Beta1-integrins in the primary cilium of MDCK cells potentiate fibronectin-induced Ca2+ signaling

Am J Physiol Renal Physiol. 2004 Nov;287(5):F969-78. doi: 10.1152/ajprenal.00096.2004. Epub 2004 Jun 29.


Because beta(1)-integrin is involved in sensing of fluid flow rate in endothelial cells, a function that in Madin-Darby canine kidney (MDCK) cells is confined to the primary cilium, we hypothesized beta(1)-integrin to be an important part of the primary ciliary mechanosensory apparatus in MDCK cells. We observed that beta(1)-integrin, alpha(3)-integrin, and perhaps alpha(5)-integrin were localized to the primary cilium of MDCK cells by combining lectin and immunofluorescence confocal microscopy. beta(1)-Integrin was also colocalized with tubulin to the primary cilia of the rat renal collecting ducts, as well as to the cilia of proximal tubules and thick ascending limbs. Immunogold-electron microscopy confirmed the presence of beta(1)-integrin on primary cilia of MDCK cells and rat collecting ducts. Intracellular Ca(2+) levels, monitored by fluorescence microscopy on fluo 4-loaded MDCK cells, significantly increased on addition of fibronectin, a beta(1)-integrin ligand, to mature MDCK cells with an IC(50) of 0.02 mg/l. In immature, nonciliated cells or in deciliated mature cells, the IC(50) was 0.40 mg/l. Blocking the fibronectin-binding sites of beta(1)-integrin with RGD peptide prevented the Ca(2+) signal. Cross-linking of beta(1)-integrins by Sambucus nigra agglutinin produced a Ca(2+) response similar to the addition of fibronectin. Furthermore, the fibronectin-induced response was not dependent on flow or a flow-induced Ca(2+) response. Finally, the flow-induced Ca(2+) response was not prevented by the fibronectin-induced signal. Although beta(1)-integrin on the primary cilium greatly potentiates the fibronectin-induced Ca(2+) signaling in MDCK cells, the flow-dependent Ca(2+) signal is not mediated through activation of beta(1)-integrin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aniline Compounds
  • Animals
  • Blotting, Western
  • Calcium Signaling / drug effects
  • Calcium Signaling / physiology*
  • Cell Line
  • Chloral Hydrate / pharmacology
  • Cilia / metabolism
  • Dogs
  • Fibronectins / pharmacology*
  • Hypnotics and Sedatives / pharmacology
  • Immunohistochemistry
  • In Vitro Techniques
  • Integrin beta1 / metabolism*
  • Kidney / cytology
  • Kidney / metabolism*
  • Kidney Tubules, Collecting / metabolism
  • Lectins
  • Male
  • Microscopy, Fluorescence
  • Rats
  • Rats, Wistar
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Xanthenes


  • Aniline Compounds
  • Fibronectins
  • Fluo 4
  • Hypnotics and Sedatives
  • Integrin beta1
  • Lectins
  • Xanthenes
  • Chloral Hydrate