Involvement of protein kinase-C in the mitogenic effect of insulin-like growth factor-I on rat astrocytes

Endocrinology. 1992 Oct;131(4):1948-54. doi: 10.1210/endo.131.4.1396338.


Insulin-like growth factor-I (IGF-I) stimulates the proliferation of many cell types, including astrocytes. Astrocytes are a population of brain cells highly enriched in IGF-I receptors, which unlike neurons, retain the ability to proliferate in the adult brain. Although astrocyte proliferation in response to IGF-I is well documented, the intracellular mechanisms that mediate this phenomenon are poorly defined. Interestingly, activation of protein kinase-C (PKC) by IGF-I has been observed in several cell types. In this report we first characterized the mitogenic effects of IGF-I on highly purified type I rat astrocyte cultures. Next, we determined whether IGF-I activates PKC in our cultures. Finally, since astrocyte proliferation is stimulated by both IGF-I and the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA), we decided to test the possible involvement of PKC in the mitogenic activity of IGF-I on astrocytes. IGF-I stimulated the DNA synthesis rate in rat astrocytes. Analysis of the time course revealed that IGF-I (10 nM) induces maximal stimulation of [3H]thymidine incorporation (a 4-fold increase) 16-18 h after exposure. TPA also stimulated mitogenesis in our cultures. The dose-response of [3H]thymidine incorporation induced by IGF-I and TPA indicated that 10 nM was the lowest concentration producing a maximal effect for both agents. Analysis of proteins by Western blot revealed that 10 nM IGF-I translocates PKC(alpha), the predominant PKC isoform in astrocyte cultures, from the cytosol to the membrane fraction within 20 min. A similar activation of PKC was achieved with 100 nM TPA. When astrocytes were exposed to IGF-I (10 nM) and TPA (10 nM) in combination, [3H]thymidine uptake was significantly higher than the uptake induced by either IGF-I (10 nM) or TPA (10 nM) alone. However, the effect of IGF-I plus TPA was not fully additive. In a second experiment, the mitogenic effect of IGF-I was partially abolished in cells depleted of PKC by preincubation with high concentrations of TPA (300 nM). Finally, incubation of astrocytes with the PKC inhibitor H-7 at 20 microM, a concentration that completely blocked the mitogenic action of TPA, only reduced the ability of IGF-I to stimulate DNA synthesis by 50%. In summary, our results demonstrate that IGF-I can rapidly activate PKC in astrocytes, and that PKC activation is involved in the mitogenic effect of IGF-I on these cells. However, we conclude that IGF-I also stimulates astrocyte proliferation through PKC-independent pathways.

Publication types

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

MeSH terms

  • 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine
  • Animals
  • Astrocytes / drug effects*
  • Cells, Cultured
  • Drug Combinations
  • Insulin-Like Growth Factor I / pharmacology*
  • Isoquinolines / pharmacology
  • Mitogens / pharmacology*
  • Piperazines / pharmacology
  • Protein Kinase C / chemistry
  • Protein Kinase C / metabolism
  • Protein Kinase C / physiology*
  • Protein Kinase Inhibitors
  • Rats
  • Tetradecanoylphorbol Acetate / pharmacology
  • Thymidine / metabolism


  • Drug Combinations
  • Isoquinolines
  • Mitogens
  • Piperazines
  • Protein Kinase Inhibitors
  • Insulin-Like Growth Factor I
  • 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine
  • Protein Kinase C
  • Tetradecanoylphorbol Acetate
  • Thymidine