Strengthening Multi-Factor Authentication Through Physically Unclonable Functions in PVDF-HFP-Phase-Dependent a-IGZO Thin-Film Transistors

For enhanced security in hardware-based security devices, it is essential to extract various independent characteristics from a single device to generate multiple keys based on specific values. Additionally, the secure destruction of authentication information is crucial for the integrity of the data. Doped amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) using poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) induce a dipole doping effect through a phase-transition process, creating physically unclonable function (PUF) devices for secure user information protection. The PUF security key, generated at VGS = 20 V in a 20 × 10 grid, demonstrates uniformity of 42% and inter-Hamming distance (inter-HD) of 49.79% in the β-phase of PVDF-HFP. However, in the γ-phase, the uniformity drops to 22.5%, and inter-HD decreases to 35.74%, indicating potential security key destruction during the phase transition. To enhance security, a multi-factor authentication (MFA) system is integrated, utilizing five security keys extracted from various TFT parameters. The security keys from turn-on voltage (VON), VGS = 20 V, VGS = 30 V, mobility, and threshold voltage (Vth) exhibit near-ideal uniformities and inter-HDs, with the highest values of 58% and 51.68%, respectively. The dual security system, combining phase transition and MFA, establishes a robust protection mechanism for privacy-sensitive user information.

Imitating Synapse Behavior: Exploiting Off-Current in TPBi-Doped Small Molecule Phototransistors for Broadband Wavelength Recognition

Phototransistors have gained significant attention in diverse applications such as photodetectors, image sensors, and neuromorphic devices due to their ability to control electrical characteristics through photoresponse. The choice of photoactive materials in phototransistor research significantly impacts its development. In this study, we propose a novel device that emulates artificial synaptic behavior by leveraging the off-current of a phototransistor. We utilize a p-type organic semiconductor, dinaphtho[2,3-b:2',3'- f]thieno[3,2-b]thiophene (DNTT), as the channel material and dope it with the organic semiconductor 2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) on the DNTT transistor. Under light illumination, the general DNTT transistor shows no change in off-current, except at 400 nm wavelength, whereas the TPBi-doped DNTT phototransistor exhibits increased off-current across all wavelength bands. Notably, DNTT phototransistors demonstrate broad photoresponse characteristics in the wavelength range of 400-1000 nm. We successfully simulate artificial synaptic behavior by differentiating the level of off-current and achieving a recognition rate of over 70% across all wavelength bands.

Machine Learning Attacks-Resistant Security by Mixed-Assembled Layers-Inserted Graphene Physically Unclonable Function

Mixed layers of octadecyltrichlorosilane (ODTS) and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FOTS) on an active layer of graphene are used to induce a disordered doping state and form a robust defense system against machine-learning attacks (ML attacks). The resulting security key is formed from a 12 × 12 array of currents produced at a low voltage of 100 mV. The uniformity and inter-Hamming distance (HD) of the security key are 50.0 ± 12.3% and 45.5 ± 16.7%, respectively, indicating higher security performance than other graphene-based security keys. Raman spectroscopy confirmed the uniqueness of the 10,000 points, with the degree of shift of the G peak distinguishing the number of carriers. The resulting defense system has a 10.33% ML attack accuracy, while a FOTS-inserted graphene device is easily predictable with a 44.81% ML attack accuracy.

Imidazole-based artificial synapses for neuromorphic computing: a cluster-type conductive filament via controllable nanocluster nucleation

