|Budget Amount *help
¥1,800,000 (Direct Cost : ¥1,800,000)
Fiscal Year 1998 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1997 : ¥1,000,000 (Direct Cost : ¥1,000,000)
We have recently found that retinoic acids (RAs) evoke anticoagulant effect by upregulating thrombomodulin (TM) and downregulating tissue factor (TF) expression in acute promyelocytic leukemia (APL) and monoblastic leukemia cells. Two classes of nuclear RA receptors, termed retinoic acid receptors (RARs) and retinoid X receptors, have already been identified. Each receptor class consists of three subtypes. We have used several synthetic retinoids to find which receptor subtypes are involved in the regulation of TM and TF expression in APL cells NB4, monoblastic leukemia cells U937 and human umbilical vein endothelial cells (HUVECs). Am8O, which does not have a binding affinity to RARgamma, Ch55, which does not bind to cytoplasmic retinoic acid binding protein (CRABP), and a specific RARalpha antagonist RQ4O-6055, have shown to upregulate TM and downregulate TE in NB4 and U937 cells similar to all-trans RA (ATRA). A specific RARalpha antagonist Ro4l-5253 efficiently suppressed the upreg
ulation of TM by ATRA and Am8O in NB4 cells, U937 cells and HUVECs. In contrast, only when both RARalpha and RARbeta antagonists were preincubated, downregulation of TF by the retinoids was suppressed in NB4 cells. Furthermore, 1,25(OH)_2D_3 has shown to have anticoagulant effects on several monocytic leukemia cells and monocytes similar to RAs.
These results indicate the mechanically distinct transactivation and transrepress ion functions of RARs, the major role of RARalpha in TM upregulation by retinoids in leukemic cells and HUVECs and the cooperative role of RARalpha and RARbeta in TF downregulation by retinoids. It is also implicated that synthetic retinoids and vitamin D derivatives will provide very useful means to control distinct targets, TM and TF genes, at the level of transcription. Synthetic retinoids and vitamin D derivatives may develop as new type of antithrombotic and antiatherosclerotic agents which change the character of cells as well as malignant cell differentiation inducers. Less