A NOVEL PHOSPHOLIPASE-C INHIBITOR AND PHORBOL ESTERS REVEAL SELECTIVEREGULATION OF THROMBIN-STIMULATED AND PARATHYROID HORMONE-STIMULATED SIGNALING PATHWAYS IN RAT OSTEOSARCOMA CELLS
M. Babich et al., A NOVEL PHOSPHOLIPASE-C INHIBITOR AND PHORBOL ESTERS REVEAL SELECTIVEREGULATION OF THROMBIN-STIMULATED AND PARATHYROID HORMONE-STIMULATED SIGNALING PATHWAYS IN RAT OSTEOSARCOMA CELLS, The Journal of pharmacology and experimental therapeutics, 269(1), 1994, pp. 172-177
Previous studies have demonstrated that parathyroid hormone (PTH) and
human alpha-thrombin mobilize intracellular calcium from distinct pool
s in UMR 106-H5 rat osteosarcoma cells. The present studies were desig
ned to explore the molecular basis of this differential signaling. Max
imally effective concentrations of both PTH (240 nM) and thrombin (10
U/ml) produced a rapid intracellular free calcium (Ca-i(++)) transient
(a 2- to 3-fold increase) that was inhibited by pretreatment with the
phospholipase C inhibitor 1-[6-[[17 5(10)-trien-17-yl]amino]hexyl]1H-
pyrrole-2,5-dione (U73,122) in a dose-dependent manner (IC50 = 3 mu M)
. Inhibition by U73,122 was not associated with a change in PTH-stimul
ated adenylate cyclase activity, whereas inositol phosphate accumulati
on, detected only in response to thrombin, was inhibited 23 to 45%. Pr
ior exposure of cells for 5 min with the protein kinase C activators p
horbol 12-myristate 13-acetate (8-80 nM) and phorbol 12,13-dibutyrate
(80 nM) weakly inhibited (less than or equal to 30%) the peak Ca-i(++)
increase in response to thrombin but completely blocked the Ca-i(++)
response to PTH. In contrast, 12-myristate 13-acetate produced a 1.55-
fold increase in the maximal stimulatory effect of PTH on adenylate cy
clase activity. These data suggest that activation of phospholipase C
is a prerequisite for both PTH- and thrombin-stimulated increases in C
a-i(++) and that protein kinase C differentially regulates the ability
of these agents to raise Ca-i(++). Collectively the results support t
he notion that the IP3/calcium mobilizing pathways utilized by PTH and
thrombin are compartmentalized. Further, the finding that phorbol est
ers produce opposite effects on PTH-stimulated adenylate cyclase and C
a-i(++) suggests that protein kinase C can alter the cellular response
to PTH by regulating the relative strength of signaling via these pat
hways.