Regulation of the cellular retinoid-binding proteins and their messenger ribonucleic acids during P19 embryonal carcinoma cell differentiation induced by retinoic acid.

P19 embryonal carcinoma (EC) cells can be induced to differentiate in vitro into a variety of cell types by treatment with different concentrations of retinoic acid (RA). A study was conducted to explore the regulation of expression of the genes for cellular retinoic acid-binding protein (CRABP) and cellular retinol-binding protein (CRBP) in P19 cells induced to differentiate by RA. For each retinoid-binding protein, both the level of specific mRNA and of immunoreactive protein were measured, respectively, by RNase protection assay and by a specific RIA. Dramatic increases in CRABP and CRBP were seen, at both the mRNA and protein levels, during the RA-induced differentiation. CRBP induction differed from that of CRABP in several major ways. 1) Induction of CRBP occurred at lower concentrations of RA (10(-9) M) than did that of CRABP (10(-8)-10(-7) M). 2) CRBP induction was an early response (within 3 h) to RA treatment, whereas CRABP induction occurred at a later time (12-24 h). 3) Induction of CRABP mRNA by RA was blocked by the protein synthesis inhibitor cycloheximide, whereas induction of CRBP mRNA was not. 4) Several differentiation inducers were tested for their effects on the expression of CRABP and CRBP in P19 cells. CRBP induction occurred with a wider spectrum of inducers than did that of CRABP. 5) In addition, the induction of CRABP and CRBP mRNAs by RA was examined in six different cell lines, including three EC lines. CRBP induction occurred in a wider spectrum of cell lines than did that of CRABP. The induction of CRABP in EC cells seems, in general, to correlate with their differentiation into neuron-like cells. Taken together, our results suggest that CRBP induction may be a direct response to RA and represent a general event in RA-induced cell differentiation, whereas CRABP induction may be an indirect response and represent a later event restricted to only certain differentiation pathways. CRBP may be an early response gene induced by RA.