Signal transduction involved in CTGF-induced production of chemokines in mesangial cells

Objective and design. This study investigates the regulatory role of connective tissue growth factor (CTGF) on production of fractalkine, monocyte-chemoattractant protein-1 (MCP-1) and regulated on activation, normal T cell expressed and secreted (RANTES) in human mesangial cells, and explore the mechanisms of CTGF action.

Methods. Cultured human mesangial cells were treated with CTGF. Expressions of mRNA and proteins of fractalkine, MCP-1 and RANTES were analyzed by real-time polymerase chain reaction (PCR) and by enzyme-linked immunosorbent assay, respectively. Expressions of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), phosphoinositide 3-kinase (PI3-K) and protein kinase B (PKB) were assessed by Western blotting. Activities of nuclear factor-κB (NF-κB) were determined by NF-κB luciferase reporter assay.

Results. CTGF enhanced the mRNA expressions and protein release of fractalkine, MCP-1 and RANTES, and the expressions of phosphorylated ERK1/2, PI3-K and PKB, and activities of NF-κB. Blockade of ERK1/2 inhibited the CTGF-induced expression of phosphorylated ERK1/2 and NF-κB, and partially decreased the expressions of the above chemokines. PI3-K blockade downregulated the CTGF-stimulated expressions of phosphorylated PI3-K, PKB and NF-κB but not phosphorylated ERK1/2, partially decreased the expressions of the above chemokines. NF-κB blockade abrogated the CTGF-activated NF-κB and partially decreased the expressions of the above chemokines. Soluble heparin and K252a, an inhibitor of Trk, blocked CTGF-induced production of the above chemokines and the activation of the above signaling proteins.

Conclusion. These results demonstrated that CTGF induces production of fractalkine, MCP-1 and RANTES via ERK1/2 and PI3-K/PKB/NF-κB-dependent signal pathway mediated by cell surface heparin sulfate proteoglycans and the tyrosine kinase receptor TrkA in human mesangial cells.     

脂氧素A4拮抗肿瘤坏死因子α对系膜细胞Jak1/STAT3途径的活化

目的：验证脂氧素A4(LXA4) 是否抑制肿瘤坏死因子α(TNFα) 所致的大鼠肾小球系膜细胞的增殖，并探讨其作用中信号转导的分子机制。 方法： 对体外培养的大鼠肾小球系膜细胞，用不同浓度的LXA4 预刺激，再加入TNFα共同孵育，或单用TNFα刺激系膜细胞。用MTT渗入法检测细胞的增殖。用凝胶电泳迁移率试验（EMSA）检测信号转导子和转录激活子-3（STAT3）的活性。用RT-PCR法检测细胞周期素E的mRNA表达。用Western blotting法检测细胞周期素E的蛋白表达量。结果： LXA4呈剂量依赖性地抑制TNFα诱导的肾小球系膜细胞的增殖、STAT3结合活性增加、细胞周期素E mRNA表达与蛋白合成的亢进。结论： LXA4能够抑制TNFα所致的大鼠系膜细胞的增殖，其机制可能是阻断Jak1/STAT3信号转导途径。     

Coronarin D suppresses proliferation,invasion and migration of glioma cells via activating JNK signaling pathway

Coronarin D (CD) is one of the primary components of the Hedychium coronarium rhizomes and possesses strong anticancer effects via preventing cell growth in many cancer cells. The study was aimed to explore the molecular mechanisms underlying effects of CD on proliferation, invasion and migration of gliomas cells. Gliomas cell lines U251 was employed for detecting cells viability and proliferation by Cell Counting Kit-8 assay and colony formation assay. In addition, scratch wound healing and transwell assays were performed for the analysis of U251 cells invasion and migration respectively. Furthermore, the expression of p-Akt/Akt, p-p38/p38, p-ERK/ERK, p-JNK/JNK, p-STAT3/STAT3, cyclinE, cyclinD1, CTGF, MMP-2 and MMP-9 were measured by Western blotting. CD could suppress proliferation, invasion and migration of glioma cells and induced reduction of cyclinE, cyclinD1, CTGF, MMP-2 and MMP-9 expression via activating JNK signaling pathway. CD treatment suppressed expression of p-AKT, p38, and ERK and elevated expression of p-JNK in concentration- and time-dependent manners. Moreover, CD significantly induced reduction of phosphorylated STAT3 expression. Exposure of cells to the JNK-specific inhibitor SP600125 reduced the cytotoxicity effects of CD, combination of CD and SP600125 corrected overexpression of phosphorylated JNK and reduction of phosphorylated STAT3. Pretreatment of SP600125 also improves gliomas cells viability and invasion. The results revealed that CD may remarkably suppress gliomas cell growth through JNK and STAT3 signaling. In present study, these findings revealed that CD induces suppression of cell viability in gliomas cells and possesses therapeutic effect on gliomas.     

