Abstract: Abstract：Objective To study the effects of 9-cis retinoic acid(9-cisRA) on cell cycle and expressions of CyclinD1 and CDK44 in thyroid squamous cell carcinoma cells(SW579).Methods Treated with different dose of 9-cisRA (final concentration of 10-7 mol/L、10-6 mol/L、5×10-6mol/L、10-5mol/L). the proliferation of the cells was observed with MTT and the cell cycle was measured by flow cytometry;the CDK4 and CyclinD1 mRNA expression levels were determined by RT-PCR;CDK4 and CyclinD1 protein expression were determined by western blotting. Results After cells were treated with 9-cisRA the proliferation index decreased markedly with a dose-dependent manner.Flow cytometry analysis showed the percent of G1 phase cells was significantly higher than that of the control groups and the percent of S phase cells was lower than that of the control groups .The cell cycle was arrested at G1 stage;The mRNA expression of the CDK4 was not increased; the mRNA expression of CyclinD1 was. descreased dramatically; Distinct changes in the expressions of CDK4 protein was not observed; the expressions of CyclinD1 protein was. descreased dramatically; Conclusions 9-cisRA inhibited the proliferation of SW579 cell in a dose-dependent manner,It was related with down-regulation of CyclinD1 and arresting sw579cell at G1 phase.

Key words: Key words: 9-cis- retinoic acid, SW579, cell cycle, CyclinD1, CDK4