We tested whether double cortin-like kinase-short (DCLK-short), a microtubule-associated Ser/Thr kinase predominantly expressed in the brain, is downstream of the ERK signaling pathway and is involved in proopiomelanocortin gene (POMC) expression in endocrine pituitary melanotrope cells of Xenopus laevis. Melanotropes form a well-established model to study physiological aspects of neuroendocrine plasticity. The amphibian X. laevis adapts its skin color to the background light intensity by the release of α-MSH from the melanotrope cell. In frogs on a white background, melanotropes are inactive but they are activated during adaptation to a black background. Our results show that melanotrope activation is associated with an increase in DCLK-short mRNA and with phosphorylation of DCLK-short at serine at position 30 (Ser-30). Upon cell activation phosphorylated Ser-30-DCLK-short was translocated from the cytoplasm into the nucleus, and the ERK blocker U0126 inhibited this process. The mutation of Ser-30 to alanine also inhibited the translocation and reduced POMC expression, whereas overexpression stimulated POMC expression. This is the first demonstration of DCLK-short in a native endocrine cell. We conclude that DCLK-short is physiologically regulated at both the level of its gene expression and protein phosphorylation and that the kinase is effectively regulating POMC gene expression upon its ERK-mediated phosphorylation.
The extracellular signal-regulated kinase (ERK) pathway is important in the regulation of neuronal plasticity, although a role for the kinase in regulating plasticity of neuroendocrine systems has not been examined. The melanotroph cells in the pars intermedia of pituitary gland of the amphibian Xenopus laevis are highly plastic, undergoing very strong growth to support the high biosynthetic and secretory activity involving α-melanophore-stimulating hormone (α-MSH), a peptide that causes pigment dispersion in dermal melanophores during the adaptation of the animal to a dark background. In the present study, we tested our hypothesis that ERK-signalling is involved in the regulation of melanotroph cell function during black-background adaptation, namely in the production of pro-opiomelanocortin (POMC), the precursor of α-MSH. Using western blot analyses, we found elevated levels of the activated (phosphorylated) form of ERK in melanotrophs of black- versus white-adapted animals. Treatment of melanotrophs in vitro with the mitogen-activated protein kinase kinase inhibitor U0126 markedly reduced ERK phosphorylation and lowered the transcription as well as the translation of POMC. This same treatment also reduced the expression of BDNF transcript IV and of the immediate early genes c-Fos and Nur77. We conclude that ERK-mediated signalling is important for the maintenance of the melanotroph cells in an active state.
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.