心肌营养素-1在心肌成纤维细胞增殖中的作用

目的：探讨心肌营养素-1（CT-1）在高血压心室重塑中的作用。方法：3-4代心肌成纤维细胞用于实验，分为对照组、助溶剂（二甲亚砜，DMSO）组、CT-1反义寡核苷酸组（ASODN）、正义寡核苷酸对照组（SODN）、PD98059组、AG490组、LY294002组。利用自制压力培养装置，将各组细胞置于160 mmHg压力下培养8 h。 STAT3、ERK1/2和PI3-K的活性通过Western blotting分析测定；MTT测定心肌成纤维细胞增殖。结果：高静水压明显促进心肌成纤维增殖，CT-1表达上调，CT-1ASODN干预后，CT-1ASODN能抑制高静水压所致的细胞增殖（0.132±0.013 vs 0.154±0.011，P<0.05），STAT3、ERK1/2和 PI3-K蛋白表达水平明显低于对照组（2.09±0.25 vs 2.47±0.28,P<0.05)、(1.13±0.19 vs 1.61±0.22,P<0.05)、（1.25±0.23 vs1.71±0.25,P<0.05)。AG490组明显减弱高静水压的促增殖作用（0.118±0.018 vs 0.155±0.010，P<0.05）并且增加ERK1蛋白磷酸化（1.85±0.18 vs 1.45±0.23，P<0.05）;PD98059增强高静水压的促增殖（0.185±0.011 vs 0.155±0.010，P<0.05）并且增加STAT3蛋白磷酸化（1.83±0.23 vs 1.58±0.22，P<0.05）, PI3/K阻断剂LY294002干预后对高静水压的促增殖作用无影响（0.157±0.015 vs 0.155±0.010，P>0.05）；SOND (0.151±0.010 vs 0.154±0.011, P>0.05) 和DMSO组(0.141±0.017 vs 0.155±0.010, P>0.05)与对照组相比对心肌成纤维细胞增殖无明显差别。结论：高静水压下，心肌成纤维细胞增殖主要通过STAT3通路；ERK1/2通路通过抑制STAT3的活性起负向调节作用，可能在防止心肌成纤维细胞过度增殖起重要的作用；PI3-K没有参与这一作用。上述STAT3通路与ERK1/2通路之间的相互作用可能有助于防止诱导成纤维细胞过度增殖。     

Regulation of DNA synthesis in mouse embryonic stem cells by transforming growth factor-alpha: involvement of the PI3-K/Akt and Notch/Wnt signaling pathways

This study examined the mechanisms by which transforming growth factor (TGF)-alpha regulates proliferation of mouse embryonic stem (ES) cells. TGF-alpha increased [3H] thymidine and BrdU incorporation in a time- (0-72 h) and dose-dependent (0-10 ng/ml) manner. TGF-alpha stimulated the phosphorylation of Akt, mammalian target of rapamycin (mTOR), p70S6K1 and p44/42 mitogen-activated protein kinases (MAPKs). TGF-alpha also increased the protein levels of Notch, Notch intracellular domain, Hes-1 and Wnt1. However, TGF-alpha-induced DNA synthesis was blocked by inhibition of Akt, mTOR, p44/42 MAPKs and Notch. TGF-alpha increased the gene expression of c-jun, c-myc and c-fos. Moreover, TGF-alpha increased cyclin D/CDK 4 and cyclin E/CDK 2 levels, while decreasing p21cip1/waf1 and p27kip1, which were blocked by the inhibition of Akt, mTOR and Notch. In conclusion, TGF-alpha regulated DNA synthesis of mouse ES cells via PI3-K/Akt, p44/42 MAPKs and Notch/Wnt pathways.     

