Katsuyoshi Sugimoto

Cyclin D1-CDK4 complex,a possible critical factor for cell proliferation and prognosis in laryngeal squamous cell carcinomas

Cyclin D1 and its catalytic partner CDK4 are known to play important roles in the G1/S checkpoint of the cell cycle. The complex formed by CDK4 and cyclin D1 has been strongly implicated in the control of cell proliferation and prognoses in human malignancies. We investigated the immunohistochemical expression of cyclin D1, CDK4 and proliferating cell nuclear antigen (PCNA) in 102 patients with laryngeal squamous cell carcinoma (LSCC). Cyclin D1 overexpression was observed in 59 cases (57.8%) of LSCC, and was significantly correlated with tumor site, tumor size, lymph node metastasis and advanced stage. CDK4 overexpression was observed in 48 cases (47.1%), and was significantly correlated with tumor size and advanced stage. Cyclin D1 and CDK4 expression was significantly associated with cell proliferation measured by PCNA (r = 0.812, p < 0.0001 and r = 0.725, p < 0.0001, respectively). The Kaplan–Meier analysis showed that cyclin D1 overexpression was significantly associated with disease‐free survival and overall survival. CDK4 overexpression was significantly associated with overall survival. When cyclin D1 and CDK4 are combined, the patients with co‐overexpression of cyclin D1‐CDK4 revealed the poorest overall survival. Additionally, in early‐stage (I‐II) cases, co‐overexpression of cyclin D1‐CDK4 was also revealed to possess a significant prognostic role. By multivariate analysis, cyclin D1 overexpression, lymph node metastasis and advanced stage were independent prognostic factors for disease‐free survival. Cyclin D1 overexpression, CDK4 overexpression, tumor grade, lymph node metastasis and advanced stage were independent prognostic factors for overall survival. These findings indicate that cyclin D1 and CDK4 overexpression and/or co‐overexpression of these proteins may play a pivotal role in the biological behavior of LSCC and may provide a strong prognostic implication.

Post-synaptic density-95 promotes calcium/calmodulin-dependent protein kinase II-mediated Ser847 phosphorylation of neuronal nitric oxide synthase.

Post-synaptic density-95 (PSD-95) is a neuronal scaffolding protein that associates with N -methyl-D-aspartate (NMDA) receptors and links them to intracellular signalling molecules. In neurons, neuronal nitric oxide synthase (nNOS) binds selectively to the second PDZ domain (PDZ2) of PSD-95, thereby exhibiting physiological activation triggered via NMDA receptors. We have demonstrated previously that Ca(2+)/calmodulin-dependent protein kinase IIalpha (CaM-K IIalpha) directly phosphorylates nNOS at residue Ser(847), and can attenuate the catalytic activity of the enzyme in neuronal cells [Komeima, Hayashi, Naito and Watanabe (2000) J. Biol. Chem. 275, 28139-28143]. In the present study, we examined how CaM-K II participates in the phosphorylation by analysing the functional interaction between nNOS and PSD-95 in cells. The results showed that PSD-95 directly promotes the nNOS phosphorylation at Ser(847) induced by endogenous CaM-K II. In transfected cells, this effect of PSD-95 required its dual palmitoylation and the PDZ2 domain, but did not rely on its guanylate kinase domain. CaM-K Ialpha and CaM-K IV failed to phosphorylate nNOS at Ser(847) in transfected cells. Thus PSD-95 mediates cellular trafficking of nNOS, and may be required for the efficient phosphorylation of nNOS at Ser(847) by CaM-K II in neuronal cells.

Nitric oxide-mediated modulation of calcium/calmodulin-dependent protein kinase II.

The mechanisms of NO inhibition of CaMK [Ca(2+)/CaM (calmodulin)-dependent protein kinase] II activity were studied. In rat pituitary tumour GH3 cells, TRH [thyrotrophin (TSH)-releasing hormone]-stimulated phosphorylation of nNOS [neuronal NOS (NO synthase)] at Ser(847) was sensitive to an inhibitor of CaMKs, KN-93, and was enhanced by inhibition of nNOS with 7NI (7-nitroindazole). Enzyme activity of CaMKII following in situ treatment with 7NI was also increased. The in vitro activity of CaMKII was inhibited by co-incubation either with nNOS and L-arginine or with NO donors SNAP (S-nitroso-N-acetyl-DL-penicillamine) and DEA-NONOate [diethylamine-NONOate (diazeniumdiolate)]. Once inhibited by these treatments, CaMKII was observed to undergo full reactivation on the addition of a reducing reagent, DTT (dithiothreitol). In transfected cells expressing CaMKII and nNOS, treatment with the calcium ionophore A23187 further revealed nNOS phosphorylation at Ser(847), which was enhanced by 7NI and CaMKII S-nitrosylation. Mutated CaMKII (C6A), in which Cys(6) was substituted with an alanine residue, was refractory to 7NI-induced enhancement of nNOS phosphorylation or to CaMKII S-nitrosylation. Furthermore, we could identify Cys(6) as a direct target for S-nitrosylation of CaMKII using MS. In addition, treatment with glutamate caused an increase in CaMKII S-nitrosylation in rat hippocampal slices. This glutamate-induced S-nitrosylation was blocked by 7NI. These results suggest that inactivation of CaMKII mediated by S-nitrosylation at Cys(6) may contribute to NO-induced neurotoxicity in the brain.

