PKN associates and phosphorylates the head-rod domain of neurofilament protein

PKN is a fatty acid-activated serine/threonine kinase that has a catalytic domain highly homologous to that of protein kinase C in the carboxyl terminus and a unique regulatory region in the amino terminus. Recently, we reported that the small GTP-binding protein Rho binds to the amino-terminal region of PKN and activates PKN in a GTP-dependent manner, and we suggested that PKN is located on the downstream of Rho in the signal transduction pathway (Amano, M., Mukai, H., Ono, Y., Chihara, K., Matsui, T., Hamajima, Y., Okawa, K., Iwamatsu, A., and Kaibuchi, K. (1996) Science 271, 648-650; Watanabe, G., Saito, Y., Madaule, P., Ishizaki, T., Fujisawa, K., Morii, N., Mukai, H., Ono, Y. Kakizuka, A., and Narumiya, S. (1996) Science 271, 645-648). To identify other components of the PKN pathway such as substrates and regulatory proteins of PKN, the yeast two-hybrid strategy was employed. By this screening, a clone encoding the neurofilament L protein, a subunit of neuron-specific intermediate filament, was isolated. The amino-terminal regulatory region of PKN was shown to associate with the head-rod domains of other subunits of neurofilament (neurofilament proteins M and H) as well as neurofilament L protein in yeast cells. The direct binding between PKN and each subunit of neurofilament was confirmed by using the in vitro translated amino-terminal region of PKN and glutathione S-transferase fusion protein containing the head-rod domain of each subunit of neurofilament. PKN purified from rat testis phosphorylated each subunit of the native neurofilament purified from bovine spinal cord and the bacterially synthesized head-rod domain of each subunit of neurofilament. Polymerization of neurofilament L protein in vitro was inhibited by phosphorylation of neurofilament L protein by PKN. The identification and characterization of the novel interaction with PKN may contribute toward the elucidation of mechanisms regulating the function of neurofilament.

Cyclin-dependent kinase-2 (Cdk2) forms an inactive complex with cyclin D1 since Cdk2 associated with cyclin D1 is not phosphorylated by Cdk7-cyclin-H

Cyclin-dependent kinases (Cdks) form complexes with cyclins, and as a consequence they generally express kinase activities. One of these Cdks, Cdk2, is known to bind with cyclins A and E, and plays an important role in the progression of the cell cycle via phosphorylation of target proteins such as the product of the retinoblastoma tumor-suppressor gene (pRB). It has been suggested that Cdk2 bound with cyclin D1 and Cdk2-cyclin-D1 complex show neither H1 histone nor pRB kinase activity. However, it is not clear whether Cdk2-cyclin-D1 has unknown targets and why Cdk2 is not activated by binding with cyclin D1. We investigated these questions using Cdk, cyclin and Cdk-cyclin complexes produced in a baculovirus expression system. Cdk2 formed a complex with cyclin D1 in this system. After extensive purification, Cdk2 was still bound to cyclin D1. The Cdk2-cyclin-D1 complex did not phosphorylate any tested substrates, such as H1 histone, pRB, SV40 large T antigen, p53, E2F-1 or a preparation of nuclear proteins from HeLa cells; in contrast, Cdk2-cyclin-E and Cdk2-cyclin-A phosphorylated these proteins. Moreover, the Cdk2-cyclin-D1 complex was not activated by incubation with Cdk4 or cyclin E. Thus, Cdk2 and cyclin D1 formed a stable complex that was not activated. In order to determine why Cdk2-cyclin-D1 lacks kinase activity, we investigated the phosphorylation of Cdk2. Under-shifted Cdk2, the active form of Cdk2, was not detected in the Cdk2-cyclin-D1 complex in the baculovirus system. In human WI-38 cells, cyclin D1 began to form a complex with Cdk2 as well as with Cdk4 from the mid-G1 phase of the cell cycle. The Cdk2 bound to cyclin D1 in human cells was also the inactive form that was slowly migrated. Moreover, we found that Cdk2 bound to cyclin D1 was not phosphorylated by Cdk7-cyclin-H, while Cdk2 bound to cyclin E, as well as free Cdk2, was was phosphorylated by Cdk7-cyclin-H. Additionally, Cdk2 phosphorylated by Cdk7-cyclin-H did not bind to cyclin D1. These results strongly suggest that Cdk2 forms a stable complex with cyclin D1 but is not activated because the Cdk2 molecule in the complex is not phosphorylated by Cdk7-cyclin-H and the phosphorylated Cdk2, an active form, does not bind to cyclin D1.