Mycophenolate mofetil and roscovitine decrease cyclin expression and increase p27(kip1) expression in anti Thy1 mesangial proliferative nephritis

The response of mesangial cells to a phlogistic challenge includes cell proliferation and mesangial matrix expansion. Cell proliferation is a highly regulated process which includes enhancing factors such as cyclins, cyclin dependent kinases, and inhibitory proteins, such as p27(kip1). The aim of the study was to evaluate the effects of Mycophenolate mofetil (MMF), and roscovitine (R), on the cell cycle regulatory system when administered in the florid phase of the experimental model of mesangial proliferative nephritis induced by the anti Thy-1 antigen monoclonal antibody. Three days after nephritis induction, different groups were given MMF and R. Rats treated with MMF or R showed a slight decrease in mesangial proliferation and matrix expansion. Samples of cortical tissue were tested by 'real time' RT-PCR in order to study gene expression of cyclins B, D1, D2, D3, E, and the cyclin inhibitor p27(kip1). Localization of mRNA was evaluated by in situ hybridization. Real time RT-PCR analysis showed a significant decrease in cyclins B, D1, D2, and D3 in rats treated with either MMF or R as compared to controls. Both MMF and R treatment induced a significant increase in p27(kip1) mRNA expression. In situ hybridization showed a mesangial-endothelial expression pattern in glomeruli. The number of labelled cells per glomerulus, the number of positive glomeruli in each examined slide as well as cyclin D2 and D3 signal intensity was significantly lower in rats treated with MMF or R as compared to controls, whereas MMF or R treatment up-regulated p27(kip1) mRNA expression. Immunohistochemical evaluation of p27(kip1) aimed to examine the influence of MMF or R on protein expression confirmed up-regulation.     

肾癌中cyclinD1和p27kip1的表达及其意义

目的探讨cyc lin D1、p27k ip1在普通型肾细胞癌(renal cell carc inom a,RCC)发生、发展中的作用。方法用半定量RT-PCR方法检测25例普通型RCC和10例肿瘤远端的正常肾组织中cyc lin D1的mRNA含量,用免疫组化方法检测76例普通型RCC中cyc lin D1和p27k ip1蛋白的表达,并对cyc lin D1、p27k ip1蛋白表达与临床病理参数的关系进行分析。结果普通型RCC中cyc lin D1的mRNA含量0.488±0.399,高于正常对照组0.089±0.066(P<0.01)。cyc lin D1的表达与肿瘤体积大小有关,体积大者cyc lin D1高表达(P<0.05)。普通型RCC中p27k ip1表达低于正常对照组,随着p27k ip1表达的降低,肿瘤的细胞核Fu-hrm an分级、TNM分期增高。结论cyc lin D1高表达和p27k ip1的低表达与普通型RCC的发生有关;p27k ip1的低表达可能促进肿瘤的演进,p27k ip1的表达可作为评价普通型RCC预后的参考指标。     

ERK1/2和PI3-K通路在蛛网膜下腔出血大鼠海马区对神经细胞自噬的调控作用

目的:探讨细胞外信号调节激酶(extracellular regulated protein kinases,ERK1/2)和磷脂酰肌醇3-激酶(phosphatidylinositol 3-kinase,PI3-K)通路对大鼠蛛网膜下腔出血(subarachnoid hemorrhage,SAH)后神经细胞自噬的调控作用。方法:雄性SD大鼠160只,分为假手术(Sham)组、模型(SAH)组、ERK1/2抑制剂U0126组和PI3-K抑制剂LY294002组。采用二次注血法制作SAH大鼠模型,HE染色观察海马区神经细胞的形态变化;免疫组织化学染色法检测海马区磷酸化ERK1/2、PI3-K、自噬相关蛋白Beclin-1和微管相关蛋白1轻链(LC3)-II的表达实时荧光定量PCR检测海马区ERK1/2、PI3-K、自噬相关蛋白Beclin-1和微管相关蛋白LC3的表达。结果:SAH组海马区神经细胞存活率低于Sham组,ERK1/2、PI3-K、Beclin-1和LC3的表达水平高于Sham组(P0.05);U0126组和LY294002组海马区神经细胞存活率均高于SAH组,ERK1/2、PI3-K、Beclin-1和LC3表达均低于SAH组(P0.05);U0126组和LY294002组两组间海马区神经细胞存活率差异无统计学意义(P0.05),U0126组ERK1/2、Beclin-1和LC3表达水平低于LY294002组(P0.05),PI3-K表达水平高于LY294002组(P0.05)。结论:ERK1/2和PI3-K通路激活共同参与SAH后神经细胞自噬的调节,且以PI3-K通路更为主要。     

