentalizes with rab 5 and rab11, markers for the early/sorting and recycling compartments respectively. Here we have examined the role of several rab11 downstream effector proteins (rab11 FIPs) in regulating adiponectin trafficking and secretion. Overexpression of wild type rab11 FIP1, FIP3 and FIP5 decreased the amount of secreted adiponectin expressed in HEK293 cells, whereas overexpression of rab11 FIP2 or FIP4 had no effect. Furthermore shRNA-mediated depletion of FIP1 enhanced adiponectin release whereas knock down of FIP5 decreased adiponectin secretion. Knock down of FIP3 had no effect. In 3T3L1 adipocytes, endogenous FIP1 co-distributed intracellularly with endogenous adiponectin and FIP1 depletion enhanced adiponectin release without altering insulin-mediated trafficking of the glucose transporter Glut4. While adiponectin receptors internalized with transferrin receptors, there were no differences in transferrin receptor recycling between wild type and FIP1 depleted adipocytes. Consistent with its inhibitory role, FIP1 expression was decreased during adipocyte differentiation, by treatment with thiazolidinediones, and with increased BMI in humans. In contrast, FIP1 expression increased upon exposure of adipocytes to TNFα. In all, our findings identify FIP1 as a novel protein involved in the regulation of adiponectin trafficking and release.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism*
  • Adipocytes / cytology
  • Adipocytes / metabolism
  • Adiponectin / metabolism*
  • Animals
  • Body Mass Index
  • Endosomes / metabolism
  • Gene Expression Regulation
  • Glucose Transporter Type 4 / metabolism
  • HEK293 Cells
  • Humans
  • Membrane Proteins / metabolism*
  • Mice
  • Monomeric GTP-Binding Proteins / metabolism*
  • NIH 3T3 Cells
  • Obesity / metabolism
  • Protein Binding
  • Protein Transport
  • Transferrin / metabolism
  • mRNA Cleavage and Polyadenylation Factors / metabolism*
  • rab GTP-Binding Proteins / metabolism*
  • rab5 GTP-Binding Proteins / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Adiponectin
  • FIP1L1 protein, human
  • Glucose Transporter Type 4
  • Membrane Proteins
  • RAB11FIP1 protein, human
  • SLC2A4 protein, human
  • Slc2a4 protein, mouse
  • Transferrin
  • mRNA Cleavage and Polyadenylation Factors
  • FiP1 protein, mouse
  • rab11 protein
  • Monomeric GTP-Binding Proteins
  • rab GTP-Binding Proteins
  • rab5 GTP-Binding Proteins

Grants and funding

This work was funded by a research grant from Diabetes UK (www.diabetes.org.uk). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.