Inhibition of aberrant and constitutive phosphorylation of the high-molecular-mass neurofilament subunit by CEP-1347 (KT7515), an inhibitor of the stress-activated protein kinase signaling pathway

Previous studies have implicated stress-activated protein kinases (SAPKs) i n aberrant phosphorylation of the high-molecular-mass neurofilament subunit (NFH). We now present direct evidence for this involvement using CEP-1347, a specific inhibitor of SAPK activation. Inhibition by this drug of stress -induced phosphorylation of NFH and the middle-molecular-mass neurofilament subunit in the perikaryon of dorsal root ganglion (DRG) neurons paralleled the decrease in levels of activated SAPKs and was essentially complete at 1 muM CEP-1347. In addition, a role for SAPKs in the constitutive phosphory lation of NFH was demonstrated. Longterm treatment of unstressed DRG neuron s with CE-1347 lowered the steady-state phosphorylation level of NFH in neu rites, No such effect was seen in neurons treated with PD 098059, which blo cks activation of extracellular signal-regulated kinase 1/2. DRG neurites w ere shown to contain high basal levels of activated SAPKs. These included a 55-kDa SAPK whose activation was completely abolished at 0.05 muM CEP-1347 and a 45-kDa SAPK that was not affected by the drug. These results indicat e that SAPKs are involved in both stress-induced and constitutive phosphory lation of NFH, The differing responses of SAPKs in neurites and cell bodies to CEP-1347 inhibition further suggest the presence of different signaling pathways in the two neuronal compartments.