Cyclic AMP can profoundly influence the growth and differentiation of neuronal cells in culture. In this study, the relationship between this second messenger signal transduction pathway, cell differentiation, and the expression of a
retinoid-responsive,
thymosin beta-10 gene was examined.
Thymosin beta-10 and cognate
mRNA were expressed at high levels in actively proliferating rat B104
neuroblastoma cells cultured in medium containing 10% FCS. These cells were induced to differentiate in the presence of the cAMP analog N6, 2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (Bt2-cAMP) (1 mM) and the
phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (
IBMX) (100 microM). Expression of
thymosin beta-10
mRNA was markedly inhibited (greater than 90% and 70%, respectively) by these compounds. Addition of
sodium butyrate (NaB, 1 mM) indicated that at least part of the inhibitory actions of Bt2-cAMP were due to
esterase-induced release of
butyrate from this compound.
Adenosine (50 microM), a metabolic precursor to endogenous
cyclic AMP, also inhibited accumulation of
thymosin beta-10
mRNA (to less than 70% of control levels). The inhibitory action of Bt2-cAMP upon
thymosin beta-10
mRNA levels was time dependent; levels were inhibited by greater than 50% 24 hours after addition of the cAMP analog and by greater than 90% after 72 hours. Serum
starvation (0.2% FCS for seven days) provoked a marked increase in neurite out-growth; this morphological change was also accompanied by a modest inhibition of
thymosin beta-10
mRNA accumulation. These findings together with previous observations imply that both
cyclic AMP-dependent and
retinoid-responsive mechanisms coordinate
thymosin beta-10 gene expression during neuroembryogenesis.