Memristive synapses based on conductive bridging RAMs (CBRAMs) utilize a switching layer having low binding energy with active metals for excellent analog conductance modulation, but the resulting unstable conductive filaments cause fluctuation and drift of the conductance. This tunability-stability dilemma makes it difficult to implement practical neuromorphic computing. A novel method is proposed to enhance the stability and controllability of conductive filaments by introducing imidazole groups that boost the nucleation of Cu nanoclusters in the ultrathin polymer switching layer through the initiated chemical vapor deposition (iCVD) process. It is confirmed that conductive filaments based on nanoclusters with specific gaps are generated in the copolymer medium using this method. Furthermore, by modulating the tunneling gaps, an ultra-wide conductance range of analog tunable conductive filaments is achieved from several hundreds of nS to a few mS with a sub-1 V driving voltage. Through this, both reliable and stable analog switching are achieved with low cycle-to-cycle and device-to-device weight update variations and separable state retention with 32 states. This approach paves the way for the extension of state availability in synaptic devices to overcome the tunability-stability dilemma, which is essential for the synaptic elements in neuromorphic systems.

Preventing Vanishing Gradient Problem of Hardware Neuromorphic System by Implementing Imidazole-Based Memristive ReLU Activation Neuron

With advances in artificial intelligent services, brain-inspired neuromorphic systems with synaptic devices are recently attracting significant interest to circumvent the von Neumann bottleneck. However, the increasing trend of deep neural network parameters causes huge power consumption and large area overhead of a nonlinear neuron electronic circuit, and it incurs a vanishing gradient problem. Here, a memristor-based compact and energy-efficient neuron device is presented to implement a rectifying linear unit (ReLU) activation function. To emulate the volatile and gradual switching of the ReLU function, a copolymer memristor with a hybrid structure is proposed using a copolymer/inorganic bilayer. The functional copolymer film developed by introducing imidazole functional groups enables the formation of nanocluster-type pseudo-conductive filaments by boosting the nucleation of Cu nanoclusters, causing gradual switching. The ReLU neuron device is successfully demonstrated by integrating the memristor with amorphous InGaZnO thin-film transistors, and achieves 0.5 pJ of energy consumption based on sub-10 µA operation current and high-speed switching of 650 ns. Furthermore, device-to-system-level simulation using neuron devices on the MNIST dataset demonstrates that the vanishing gradient problem is effectively resolved by five-layer deep neural networks. The proposed neuron device will enable the implementation of high-density and energy-efficient hardware neuromorphic systems.

Double-Floating-Gate van der Waals Transistor for High-Precision Synaptic Operations

Two-dimensional materials and their heterostructures have thus far been identified as leading candidates for nanoelectronics owing to the near-atom thickness, superior electrostatic control, and adjustable device architecture. These characteristics are indeed advantageous for neuro-inspired computing hardware where precise programming is strongly required. However, its successful demonstration fully utilizing all of the given benefits remains to be further developed. Herein, we present van der Waals (vdW) integrated synaptic transistors with multistacked floating gates, which are reconfigured upon surface oxidation. When compared with a conventional device structure with a single floating gate, our double-floating-gate (DFG) device exhibits better nonvolatile memory performance, including a large memory window (>100 V), high on-off current ratio (∼10⁷), relatively long retention time (>5000 s), and satisfactory cyclic endurance (>500 cycles), all of which can be attributed to its increased charge-storage capacity and spatial redistribution. This facilitates highly effective modulation of trapped charge density with a large dynamic range. Consequently, the DFG transistor exhibits an improved weight update profile in long-term potentiation/depression synaptic behavior for nearly ideal classification accuracies of up to 96.12% (MNIST) and 81.68% (Fashion-MNIST). Our work adds a powerful option to vdW-bonded device structures for highly efficient neuromorphic computing.

Amorphous ITZO-Based Selector Device for Memristor Crossbar Array

In the era of digital transformation, a memristor and memristive circuit can provide an advanced computer architecture that efficiently processes a vast quantity of data. With the unique characteristic of memristor, a memristive crossbar array has been utilized for realization of nonvolatile memory, logic-in-memory circuit, and neuromorphic system. However, the crossbar array architecture suffers from leakage of current, known as the sneak current, which causes a cross-talk interference problem between adjacent memristor devices, leading to an unavoidable operational error and high power consumption. Here, we present an amorphous In-Sn-Zn-O (a-ITZO) oxide semiconductor-based selector device to address the sneak current issue. The a-ITZO-selector device is realized with the back-to-back Schottky diode with nonlinear current-voltage (I-V) characteristics. Its nonlinearity is dependent on the oxygen plasma treatment process which can suppress the surface electron accumulation layer arising on the a-ITZO surface. The a-ITZO-selector device shows reliable characteristics against electrical stress and high temperature. In addition, the selector device allows for a stable read margin over 1 Mbit of memristor crossbar array. The findings may offer a feasible solution for the development of a high-density memristor crossbar array.

