... via the protein kinase A (PKA)-mediatedphosphorylation of CREB at Ser133 [19]. Ser133 phos-phorylation of CREB, in turn, promotes recruitment of the coactivator paralogs CREB-binding protein and p300 ... different doses of BetA as indicated for 48 h, and then incubated with [3H]thymidine for 2 h tomeasure the inhibitory effect of BetA on cell differentiation by the [3H]thymidine incorporation ... control, whereas the pCREBlevel decreased by 42%. On the other hand, over-expression of CREB in the presence of BetAincreased the CREB level 1.7-fold, but did notincrease the pCREB level,...