Biological characteristics of multiple myeloma

On a series of thirty trephine bone marrow biopsies from patients with multiple myeloma, the authors evaluated expression of markers of cell proliferation or of its blockade (Ki-67, PCNA, topoisomerase IIa, cyclin D-1, AgNOR, and p27kip1) and markers indicating multidrug resistance (P-170 and Bcl-2). Expression of Ki-67 and of topoisomerase IIa was unfrequent. Marked positivity of PCNA was expressed in about one third of cases, negative staining was exceptional. No expression of cyclin D-1 was noted. Positivity of p27kip1 was frequent. P-170 was demonstrated in a small number of cases, Bcl-2 was strongly positive in most cases. The results characterise multiple myeloma as a tumour with low proliferation rate and, simultaneously, with high resistance to apoptosis.     

Interferon-gamma inhibits hepatocyte growth factor-stimulated cell proliferation of human bronchial epithelial cells: upregulation of p27(kip1) cyclin-dependent kinase inhibitor.

Proliferation of bronchial epithelial cells is an important biologic process in a variety of physiologic and pathologic conditions. In this study, we demonstrate that hepatocyte growth factor (HGF) stimulates proliferation of human bronchial epithelial cells obtained from healthy volunteers. The mitogenic effect of HGF is dependent on costimulation with serum and is completely abrogated by interferon-gamma (IFN-gamma). In the absence of serum, HGF is capable of inducing activation of extracellular signal-regulated kinases (ERK)1 and ERK2, but fails to stimulate proliferation by itself. These effects of HGF and IFN-gamma were reproduced faithfully in BEAS-2B cells, which are an immortalized cell line derived from human bronchial epithelial cells. Further, we investigated the molecular mechanisms underlying the effects of HGF and IFN-gamma in BEAS-2B cells and found that the MEK1 inhibitor PD98059, but not the p38 M-associated protein kinase inhibitor SB203580, abrogates HGF-induced ERK activation and proliferation in response to HGF and serum. In addition, LY294002, which is the specific inhibitor of phosphatidyl inositol 3-kinase, partially inhibited HGF- and serum-stimulated proliferation. We also found that HGF by itself is capable of inducing a G1 cyclin, cyclin D1, but fails to downregulate p27(kip1) cyclin-dependent kinase (CDK) inhibitor, which is a requisite for G1 to S phase cell cycle progression. IFN-gamma does not interfere with the effects of HGF on either ERK activation or cyclin D1 induction; however, it prevents the downregulation of p27(kip1) CDK inhibitor that takes place in response to a combination of HGF and serum. These results indicate that the MEK-ERK signaling pathway is necessary but not sufficient for human bronchial epithelial cell proliferation, and implicate the significance of HGF and IFN-gamma in the repair processes of injured human bronchial epithelial cells.     

Activated Akt as an indicator of prognosis in gastric cancer

The immunohistochemical expression of phosphorylated (activated) Akt (pAkt) in 50 advanced gastric carcinomas has been analyzed and the results correlated with age, sex, location in the stomach, histotype, stage, survival, mitotic and apoptotic index, some cell cycle regulators (cyclin D1, cyclin E, p34/cdc2, p27/kip1), and cell proliferation. There was a statistically significant direct correlation between pAkt expression (both cytoplasmatic and nuclear) and depth of infiltration of the tumor, number of infiltrated lymph nodes and p34/cdc2 expression, and between prevalently nuclear pAkt and cyclin D1 and cyclin E. Conversely, there was a significant inverse correlation between nuclear pAkt and apoptotic index and between cytoplasmatic and nuclear pAkt and patient survival. No correlation was found between pAkt and sex, age, tumor location, histotype, mitotic index, and cell proliferation. These findings suggest that pAkt may be considered an indicator of tumor progression and patient survival in gastric cancer.     

