Intracellular signal transduction cascades, particularly those linked to protein kinases A (PKA) and C (PKC), have been implicated in mood disorders. This study examined the activity of PKA and PKC, as well as levels of PKA regulatory (R) and catalytic (C) subunit proteins, in fibroblasts cultured from skin biopsies from patients with major depression, melancholic subtype, in contrast to non-melancholic depressives and controls (n = 12 each group). PKA activity was determined as a function of the transfer of 32P to a target polypeptide, Kemptide. R and C subunit expression was assayed in the melancholic depressed and normal control groups by Western blots. In a separate experiment, the degree of phosphorylation of the endogenous substrate cAMP response element-binding protein (CREB) was estimated in samples from melancholic and non-melancholic patients and normal controls (n = 8 each) after incubation with isoproterenol or phorbol ester, which activate PKA and PKC respectively. Melancholics had significantly reduced phosphorylation of Kemptide in contrast to non-melancholics and controls. This was associated with lower levels of PKA RII alpha, C alpha, and C beta subunit isoform proteins, but not RI alpha, RI beta, or RII beta. Furthermore, activation of both PKA and PKC was associated with reduced CREB-P in melancholics relative to normal controls. Finally, PKA activity was found to correlate positively with Hamilton depression scores after 16 weeks of treatment with serotonin reuptake inhibitor antidepressants. These data further implicate signal transduction abnormalities in melancholic major depression, particularly PKA and PKC. This suggests an abnormality of factors controlling the expression or degradation of these enzymes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.