Ikuo Katayama

αNAC depletion as an initiator of ER stress-induced apoptosis in hypoxia

Accumulation of unfolded proteins triggers endoplasmic reticulum (ER) stress and is considered a part of the cellular responses to hypoxia. The nascent polypeptide-associated complex (NAC) participates in the proper maturation of newly synthesized proteins. However, thus far, there have been no comprehensive studies on NAC involvement in hypoxic stress. Here, we show that hypoxia activates glycogen synthase kinase-3β (GSK-3β) and that the activated GSK-3β destabilizes αNAC with the subsequent apoptosis of the cell. Hypoxia of various cell types and the mouse ischemic brain was associated with rapid downregulation of αNAC and ER stress responses involving PERK, ATF4, γ-taxilin, elF2α, Bip, and CHOP. Depletion of αNAC by RNA interference specifically activated ER stress responses and caused mitochondrial dysfunction, which resulted in apoptosis through caspase activation. Interestingly, we found that the hypoxic conditions activated GSK-3β, and that GSK-3β inhibition prevented αNAC protein downregulation in hypoxic cells and rescued the cells from apoptosis. In addition, αNAC overexpression increased the viability of hypoxic cells. Taken together, these results suggest that αNAC degradation triggers ER stress responses and initiates apoptotic processes in hypoxic cells, and that GSK-3β may participate upstream in this mechanism.

Ionizing Radiation Induces Macrophage Foam Cell Formation and Aggregation Through JNK-Dependent Activation of CD36 Scavenger Receptors

PURPOSE Irradiated arteries of cancer patients can be associated with atherosclerosis-like lesions containing cholesterol-laden macrophages (foam cells). Endothelial cell damage by irradiation does not completely explain the foam cell formation. We investigated the possible underlying mechanisms for ionizing radiation (IR)-induced foam cell formation. METHODS AND MATERIALS Human peripheral blood monocytes were activated by macrophage colony-stimulating factor and then treated with varying doses of IR in vitro in the absence of endothelial cells. Scavenger receptor expression and foam cell formation of IR-treated macrophages were investigated in the presence or absence of oxidized low-density lipoprotein. We also assessed the importance of mitogen-activated protein kinase activity in the macrophage colony-stimulating factor-activated human monocytes (macrophages) for the foam cell formation. RESULTS We found that IR treatment of macrophage colony-stimulating factor-activated human peripheral blood monocytes resulted in the enhanced expression of CD36 scavenger receptors and that cholesterol accumulated in the irradiated macrophages with resultant foam cell formation in the presence of oxidized low-density lipoprotein. Furthermore, when cultured on collagen gels, human macrophages formed large foam cell aggregates in response to IR. Antibodies against CD36 inhibited the IR-induced foam cell formation and aggregation, indicating that the IR-induced foam cell formation and the subsequent aggregation are dependent on functional CD36. In addition, we found that IR of human macrophages resulted in c-Jun N-terminal kinase activation and that c-Jun N-terminal kinase inhibition suppressed IR-induced CD36 expression and the subsequent foam cell formation and aggregation. CONCLUSION Taken together, these results suggest that IR-induced foam cell formation is mediated by c-Jun N-terminal kinase-dependent CD36 activation.

Simple and Reliable Determination of Intravoxel Incoherent Motion Parameters for the Differential Diagnosis of Head and Neck Tumors

Intravoxel incoherent motion (IVIM) imaging can characterize diffusion and perfusion of normal and diseased tissues, and IVIM parameters are authentically determined by using cumbersome least-squares method. We evaluated a simple technique for the determination of IVIM parameters using geometric analysis of the multiexponential signal decay curve as an alternative to the least-squares method for the diagnosis of head and neck tumors. Pure diffusion coefficients (D), microvascular volume fraction (f), perfusion-related incoherent microcirculation (D*), and perfusion parameter that is heavily weighted towards extravascular space (P) were determined geometrically (Geo D, Geo f, and Geo P) or by least-squares method (Fit D, Fit f, and Fit D*) in normal structures and 105 head and neck tumors. The IVIM parameters were compared for their levels and diagnostic abilities between the 2 techniques. The IVIM parameters were not able to determine in 14 tumors with the least-squares method alone and in 4 tumors with the geometric and least-squares methods. The geometric IVIM values were significantly different (p<0.001) from Fit values (+2±4% and −7±24% for D and f values, respectively). Geo D and Fit D differentiated between lymphomas and SCCs with similar efficacy (78% and 80% accuracy, respectively). Stepwise approaches using combinations of Geo D and Geo P, Geo D and Geo f, or Fit D and Fit D* differentiated between pleomorphic adenomas, Warthin tumors, and malignant salivary gland tumors with the same efficacy (91% accuracy = 21/23). However, a stepwise differentiation using Fit D and Fit f was less effective (83% accuracy = 19/23). Considering cumbersome procedures with the least squares method compared with the geometric method, we concluded that the geometric determination of IVIM parameters can be an alternative to least-squares method in the diagnosis of head and neck tumors.

