Biomedical subjects

Abdel-Majid Khatib

Publications and source records attributed to Abdel-Majid Khatib.

12 recordsLinked to original sources

PubMed2007

Potential opportunity in the development of new therapeutic agents based on endogenous and exogenous inhibitors of the proprotein convertases.

The proprotein convertases (PCs) are responsible for the endoproteolytic processing of various protein precursors (e.g., growth factors, receptors, adhesion molecules, and matrix metalloproteinases) implicated in several diseases such as obesity, diabetes, atherosclerosis, cancer, and Alzheimer disease. The potential clinical and pharmacological role of the PCs has fostered the development of various PC-inhibitors. In this review we summarized the recent findings on PCs inhibitors, their mode of actions and potential use in the therapy of various diseases.

Humans↗

PubMed2006

Tumor necrosis factor-alpha down-regulates human Cu/Zn superoxide dismutase 1 promoter via JNK/AP-1 signaling pathway.

Overexpression of Cu/Zn superoxide dismutase 1 (SOD1) in monocytes blocks reactive oxygen species-induced inhibition of cell growth and apoptosis and renders cells resistant to the toxic effect of tumor necrosis factor (TNF)-alpha, suggesting that TNF-alpha represses the SOD1 gene in these cells. We herein show that TNF-alpha decreases SOD1 mRNA, protein, and promoter activity in U937 cells. Electrophoretic mobility-shift assays (EMSA) show that TNF-alpha decreased binding of three different complexes. Ectopic Sp1 overexpression markedly increased SOD1-basal promoter activity and partially antagonized the TNF-alpha inhibitory effect. In contrast, ectopic c-Jun overexpression mimics TNF-alpha inhibitory effects and antagonizes Sp1 stimulatory effects. In agreement with these findings, EMSA shows a TNF-alpha-induced increase in AP-1 and a decrease in Sp1 DNA binding. Disruption of the C/EBP site decreases, whereas mutation in the Sp1/Egr-1 site completely abolishes DNA-binding and promoter activity. A JNK inhibitor antagonized the negative effects of TNF-alpha on SOD1 promoter activity, suggesting that JNK signaling through c-Jun protein activation is critical for the TNF-alpha-dependent SOD1 repression. A greater understanding of the mechanisms of TNF-alpha-induced SOD1 repression could facilitate the design and development of novel therapeutic drugs for inflammatory conditions.

Base Sequence↗

PubMed2006

Endothelin-1 (ET-1) promotes MMP-2 and MMP-9 induction involving the transcription factor NF-kappaB in human osteosarcoma.

In the present study, we have investigated the effect of (i) ET-1 (endothelin-1) and its precursor, big ET-1, on MMP (matrix metalloproteinase)-2 and MMP-9 synthesis and activity in osteosarcoma tissue, and (ii) ET-1 receptor antagonists on cell invasion. Using Western blotting, zymography, RT-PCR (reverse transcription-PCR), immunohistochemistry, immunofluorescence and Northern blotting, we have shown that ET-1 and ET-1 receptors (ET(A) and ET(B)) were expressed in these cells. Additionally, we have demonstrated that ET-1 markedly induced the synthesis and activity of MMP-2, which was significantly increased when compared with MMP-9. Furthermore, inhibition of NF-kappaB (nuclear factor kappaB) activation blocked MMP-2 production and activity, indicating the involvement of NF-kappaB, a ubiquitous transcription factor playing a central role in the differentiation, proliferation and malignant transformation. Since ET-1 acts as an autocrine mediator through gelatinase induction and because inhibition of ET(A) receptor is beneficial for reducing both basal and ET-1-induced osteosarcoma cell invasion, targeting this receptor could be an attractive therapeutic alternative for the successful treatment of osteosarcoma.

Adolescent↗

PubMed2006

Proprotein convertases: lessons from knockouts.

