All-trans-retinoic acid-mediated growth inhibition involves inhibition of human kinesin-related protein HsEg5

In this study we used differential display reverse transcription-polymerase chain reaction to search for differentially expressed all-trans-retinoic a cid (ATRA)-responsive genes in pancreatic carcinoma cells. We identified th e kinesin-related protein HsEg5, which plays an essential role in spindle a ssembly and spindle function during mitosis, as a novel molecule involved i n ATRA-mediated growth inhibition. Using Northern and Western blot analysis we demonstrated that ATRA significantly inhibits HsEg5 expression in vario us pancreatic carcinoma cell lines as well as in HaCat keratinocytes, Inhib ition of HsEg5 expression by ATRA occurs at the posttranscriptional level. As a consequence, tumor cells synchronized in S-phase revealed a retarded p rogression through G(2)/M phase of the cell cycle indicating that HsEg5 inh ibition results in a delayed progression through mitosis, Furthermore, a si gnificant decrease of HsEg5 protein expression achieved by antisense transf ection revealed a significant growth inhibition compared with control cells . Therefore, HsEg5 represents a novel molecule involved in ATRA-mediated gr owth inhibition, suggesting that vitamin A derivatives can interact with th e bipolar spindle apparatus during mitosis.