Aims: 

Bone cell differentiation and homeostasis could be influenced by melatonin receptors MT1 and MT2.

Methods: 

Therefore, we investigated expression of MT1 and MT2 in human osteoblasts (hOB), osteosarcoma cell lines (HOS- and MG-63), bone marrow stromal cells (BMSC), and specimens from 30 osteosarcomas and 11 benign bone tumours using quantitative RT-PCR (values are expressed as n-fold enrichment compared to a control specimens).

Results: 

MT1, but not MT2 was detectable in hOB, BMSC and bone tumour cell lines. Remarkably, high expression levels of MT1-mRNA together with low OPG-mRNA were found in both cancer cell lines, while in normal hOB and BMSC, high OPG-mRNA levels were associated with low MT1-mRNA levels. MT1-mRNA expression levels were similar in malignant (4.39 ± 4.98-fold) and benign tumours (4.64 ± 6.81-fold). This was also observed for mRNA expression levels of the osteoclast activity stimulating receptor activator of nuclear factor-kB ligand (RANKL, 7.38 ± 9.61-fold vs. 3.57 ± 3.11-fold, p = 0.207) and its opponent osteoprotegerin (OPG: 23.45 ± 32.76 vs. 8.07 ± 7.23-fold, p = 0.13). MT1 was also detected by Western blotting in both osteosarcoma cell lines. Double-immunofluorescence staining experiments in osteosarcoma cell lines with antibodies against MT1 and glial fibrilary acidic protein (GFAP) revealed that localization of MT1 in subcellular compartments is dependent on cellular growth conditions.

Conclusion: 

High expression levels of MT1 in human bone tumours as well as in osteosarcoma cells lines and moderate levels in non-transformed hOB and BMSC suggest that MT1 participates in the regulation of human bone cell growth.