The physiological role of the subtilisin/kexin-like proprotein convertases (PCs) in rodents has been examined through the use of knockout mice. This review will summarize the major in vivo defects that result from the disruption of the expression of their genes. This includes abnormal embryonic development, hormonal disorder, infertility, and/or modified lipid/sterol metabolism. Members of the PC family play a central role in the processing of various protein precursors ranging from hormones and growth factors to bacterial toxins and viral glycoproteins. Proteolysis occurring at basic residues is mediated by the basic amino acid-specific proprotein convertases, namely: PC1/3, PC2, furin, PACE4, PC4, PC5/6, and PC7. In contrast, proteolysis at nonbasic residues is performed by the subtilisin/kexin-like isozyme-1 (SKI-1/S1P) and the newly identified neural apoptosis-regulated convertase-1 (PCSK9/NARC-1). In addition to their requirement for many physiological processes, these enzymes are also involved in various pathologies such as cancer, obesity, diabetes, lipid disorders, infectious diseases, atherosclerosis and neurodegenerative diseases.

Animals↗

PubMed2005

Regulation of the stepwise proteolytic cleavage and secretion of PDGF-B by the proprotein convertases.

Platelet-derived growth factor-B (PDGF-B) is important for normal tissue growth and maintenance and its overexpression has been linked to several diseases, including cancer, fibrotic disease and atherosclerosis. Here, we show that synthesized as a precursor, proPDGF-B is converted to a mature form by proteolytic cleavage at two sites and its N-terminal cleavage is a prerequisite for processing at its C-terminus. The first cleavage occurs at residues RGRR81/, and the second cleavage close to residues ARPVT190, just before the C-terminal amino-acid sequence crucial for PDGF-B retention to cell surface. Cotransfection of a Furin-deficient cell line LoVo-C5 with proPDGF-B and different PC members revealed that Furin, PACE4, PC5, and PC7 are candidate proPDGF-B convertases. This finding is consistent with the in vitro digestions of a synthetic peptide mimicking the cleavage site of proPDGF-B. The processing of proPDGF-B is blocked by site-directed mutagenesis of the RGRR81/ sequence and by various PC inhibitors. Mutation of the PDGF-A and/or PDGF-B convertase sites, revealed that processing of both A and B chains is required for the formation of mature PDGF-B dimers and that the processing of the B chain controls the level of secreted and matrix-bound PDGF-BB forms. Our findings emphasize the importance of the convertase-directed processing of proPDGF-B at the RGRR81/ sequence for PDGF-B maturation and secretion.

Amino Acid Sequence↗

PubMed2005

Endo/exo-proteolysis in neoplastic progression and metastasis.

Biological control of individual cells, organs, and organisms is achieved through interplay of a host of specific interactions that involve various peptidic molecules as modulators or effectors. In tumor cells, these processes may result in uncontrolled growth as a consequence of autocrine and/or paracrine actions. In recent years, growing evidence has accumulated for the important role of proprotein convertases (PCs) and peptide alpha-amidation enzymes in these processes. The widespread belief that these enzymes are involved in the major features of tumor progression, namely, invasiveness and metastasis, has taken place because of their capacity to process and activate many protein precursors involved in the neoplastic progression and metastasis. This includes degrading extracellular matrix proteases, growth promoting factors, and adhesion molecules. Usually, when the processing of these precursor proteins is achieved by one or more of the known PC family members within the general motif (K/R)-(X)n-(K/R) downward arrow, where n=0, 2, 4, or 6, and X, any amino acid except Cys, the accomplishment of the maturation of these molecules is attained by various posttranslational modifications, including the carboxy-terminal alpha-amidation. This review article summarizes recent findings on the role of these enzymatic systems in multiple cellular functions that impact on the invasive/metastatic potential of cancer cells and highlight the potential use of their inhibitors in the treatment of multiple cancers.

Cell Transformation, Neoplastic↗

PubMed2005

Characterization of the host proinflammatory response to tumor cells during the initial stages of liver metastasis.

