[Mechanism of tissue factor expression on NB4 cells down-regulated by all-trans retinoic acid and arsenic trioxide]

Area of Science:

• Hematology
• Molecular Biology
• Oncology

Background:

• Tissue factor (TF) plays a critical role in thrombosis and cancer progression.
• Acute promyelocytic leukemia (APL) is characterized by the PML-RARalpha fusion protein.
• All-trans retinoic acid (ATRA) and arsenic trioxide (As(2)O(3)) are effective treatments for APL.

Purpose of the Study:

• To elucidate the molecular mechanisms by which ATRA and As(2)O(3) down-regulate TF expression in NB4 APL cells.
• To investigate the role of de novo protein and RNA synthesis in ATRA-mediated TF regulation.
• To assess the impact of the PML-RARalpha fusion protein on TF expression and its modulation by ATRA and As(2)O(3).

Main Methods:

• Cyclohexamide (CHX) inhibition assays to assess de novo protein synthesis.
• Actinomycin D (Act D) inhibition assays to evaluate RNA synthesis and mRNA stability.
• Detection of TF antigen in U937 cells transfected with PML-RARalpha construct and treated with ATRA/As(2)O(3).

Main Results:

• ATRA's down-regulation of TF mRNA expression was abolished by CHX, indicating a requirement for new protein synthesis.
• Act D treatment shortened the half-life of TF mRNA in NB4 cells, suggesting mRNA destabilization.
• U937 cells expressing PML-RARalpha showed elevated TF antigen levels, which were reduced by ATRA and As(2)O(3).

Conclusions:

• ATRA's modulation of TF mRNA expression in NB4 cells appears to be an indirect process involving TF mRNA destabilization.
• The elevated TF antigen in PML-RARalpha-transfected cells may be linked to the fusion protein.
• ATRA and As(2)O(3) down-regulate TF expression in U937 cells, potentially independent of the PML-RARalpha fusion protein.