Abstract
At the initial phase of cell differentiation in mouse neuroblastoma (N18) induced by dibutyrylcyclic AMP (dbcAMP), an additional site of histone H1 was extensively phosphorylated. Forskolin and various phosphodiesterase inhibitors also induced both cell differentiation and H1 phosphorylation at the identical site. The phosphorylation preferentially occurred in a single H1 subtype (H1c) among the five (H1a-e) fractionated by high performance liquid chromatography. The three H1 subtypes of N18 (H1c, H1d, and H1e) were phosphorylated in vitro, and their amino acid sequences of the phosphopeptides were identical to the known sequence of rabbit H1 peptides containing a serine 37 residue. However, the amount of H1a and H1b phosphorylations was negligible. The serine residue was replaced by threonine residue in H1a, and H1b did not have a homologous peptide. The tryptic phosphopeptides of H1 in N18 were identical to that in rat liver H1 induced by glucagon (Langan, T.A. (1969) Proc. Natl. Acad. Sci. USA 64, 1276-1283). The results indicate that 1) the response of H1 subtypes to cAMP-dependent protein kinase in vivo and in vitro is H1 subtype-specific, and 2) the H1c phosphorylation may play an important role in the restrictive area of chromatin in both cell differentiation and hormonal stimulation mediated by cAMP.
Highlights
Forskolin and various phosphodiesterase inhibitors induced both cell differentiation and Hl phosphorylation at the identical site
Dependent protein kinase in vivo and in vitro is Hl subtype-specific, and 2) the Hlc phosphorylation may play an important role in the restrictive area of chromatin in both cell differentiation and hormonal stimulation mediated by cyclic AMP (CAMP)
The results indicated that 1) the CAMP-dependent phosphorylation site in Hl was extensively phosphorylated in uiuo at the initial phase of N18 cell differentiation, 2) the phosphorylation preferentially occurred in a single Hl subtype, and 3) the characteristics of the phosphorylation were quite similar to the rat liver Hl phosphorylation induced by glucagon [16]
Summary
Forskolin and various phosphodiesterase inhibitors induced both cell differentiation and Hl phosphorylation at the identical site. Hl subtypes of N18 (Hlc, Hld, and Hle) were phosphorylated in vitro, and their amino acid sequences of the phosphopeptides were identical to the known sequence of rabbit Hl peptides containing a serine 37 residue. Dependent protein kinase in vivo and in vitro is Hl subtype-specific, and 2) the Hlc phosphorylation may play an important role in the restrictive area of chromatin in both cell differentiation and hormonal stimulation mediated by CAMP. The morphological observation of the cell differentiation indicated that the cell extruded neurites, as axon-like processes, and the nucleus enlarged at the initial phase of cell differentiation [1] Since these inducers all elevate directly or indirectly the intracellular level of CAMP, the CAMP-dependent protein kinase is activated in the cells [5, 6]. It is known that various functional proteins in cells are phosphorylated with the CAMP-dependent protein kinase [7]
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