The influx of metastatic tumor cells into the liver triggers a rapid proinflammatory cytokine cascade. To further analyze this host response, we used intrasplenic/portal inoculation of green fluorescent protein-marked human and murine carcinoma cells and a combination of immunohistochemistry and confocal microscopy. The metastatic murine lung carcinoma H-59 or human colorectal carcinoma CX-1 cells triggered tumor necrosis factor (TNF)-alpha production by Kupffer cells located in sinusoidal vessels around the invading tumor cells. H-59 cells rapidly elicited a fourfold increase in the number of TNF-alpha(+) Kupffer cells relative to basal levels within 2 hours and this response declined gradually after 6 hours. Increased cytokine production in these mice was confirmed by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay performed on isolated Kupffer cells. CX-1 cells elicited a more gradual response that peaked at 10 to 16 hours, remained high up to 48 hours, and involved CX-1-Kupffer cell attachment. Furthermore, the rapidly induced production of TNF-alpha was followed by increased expression of the vascular adhesion receptors E-selectin P-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 on sinusoidal endothelial cells. This proinflammatory response was tumor-specific and was not observed with nonmetastatic murine M-27 or human MIP-101 carcinoma cells. These results identify Kupffer cell-mediated TNF-alpha production as an early, tumor-selective host inflammatory response to liver-invading tumor cells that may influence the course of metastasis.

Animals↗

PubMed2004

Method for selecting populations of rat articular chondrocytes that exhibit distinct growth and metabolic characteristics, and their responses to growth factors, PMA and vitamin D3.

Chondrocytes were released from articular cartilage fragments of 6-week-old Wistar rats by a 2-hour treatment with bacterial collagenase. The cells from one animal were seeded in a 25-cm2 culture flask at a density of 10(5) cells/cm2. After 1 h, the flask was gently shaken and the medium, containing nonadherent cells, was transferred to a new flask. The attached cells were incubated with 5 ml of fresh medium. This procedure was repeated after 3, 24, 48 and 96 h. Resulting cell populations were then analyzed. The earlier cells attached, the more rapidly they proliferated, and the less collagen and proteoglycan (PG) they produced. The cells that attached after 24 h grew much more slowly, piled up in many areas, exhibited strong alkaline phosphatase activity and calcified extracellular matrix (ECM). Differences in deoxyribonucleic acid (DNA) and protein/PG synthesis were also observed when these cell populations were challenged with growth factors and 12-myristate 13-acetate (PMA). Pretreatment of cells for 2 h with PMA strongly enhanced DNA and PG synthesis only in cultures containing insulin-like growth factor-1. Nonselected rat articular chondrocytes (AC) subcultured at least four times as monolayers still expressed mRNA specific for aggrecan and type II collagen, suggesting conservation of the chondrogenic phenotype. In conclusion, AC of young individuals seem to be heterogeneous with respect to their capacity to proliferate and synthesize ECM. By selecting and expanding in vitro the appropriate cell population, this method could be potentially useful for studies aimed at repairing damaged cartilage.

Alkaline Phosphatase↗

PubMed2003

The proteolytic processing of pro-platelet-derived growth factor-A at RRKR(86) by members of the proprotein convertase family is functionally correlated to platelet-derived growth factor-A-induced functions and tumorigenicity.

Although altered expression of platelet-derived growth factor (PDGF)-A is a hallmark of many cancers, the importance of pro-PDGF-A conversion to PDGF-A in tumorigenesis and the cognate protease(s) is unknown. Pro-PDGF-A processing occurs at pairs of basic residues, likely involving the proprotein convertases (PCs). In the colon carcinoma cell line LoVo, we found that Furin is the most potent PDGF-A convertase. Mutation of the PC-site RRKR(86) to ARKA(86) inhibited pro-PDGF-A processing, its receptor tyrosine phosphorylation, and cell proliferation. This processing is also blocked by the PC preprosegments (pps) ppFurin, ppPC5, and ppPACE4, and by the Furin-variants of alpha2-macroglobulin and alpha1-antitrypsin. Chinese hamster ovary cells overexpressing pro-PDGF-A (ARKA(86)) failed to induce tumors in nude mice. Thus, PC-directed inhibitors might represent new agents for therapy in neoplasia induced by PDGF-A.