Inhibition of neuronal nitric-oxide synthase by phosphorylation at Threonine1296 in NG108-15 neuronal cells.

We demonstrate that neuronal nitric‐oxide synthase (nNOS) is directly inhibited through the phosphorylation of Thr1296 in NG108‐15 neuronal cells. Treatment of NG108‐15 cells expressing nNOS with calyculin A, an inhibitor of protein phosphatase 1 and 2A, revealed a dose‐dependent inhibition of nNOS enzyme activity with concomitant phosphorylation of Thr1296 residue. Cells expressing a phosphorylation‐deficient mutant in which Thr1296 was changed to Ala proved resistant to phosphorylation and suppression of NOS activity. Mimicking phosphorylation mutant of nNOS in which Thr1296 is changed to Asp showed a significant decrease in nNOS enzyme activity, being competitive with NADPH, relative to the wild‐type enzyme. These data suggest that phosphorylation of nNOS at Thr1296 may involve the attenuation of nitric oxide production in neuronal cells through the decrease of NADPH‐binding to the enzyme.

Cyclin-dependent kinase inhibitor p27 is related to cell proliferation and prognosis in laryngeal squamous cell carcinomas

An immunohistochemical study of both p27 and proliferating cell nuclear antigen (PCNA) was performed on 102 cases of laryngeal squamous cell carcinomas (LSCCs), and large variations in p27 expression were found among the tumours. Reduced expression of p27 was revealed in 54 (52.9 per cent) cases and correlated with tumour size, lymph node metastasis, and clinical stage, but did not correlate with age, sex, tumour site, or tumour grade. A significant positive correlation was found between the percentage of loss of p27 expression and the PCNA index (r = 0.844, p < 0.0001). Reduced expression of p27 was significantly correlated with both reducing disease-free and overall survival by univariate analysis. By multivariate analysis, reduced expression of p27, tumour grade, tumour size, lymph node metastasis as well as clinical stage were independent prognostic factors for overall survival of LSCCs. These findings indicate that reduced expression of p27 may be correlated with the malignant biological behaviour of LSCCs.

p90 RSK-1 associates with and inhibits neuronal nitric oxide synthase

Evidence is presented that RSK1 (ribosomal S6 kinase 1), a downstream target of MAPK (mitogen-activated protein kinase), directly phosphorylates nNOS (neuronal nitric oxide synthase) on Ser847 in response to mitogens. The phosphorylation thus increases greatly following EGF (epidermal growth factor) treatment of rat pituitary tumour GH3 cells and is reduced by exposure to the MEK (MAPK/extracellular-signal-regulated kinase kinase) inhibitor PD98059. Furthermore, it is significantly enhanced by expression of wild-type RSK1 and antagonized by kinase-inactive RSK1 or specific reduction of endogenous RSK1. EGF treatment of HEK-293 (human embryonic kidney) cells, expressing RSK1 and nNOS, led to inhibition of NOS enzyme activity, associated with an increase in phosphorylation of nNOS at Ser847, as is also the case in an in vitro assay. In addition, these phenomena were significantly blocked by treatment with the RSK inhibitor Ro31-8220. Cells expressing mutant nNOS (S847A) proved resistant to phosphorylation and decrease of NOS activity. Within minutes of adding EGF to transfected cells, RSK1 associated with nNOS and subsequently dissociated following more prolonged agonist stimulation. EGF-induced formation of the nNOS-RSK1 complex was significantly decreased by PD98059 treatment. Treatment with EGF further revealed phosphorylation of nNOS on Ser847 in rat hippocampal neurons and cerebellar granule cells. This EGF-induced phosphorylation was partially blocked by PD98059 and Ro31-8220. Together, these data provide substantial evidence that RSK1 associates with and phosphorylates nNOS on Ser847 following mitogen stimulation and suggest a novel role for RSK1 in the regulation of nitric oxide function in brain.