[Increased CA19-9 level in serum and bronchoalveolar lavage fluid from a patient with pulmonary tuberculosis]

A 66-year-old woman was admitted to the hospital because of general malaise and loss of appetite. Laboratory examination revealed an abnormally high level of CA19-9 in serum and a chest roentgenogram revealed soft reticular shadows in the right mid-lung field. An extensive examination revealed no malignant disease. Bronchoalveolar lavage fluid obtained from the right B5 contained an abnormally high level of CA19-9. Immunochemical staining for CA19-9 was positive in the epithelial cells of respiratory bronchioles. The level of CA19-9 decreased during anti-tuberculosis therapy. This case suggests that the CA19-9 level can reflect the activity of pulmonary tuberculosis.

The role of the unique motifs in the amino-terminal region of PKN on its enzymatic activity

The yeast two-hybrid system and in vitro binding assay were carried out to characterize the interaction between the amino-terminal and carboxyl-terminal region of PKN. It was revealed that the amino-terminal region containing the regulatory domain associated with the carboxyl-terminal catalytic region. A synthetic peptide, corresponding to the amino acid residues of PKN from 39 to 53, with substitution of isoleucine46 with serine was shown to become a potent substrate for PKN, and its wild type synthetic peptide inhibited the phosphorylation by PKN. These results suggest that the amino-terminal region of PKN contains the pseudosubstrate sequence and acts as an autoinhibitory region.

[Diffuse alveolar septal amyloidosis associated with multiple myeloma (IgA lambda type)]

A 75-year-old man with multiple myeloma presented with fever and respiratory symptoms. A chest roentgenogram showed interstitial shadows and transbronchial lung biopsy revealed diffuse infiltration of amyloid in the alveolar walls. Analysis of bronchoalveolar lavage fluid showed the presence of an IgA-lambda paraprotein, and the IgA/albumin ratio was similar to that in serum. However, plasma cells could not be detected in the cells obtained by lavage. We know of no previous case in Japan in which bronchoalveolar lavage fluid was examined in a case of diffuse alveolar septal amyloidosis.

Histomorphometric study of ribs with looser zones in Itai-itai disease

Twelve Looser zones and 17 healing bands of the ribs obtained from autopsy cases of Itai-itai disease were analyzed by bone histomorphometry. Furthermore, proper cancellous tissue of the ribs from 24 autopsy cases of Itai-itai disease with Looser zones or with the healing bands, 27 autopsy cases of Itai-itai disease without such lesions, and 29 control cases were studied by the same method to pursue the histogenesis of Looser zones. In translucent zones of Looser zones, 94% of the cancellous bone was occupied by thick woven bone in which 72% was woven osteoid and 22% was woven mineralized bone. In adjacent scleroses, 71% of the cancellous bone was occupied by woven bone in which 37% was woven mineralized bone, and 34% was woven osteoid; 53% of the cancellous bone consisted of mineralized bone. As compared with those in translucent zones, woven osteoid was decreased, and mineralized bone was increased significantly in the cancellous bone of adjacent scleroses. A significant increase of lamellar mineralized bone and a decrease of woven bone in healing bands were observed as compared with those in Looser zones. These findings suggest that the healing starts from the edge of the Looser zone, and slowly proceeds toward the center. In the cancellous bone of the ribs, the volume, thickness, and surface of osteoid and woven bone were significantly increased in patients with Itai-itai disease, with Looser zones as compared with those without Looser zones. It was concluded that Looser zones seem to occur in severe osteomalacic bones that contain abundant woven bone in the patients of Itai-itai disease.

