PPP1R1B and neuroblastoma: We also uncovered a decrease in the expression of many other PKA substrates in HPRT-deficient human and mouse neuroblastoma cell lines, including tyrosine hydroxylase (TH) (Ser40) and DARPP-32 (Thr34) (data not shown) that are also important effectors of neuronal function [28], [38], [39].