Stimulation of MCM3 gene expression in osteoblast by low level laser irradiation.

Biostimulatory effect of cell proliferation and bone formation by laser irradiation has been reported, however, very little is known about the molecular basis of mechanisms. We previously constructed the cDNA library of mouse osteoblastic cells (MC3T3-E1) which enhanced gene expression by laser irradiation using a subtracted gene cloning procedure. In the present study, we focused on a gene clone, designated as MCL-140, which exhibited the high homology of DNA sequence with mouse minichromosome maintenance (MCM) 3 gene. MCM3 is involved in the initiation of DNA replication as licensing factor in eukaryotic cells. Nucleotide sequence of MCL-140 insert was determined and assessed in the nucleic acid databases. The transcription level of MCL-140 was examined by Northern blot analysis. The DNA sequences of clone MCL-140 insert exhibited 96.2% homology with MCM 3 gene coding P1 protein. Higher MCM3 mRNA levels were observed in laser-irradiated cells compared to the levels in non-irradiated cells: furthermore, radiolabelled thymidine incorporation was increased by laser irradiation. These findings suggest that low-level laser irradiation may enhance DNA replication and play a role in stimulating proliferation of osteoblast through the enhancement of the MCM3 gene expression.