Association of Protein Phosphatase 1 Delta with Nucleolin in Osteoblastic Cells and Cleavage of Nucleolin in Apoptosis-induced Osteoblastic Cells

Abstract

Protein phosphorylation and dephosphorylation has been recognized as a key mechanism in cell function. Okadaic acid is a potent inhibitor of PP1 and PP 2A and induces apoptosis in human or mouse cells including osteoblasts. Nucleolin is an abundantly expressed nucleolar phosphoprotein and is located mainly in the nucleolus. The staining pattern of nucleolin in cultured osteoblastic cells is similar to that of PP1d. Nucleolin was demonstrated to bind to PP1d in nucleolus in human osteoblastic cells by using immunocytochemical and immunoprecipitation methods. AgNORs and nucleolin, visible as dots in the nuclei of the control osteoblastic cells, disappeared from the nuclei of the osteoblastic cells treated with okadaic acid. A major band, 110 kDa, was detected in the proteins obtained from osteoblastic cells. The level of the 110 kDa protein decreased in the apoptotic osteoblastic cells, whereas an additional band, 80 kDa, appeared and the level of this protein increased in the proteins prepared from okadaic acid-induced apoptotic osteoblastic cells. Our results indicate that PP1d directly binds to nucleolin in the nucleolus of osteoblastic cells and that nucleolin is cleaved during apoptosis in osteoblastic cells.

Expression of PTEN and Akt phosphorylation in lipopolysaccharide‐treated NIH3T3 cells

“…We previously reported that calyculin A or okadaic acid, potent inhibitors of protein phosphatases type 1 and type 2A, induced apoptosis in osteoblastic cells Haneji, 2005) and oral squamous carcinoma cells (Fujita et al, 2004;Okamura et al, 2004). We also obtained evidence PTEN implicating in the initiation and progression of calyculin A-or okadaic acid-induced apoptosis (Okamura et al, 2005).…”

“…PTEN (phosphatase and tensin homolog deleted on chromosome ten), also referred to as mutated in multiple advanced cancers (MMAC), was discovered as a tumor suppressor gene (Li et al, 1997;Steck et al, 1997). We previously reported that calyculin A or okadaic acid, potent inhibitors of protein phosphatases type 1 and type 2A, induced apoptosis in osteoblastic cells Haneji, 2005) and oral squamous carcinoma cells (Fujita et al, 2004;Okamura et al, 2004). We also obtained evidence PTEN implicating in the initiation and progression of calyculin A-or okadaic acid-induced apoptosis (Okamura et al, 2005).…”

PI3K/Akt mediates expression of TNF‐α mRNA and activation of NF‐κB in calyculin A‐treated primary osteoblasts

“…Protein phosphatases can dephosphorylate many different substrates in vitro and in vivo (Honkanen and Golden, 2002). They are involved in various aspects of cell regulation, and play important roles in metabolism (Yoshida et al , 2003; Haneji, 2005; Morimoto et al , 2005; Moorhead et al , 2007). Intracellular phosphatases play a central role in signal transduction pathways related to inflammation (Shanley et al , 2001).…”

Cobalt chloride induces apoptosis and zinc chloride suppresses cobalt-induced apoptosis by Bcl-2 expression in human submandibular gland HSG cells

“…Apoptosis is one of the essential steps in the maintenance of normal cell populations of adult mammals and occurs continually in various cell populations. Apoptosis is a morphologically and biochemically distinct mode of cell death that plays major roles during embryogenesis, carcinogenesis, cancer treatment, or immune and toxic cell killing (1)(2)(3)(4)(5). The cytologically apparent stages of apoptosis are rapid condensation of chromatin and fragmentation of the cells with membraneenclosed apoptotic bodies that are phagocytosed and digested by nearby resident cells (6).…”