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 (GCNO), the major NO target, is involved in important regulatory functions in the cardiovascular, gastrointestinal and central nervous systems. GCNO exists as heterodimers of α(1/2) and β1 subunits. Deletion of the obligate β1 dimerizing partner abrogates NO/cGMP signaling and shortens the life span of KO mice. Localization studies in the CNS have shown that β1 is more widespread than α subunits and in some areas is the only GCNO subunit expressed, suggesting that β1 may have GCNO-independent functions. GCNO is predominantly cytosolic, but association to membranes and other intracellular structures has been described. Here, we show localization of β1 in cytoplasm and nucleus of cells expressing α subunits and GCNO activity (astrocytes, C6 cells), as well as in cells devoid of α subunits and GCNO activity (microglia). In both cell types β1 associates peripherally to chromosomes in all phases of mitosis. Immunodepletion of β1 in C6 cells enhances chromatin condensation in an in vitro assay. Moreover, silencing β1 by siRNA induces cell cycle re-entry as determined by flow cytometry, and increases proliferation rate in a MTT-assay, whereas infection with β1-containing adenovirus has the opposite effect. These actions are independent of cGMP formation. We postulate that β1 is a multifunctional protein that regulates chromatin condensation and cell cycle progression, in addition to being an obligate monomer in functional GCNO heterodimers.