NO-sensitive guanylyl cyclase β1 subunit is peripherally associated to chromosomes during mitosis. Novel role in chromatin condensation and cell cycle progression

NO-sensitive guanylyl cyclase (GC(NO)), the major NO target, is involved in important regulatory functions in the cardiovascular, gastrointestinal and central nervous systems. GC(NO) exists as heterodimers of alpha(1/2) and beta 1 subunits. Deletion of the obligate RI dimerizing partner abrogates NO/cGMP signaling and shortens the life span of KO mice. Localization studies in the CNS have shown that beta 1 is more widespread than alpha subunits and in some areas is the only GC(NO) subunit expressed, suggesting that beta 1 may have GC(NO)-independent functions. GC(NO) is predominantly cytosolic, but association to membranes and other intracellular structures has been described. Here, we show localization of beta 1 in cytoplasm and nucleus of cells expressing a subunits and GC(NO) activity (astrocytes, C6 cells). as well as in cells devoid of a subunits and GC(NO) activity (microglia). In both cell types beta 1 associates peripherally to chromosomes in all phases of mitosis. Immunodepletion of beta 1 in C6 cells enhances chromatin condensation in an in vitro assay. Moreover, silencing beta 1 by siRNA induces cell cycle re-entry as determined by flow cytometry, and increases proliferation rate in a MTT-assay, whereas infection with beta 1-containing adenovirus has the opposite effect. These actions are independent of cGMP formation. We postulate that beta 1 is a multifunctional protein that regulates chromatin condensation and cell cycle progression, in addition to being an obligate monomer in functional GC(NO) heterodimers. (C) 2009 Elsevier Ltd. All rights reserved.