Altered synthesis of the 26-kDa heat stress protein family and thermotolerance in cell lines with elevated levels of calcium-binding proteins.
Using a bovine papilloma virus-based vector, mouse mammary adenocarcinoma cells have been transformed to express elevated amounts of functional calmodulin (CaM) (Rasmussen and Means, 1987) and another Ca2(+)-binding protein, parvalbumin (PV) (Rasmussen and Means, 1989) that is not normally synthesized in these cells. Parental cells (C127) and cells transformed by the vector alone (BPV-1), the vector containing a CaM gene (CM-1), or the vector containing parvalbumin (PV-1) were used to study the effect of increased synthesis of Ca2(+)-binding proteins on heat-stress protein (HSP) synthesis and cell survival following heating at 43 degrees C. The induction, stability, and repression of the synthesis of most HSPs after 43 degrees C heating was not significantly affected by increased amounts of Ca2(+)-binding proteins, but the rate of synthesis of all three isoforms of the 26-kDa HSP (HSP26) was greatly reduced. C127 cells, which have about one half as much CaM as do BPV-1 cells, synthesized the most HSP26. CM-1 cells, which have more than fourfold higher levels of CaM than do BPV-1 cells, had a rate of synthesis of HSP26 approaching that of unheated cells. BPV-1 cells, with a two-fold increase in CaM, were intermediate in HSP26 synthesis. This effect on HSP26 synthesis may be largely related to the Ca2(+)-binding capacity of CaM rather than to a specific CaM-regulated function, since PV-1 cells also showed reduced rates of HSP26 synthesis. Survival experiments showed that reduced HSP26 synthesis in cells with increased amounts of Ca2(+)-binding proteins did not significantly alter intrinsic resistance to continuous 43 degrees C heating. Thermotolerance was not reduced and appeared to develop more rapidly in CM-1 and PV-1 cells. These results suggest that (1) the signal for HSP26 synthesis can be largely abrogated by elevated Ca2+ binding protein levels, and (2) if these HSPs are involved in thermotolerance development, that function may be associated with intracellular Ca2+ homeostasis.
Evans
D P
DP
Department of Tumor Biology, University of Texas M. D. Anderson Cancer Center, Houston.
Simonette
R A
RA
Rasmussen
C D
CD
Means
A R
AR
Tomasovic
S P
SP
D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival; D015180:Electrophoresis, Gel, Two-Dimensional; D006360:Heat-Shock Proteins / Q000096:biosynthesis*; D006358:Hot Temperature; D051379:Mice; D008970:Molecular Weight; D010320:Parvalbumins / Q000502:physiology; D014162:Transfection
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D006360:Heat-Shock Proteins; D010320:Parvalbumins