[Acute lupus pneumonitis presenting as multiple nodular shadows]

A 24-year-old woman consulted a physician because of fever, dry cough, and arthralgia of one month duration. She was transferred to our hospital for more detailed examination of pancytopenia and diffuse infiltrative shadows on a chest X-ray film. On admission she was depressed, and had oral ulcers. Pleural and pericardial effusions were observed. Laboratory studies were positive for anti-nuclear antibody, anti-DNA antibody, and lupus erethymatosus. Casts were found in the urine, and systemic lypus erythematosus was diagnosed. Chest radiography and CT scan showed nodular shadows in the right S8 (2nodules with 1 cm diameter)(1 cm x 2), right S10 (0.5 cm diameter), and left S8 (0.5 cm diameter) regions, as well as diffuse infiltrative shadows in both lower lung fields. A specimen obtained by transbronchial lung biopsy revealed acute interstitial pneumonia with arteritis. After treatment with prednisolone (60 mg/day), the nodular and infiltrative shadows rapidly disappeared. Cases of lupus pneumonitis presenting as nodular shadows are very rare and are valuable in diagnostic imaging.

Optimal conditions for collection of blood samples for assay of alpha 2-macroglobulin-trypsin complex-like substance (MTLS)

We have developed an enzyme-linked immunosorbent assay (ELISA) for the specific quantification of alpha 2-macroglobulin-trypsin complex-like substance (MTLS). To exclude artifacts in measured values of MTLS, the conditions for collection of blood samples are critical. In the present study, we have determined the optimal conditions for blood collection and investigated the role of MTLS as a clinical tool for diagnosis in pancreatitis. Results obtained are as follows: (1) MTLS levels of all sera were more than 10-fold higher than the corresponding plasma; (2) MTLS levels of heparinized plasma were the lowest among plasma with three anticoagulants (sodium citrate, sodium EDTA and heparin); (3) some kinds of blood collection tubes containing heparin were not suitable for the sampling; (4) MTLS values of plasma obtained by blood collection tubes containing Trasylol and sodium EDTA were demonstrated more stable and lower than those obtained by heparin tubes; and (5) under these conditions, we can exclude elevation of MTLS values caused by inappropriate blood sampling and find the time course of the elevation reflecting clinical course of a patient with acute pancreatitis and a patient after endoscopic retrograde cholangiopancreatography (ERCP). The optimal conditions for collection of blood samples were as follows. Blood sampling should be performed by blood collection tubes containing Trasylol (50 microliters/ml blood) and sodium EDTA (1.5 mg/ml blood). The samples were immediately stored at 4 degrees C and centrifuged at 3,000 rpm for 15 min. The plasma were stored in plastic tubes at 4 degrees C until assayed.

Plasma alpha 2-macroglobulin-trypsin complexlike substance (MTLS) in pancreatic disease

alpha 2-macroglobulin-trypsin complexlike substance (MTLS) was determined in plasma of pancreatic and nonpancreatic diseases using a two-step enzyme immunoassay to study the diagnostic and pathophysiological significance of MTLS. Plasma levels of MTLS in acute pancreatitis (mean +/- SD = 265.6 +/- 346.2 ng/ ml, n = 9), calcified chronic pancreatitis (128.6 +/- 257.4, n = 13), and noncalcified chronic pancreatitis (13.5 +/- 12.5, n = 10) were significantly higher than that in controls (3.6 +/- 1.8, n = 81). In other diseases such as gastric cancer, hepatoma, diabetes mellitus, and gallstones, MTLS values were not different from those of control. Plasma MTLS values showed low correlation with serum trypsin, elastase 1, pancreatic amylase, lipase, and pancreatic secretory trypsin inhibitor (PSTI). The elevation of plasma MTLS values in acute pancreatitis suggests that plasma MTLS levels reflect that protease is inappropriately activated in pancreatic acinar cell and released into the circulation and that the determination of MTLS can be useful for diagnosis and pathophysiology of acute pancreatitis and chronic pancreatitis.