Graphene Oxide-Based Memristive Logic-in-Memory Circuit Enabling Normally-Off Computing

Memristive logic-in-memory circuits can provide energy- and cost-efficient computing, which is essential for artificial intelligence-based applications in the coming Internet-of-things era. Although memristive logic-in-memory circuits have been previously reported, the logic architecture requiring additional components and the non-uniform switching of memristor have restricted demonstrations to simple gates. Using a nanoscale graphene oxide (GO) nanosheets-based memristor, we demonstrate the feasibility of a non-volatile logic-in-memory circuit that enables normally-off in-memory computing. The memristor based on GO film with an abundance of unusual functional groups exhibited unipolar resistive switching behavior with reliable endurance and retention characteristics, making it suitable for logic-in-memory circuit application. In a state of low resistance, temperature-dependent resistance and I-V characteristics indicated the presence of a metallic Ni filament. Using memristor-aided logic (MAGIC) architecture, we performed NOT and NOR gates experimentally. Additionally, other logic gates such as AND, NAND, and OR were successfully implemented by combining NOT and NOR universal logic gates in a crossbar array. These findings will pave the way for the development of next-generation computer systems beyond the von Neumann architecture, as well as carbon-based nanoelectronics in the future.

Hardware-Intrinsic Physical Unclonable Functions by Harnessing Nonlinear Conductance Variation in Oxide Semiconductor-Based Diode

With the advancement of the Internet of Things (IoT), numerous electronic devices are connected to each other and exchange a vast amount of data via the Internet. As the number of connected devices increases, security concerns have become more significant. As one of the potential solutions for security issues, hardware intrinsic physical unclonable functions (PUFs) are emerging semiconductor devices that exploit inherent randomness generated during the manufacturing process. The unclonable security key generated from PUF can address the inherent limitations of conventional electronic systems which depend solely on software. Although numerous PUFs based on the emerging memory devices requiring switching operations have been proposed, achieving hardware intrinsic PUF with low power consumption remains a key challenge. Here, we demonstrate that the process-induced nonlinear conductance variations of oxide semiconductor-based Schottky diodes provide a suitable source of entropy for the implementation of PUF without switching operation. Using a mild oxygen plasma treatment, the surface electron accumulation layer that forms naturally in oxide semiconductor film can be partially eliminated, resulting in a large variation of nonlinearity as an exotic entropy source. The mild plasma-treated Schottky diodes showed near ideal 50% average uniformity and uniqueness, as well as an ideal entropy value without the need for additional hardware area and power costs. These findings will pave the way for the development of hardware intrinsic PUFs to realize energy-efficient cryptographic hardware.

Disordered Mixture of Self-Assembled Molecular Functional Groups on Heterointerfaces with p-Si Leads to Multiple Key Generation in Physical Unclonable Functions

Physical unclonable function (PUF) security devices based on hardware are becoming an effective strategy to overcome the dependency of the internet cloud and software-based hacking vulnerabilities. On the other hand, existing Si-based artificial security devices have several issues, including the absence of a method for multiple key generation, complex and expensive fabrication processes, and easy prediction compared to devices retaining natural randomness. Herein, to generate unique and unpredictable multiple security keys, this paper proposes novel PUF devices consisting of a disordered random mixture of two self-assembled monolayers (SAMs) formed onto p-type Si. The proposed PUF devices exhibited multikeys at different voltage biasing, including 0 V, through the arbitrary dipole effect. As a result, multiple unpredictable hardware security keys were generated from one device using a simple solution-coating process. The PUF security device based on the mixture of materials with different dipoles developed in this study can provide valuable insights for implementing various PUF devices in the future.

