E. Canalis et al., INSULIN-LIKE GROWTH-FACTORS INHIBIT INTERSTITIAL COLLAGENASE SYNTHESIS IN BONE CELL-CULTURES, Endocrinology, 136(4), 1995, pp. 1348-1354
Insulin-Like growth factor-I (IGF-I) and IGF-II are among the most pre
valent growth factors secreted by bone cells and are presumed to act a
s autocrine regulators of bone formation. We recently demonstrated tha
t IGFs inhibit bone collagen degradation, and we postulated that they
may either inhibit the expression of interstitial collagenase or stimu
late the synthesis of tissue inhibitors of metalloproteinase-1 (TIMP-1
), -2, or -3. We tested the effects of IGF-I and -II on collagenase an
d TIMP-1, -2, and -3 expression in cultures of osteoblast-enriched cel
ls from 22-day-old fetal rat calvariae (Ob cells). Steady state messen
ger RNA (mRNA) levels were determined by Northern blot analysis, and c
ollagenase concentrations were determined in the culture medium by a s
pecific immunoassay. After 2-6 h of treatment, IGF-I and -II decreased
collagenase transcripts by up to 80%. IGF-I was a more potent inhibit
or than IGF-II, because it was active at doses as low as 10 nM, wherea
s a dose of 100 nM was required to observe the IGF-II effect. In addit
ion, IGF-I and -II opposed the stimulatory effect of retinoic acid on
collagenase transcripts. Immunoreactive collagenase levels were not de
tectable in control or IGF-treated cultures, but IGF-I and -II decreas
ed the levels induced by retinoic acid by 70-90%. The protein synthesi
s inhibitor cycloheximide superinduced collagenase transcripts, and IG
F-I or -II decreased this mRNA induction to levels similar to, but not
lower than, those observed in control cultures. The effects of IGF-I
and -II on collagenase transcripts were not modified by the DNA synthe
sis inhibitor hydroxyurea at 1 mM. Neither IGF-I nor IGF-II modified t
he expression of TIMP-1, -2, or -3 mRNA in Ob cells. TIMP protein leve
ls were not determined, and our study does not exclude a translational
or posttranslational effect of IGF. In conclusion, IGF-I and -II decr
ease interstitial collagenase transcripts as well as induced protease
levels in Ob cells, and this effect may contribute to their inhibitory
actions on bone collagen degradation.