Blockade of PKC epsilon activation attenuates phorbol ester-induced increase of alpha-secretase-derived secreted form of amyloid precursor protein

The role of PKC epsilon in amyloid precursor protein (APP) processing was investigated using APP-overexpressing B103 cells. As reported previously, a PKC activator, phorbol-12,13-dibutyrate (PDBu), enhanced secretion of APP alpha, and this effect was blocked by a PKC inhibitor, GF109203X in this system. Selective inhibition of PKC epsilon by overexpressing the PKC epsilon V1 region, which binds specifically to the receptor for activated C-kinase (RACK), blocked PDBu-induced enhancement of APP alpha secretion as well as PDBu-induced decrease in beta-secretase-derived APP C-terminal fragment production. On the other hand, the level of PKC epsilon, but not that of PKC alpha or PKC gamma, was substantially lower in the brains of Alzheimer's disease patients compared to age-matched controls. These results add to a growing body of evidence that PKC epsilon plays an important role in modulating APP processing, and suggest that reduced PKC epsilon activity may contribute to the development of Alzheimer's disease.

Overexpression of protein kinase C delta represses expression of proliferin in NIH3T3 cells that regulates cell proliferation

Protein kinase C (PKC) delta is known to inhibit proliferation of many cell types. In this study we found that overexpression of PKCdelta reduced proliferation of NIH3T3 cells. To identify specific genes regulated by PKCdelta in regulation of cell proliferation, we used differential display-polymerase chain reaction in PKCdelta-overexpressing NIH3T3 cells and found that the expression of proliferin, a secreted protein known to stimulate cell proliferation, was significantly repressed. Transient transfection study indicated that the repression of proliferin expression was inversely proportional to the expression levels of PKCdelta. Addition of an anti-proliferin antibody to culture medium to neutralize the secreted proliferin decreased cell proliferation in a dose-dependent manner. Our results, therefore, suggest that overexpression of PKCdelta induces transcriptional repression of proliferin, thereby resulting in inhibition of cell proliferation.

Assignments of the tyrosinase related protein-1 and -2 genes to human chromosome bands 9p23 and 13q32.1 by in situ hybridization

To determine the precise chromosomal localization of tyrosine related protein-1 and -2 (TRP-1 and TRP-2) genes by fluorescence in situ hybridization, we used DNAs isolated from human bacterial artificial chromosome clones. They contain genomic sequences with approximately 120 kb inserts for TRP-1 and TRP-2. The TRP-1 and TRP-2 genes were assigned to human chromosome bands 9p23 and 13q32.1, respectively. These results confirmed the previously mapped location for the TRP-1 gene and more precisely located the TRP-2 gene, which had previously been mapped to chromosome 13q31-q32.

Cdc2 and Cdk2 kinase activated by transforming growth factor-beta1 trigger apoptosis through the phosphorylation of retinoblastoma protein in FaO hepatoma cells

The signaling pathway leading to TGF-beta1-induced apoptosis was investigated using a TGF-beta1-sensitive hepatoma cell line, FaO. Cell cycle analysis demonstrated that the accumulation of apoptotic cells was preceded by a progressive decrease of the cell population in the G(1) phase concomitant with a slight increase of the cell population in the G(2)/M phase in response to TGF-beta1. TGF-beta1 induced a transient increase in the expression of Cdc2, cyclin A, cyclin B, and cyclin D1 at an early phase of apoptosis. During TGF-beta1-induced apoptosis, the transient increase in cyclin-dependent kinase (Cdk) activities coincides with a dramatic increase in the hyperphosphorylated forms of RB. Treatment with roscovitine or olomoucine, inhibitors of Cdc2 and Cdk2, blocked TGF-beta1-induced apoptosis by inhibiting RB phosphorylation. Overexpression of Bcl-2 or adenovirus E1B 19K suppressed TGF-beta1-induced apoptosis by blocking the induction of Cdc2 mRNA and the subsequent activation of Cdc2 kinase, whereas activation of Cdk2 was not affected, suggesting that Cdc2 plays a more critical role in TGF-beta1-induced apoptosis. In conclusion, we present the evidence that Cdc2 and Cdk2 kinase activity transiently induced by TGF-beta1 phosphorylates RB as a physiological target in FaO cells and that RB hyperphosphorylation may trigger abrupt cell cycle progression, leading to irreversible cell death.

Analysis of protein kinase C isoforms involved in the activation of laminin receptor in Raw264.7 macrophages

Adherence of hematopoietic macrophages to a laminin (LM) substratum requires protein kinase C (PKC)-dependent activation of LM receptor. This study was performed to analyze PKC isoform(s) leading to the activation of LM receptor during Raw264.7 macrophage-like cell adhesion to a LM substratum. Raw264.7 cells expressed multiple PKC isoforms, including alpha, beta I, delta, epsilon, zeta, lambda/iota, and mu. Among the PKC isoforms expressed, selective activation of PKC delta and epsilon was sufficient to induce cell adhesion to LM. PKC-dependent cell adherence was blocked by the selective inhibition of PKC delta, suggesting that PKC delta was the responsible PKC isoform leading to activation of LM receptor. PKC delta appeared to activate LM receptor in an intact microfilament-dependent pathway, because disruption of microfilament inhibited cell adhesion to LM without affecting PKC delta activation.