A case of transverse colon cancer secondarily involving the liver, duodenum, and pancreas

A 68-year-old woman presented with transverse colon cancer invading the liver, duodenum, and pancreas. The patient underwent a curative resection including a right hemicolectomy, partial hepatectomy, and pancreaticoduodenectomy (PD). The pathological examination showed adenocarcinoma of the colon with a direct extension into the duodenum, liver, and pancreas. Several lymph nodes were also involved. The patient is still alive and disease-free 2 years and 6 months after the operation. This case illustrates that even in patients with locally advanced colon cancer, a favorable prognosis can be obtained by aggressive surgery incorporating the resection of the adjacent involved organs.

Identification of Schizosaccharomyces pombe gene psk1+, encoding a novel putative serine/threonine protein kinase, whose mutation conferred resistance to phenylarsine oxide

We have identified a novel putative protein kinase-encoding gene from Schizosaccharomyces pombe (Sp), designated psk1+, by using a highly conserved amino acid (aa) sequence motif to design amplification of DNA fragments using PCR. The putative translation product of psk1+ contains 436 aa, with a molecular mass of 49,317 Da. A single psk1+ was identified by genomic Southern blot analysis, and the genomic mapping indicated that psk1+ was localized in Sp chromosome III. Growth of wild-type Sp cells was inhibited by 0.5 microM phenylarsine oxide, a protein tyrosine phosphatase inhibitor, but psk1- cells were relatively resistant to this drug.

Differences in substrate specificity between Cdk2-cyclin A and Cdk2-cyclin E in vitro

Cyclin-dependent kinase 2 (Cdk2), when bound to either cyclin A or cyclin E, recognizes the Ser/Thr-Pro-X-basic amino acid (motif A) as a phosphorylation site. In this study, we designed several peptides based on motif A and examined the substrate specificity of Cdk2-cyclin A and Cdk2-cyclin E using these peptides. Peptides containing a proline residue in the sequence Pro-X-Thr-Pro-X-basic amino acid (motif B) had higher affinity for both Cdk2 complexes than peptides containing motif A. Furthermore, differences in substrate affinity between the two Cdk2 complexes were caused by a proline residue adjacent to or three positions before the threonine residue. Similarly, the presence of different basic amino acids in motif B also had different effects on affinity for each complex. We demonstrate the possibility that the substrate specificity of Cdk2 bound to cyclin might be regulated by the species of cyclin.

Cloning, expression, and chromosomal localization of a novel cadherin-related protein, protocadherin-3

To study the diversity of the protocadherin family, the cDNA clones for a novel protocadherin were isolated by screening rat brain cDNA libraries with a cDNA fragment obtained by PCR, and some of the properties were then characterized. The overall structure of the protein defined by the clone is similar to that of previously identified protocadherins; however, the cytoplasmic domain is distinct from those of previously cloned protocadherins or any other protein sequences in the data bank. We named this protocad herin-3 (Pcdh3) since this is the third protocadherin of which the entire coding sequence has been determined. Most of the deduced amino acid sequences of other cDNA clones obtained by the screening show high homology with but are distinct from that of Pcdh3, indicating that most of these sequences correspond to homologous but different protocadherins. These results demonstrate that Pcdh3 and the protocadherins defined by these clones constitute a protocadherin subfamily. Chromosome mapping indicates that mouse Pcdh3 is located in a specific region of mouse chromosome 18, close to the location of previously cloned protocadherins, suggesting that various protocadherins form a cluster in this region. In situ hybridization results showed that Pcdh3 and its related proteins were expressed at various areas in brain. The expressed Pcdh3 protein from the cDNA in mouse L cells was about 100 kDa in molecular weight and was localized at cell-cell contact sites. In contrast to the classical cadherins, however, the expressed Pcdh3 was sensitive to trypsin even in the presence of Ca2+, and the transfectants did not show strong Ca(2+)-dependent cell aggregation activity. These results indicate the structural and possibly functional diversity of the protocadherin family and suggest a distinctive biological role for Pcdh3.