3T3 Cells↗

PubMed2003

The secretory proprotein convertases furin, PC5, and PC7 activate VEGF-C to induce tumorigenesis.

The secretory factor VEGF-C has been directly implicated in various physiological processes during embryogenesis and human cancers. However, the importance of the conversion of its precursor proVEGF-C to mature VEGF-C in tumorigenesis, and vessel formation and the identity of the protease(s) that regulate these processes is/are not known. The intracellular processing of proVEGF-C that occurs within the dibasic motif HSIIRR(227)SL suggests the involvement of the proprotein convertases (PCs) in this process. In addition, furin and VEGF-C were found to be coordinately expressed in adult mouse tissues. Cotransfection of the furin-deficient colon carcinoma cell line LoVo with proVEGF-C and different PC members revealed that furin, PC5, and PC7 are candidate VEGF-C convertases. This finding is consistent with the in vitro digestions of an internally quenched synthetic fluorogenic peptide mimicking the cleavage site of proVEGF-C ((220)Q-VHSIIRR downward arrow SLP(230)). The processing of proVEGF-C is blocked by the inhibitory prosegments of furin, PC5, and PACE4, as well as by furin-motif variants of alpha2-macroglobulin and alpha1-antitrypsin. Subcutaneous injection of CHO cells stably expressing VEGF-C into nude mice enhanced angiogenesis and lymphangiogenesis, but not tumor growth. In contrast, expression of proVEGF-C obtained following mutation of the cleavage site (HSIIRR(227)SL to HSIISS(227)SL) inhibits angiogenesis and lymphangiogenesis as well as tumor growth. Our findings demonstrate the processing of proVEGF-C by PCs and highlight the potential use of PC inhibitors as agents for inhibiting malignancies induced by VEGF-C.

Amino Acid Motifs↗

PubMed2002

Inhibition of hepatic endothelial E-selectin expression by C-raf antisense oligonucleotides blocks colorectal carcinoma liver metastasis.

Cytokine-dependent induction of E-selectin expression is mediated through cooperative signaling involving the Ras/Raf/mitogen-activated protein kinase pathway. We previously reported that metastatic tumor cells entering the hepaticcirculation rapidly induce a cytokine cascade leading to E-selectin induction (A-M. Khatib, et al., Cancer Res., 59:1356-1361, 1999).Here, we investigated the effect of a blockade of E-selectin induction on colorectal carcinoma metastasis using rodent (host)-specific C-raf antisense oligonucleotides and human colorectal carcinoma CX-1 cells. Pretreatment of hepatic endothelial cells in vitro with the antisense oligonucleotides abrogated E-selectin-dependent CX-1 adhesion. In vivo, pretreatment of nude mice with these oligonucleotides abrogated E-selectin induction in response to intrasplenic/portal inoculation of CX-1 cells, and this reduced the number of liver metastases by 86% relative to controls. The results suggest that the inhibition of tumor-induced, hepatic microvessel E-selectin expression may provide a useful strategy for the prevention of hepatic metastasis.

Animals↗

PubMed2002

Proprotein convertases in tumor progression and malignancy: novel targets in cancer therapy.

The mammalian subtilisin/kexin-like proprotein convertase (PC) family has been implicated in the activation of a wide spectrum of proteins. These proteins are usually synthesized as inactive precursors before their conversion to fully mature bioactive forms. A large majority of these active proteins such as matrix metalloproteases, growth factors, and adhesion molecules are crucial in the processes of cellular transformation, acquisition of the tumorigenic phenotype, and metastases formation. Inhibition of PCs significantly affects the malignant phenotype of various tumor cells. In addition to direct tumor cell proliferation and migration blockade, PC inhibitors can also be used to target tumor angiogenesis. In this Review article we discuss a number of recent findings on the clinical relevance of PCs in cancer patients, their implication in the regulation of multiple cellular functions that impact on the invasive/metastatic potential of cancer cells. Thus, PC inhibitors may constitute new promising agents for the treatment of multiple tumors and/or in adjuvant therapy to prevent recurrence.

Animals↗