Conductive-bridging random-access memories for emerging neuromorphic computing

With the increasing utilisation of artificial intelligence, there is a renewed demand for the development of novel neuromorphic computing owing to the drawbacks of the existing computing paradigm based on the von Neumann architecture. Extensive studies have been performed on memristors as their electrical nature is similar to those of biological synapses and neurons. However, most hardware-based artificial neural networks (ANNs) have been developed with oxide-based memristors owing to their high compatibility with mature complementary metal-oxide-semiconductor (CMOS) processes. Considering the advantages of conductive-bridging random-access memories (CBRAMs), such as their high scalability, high on-off current with a wide dynamic range, and low off-current, over oxide-based memristors, extensive studies on CBRAMs are required. In this review, the basics of operation of CBRAMs are examined in detail, from the formation of metal nanoclusters to filament bridging. Additionally, state-of-the-art experimental demonstrations of CBRAM-based artificial synapses and neurons are presented. Finally, CBRAM-based ANNs are discussed, including deep neural networks and spiking neural networks, along with other emerging computing applications. This review is expected to pave the way toward further development of large-scale CBRAM array systems.

Polymer Analog Memristive Synapse with Atomic-Scale Conductive Filament for Flexible Neuromorphic Computing System

With the advent of artificial intelligence (AI), memristors have received significant interest as a synaptic building block for neuromorphic systems, where each synaptic memristor should operate in an analog fashion, exhibiting multilevel accessible conductance states. Here, we demonstrate that the transition of the operation mode in poly(1,3,5-trivinyl-1,3,5-trimethyl cyclotrisiloxane) (pV3D3)-based flexible memristor from conventional binary to synaptic analog switching can be achieved simply by reducing the size of the formed filament. With the quantized conductance states observed in the flexible pV3D3 memristor, analog potentiation and depression characteristics of the memristive synapse are obtained through the growth of atomically thin Cu filament and lateral dissolution of the filament via dominant electric field effect, respectively. The face classification capability of our memristor is evaluated via simulation using an artificial neural network consisting of pV3D3 memristor synapses. These results will encourage the development of soft neuromorphic intelligent systems.

Functional Circuitry on Commercial Fabric via Textile-Compatible Nanoscale Film Coating Process for Fibertronics

Fabric-based electronic textiles (e-textiles) are the fundamental components of wearable electronic systems, which can provide convenient hand-free access to computer and electronics applications. However, e-textile technologies presently face significant technical challenges. These challenges include difficulties of fabrication due to the delicate nature of the materials, and limited operating time, a consequence of the conventional normally on computing architecture, with volatile power-hungry electronic components, and modest battery storage. Here, we report a novel poly(ethylene glycol dimethacrylate) (pEGDMA)-textile memristive nonvolatile logic-in-memory circuit, enabling normally off computing, that can overcome those challenges. To form the metal electrode and resistive switching layer, strands of cotton yarn were coated with aluminum (Al) using a solution dip coating method, and the pEGDMA was conformally applied using an initiated chemical vapor deposition process. The intersection of two Al/pEGDMA coated yarns becomes a unit memristor in the lattice structure. The pEGDMA-Textile Memristor (ETM), a form of crossbar array, was interwoven using a grid of Al/pEGDMA coated yarns and untreated yarns. The former were employed in the active memristor and the latter suppressed cell-to-cell disturbance. We experimentally demonstrated for the first time that the basic Boolean functions, including a half adder as well as NOT, NOR, OR, AND, and NAND logic gates, are successfully implemented with the ETM crossbar array on a fabric substrate. This research may represent a breakthrough development for practical wearable and smart fibertronics.

