Nuclear translocation of the 1,25D3-MARRS (membrane associated rapid response to steroids) receptor protein and NFκB in differentiating NB4 leukemia cells

Abstract

1,25 Dihydroxyvitamin D3 (1,25D3) primes NB4 promyelocytic leukemia cells to differentiate along the monocyte/macrophage lineage through a non-genomic mechanism. Here we show that NB4 cells express high levels of the recently identified membrane receptor for 1,25D3, which is a distinct gene product from the classical nuclear vitamin D receptor. This 57 kDa protein, named 1,25D3-MARRS (Membrane Activated Rapid Response to Steroids)/ERp57/PIA3 appears to associate in a complex with the transcription factor, nuclear factor kappa B (NFκB). In unstimulated cells, 1,25D3-MARRS can be co-immunoprecipitated with antibodies directed at NFκB, and NFκB is co-precipitated when antibodies against 1,25D3-MARRS or ERp57 are used. Confocal microscopy and subcellular fractionation studies demonstrate that both 1,25D3-MARRS and NFκB begin translocating to the nucleus within minutes of co-stimulation with 1,25D3 and phorbol ester. The predominant nuclear localization of both proteins precedes the expression of the monocyte/macrophage phenotype and suggests that this event may be critical to the differentiation pathway. This suggests a role for 1,25D3-MARRS in the nucleus as a regulator of gene expression. Here it may also regulate the activity of NFκB and other factors with which it may be interacting.