engleski

Regulated production of leukemia inhibitory factor mRNA and bioactivity by bone cells

Leukemia inhibitory factor (LIF) is a recently purified glycoprotein with multiple effects on bone cell functions. We examined if LIF could be a local regulator of bone metabolism by determining if it was produced by a variety of osteoblast-like bone cells. Furthermore, we examined if LIF production was regulated.Steady-state LIF mRNA was determined by Northern blot hybridization of total cellular RNA to a cDNA for human LIF. Production of LIF was confirmed by a bioassay (inhibition of M1 cell replication). Mouse and rat osteoblast- like cells, MC3T3-E1 and Pyla, did not express LIF mRNA constitutively, but did show LIF message and bioactivity after stimulation with either 10ug/ml LPS, 1ng/ml TGF beta or 100ng/ml TNF alpha. LIF mRNA was seen 3h after stimulation with LPS and 24h after TGF beta and TNF alpha. Unlike rodent bone cell modeks, human osteosarcoma cell lines, SaOS and U2, constitutively expressed LIF mRNA amd LPS had no additional effect on these cells. However, in SaOS cells, but not U2 cells, the phorbol ester PMA (5ng/ml) increased LIF mRNA by 10-fold after 6 hours. The effect of PMA on LIF mRNA in SaOS cells was paralleled by similar effects on LIF bioactivity in the conditioned medium. Neither UMR-106 nor ROS 17/2.8 cells expressed LIF mRNA constitutively or after LPS treatment. These results demonstrate that LIf is produced by a variety of osteoblast-like bone cells and that this production can be regulated. Hence, it is likely that LIF is an autocrine regulator of bone metabolism which may be important for both bone cell homeostasis and response to inflammation.

Leukemia inhibitory factor

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