Calbrain, a Novel Two EF-hand Calcium-binding Protein That Suppresses Ca2+/Calmodulin-dependent Protein Kinase II Activity in the Brain

A cDNA clone that encodes a novel Ca2+-binding protein was isolated from a human brain cDNA library. The gene for this clone, termed calbrain, encodes a 70-amino acid polypeptide with a predicted molecular mass of 8.06 kDa. The analysis of deduced amino acid sequence revealed that calbrain contains two putative EF-hand motifs that show significantly high homology to those of the calmodulin (CaM) family rather than two EF-hand protein families. By Northern hybridization analysis, an approximate 1.5-kilobase pair transcript of calbrain was detected exclusively in the brain, and in situ hybridization study revealed its abundant expression in the hippocampus, habenular area in the epithalamus, and in the cerebellum. A recombinant calbrain protein showed a Ca2+ binding capacity, suggesting the functional potency as a regulator of Ca2+-mediated cellular processes. Ca2+/calmodulin-dependent kinase II, the most abundant protein kinase in the hippocampus and strongly implicated in the basic neuronal functions, was used to evaluate the physiological roles of calbrain. Studies in vitro revealed that calbrain competitively inhibited CaM binding to Ca2+/calmodulin-dependent kinase II (K i = 129 nm) and reduced its kinase activity and autophosphorylation.

Expression and subcellular localization of multifunctional calmodulin-dependent protein kinases-I, -II and -IV are altered in rat hippocampal CA1 neurons after induction of long-term potentiation.

Long-term potentiation (LTP) is considered to be associated with an increase in expression as well as activity of Ca(2+)/calmodulin-dependent protein kinases (CaMKs). LTP-induced and control hippocampal slices were studied by immunohistochemical and electronmicroscopic analyses using anti-CaMK-I, -II and -IV antibodies. All three kinases were demonstrated to increase their expression in CA1 neurons. CaMK-I was shown to mainly localize in the cytoplasm of the control and LTP-induced neurons, and a significant increase of immunoreactivity was observed in the latter neurons. A part of CaMK-I was found to translocate to the nuclei of LTP-induced hippocampal CA1 neurons. Direct evidence of the translocation of CaMK-II from cytoplasm to nuclei in LTP was demonstrated by immuno-electronmicroscopy. A significant increase in expression of CaMK-IV in the nuclei was also observed. Our data suggest that all the three CaMKs were actively involved in nuclear Ca(2+)-signaling in LTP.

Nitric oxide prevents phosphorylation of neuronal nitric oxide synthase at serine1412 by inhibiting the Akt/PKB and CaM-K II signaling pathways.

Neuronal nitric oxide synthase (nNOS) is an important regulatory enzyme in the central nervous system catalyzing the production of NO, which regulates multiple biological processes in the central nervous system. However, the mechanisms by which nNOS activity is regulated are not completely understood. In the present study, the effects of protein kinases on the phosphorylation of nNOS in GH3 rat pituitary tumor cells were evaluated. We show that phosphorylation of nNOS at Ser1412 could be induced by the phosphatidylinositol 3-kinase/protein kinase B (Akt/PKB) agonist insulin, the calcium/calmodulin-dependent protein kinase II (CaM-K II) agonist A23187 or the cAMP-dependent protein kinase A (PKA) agonist IBMX, respectively. The phosphorylation levels of nNOS at Ser1412, induced by activation of Akt/PKB or CaM-K II, but not by PKA signaling, were reduced by pre-treatment with the NO donor diethylamine-NONOate. This inhibitory effect could be reversed by addition of a reducing reagent, dithiothreitol. Furthermore, the levels of phosphorylation of nNOS at Ser1412, induced by Akt/PKB or CaM-K II but not by PKA signaling, were enhanced by inhibition of nNOS activity with 7-nitroindazole. These findings suggest that the activation of nNOS can be catalyzed by at least three protein kinases, Akt/PKB, CaM-K II or PKA. NO generated from nNOS feedback prevents the activation of nNOS by inhibiting either Akt/PKB or CaM-K II but not PKA signaling.

The expression of Ca2+/calmodulin-dependent protein kinase I in rat retina is regulated by light stimulation.

Ca2+/calmodulin-dependent protein kinase I (CaM-kinase I) in rat retina was analyzed by immunohistochemical analysis, Western blot analysis and kinase activity assay. Western blot analysis revealed two immunoreactive bands similar to those detected in the brain. Developmental studies revealed that CaM-kinase I expression increased in accordance with postnatal development. Expression of CaM-kinase I in the retinas of rats raised in the complete darkness markedly decreased. CaM-kinase I activity assay supported these findings. Synapsin I was shown to be a possible intrinsic substrate of CaM-kinase I in rat retina. These results elucidated that CaM-kinase I is expressed in the retina and may play an important role in the retinal functions and that the expression of CaM-kinase I is regulated by light stimulation.