Flexible Nonvolatile Polymer Memory Array on Plastic Substrate via Initiated Chemical Vapor Deposition

Resistive random access memory based on polymer thin films has been developed as a promising flexible nonvolatile memory for flexible electronic systems. Memory plays an important role in all modern electronic systems for data storage, processing, and communication; thus, the development of flexible memory is essential for the realization of flexible electronics. However, the existing solution-processed, polymer-based RRAMs have exhibited serious drawbacks in terms of the uniformity, electrical stability, and long-term stability of the polymer thin films. Here, we present poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3)-based RRAM arrays fabricated via the solvent-free technique called initiated chemical vapor deposition (iCVD) process for flexible memory application. Because of the outstanding chemical stability of pV3D3 films, the pV3D3-RRAM arrays can be fabricated by a conventional photolithography process. The pV3D3-RRAM on flexible substrates showed unipolar resistive switching memory with an on/off ratio of over 10(7), stable retention time for 10(5) s, excellent cycling endurance over 10(5) cycles, and robust immunity to mechanical stress. In addition, pV3D3-RRAMs showed good uniformity in terms of device-to-device distribution. The pV3D3-RRAM will pave the way for development of next-generation flexible nonvolatile memory devices.

Overexpression of short heterodimer partner recovers impaired glucose-stimulated insulin secretion of pancreatic beta-cells overexpressing UCP2

The short heterodimer partner (SHP) (NR0B2) is an orphan nuclear receptor whose function in pancreatic beta-cells is unclear. Mitochondrial uncoupling protein (UCP2) in beta-cells is upregulated in obesity-related diabetes, causing impaired glucose-stimulated insulin secretion (GSIS). We investigated whether SHP plays a role in UCP2-induced GSIS impairment. We overexpressed SHP in normal islet cells and in islet cells overexpressing UCP2 by an adenovirus-mediated infection technique. We found that SHP overexpression enhanced GSIS in normal islets, and restored GSIS in UCP2-overexpressing islets. SHP overexpression increased the glucose sensitivity of ATP-sensitive K+ (KATP) channels and enhanced the ATP/ADP ratio. A peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist, GW9662, did not block the SHP effect on GSIS. SHP overexpression also corrected the impaired sensitivity of UCP2-overexpressing beta-cells to methylpyruvate, another energy fuel that bypasses glycolysis and directly enters the Krebs cycle. KATP channel inhibition mediated by dihydroxyacetone, which gives reducing equivalents directly to complex II of the electron transport system, was similar in Ad-Null-, Ad-UCP2- and Ad-UCP2+Ad-SHP-infected cells. The mitochondrial metabolic inhibitor sodium azide totally blocked the effect of SHP overexpression on GSIS. These results suggest that SHP positively regulates GSIS in beta-cells and restores glucose sensitivity in UCP2-overexpressing beta-cells by enhancing mitochondrial glucose metabolism, independent of PPARgamma activation.

Serum withdrawal-induced post-transcriptional stabilization of cyclooxygenase-2 mRNA in MDA-MB-231 mammary carcinoma cells requires the activity of the p38 stress-activated protein kinase

Overexpression of the cyclooxygenase-2 (COX-2) gene is observed in several neoplastic diseases. However, molecular mechanisms involved in the regulation of expression of COX-2 are not well understood. In this report, we describe a unique post-transcriptional regulatory mechanism of COX-2 mRNA stabilization in MDA-MB-231 cells, a highly metastatic cell line derived from a human mammary tumor. High levels of COX-2 mRNA, protein, and enzyme activity were induced by serum withdrawal, which were potently inhibited by the addition of serum or >100-kDa serum factor. Nuclear run-on analysis and actinomycin D chase experiments indicate that regulation is primarily at the level of post-transcriptional mRNA stability. Interestingly, SB203580, an inhibitor of the p38 stress-activated protein kinase (SAPK), and overexpression of the dominant-negative p38alpha construct potently inhibited the serum withdrawal-induced COX-2 mRNA levels. Indeed, the half-life of COX-2 mRNA decreased from 9 to 4.5 h after SB203580 treatment, suggesting that signal transduction by the p38 SAPK pathway is required for COX-2 mRNA stability.

