AMPK regulation of the growth of cultured human keratinocytes.
AMP kinase (AMPK) is a fuel sensing enzyme that responds to cellular energy depletion by increasing processes that generate ATP and inhibiting others that require ATP but are not acutely necessary for survival. In the present study, we examined the relationship between AMPK activation and the growth (proliferation) of cultured human keratinocytes and assessed whether the inhibition of keratinocyte growth by vitamin D involves AMPK activation. In addition, we explored whether the inhibition of keratinocyte proliferation as they approach confluence could be AMPK-related. Keratinocytes were incubated for 12 h with the AMPK activator, 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). At concentrations of 10(-4) and 10(-3) M, AICAR inhibited keratinocyte growth by 50% and 95%, respectively, based on measurements of thymidine incorporation into DNA. It also increased AMPK and acetyl CoA carboxylase phosphorylation (P-AMPK and P-ACC) and decreased the concentration of malonyl CoA confirming that AMPK activation had occurred. Incubation with the thiazolidinedione, troglitazone (10(-6) M) caused similar alterations in P-AMPK, P-ACC, and cell growth. In contrast, the well known inhibition of keratinocyte growth by 1,25-dihydroxyvitamin D3 (10(-7) and 10(-6) M) was not associated with changes in P-AMPK or P-ACC. Like most cells, the growth of keratinocytes diminished as they approached confluence. Thus, it was of note that we found a progressive increase in P-AMPK (1.5- to 2-fold, p < 0.05) as keratinocytes grown in control medium went from 25% to 100% confluence. In conclusion, the data are consistent with the hypothesis that activation of AMPK acts as a signal to diminish the proliferation of cultured keratinocytes as they approach confluence. They also suggest that AMPK activators, such as AICAR and troglitazone, inhibit keratinocyte growth and that the inhibition of cell growth by 1,25-dihydroxyvitamin D3 is AMPK-independent.
Saha
Asish K
AK
Endocrinology, Diabetes and Nutrition, Department of Medicine, Boston University School of Medicine, Boston, MA, USA.
Persons
Kelly
K
Safer
Joshua D
JD
Luo
Zhijun
Z
Holick
Michael F
MF
Ruderman
Neil B
NB
D055372:AMP-Activated Protein Kinases; D000818:Animals; D002762:Cholecalciferol / Q000378:metabolism; D002839:Chromans / Q000494:pharmacology; D003470:Culture Media / Q000378:metabolism; D005343:Fibrinolytic Agents / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D015603:Keratinocytes / Q000201:enzymology* / Q000378:metabolism; D008316:Malonyl Coenzyme A / Q000378:metabolism; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism / Q000502:physiology*; D041681:NIH 3T3 Cells; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D045162:Thiazolidinediones / Q000494:pharmacology; D000077288:Troglitazone; D014807:Vitamin D / Q000378:metabolism
D002839:Chromans; D003470:Culture Media; D005343:Fibrinolytic Agents; D009097:Multienzyme Complexes; D045162:Thiazolidinediones; D014807:Vitamin D; D002762:Cholecalciferol; D008316:Malonyl Coenzyme A; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D000077288:Troglitazone