Aberrant expression of interferon regulatory factor 3 in human lung cancer

We analyzed the subcellular distributions and gene structures of interferon regulatory factor 3 (IRF3) transcription factor in 50 cases of human primary lung cancer. The immunohistochemical analyses revealed substantially aberrant IRF3 expression specific to the cancer lesions (2 and 6 tumors with nuclear staining, and 4 and 5 tumors with negative staining, in adenocarcinoma and squamous cell carcinoma, respectively), while the morphologically normal region around the tumors exhibited only cytoplasmic staining. In addition, we determined the sequence of the entire IRF3 coding region, and found two novel variants with the amino acid changes (S(175)(AGC)-->R(175)(CGC) and A(208)(GCC)-->D(208)(GAC)). The R(175) variant was also detected in a morphologically normal region around the nuclear staining squamous cell carcinoma, and exhibited almost the same functions as the wild type IRF3. On the other hand, the D(208) variant, found in the negative staining squamous cell carcinoma cases, reduced the nuclear translocation in response to IkappaB kinase epsilon stimulation, as compared to the wild type IRF3, but the same variant was detected in the surrounding morphologically normal region. The aberrant expression of IRF3 and the novel D(208) variant may provide clues to elucidate the etiology of primary lung cancer.

GSK-3β-dependent downregulation of γ-taxilin and αNAC merge to regulate ER stress responses

The signaling pathway leading to the endoplasmic reticulum (ER) stress responses has not been fully elucidated. Here we showed that glycogen synthase kinase-3β (GSK-3β)-dependent downregulation of γ-taxilin and nascent polypeptide-associated complex α-subunit (αNAC) mediates hypoxia-induced unfolded protein responses (UPRs) and the subsequent apoptotic and autophagic pathways. The degradation of γ-taxilin or αNAC was sufficient to initiate UPRs in normoxic cells. However, the ER stress signaling pathways initiated by γ-taxilin or αNAC were distinct, triggering different ER stress sensors and activating different downstream pathways. Hypoxia caused GSK-3β-dependent tau hyperphosphorylation and cleavage in neuronal cells, but γ-taxilin ablation induced tau hyperphosphorylation alone and αNAC ablation induced neither changes. Notably, downregulation of γ-taxilin and αNAC occurs in the brain of patients with Alzheimer’s disease. These results suggest that GSK-3β-dependent downregulation of γ-taxilin and αNAC, which differently activate the UPRs, merge to regulate hypoxia-induced ER stress responses and provide a new insight into the pathogenesis of neurodegenerative diseases.

Comparison between ultrasonography and MR imaging for discriminating squamous cell carcinoma nodes with extranodal spread in the neck

OBJECTIVE To compare the diagnostic ability of ultrasonography (US) and MR imaging for discriminating squamous cell carcinoma (SCC) nodes with extranodal spread (ENS) in the neck. METHODS US and MR imaging was retrospectively evaluated for differentiating ENS-positive (n=28) from ENS-negative (n=26) SCC nodes (>10mm short-axis diameter) in 50 patients with head and neck SCCs. We assessed nodal size on US and MR images; irregular nodal margin on US; and vanishing nodal border, flare, and shaggy nodal margin signs on T1-, fat-suppressed T2-, and contrast-enhanced T1-weighted MR images, respectively. US and MR images were analyzed by 3 radiologists in consensus and the results were compared between ENS-positive and ENS-negative SCC nodes. RESULTS The nodal sizes of ENS-positive nodes (21±9 mm) were significantly larger than those of ENS-negative SCC nodes (14±4 mm) (p<0.001). Irregular nodal margins were more frequently observed in ENS-positive SCC nodes (75%) than in ENS-negative SCC nodes (12%). The vanishing nodal margin, flare, and shaggy nodal margin signs were more frequently observed in ENS-positive SCC nodes (93%, 89%, and 82%, respectively) than in ENS-negative nodes (46%, 19%, and 19%, respectively). A combination of size (≥22 mm) and imaging criteria (irregular margin or flare sign) best discriminated ENS-positive SCC nodes with 82% sensitivity, 89% specificity, and 85% accuracy for US and 89% sensitivity, 81% specificity, and 85% accuracy for MR imaging. CONCLUSION US discriminated ENS-positive from ENS-negative SCC nodes with comparable accuracy and higher specificity than MR imaging.

