AJP - Cell Physiology, Vol 259, Issue 1 C77-C83, Copyright © 1990 by American Physiological Society
Calcium and the heat-shock response in the human monocytic line U-937
S. Kantengwa, A. M. Capponi, J. V. Bonventre and B. S. Polla
Respiratory Division and Allergy Unit, Geneva University Hospital, Switzerland.
In the human monocytic line U-937, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]
increases cytosolic free calcium concentration ([Ca2+]i). 1,25-(OH)2D3 also
enhances the synthesis of heat-shock proteins (HSPs) when U-937 cells are
exposed to elevated temperatures. To establish whether these two effects of
1,25-(OH)2D3 are related, we examined the effects of calcium on the
heat-shock (HS) response, as well as the influence of 1,25-(OH)2D3 on this
system. The equilibrium dissociation constant (Kd) of the fluorescent probe
used to measure [Ca2+]i, fura-2, at 37 and 45 degrees C was found to be 191
and 234 nM, respectively. Exposure of U-937 cells to 45 degrees C did not
increase [Ca2+]i under conditions in which active efflux of the dye was
prevented by the organic anion transport inhibitor probenecid (1 mM). In
cells preincubated in calcium-free medium, with subsequent addition of 4 mM
EGTA before HS, or exposed to the calmodulin antagonist
N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7), the increase in
HSPs synthesis was not affected. Cell viability, assessed by [3H]thymidine
uptake, was not different between cells exposed to HS in calcium-containing
or calcium-free media. Moreover, the effects of 1,25-(OH)2D3 on the HS
response were also observed in a calcium-depleted medium, indicating that
the effects of 1,25-(OH)2D3 on HSP synthesis were not mediated by [Ca2+]i.