Coexpression of cyclooxygenase-2 and matrix metalloproteinases in human aortic atherosclerotic lesions

Inflammation appears to have a major role in the development of atherosclerosis. Cyclooxygenase-2 (COX-2) is involved in the inflammatory response via the generation of prostanoids that, in turn, are involved in the production of matrix metalloproteinases (MMPs). This study aimed to investigate atherosclerosis in human aortas for in situ tissue distribution of COX-2, MMPs including MMP-9 and membrane type 1 MMP (MT1-MMP), and tissue inhibitor of metalloproteinase-2 (TIMP-2). Immunohistochemical studies were performed on atherosclerotic lesions of aortas from patients with aortic aneurysms (n = 4) and dissections (n = 3) by using antibodies to COX-2, MMP-9, MT1-MMP, and TIMP-2. Control tissues were obtained from traumatically dissected aortas (n = 2). All specimens from diseased aortas had atherosclerotic lesions ranging from fatty streak to atheromatous plaques. In control, there was no expression of COX-2, MMP-9, and MT1-MMP in all aortic layers. Immunoreactivity for COX-2 was predominantly noted in macrophages and smooth muscle cells (SMCs) of the intima including atherosclerotic plaque itself and the medial layer of the plaque base, as well as in SMCs and endothelial lining of the vasa vasorum in the adventitia. Immunoreactivity for MMP-9 and MT1-MMP was found in the same distribution as that of COX-2. Additionally, the expression of TIMP-2 increased in relation to MMP-9 expression. This study demonstrates that COX-2 is coexpressed with MMP-9 and MT1-MMP, not only by macrophages and SMCs in atherosclerotic lesions, but also in endothelial lining of the vasa vasorum of human aortas. Thus, vascular inflammatory reactions may influence extracellular matrix remodeling by coactivation of MMPs in the development of atherosclerosis and, in turn, the progression of disease.

Expression of mitogen-inducible cyclooxygenase induced by lipopolysaccharide: mediation through both mitogen-activated protein kinase and NF-kappaB signaling pathways in macrophages

The mitogen-inducible cyclooxygenase (COX-2) is selectively expressed in lipopolysaccharide (LPS)-stimulated macrophages. However, the signaling pathways that lead to the expression of COX-2 in LPS-stimulated macrophages are not well understood. LPS activates members of mitogen-activated protein kinases (MAPKs) and NF-kappaB transcription factor in macrophages. We have shown that protein tyrosine kinase (PTK) inhibitors suppress the LPS-induced expression of COX-2 in macrophages (Chanmugam et al., J Biol Chem 270: 5418-5426, 1995). These PTK inhibitors also inhibit LPS-induced activation of MAPKs. Thus, in the present study, we determined whether the activation of MAPKs and NF-kappaB is necessary for the signaling pathway for the LPS-induced expression of COX-2 in the murine macrophage cell line RAW 264.7. The findings demonstrated that inhibition of extracellular signal-regulated protein kinases 1 and 2 (ERK-1 and -2) by the selective inhibitor PD98059 or inhibition of P38 by the specific inhibitor SB203580 results in partial suppression of COX-2 expression. However, activation of MAPKs by phorbol 12-myristate 13-acetate, H2O2, sorbitol, sodium vanadate, or a combination of these agents failed to induce the expression of COX-2. Inhibitors of NF-kappaB suppressed COX-2 expression without affecting tyrosine phosphorylation of MAPKs. The PTK inhibitors that suppressed the activation of MAPKs and COX-2 expression also inhibited the degradation of IkappaB-alpha. Together, these results indicate that the activation of NF-kappaB is required to induce the expression of COX-2 in LPS-stimulated RAW 264.7 cells. Inhibition of ERK-1 and 2 or P38 results in partial suppression of COX-2 expression. However, the activation of MAPKs alone is not sufficient to induce the expression of COX-2 in these cells.