Magnetic resonance imaging-based differentiation between juvenile recurrent parotitis and juvenile Sjögren’s syndrome

Differentiation between juvenile recurrent parotitis and juvenile Sjögren’s syndrome may be difficult on the basis of clinical symptoms and imaging examinations, such as sialography and ultrasonography. Histological findings of the labial glands may also not be definitive for this purpose. Here, we report three cases of patients with juvenile recurrent parotitis who underwent magnetic resonance imaging examinations. The imaging results suggest that magnetic resonance imaging may be an effective tool for differentiating between these two distinct salivary gland diseases.

Perfusion MR imaging detection of carcinoma arising from preexisting salivary gland pleomorphic adenoma by computer-assisted analysis of time-signal intensity maps

Tumor perfusion can be evaluated by analyzing the time-signal intensity curve (TIC) after dynamic contrast-enhanced (DCE) MR imaging. Accordingly, TIC profiles are characteristic of some benign and malignant salivary gland tumors. A carcinoma ex pleomorphic adenoma (CXPA) arises from a long-standing pleomorphic adenoma (PA) and has a distinctive prognostic risk depending on the tumor growth potential such as invasion beyond the preexisting capsule. Differentiating CXPA from PA can be very challenging. In this study, we have attempted to discriminate CXPA from PA based on a two-dimensional TIC mapping algorithm. TIC mapping analysis was performed on 8 patients with CXPA and 20 patients with PA after dynamic contrast-enhanced (DCE) MR imaging using a 1.5-T MR system. The TIC profiles obtained were automatically categorized into 5 types based on the enhancement ratio, maximum time, and washout ratio (Type 1 TIC with flat profile, Type 2 TIC with slow uptake, Type 3 TIC with rapid uptake and a low washout ratio, Type 4 TIC with rapid uptake and a high washout ratio, and Type 5 TIC not otherwise specific). The percentage tumor areas with each of the 5 TIC types were compared between CXPAs and PAs. Stepwise differentiation and cluster analysis using multiple TIC cut-off thresholds distinguished CXPAs from PAs with 75% sensitivity, 95% specificity, 86% accuracy, and 86% positive and 90% negative predictive values, when tumors with ≤1.1% Type 1 and ≥15% Type 4, or those with ≤1.1% Type 1, ≥78.1% Type 2, ≥16.1% Type 3, and <15% Type 4, or those with >1.1% Type 1, ≥78.1% Type 2, and ≥16.1% Type 3 areas were diagnosed as CXPAs. The overall TIC profiles predicted some aggressive CXPA growth patterns. These results suggest that stepwise differentiation based on TIC mapping is helpful in differentiating CXPAs from PAs.

Magnetic resonance perfusion and diffusion characteristics of granulomatous diseases mimic those of malignant lesions: six case reports

The perfusion and diffusion properties of a tumor are important clues in evaluating its growth potential and predicting its histological type, such as benign or malignant. Tumor perfusion can be estimated by assessing time-dependent changes in the intratumoral levels of the contrast agent during dynamic contrast-enhanced magnetic resonance (MR) imaging, whereas tumor diffusion can be estimated by assessing intratumoral water diffusivity on diffusion-weighted MR imaging. Granulomatous diseases with different etiologies occur in various head and neck regions, including the mandible, maxillary sinus, salivary glands, and lymph nodes. However, the perfusion and diffusion properties of granulomatous diseases in the head and neck regions are not well documented. In this study, we assessed the time–signal intensity curves and apparent diffusion coefficients of six granulomatous diseases of various histological types that appeared in the soft tissues of the head and neck. Our data show that the perfusion and diffusion characteristics of granulomatous diseases mimic those of malignant diseases, highlighting the need for careful interpretation of MR perfusion and diffusion findings to distinguish between granulomatous diseases and cancers of the head and neck region. Clinicians should pay particular attention to blood examination and biopsy results when interpreting imaging findings.