cAMP signalling is decisive for recovery of nuclear bodies (PODs) during maturation of RA-resistant t(15;17) promyelocytic leukemia NB4 cells expressing PML-RAR alpha.

We analysed the expression of retinoid receptors and PML in relation to the morphology of PML-containing nuclear bodies (PODs) in maturation sensitive (NB4) and resistant subclones (NB4-R1 and R2) of the promyelocytic NB4 cell line. The basal level of RARalpha, RXRalpha and PML mRNA and protein were roughly the same in the three cell lines. While NB4 and NB4-R1 cells express comparable amounts of PM-RARalpha mRNA and 120 kDa protein, NB4-R2 cells despite normal mRNA levels the 120 kDa protein was not detectable. In NB4-R2 cells however, two novel PML-related entities of 65 kDa and 85 kDA were detected with a anti-PML antibody, in addition to the two PML isoforms of 78 and 97 kDa found in any NB4 cells. Despite the 120 kDa PML-RARalpha defect, NB4-R2 cells show micropunctuated nuclear bodies typical of APL cells. Contrasting with NB4 cells, neither NB4-R1 cells which express PML-RARalpha, nor NB4-R2 cells lacking the 120 kDa PML-RARalpha reorganised nuclear bodies (PODs) in response to RA. Importantly, in RA-primed NB4-R1 cells, a secondary event triggered by cAMP restored PODs, concomitant to maturation. This indicates that the recovery of nuclear bodies in APL is dissociated from the early action of RA in cell maturation. Finally, the key finding of this work is that cAMP signalling ultimately determines the recovery of nuclear bodies associated to cell maturation.