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Expression of annexin I, II, V, and VI by rat osteoblasts in primary culture: Stimulation of annexin I expression by dexamethasone
Author(s) -
Suarez Françoise,
Rothhut Bernard,
Comera Christine,
Touqui Lhousseine,
Marie Françoise Russo,
Silve Caroline
Publication year - 1993
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650081007
Subject(s) - annexin , endocrinology , dexamethasone , medicine , annexin a2 , stimulation , osteoblast , glucocorticoid , cell culture , alkaline phosphatase , chemistry , biology , apoptosis , in vitro , biochemistry , enzyme , genetics
To determine whether rat osteoblasts synthesize proteins of the annexin family and to evaluate the extent to which glucocorticoids modulate the expression of annexins by these cells, osteoblasts were grown in primary cultures in the absence or presence of dexamethasone, and the expression of annexins was evaluated by immunoblotting using polyclonal antibodies against human annexins. Four different annexins (I, II, V, and VI) were found to be expressed by rat osteoblasts. The expression of annexin I, but not the other annexins studied, was increased in osteoblasts cultured in the presence of dexamethasone (173 ± 33% increase comparing untreated cells and cells treated for 10 days with 5 × 10 −7 M dexamethasone). Increased expression of annexin I was observed after the third day of exposure to dexamethasone and rose thereafter until day 10; annexin I expression increased with dexamethasone concentrations above 10 −10 M throughout the range of concentrations studied. The increase in annexin I protein was associated with an increase in annexin I mRNA and was completely blocked by the concomitant addition of the glucocorticoid receptor antagonist RU 38486. The increase in annexin I content following dexamethasone treatment was associated with an increase in alkaline phosphatase activity and PTH‐induced cAMP stimulation, whereas phospholipase A 2 activity in the culture medium was reduced to undetectable levels. The finding that four annexins are expressed in rat osteoblasts in primary culture raises the possibility that these proteins could play an important role in bone formation by virtue of their ability to bind calcium and phospholipids, serve as Ca 2+ channels, interact with cytoskeletal elements, and/or regulate phospholipase A 2 activity. In addition, the dexamethasone‐induced increase in annexin I may represent a mechanism by which glucocorticoids modify osteoblast function.