Proliferative activity and p53 over-expression of ovarian epithelial tumors

Proliferative activity (PA) and p53 over-expression were assessed in 68 cases of primary ovarian epithelial tumors of variable grades of malignancy by immunohistochemical methods using antibodies to PCNA (proliferative cell nuclear antigen) and p53 molecule. First, we compared the values in benign tumors, tumors of borderline malignancy and malignant tumors. Malignant tumors possessed higher PA value (26.8 +/- 14.7%) than benign tumors (1.6 +/- 1.4%), and tumors of borderline malignancy exhibited an intermediate value (11.4 +/- 5.1%). Intranuclear accumulations of p53 product were more frequently observed in malignant tumors (16/32, 50%) than in tumors of borderline malignancy (3/9, 33%). None of the benign tumors exhibited p53 over-expression. In malignant tumors, PA correlated well with the histologic grade of tumors, although the histologic type and stage of the diseases did not correlate significantly with PA. Then, we focussed on the cases of malignant ovarian cancer composed of heterogeneous lesions showing a different grade of malignancy; invasive lesion (IL), non-invasive lesion (NIL), and benign appearing lesion (BAL). PA of NIL was almost identical with that of IL (19.6 +/- 13.5% vs. 23.3 +/- 12.6%), while BAL showed significantly lower PA (2.1 +/- 3.0%, p < 0.001) than the above two lesions and was similar to that of benign tumors. Furthermore, p53 over-expression was never observed in BAL, even in cases in which IL and/or NIL showed p53 over-expression. Thus, the results indicated that histologically benign-appearing lesions of malignant ovarian epithelial tumors possessed a biologic character similar to benign tumors. Collectively, all these findings would support the concept that a part of malignant ovarian epithelial tumors would be derived from benign tumors through progressive transformation.

Purification and characterization of a fatty acid-activated protein kinase (PKN) from rat testis

PKN, a novel protein kinase with a catalytic domain homologous to that of the protein kinase C (PKC) family and unique N-terminal leucine-zipper-like sequences, was identified by molecular cloning from a human hippocampus cDNA library [Mukai and Ono (1994) Biochem. Biophys. Res. Commun. 199, 897-904]. Recently we partially purified recombinant PKN from COS7 cells transfected with the cDNA construct encoding human PKN, and demonstrated that the recombinant PKN was activated by unsaturated fatty acids and limited proteolysis [Mukai, Kitagawa, Shibata et al. (1994) Biochem. Biophys. Res. Commun. 204, 348-356]. The present work has focused on the further purification and characterization of PKN from native rat tissue. Immunochemical measurement revealed that PKN was found in every tissue, and was especially abundant in testis, spleen and brain; subcellular fractionation of rat brain showed that half of the PKN was localized in the soluble cytosolic fraction. PKN was purified approx. 8000-fold to apparent homogeneity from the cytosolic fraction of rat testis by DEAE-cellulose chromatography, ammonium sulphate fractionation and chromatography on butyl-Sepharose, heparin-Sepharose, Mono Q and protamine-CH-Sepharose. The enzyme migrates as a band of apparent molecular mass 120 kDa. Using serine-containing peptides based on the pseudosubstrate sequence of PKC-delta as phosphate acceptors, the kinase activity was stimulated several-fold by 40 microM unsaturated fatty acids or by detergents such as 0.04% sodium deoxycholate and 0.004% SDS. In the absence of modifiers, protamine sulphate, myelin basic protein and synthetic peptides based on the pseudosubstrate site of PKCs or ribosomal S6 protein were good substrates for phosphorylation by the kinase. In the presence of 40 microM arachidonic acid the kinase activity of PKN for these phosphate acceptors was increased 2-18-fold. The autophosphorylation activity of purified PKN was partially inhibited by pretreatment with alkaline phosphatase. These properties appear to distinguish PKN from many protein kinases isolated previously.