Signalling pathway leading to an activation of mitogen-activated protein kinase by stimulating M3 muscarinic receptor

The signalling pathway leading to an activation of mitogen-activated protein (MAP) kinase subtypes Erk-1 and -2 upon stimulation of muscarinic receptor with carbachol in human neuroblastoma SK-N-BE2(C) cells was investigated. Carbachol activated Erk-1/-2 by stimulating M3 muscarinic receptor, as determined by specific antagonists for individual muscarinic receptors. The activation of Erk-1/-2 by carbachol was blocked by the inhibition or down-regulation of protein kinase C (PKC). Among the multiple PKC isoforms expressed in SK-N-BE2(C) cells, only PKCepsilon was activated by the treatment of carbachol, and selective down-regulation of PKCepsilon was sufficient to block Erk-1/-2 activation. Carbachol treatment induced activation of the serine/threonine protein kinase Raf, and an inhibition of Raf blocked Erk-1/-2 activation. Ectopic expression of inhibitory small GTPase Ras, RasN17, blocked the carbachol-induced Raf activation without affecting the activation of PKCepsilon, while the inhibition of PKC blocked the Raf activation. Thus, these results suggest that carbachol-induced activation of PKCepsilon mediates Erk-1/-2 activation by a sequential activation of Ras, Raf and MAP kinase kinase.

Modulation of MAP kinase signaling and growth characteristics by the overexpression of protein kinase C in NIH3T3 cells

This study was performed to examine effects of the overexpression of protein kinase C (PKC) isoforms (i.e., beta I, beta II, gamma, delta, eta, and zeta) on mitogen-activated protein (MAP) kinase (Erk-1 and -2) signaling and growth characteristics of NIH3T3 cells. Phorbol ester (PMA) activated endogenous and ectopically expressed PKC alpha, beta I, beta II, gamma, delta, epsilon, and eta. Overexpression of the examined PKC isoforms enhanced PMA-induced MAP kinase activation. Potentiation of MAP kinase activation was also observed upon stimulation of cells with platelet-derived growth factor (PDGF) although there was no indication for the activation PKC isoforms by PDGF. Inhibition of PKC blocked PMA- but not PDGF-induced MAP kinase activation. Thus, potentiation of PDGF-induced MAP kinase activation appears to be independent to PKC activity, while PMA-induced MAP kinase activation requires PKC activity. The ability of PKC isoforms to potentiate MAP kinase activation is not related to the growth characteristics of cells because individual PKC isoforms differentially regulated maximum density and proliferation of cells.

Inhibition of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase pathway induces p53-independent transcriptional regulation of p21(WAF1/CIP1) in human prostate carcinoma cells

Progression through the cell cycle is controlled by the induction of cyclins and the activation of cognate cyclin-dependent kinases. The 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor lovastatin induces growth arrest and cell death in certain cancer cell types. We have pursued the mechanism of growth arrest in PC-3-M cells, a p53-null human prostate carcinoma cell line. Lovastatin treatment increased protein and mRNA levels of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1), increased binding of p21 with Cdk2, markedly inhibited cyclin E- and Cdk2-associated phosphorylation of histone H1 or GST-retinoblastoma protein, enhanced binding of the retinoblastoma protein to the transcription factor E2F-1 in vivo, and induced the activation of a p21 promoter reporter construct. By using p21 promoter deletion constructs, the lovastatin-responsive element was mapped to a region between -93 and -64 relative to the transcription start site. Promoter mutation analysis indicated that the lovastatin-responsive site coincided with the previously identified transforming growth factor-beta-responsive element. These data indicate that in human prostate carcinoma cells an inhibitor of the HMG-CoA reductase pathway can circumvent the loss of wild-type p53 function and induce critical downstream regulatory events leading to transcriptional activation of p21.

Sry gene detection in gonads of intersex patients using FISH

A candidate gene for sex determination was localized within a 35 kb region of the Y chromosome immediately adjacent to the pseudoautosomal boundary. Here, we describe a study of Sry detection in the gonads of intersex patients including 5 male pseudohermaphrodite (MPH), 4 XX true hermaphrodite (TH) and each 1 mixed gonadal dysgenesis (MGD) and XX sex reversal, and in the clitoris of 3 female pseudohermaphrodite (FPH) by fluorescent in situ hybridization (FISH). Sry gene was observed in all cases of MPH and each case of MGD and sex reversal in contrast to bare expression in all cases of FPH and most of TH. To our knowledge, the Sry gene itself functions testicular determination in almost all intersex cases except true hermaphrodite, a distinguished type of intersex in a different pathogenesis. In addition, FISH might be useful to detect the translocated Sry gene and localize the signal with ease.