Lipoxins inhibit Akt/PKB activation and cell cycle progression in human mesangial cells

Lipoxins (LX) are endogenously produced eicosanoids with a spectrum of bioactions that suggest anti-inflammatory, pro-resolution roles for these agents. Mesangial cell (MC) proliferation plays a pivotal role in the pathophysiology of glomerular inflammation and is coupled to sclerosis and tubulointerstitial fibrosis. We have previously reported that LXA4 acts through a specific G-protein-coupled-receptor (GPCR) to modulate MC proliferation in response to the proinflammatory mediators LTD4 and platelet-derived growth factor (PDGF). Further investigations revealed that these effects were mediated by modulation of receptor tyrosine kinase activity. Here we have explored the underlying mechanisms and report inhibition of growth factor (PDGF; epithelial growth factor) activation of Akt/PKB by LXA4. LXA4 (10 nmol/L) modulates PDGF-induced (10 ng/ml, 24 hours) decrements in the levels of cyclin kinase inhibitors p21Cip1 and p27Kip1. PDGF-induced increases in CDK2-cyclin E complex formation are also inhibited by LXA4. The potential of LXA4 as an anti-inflammatory therapeutic is compromised by its degradation; this has been circumvented by synthesis of stable analogs. We report that 15-(R/S)-methyl-LXA4 and 16-phenoxy-LXA4 mimic the native compound with respect to modulation of cell proliferation and PDGF-induced changes in cell cycle proteins. In vivo, MC proliferation in response to PDGF is associated with TGFbeta1 production and the subsequent development of renal fibrosis. Here we demonstrate that prolonged (24 to 48 hours) exposure to PDGF is associated with autocrine TGFbeta1 production, which is significantly reduced by LXA4. In aggregate these data demonstrate that LX inhibit PDGF stimulated proliferation via modulation of the PI-3-kinase pathway preventing mitogen-elicited G1-S phase progression and suggest the therapeutic potential of LX as anti-fibrotic agents.     

Regulation of DNA synthesis in mouse embryonic stem cells by transforming growth factor-α: Involvement of the PI3-K/Akt and Notch/Wnt signaling pathways

This study examined the mechanisms by which transforming growth factor (TGF)-α regulates proliferation of mouse embryonic stem (ES) cells. TGF-α increased [³H] thymidine and BrdU incorporation in a time- (0–72 h) and dose-dependent (0–10 ng/ml) manner. TGF-α stimulated the phosphorylation of Akt, mammalian target of rapamycin (mTOR), p70S6K1 and p44/42 mitogen-activated protein kinases (MAPKs). TGF-α also increased the protein levels of Notch, Notch intracellular domain, Hes-1 and Wnt1. However, TGF-α-induced DNA synthesis was blocked by inhibition of Akt, mTOR, p44/42 MAPKs and Notch. TGF-α increased the gene expression of c-jun, c-myc and c-fos. Moreover, TGF-α increased cyclin D/CDK 4 and cyclin E/CDK 2 levels, while decreasing p21^cip1/waf1 and p27^kip1, which were blocked by the inhibition of Akt, mTOR and Notch. In conclusion, TGF-α regulated DNA synthesis of mouse ES cells via PI3-K/Akt, p44/42 MAPKs and Notch/Wnt pathways.     

Complex regulation of the cyclin-dependent kinase inhibitor p27kip1 in thyroid cancer cells by the PI3K/AKT pathway: regulation of p27kip1 expression and localization

Functional inactivation of the tumor suppressor p27(kip1) in human cancer occurs either through loss of expression or through phosphorylation-dependent cytoplasmic sequestration. Here we demonstrate that dysregulation of the PI3K/AKT pathway is important in thyroid carcinogenesis and that p27(kip1) is a key target of the growth-regulatory activity exerted by this pathway in thyroid cancer cells. Using specific PI3K inhibitors (LY294002, wortmannin, and PTEN) and a dominant active AKT construct (myrAKT), we demonstrated that the PI3K/AKT pathway controlled thyroid cell proliferation by regulating the expression and subcellular localization of p27. Results obtained with phospho-specific antibodies and with transfection of nonphosphorylable p27(kip1) mutant constructs demonstrated that PI3K/AKT-dependent regulation of p27(kip1) mislocalization in thyroid cancer cells occurred via phosphorylation of p27(kip1) at T157 and T198 (but not at S10 or T187). Finally, we evaluated whether these results were applicable to human tumors. Analysis of 100 thyroid carcinomas indicated that p27(kip1) phosphorylation at T157/T198 and cytoplasmic mislocalization were preferentially associated with activation of the PI3K/AKT pathway. Thus the PI3/AKT pathway and its effector p27(kip1) play major roles in thyroid carcinogenesis.     

