Abstract: Objective To investigate the role of Txndc5 in murine pre-osteoblast proliferation. Methods Murine pre-osteoblast cell line MC3T3-E1 was treated with estrogen. Txndc5 was either over-expressed by plasmid vector or knocked down by siRNA in MC3T3-E1 cell. The protein level of Txndc5 and Cyclins was evaluated by Western blot. The mRNA level of Cyclin A was measured by quantitative real-time PCR. Cell proliferation rate was determined by MTS assay and cell counting. Cell cycle distribution was revealed by flow cytometry analysis. Results The protein level of Txndc5 was up-regulated in estrogen-induced MC3T3-E1 proliferation. Knockdown of Txndc5 blocked estrogen-induced cell proliferation. Over-expression of Txndc5 accelerated MC3T3-E1 cell proliferation, increased the proportion of cells in S phase. Eighteen hours after the synchronized cells entered cell cycle, the expression of Cyclin A was up-regulated, and the percentage of cells in S phase was 18.69%±4.08% in cells over-expressing Txndc5, which was only 8.15%±3.68% in control cells. On the other hand, knockdown of Txndc5 inhibited the growth of MC3T3-E1 cells, decreased the proportion of cells in S phase, and down-regulated the expression of Cyclin A. Knockdown of Cyclin A attenuated the cell proliferation-enhancing effect of Txndc5. Conclusion Txndc5 mediates estrogen-accelerated pre-osteoblast proliferation through up-regulation of Cyclin A.

Key words: Txndc5, MC3T3-E1 cell, cell proliferation, estrogen