Strontium induces murine keratinocyte differentiation in vitro in the presence of serum and calcium.
Primary mouse keratinocytes in culture are induced to terminally differentiate by increasing extracellular Ca2+ concentrations (Cao) from 0.05 mM to > or = 0.1 mM. The addition of Sr2+ (> or = 2.5 mM) to medium containing 0.05 mM Ca2+ induces focal stratification and terminal differentiation, which are similar to that found after increasing the Cao to 0.12 mM. Sr2+ in 0.05 mM Ca2+ medium induces the expression of the differentiation-specific keratins, keratin 1 (K1), keratin 10 (K10), and the granular cell marker, filaggrin, as determined by both immunoblotting and immunofluorescence. Sr2+ induces the expression of those differentiation markers in a dose dependent manner, with an optimal concentration of 5 mM. In the absence of Ca2+ in the medium, the Sr2+ effects are reduced, and Sr2+ is ineffective when both Ca2+ and serum are deleted from the medium. Sr2+ treatment increases the ratio of fluorescence intensity of the intracellular Ca2+ sensitive probe, fura-2, indicating an associated rise in the level of intracellular free Ca2+ and/or Sr2+. At doses sufficient to induce differentiation, Sr2+ also increases the level of inositol phosphates in primary keratinocytes within 30 min. The uptake curves of 85Sr2+ by primary keratinocytes are similar to those of 45Ca2+. At low concentrations, the initial uptake of both 45Ca2+ and 85Sr2+ reaches a plateau within 1 hr; at higher concentrations, the uptake of both 45Ca2+ and 85Sr2+ increases continuously for 12 hr. In keratinocytes pre-equilibrated with 45Ca2+ in 0.05 mM Ca2+ medium, Sr2+ causes an increase of 45Ca2+ uptake, which is dependent on the presence of serum. These results suggest that Sr2+ utilizes the same signalling pathway as Ca2+ to induce keratinocyte terminal differentiation and that Ca2+ may be required to exert these effects.
Li
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Laboratory of Cellular Carcinogenesis and Tumor Promotion, National Cancer Institute, Bethesda, Maryland 20892.
Kruszewski
F H
FH
Punnonen
K
K
Tucker
R W
RW
Yuspa
S H
SH
Hennings
H
H
D000818:Animals; D001769:Blood; D002118:Calcium / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins / Q000096:biosynthesis; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D007633:Keratins / Q000096:biosynthesis; D051379:Mice; D015290:Second Messenger Systems / Q000187:drug effects; D013324:Strontium / Q000378:metabolism / Q000494:pharmacology*
D003470:Culture Media; D000091344:Filaggrin Proteins; D007381:Intermediate Filament Proteins; D007633:Keratins; D002118:Calcium; D013324:Strontium