Cell-free transmission of Fv-4 resistance gene product controlling Friend leukemia virus-induced leukemogenesis: a unique mechanism for interference with viral infection

Fv-4 is a mouse gene that dominantly confers resistance to infection by ecotropic murine leukemia virus (MuLV). We previously demonstrated that mixed radiation bone marrow chimeras containing Fv-4r-bearing BALB/c-Fv-4Wr (C4W) bone marrow and Fv-4r-bearing C3H/He (C3H) bone marrow grafted into C3H recipient mice (C4W+C3H-->C3H) were resistant to Friend leukemia virus (FLV)-induced leukemogenesis, even when they contained as high as 70% C3H-derived cells. This indicates that FLV-sensitive C3H-derived cells are rendered refractory to infection and/or transformation with FLV when they coexist in mice with Fv-4r-bearing cells. To investigate the mechanism of Fv-4 resistance to FLV-induced leukemogenesis, we first examined the expression of Fv-4r env antigen in the peripheral blood mononuclear cells (PBMC) of these chimeras. The Fv-4r env antigen was present not only on C4W-derived cells, but also on Fv-4r-bearing C3H-derived cells in C4W+C3H-->C3H mixed bone marrow chimeras. The Fv-4r env antigen that binds to the cells surface of C3H cells was found in sera from normal C4W mice, C4W-->C3H chimeras, and C4W+C3H-->C3H mixed chimeras. The serum Fv-4r env antigen binds to ecotropic MuLV receptors, shown by specific binding to transfectant mink cells expressing ecotropic MuLV receptor, but not to parental mink cells. To determine whether the binding of Fv-4r env antigen to the putative MuLV receptors would block FLV infection, C3H thymocytes or spleen cells that had been preincubated with C4W serum were mixed with FLV and the subsequent production of MuLV specific antigens was examined. C3H thymocytes or spleen cells treated with C4W serum became refractory to binding by FLV. These results provide evidence that the Fv-4r env antigen is released from C4W-derived cells in vivo and binds to cells expressing surface receptors for ecotropic MuLV, thereby protecting them from infection with FLV. The implication of these findings for gene therapy of retrovirus-induced disease such as acquired immune deficiency syndrome (AIDS) is discussed.

Chemical synthesis of phosphopeptides using the arylthio group for protection of phosphate: application to identification of cdc2 kinase phosphorylation sites

Synthesis of two O-phosphorylated dipeptides, N-Boc-O[S,S-bis(p-methoxyphenyl)phosphorodithioyl] -serylproline and N-Boc-O-[S,S-bis(p-methoxyphenyl) phosphorodithioyl]threonylproline, as new O-phosphorylated dipeptide building blocks for the synthesis of O-phosphorylated peptides, is described. Peptides containing phosphoserine or phosphothreonine were prepared by use of these building blocks in the Boc mode of liquid-phase peptide synthesis. Sites phosphorylated by cdc2 kinase were easily identified using these chemically synthesized phosphopeptides.

Gualamycin, a novel acaricide produced by Streptomyces sp. NK11687. II. Structural elucidation

A novel acaricide, gualamycin was isolated from the culture broth of Streptomyces sp. NK11687. The structure of gualamycin was determined to be (2R,3S,4S)-2-O-[4-O-(2-amino-2-deoxy-beta-D-gulopyranosyl)-alpha-D - galactopyranosyl]-2,3,4-trihydroxy-4-[(2S,3S,4S,5S)-3,4-dihydroxy-5-hydr oxy - methylpyrrolidin-2-yl] butanoic acid by FAB-MS, 1H and 13C NMR, COSY, HMQC, HMBC, IR, X-ray crystallographic analyses and synthetic studies.

