Low-power laser irradiation (LPLI) has come into a wide range of use in medical field. Considering basic research, LPLI can enhance
DNA synthesis and increases proliferation rate of human cells. But only a few data about the effects of LPLI on human liver or
hepatoma cells are available. The cytoskeleton plays important roles in cell function and therefore is implicated in the pathogenesis of many human
liver diseases, including malignant
tumors. In our previous study, we found the stability of
cytokeratin molecules in human hepatocytes was related to the intact microtubule network that was influenced by
colchicine. In this study, we are going to search the effect of LPLI on proliferation of human
hepatoma cell line HepG2 and J-5 cells. In addition, the stability of
cytokeratin and
synemin (one of the intermediate filament-associated
proteins) were analyzed under the action of LPLI to evaluate the possible mechanism of LPLI effects on proliferation of human
hepatoma cells. In experiment, HepG2 and J-5 cells were cultured in 24-well plate for 24 hours. After irradiation by 130 mW diode 808 nm GaAlAs continue wave
laser in different time intervals, the cell numbers were counted. Western blot and immunofluorescent staining examined the expression and distribution of
PCNA,
cytokeratin and
synemin. The cell number counting and
PCNA expression were evaluated to determine the proliferation. The organization and expression of
cytokeratin and
synemin were studied to identify the stability of cytoskeleton affected by LPLI. The results revealed that proliferation of HepG2 and J-5 cells was inhibited by LPLI since the cell number and
PCNA expression was reduced. Maximal effect was achieved with 90 and 120 seconds of exposure time (of energy density 5.85 J/cm2 and 7.8 J/cm2, respectively) for HepG2 and J-5, respectively. The decreased ratio of cell number by this dose of irradiation was 72% and 66% in HepG2 and J-5 cells, respectively. Besides that, the architecture of intermediate filaments in these cells was disorganized by
laser irradiation. The expression of intermediate filament-associated
protein,
synemin, was also reduced. Two significant findings are raised in this study: (1) Diode 808 nm GaAlAs
continuous wave laser has an inhibitory effect on the proliferation of human
hepatoma cells line HepG2 and J-5. (2) The mechanism of inhibition might be due to down-regulation of
synemin expression and alteration of
cytokeratin organization that was caused by
laser irradiation.