Distribution of phospholipase C isozymes in normal human lung tissue and their immunohistochemical localization

Phospholipase C(PLC) plays a central role in signal transduction and it is important in cellular growth, differentiation and transformation. There are currently ten known mammalian isozymes of PLC identified and cloned. However, there are no report of PLC distribution in human lung tissue or their significances in pulmonary diseases. Presence of various PLC isozymes in normal human lung tissue was studied from surgical specimens. PLC isozymes in tissue extracts of the lung were partially purified by successive chromatographic steps on heparin-sepharose CL-6B conventional and TSKgel heparin-5PW HPLC columns and their activities were assayed. PLC activity peaks identified in the chromatography were immunoblotted with specific antibodies against ten known mammalian PLC isozymes(PLC-beta 1-4, -gamma 1-2, and -delta 1-4). In addition, immunohistochemical staining of the lung tissue was performed to determine subcellular and histological localization of PLC isozymes. The results indicate that normal human lungs contain beta 1, beta 3, gamma 1, and delta 1, isozymes of PLC. The order of amount present in the lung tissue was PLC-delta 1 > gamma 1 > beta 1 >> beta 3, in descending order. On immunohistochemistry, PLC-gamma 1 was most widely distributed and was present in bronchiolar epithelium, in type I and type II pneumocytes as well as in fibroblasts of the interstitial tissue. PLC-delta 1 was present in the cytoplasm of the bronchiolar epithelium whereas PLC-beta 1 was localized to the apical membranous portion of the same epithelium. PLC-beta 3 was seen in the nucleus of the respiratory and alveolar lining epithelium as well as in the nucleus of lung fibroblasts.

Differential translocation of protein kinase C epsilon during HeLa cell adhesion to a gelatin substratum

The spreading of HeLa cells, following attachment to a collagen or gelatin substratum, requires the activation of protein kinase C (PKC). Membrane-bound PKC was previously shown to be activated during cell attachment and in response to the activation of a series of lipid second messengers turned on by the ligation of beta1-integrin collagen receptors. HeLa cells express the alpha, gamma, epsilon, zeta, lambda, and iota isozymes of PKC as determined by Western blotting with specific antibodies. Only PKCepsilon redistributed from the cytosol to the membrane during cell adhesion. Most of the PKCepsilon in cells that were in suspension was in the cytosolic fraction. During cell attachment to a gelatin matrix, all of the PKCepsilon moved out of the cytosol, with most going to the membrane fraction. After the cells became fully spread, PKCepsilon began to reappear in the cytosol. Translocation of PKCepsilon was not observed during the adhesion of cells to culture dishes where cells nonspecifically attach but do not spread. The conventional PKCalpha and -gamma isozymes were translocated from the cytosol to the membrane only when phorbol ester was present at a concentration that increases the rate and extent of cell spreading. Under normal conditions, i.e. in the absence of phorbol ester, PKCepsilon appears to be the PKC isozyme responsible for the regulation of HeLa cell adhesion to the extracellular matrix.

Terminal neuroendocrine differentiation of human prostate carcinoma cells in response to increased intracellular cyclic AMP

Recent clinicopathologic studies have shown that many prostatic adenocarcinomas express focal neuroendocrine differentiation and that neuroendocrine differentiation is most apparent in advanced anaplastic tumors. While studying growth-regulatory signal transduction events in human prostate carcinoma cell lines, we found that in two of four cell lines, the androgen-sensitive line LNCaP and the highly metastatic androgen-independent line PC-3-M, elevation of cAMP through addition of cAMP analogues or phosphodiesterase inhibitors induced a markedly neuronal morphology. Also in LNCaP cells ultrastructural analysis showed that cAMP induced the appearance of neurosecretory cell-like dense-core granules. Phenotypic analysis of untreated LNCaP and PC-3-M cells showed that both cell lines express markers of the neural crest including S-100, chromogranin A, pp60c-src, and neuron-specific enolase as well as the epithelial marker KS1/4 and stage-specific embryonic antigen 4. In PC-3-M cells, cAMP markedly elevated neuron-specific enolase protein and caused an increase in the specific activity of the neuroendocrine marker pp60c-src, and in both cell lines expression of KS1/4 and stage-specific embryonic antigen 4 was down-regulated. In addition to effects on lineage markers, cAMP treatment induced G1 synchronization, growth arrest, and loss of clonogenicity, indicating terminal differentiation. Our data provide direct evidence of plasticity in the lineage commitment of adenocarcinoma of the prostate. We have shown that cell-permeant cAMP analogues can induce terminal differentiation, suggesting that hydrolysis-resistant cyclic nucleotides may present an additional approach to the treatment of advanced prostate cancer.