Inhibition of the expression of inducible cyclooxygenase and proinflammatory cytokines by sesquiterpene lactones in macrophages correlates with the inhibition of MAP kinases

In our previous studies (Refs. 1 and 2), it was shown that protein tyrosine kinase (PTK) inhibitors, radicicol and herbimycin A, inhibit the expression of the mitogen-inducible cyclooxygenase (COX-2) and proinflammatory cytokines. Radicicol and herbimycin A possess polarized double bonds which can conjugate sulphydryl groups of proteins. Parthenolide, the predominant sesquiterpene lactone in European feverfew (Tanacetum parthenium), contains alpha-methylene-gamma-lactone (MGL) and an epoxide in its structure. These moieties can interact with biological nucleophiles such as a sulfhydryl group. Parthenolide inhibited the expression of COX-2 and proinflammatory cytokines (TNF alpha and IL-1) in lipopolysaccharide (LPS)-stimulated macrophages. The structure-function relationship indicates that the MGL moiety confers the inhibitory effect. Parthenolide suppressed LPS-stimulated protein tyrosine phosphorylation in the murine macrophage cell line (RAW 264.7). This suppression was correlated with its inhibitory effect on the expression of COX-2 and the cytokines. Among tyrosine phosphorylated proteins, mitogen-activated protein kinases (MAPKs) exhibited the most dramatic inhibition.

Radicicol, a protein tyrosine kinase inhibitor, suppresses the expression of mitogen-inducible cyclooxygenase in macrophages stimulated with lipopolysaccharide and in experimental glomerulonephritis

Two isoforms of cyclooxygenase (COX) have been identified in eukaryotic cells: a constitutively expressed COX-1 and mitogen-inducible COX-2, which is selectively expressed in response to various inflammatory stimuli. Thus, COX-2 instead of COX-1 is implicated to produce prostanoids mediating inflammatory responses. Major efforts have been focused on identifying nonsteroidal anti-inflammatory drugs (NSAIDS) which can selectively inhibit the enzyme activity of COX-2. Such NSAIDS would be more desirable anti-inflammatory agents in comparison to NSAIDS which inhibit both COX-1 and COX-2. Other than glucocorticoids, pharmacological agents which can selectively suppress the expression of COX-2 without affecting that of COX-1 have not been identified. We report here that radicicol, a fungal antibiotic, is a potent protein tyrosine kinase inhibitor, and that it inhibits the expression of COX-2 without affecting COX-1 expression in lipopolysaccharide (LPS)-stimulated macrophages with the IC50 value of 27 nM. Radicicol inhibited tyrosine phosphorylation of p53/56lyn, a Src family tyrosine kinase and one of the major tyrosine-phosphorylated proteins in LPS-stimulated macrophages. Radicicol also inhibited COX-2 expression in vivo in glomeruli of rats with experimental glomerulonephritis induced by the anti-glomerular basement membrane antibodies, in which COX-2 expression is known to be enhanced. The enzyme activity of COX-1 or COX-2 was not affected by radicicol in macrophages. Radiciciol also suppressed the COX-2 expression induced by IL-1 beta in rat smooth muscle cells. Other protein tyrosine kinase inhibitors suppressed the LPS-induced COX-2 expression in macrophages but at much higher concentrations than needed for radicicol. Radicicol did not inhibit the COX-2 expression induced by phorbol 12-myristate 13-acetate in macrophages. These results suggest that the activation of tyrosine-specific protein kinases is the proximal obligatory step in the LPS-induced signal transduction pathway leading to the induction of COX-2 expression in macrophages. The magnitude of the inhibition of COX-2 protein synthesis by radicicol was much greater than that of the steady state levels of COX-2 mRNA. These results suggest that radicicol inhibits COX-2 expression mainly at post-transcriptional steps.