IL-1a up-regulates gene expression of cathepsin K in osteoclasts via tyrosine kinase-NF-kB pathway

Suttatip Kamolmatyakul, D. of Preventive Dentistry, F. of Dentistry, PSU.
Wei Chen, D. of Medicine, Forsyth Inst., Boston, USA.
Yi-Ping Li, Assoc. Prof., Member of Staff, Forsyth Inst., Boston, USA.
Corresponding e-mail : ypli@forsyth.org

Grant : DE-10887 from the NIDR, USA
Presented : The Edward H. Hatton Award competition, the 78th general session of the Inter- national Association for Dental Research, 5-8 April 2000 Washington DC, USA
Key words : interleukin 1-alpha, cathepsin K, osteoclast, pycnodysostosis

Cathepsin K is abundantly and selectively expressed in osteoclast. Mutations of this gene cause pycnodysostosis characterized by short stature, abnormal bone and tooth development. IL-1a is the most potent osteoclast-activating factor which promote bone resorption, but the underlying mechanisms are unknown. In order to clarify the effect of IL-1a on osteoclast gene, cathepsin K expression affected by IL-1a was determined in MOPC-5 and MS-12 co-culture system. This system has been proven to be a useful model for the study of osteoclast (J. Bone Mine. Res. 13: 1112-1123, 1998). The cells were co-cultured in 6-well plates with a-MEM and 10 % FBS at 37oC and 5% CO2. IL-1a was added at various doses when MOCP-5 cells fully differentiated into osteoclasts. IL-1a was not added to controls. Cells were then harvested at different times and Northern Blot Analysis carried out. The results show that IL-1a significantly up-regulates mRNA levels of cathep-sin K in time- and dose-dependent manner. To elucidate the intracellular mechanisms involved, the effects of the MAPK pathway inhibitors (PD 98059 and SB 203580), tyrosine kinase inhibitor (Genistein) and NF-kB activation inhibitor (PDTC) were examined. Up-regulation effect of IL-1a on Cathepsin K expression is inhibited by Genistein and PDTC, whereas PD 98059 and SB 203580 show no inhibitory effect. Furthermore, pretreated MOCP-5 cells with antisense oligodeoxynucleo-tides to NF-kB (p65 and p50) suppress the up-regulation effect of IL-1a on Cathepsin K expression. Finally, EMSA experiment confirm that IL-1a activate NF-kB in the nuclei of the osteoclasts. Overall, our results demonstrate, for the first time, the regulation of cathepsin K gene by IL-1a in osteoclast through NF-kB transcription factor.
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