釉原蛋白羧基末端肽加速细胞周期促进成釉细胞系ALC细胞增殖

ORCID: 0000-0003-4338-4123(刘敏) 中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程     

CD28 induces cell cycle progression by IL-2-independent down-regulation of p27kip1 expression in human peripheral T lymphocytes

CD28 is the primary T cell costimulatory receptor, and upon ligation with its ligands, it enhances T cell proliferation and IL-2 synthesis. In this study we examined the role of CD28 in the initial proliferative response and cell cycle entry of T lymphocytes. Stimulation through CD3 alone resulted in a poor proliferative response, while in the presence of CD28 costimulation a strong increase in the number of cells in S-phase could be detected after 48 h of stimulation. CD28 costimulation enhanced expression of cyclin D3 and induced down-regulation of p27kip1 expression. Cross-linking CD28 was much more effective in inducing cyclin D3 expression and in down-regulating p27kip1 expression than addition of IL-2. Blocking experiments, using antibodies that neutralize IL-2 or the IL-2 receptor, showed that the effects induced by CD28 are independent of endogenous IL-2. Moreover, using a variety of immunosuppressants that interfere with IL-2 signaling pathways, we were able to show that IL-2 is not required for cell cycle entry induced by CD28 costimulation. From these experiments it can be concluded that CD28 and IL-2 use different signaling pathways for down-regulation of p27kip1 expression. We hypothesize that costimulation through CD28 is responsible for initial cell cycle entry of T lymphocytes, while IL-2, which is produced after costimulation, might be involved in sustaining proliferation.     

Cell Cycle Regulatory Proteins p27(kip), Cyclins Dl and E and Proliferative Activity in Oncocytic (Hurthle Cell) Lesions of the Thyroid

Cyclins are prime cell-cycle regulators central to the control of cell proliferation in eukaryotic cells. The formation of cyclin/cyclin-dependent kinases (CDK) complexes activates the kinases and initiates a cascade of events, which directs cells through the cell cycle. CDK inhibitors (CDKIs) such as p27^kip1 inhibit cyclin-CDK complexes and function as negative regulators of the cell cycle. Previous studies have shown that p27^kip1 is decreased in malignant relative to benign thyroid tumors, but its role and interaction with other cell cycle regulatory proteins have not been well established in oncocytic lesions of the thyroid. We studied the expression of p27^kip1, cyclins D1 and E, and Ki67 in 20 cases of oncocytic adenoma (AD), 6 cases of oncocytic carcinoma (CA), 8 cases of Hashimoto’s thyroiditis (HT), and 9 cases of nodular goiter with oncocytic change (NG) by immunohistochemistry. In the latter two lesions only oncocytic cells were evaluated. The positive staining was stratified into four groups. Statistical analysis was done using the Kruskal-Wallis one-way analysis of variance test, and, when significant, the Dunn multiple-comparisons procedure was used to determine pairwise differences. All 20 AD were p27^kip1 positive, 10 were 4+, 2 were 3+, and the remaining 8 were 1+. In contrast all 6 CA showed 4+ p27^kip1 staining, of the 8 HT, 2 were 4+, two 3+, three 1+, and 1 was negative. All 9 NG were p27 positive, 7 showed 4+, one 3+, and one 1+ staining. On pairwise comparison differences in p27^kip1 staining between AD and CA and between HT and CA were statistically significant (p=0.0243 and p=0.0142, respectively). In all but one case Ki67 expression was either very low (<3%) or negative. No significant differences were seen in the expression of cyclin D1 or cyclin E among the groups observed. In conclusion, the increased p27^kip1 expression in malignant oncocytic tumors relative to benign oncocytic lesions is unlike any other malignant progression reported in the thyroid and other organ systems in the body. This may reflect on the biologic nature of the oncocytic cells of the thyroid and the significance of this finding remains to be established. Proliferative activity as studied by Ki67 immunostaining was not helpful in distinguishing benign from malignant oncocytic tumors.