Asbestos fiber analysis in nine lung cancer cases with high asbestos exposure

We examined the types and sizes of 100 asbestos fibers in lung tissue obtained from 9 lung-cancer cases (5 autopsy and 4 surgical) with more than 10(4) asbestos bodies per 5 g of wet lung tissue, asbestos bodies in histological sections, and the history of occupational asbestos exposure. Evaluation of asbestos fibers by transmission electron microscopy (2,000 x magnification) revealed that most fibers were longer than 3 microns (96%) and were thicker than 0.1 micron (93%). The analytical conditions we used enabled us to identify 99.7% of all asbestos fibers as being amphibole asbestos. Crocidolite fiber, which was found most frequently (73.1%), was the predominant type of fiber found in 8 of the 9 cases; crocidolite was followed by amosite (21.7%), which was the predominant type found in the remaining case. Crocidolite fibers were thin and had a high aspect ratio (mean diameter = 0.23 micron, mean aspect ratio [length/diameter] = 85.5). Amosite fibers were long, and they also had a high aspect ratio (mean length = 21.8 microns, mean aspect ratio = 66.4). It has been suggested that such fibers with a high aspect ratio are strongly carcinogenic to pulmonary parenchyma. Review of our previous and present data with respect to the ratio of amosite to crocidolite fibers in groups of subjects who had various diseases revealed that this ratio was relatively constant in some occupations. The more predominant fibers found were crocidolite in insulation workers and amosite in railroad workers. The ratio of amosite to crocidolite fibers should be considered in tissue-burden studies.

The interactions of E2F with pRB and with p107 are regulated via the phosphorylation of pRB and p107 by a cyclin-dependent kinase

It has been postulated that the product (pRB) of the retinoblastoma gene dissociates from the E2F-pRB complex upon phosphorylation by cyclin-dependent kinase(s) (cdk). However, there is no direct evident for the regulation of formation of the E2F-pRB complex via phosphorylation by purified cdk. Therefore, we investigated the regulation of formation of this complex by phosphorylation using pRB and purified cyclin A-cdk2, cyclin E-cdk2 or cyclin D1-cdk4. Purified pRB was incubated with nuclear extracts prepared from pRB-defective cells and then subjected to gel mobility shift assays. We confirmed that unphosphorylated pRB associated with various types of E2F but pRB has been phosphorylated by cyclin A-cdk2 did not. We found that E2F-pRB complexes were disrupted as a consequence of phosphorylation by cyclin A-cdk2, and the levels of the free forms of E2Fs increased. We also found that not only the E2F-pRB complexes but also the E2F-p107 complexes were disrupted upon phosphorylation by cyclin A-cdk2. Furthermore, E2F-pRB complexes were disrupted through phosphorylation by cyclin D1-cdk4 and cyclin E-cdk2, as well as by cyclin A-cdk2. These results clearly demonstrate that the phosphorylation of pRB and p107 by cdks regulates the formation of complexes between E2F and pRB or p107.

[Elastase]

Elastases are unique among the proteases in that they are capable of hydrolyzing the scleroprotein elastin. The enzymes include pancreatic elastases 1 (Protease E) and 2, and neutrophil elastase. These three elastases also have esterase and amidase activity toward synthetic substrates such as succinyl-trialanine-p-nitroanilide. Although the three enzymes are similar to each other in enzyme activity, they are quite different in immunoactivity. Therefore, each elastase has its own specific immunoassay either by RIA or EIA. Serum immunoreactive pancreatic elastases reflect disease conditions of pancreatic diseases, especially acute pancreatitis and pancreatic cancer. On the other hand, serum neutrophil elastase increases in various inflammatory diseases or conditions.