Calcium deficiency-induced and TRP channel-regulated IGF1R-PI3K-Akt signaling regulates abnormal epithelial cell proliferation

Cell Death Differ. 2014 Apr;21(4):568-81. doi: 10.1038/cdd.2013.177. Epub 2013 Dec 13.


Calcium deficiency causes abnormal colonic growth and increases colon cancer risk with poorly understood mechanisms. Here we elucidate a novel signaling mechanism underlying the Ca(2+) deficiency-induced epithelial proliferation using a unique animal model. The zebrafish larval yolk sac skin contains a group of Ca(2+)-transporting epithelial cells known as ionocytes. Their number and density increases dramatically when acclimated to low [Ca(2+)] environments. BrdU pulse-labeling experiments suggest that low [Ca(2+)] stimulates pre-existing ionocytes to re-enter the cell cycle. Low [Ca(2+)] treatment results in a robust and sustained activation of IGF1R-PI3K-Akt signaling in these cells exclusively. These ionocytes specifically express Igfbp5a, a high-affinity and specific binding protein for insulin-like growth factors (IGFs) and the Ca(2+)-selective channel Trpv5/6. Inhibition or knockdown of Igfbp5a, IGF1 receptor, PI3K, and Akt attenuates low [Ca(2+)]-induced ionocyte proliferation. The role of Trpv5/6 was investigated using a genetic mutant, targeted knockdown, and pharmacological inhibition. Loss-of-Trpv5/6 function or expression results in elevated pAkt levels and increased ionocyte proliferation under normal [Ca(2+)]. These increases are eliminated in the presence of an IGF1R inhibitor, suggesting that Trpv5/6 represses IGF1R-PI3K-Akt signaling under normal [Ca(2+)]. Intriguingly, blockade of Trpv5/6 activity inhibits the low [Ca(2+)]-induced activation of Akt. Mechanistic analyses reveal that the low [Ca(2+)]-induced IGF signaling is mediated through Trpv5/6-associated membrane depolarization. Low extracellular [Ca(2+)] results in a similar amplification of IGF-induced PI3K-PDK1-Akt signaling in human colon cancer cells in a TRPV6-dependent manner. These results uncover a novel and evolutionarily conserved signaling mechanism that contributes to the abnormal epithelial proliferation associated with Ca(2+) deficiency.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Caco-2 Cells
  • Calcium / pharmacology*
  • Cell Proliferation / drug effects
  • Epithelial Cells / cytology
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism*
  • Humans
  • Insulin-Like Growth Factor I / pharmacology
  • Insulin-Like Growth Factor II / pharmacology
  • Larva / cytology
  • Oligonucleotides, Antisense / metabolism
  • Phosphatidylinositol 3-Kinase / genetics
  • Phosphatidylinositol 3-Kinase / metabolism
  • Phosphoinositide-3 Kinase Inhibitors
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism
  • Receptor, IGF Type 1 / antagonists & inhibitors
  • Receptor, IGF Type 1 / genetics
  • Receptor, IGF Type 1 / metabolism
  • Signal Transduction / drug effects
  • Sodium-Potassium-Exchanging ATPase / metabolism
  • TRPV Cation Channels / antagonists & inhibitors
  • TRPV Cation Channels / genetics
  • TRPV Cation Channels / metabolism*
  • Yolk Sac / cytology
  • Zebrafish / growth & development
  • Zebrafish / metabolism
  • Zebrafish Proteins / antagonists & inhibitors
  • Zebrafish Proteins / genetics
  • Zebrafish Proteins / metabolism*


  • Oligonucleotides, Antisense
  • Phosphoinositide-3 Kinase Inhibitors
  • TRPV Cation Channels
  • Zebrafish Proteins
  • trpv6 protein, zebrafish
  • Insulin-Like Growth Factor I
  • Insulin-Like Growth Factor II
  • Phosphatidylinositol 3-Kinase
  • Receptor, IGF Type 1
  • Proto-Oncogene Proteins c-akt
  • Sodium-Potassium-Exchanging ATPase
  • Calcium