Clinical, histopathological, and molecular features of IDH-wildtype indolent diffuse glioma: comparison with typical glioblastoma.

PURPOSE: IDH-wildtype (IDHwt) diffuse gliomas are treated as glioblastoma, however, some of these may show less aggressive clinical courses. The authors investigated the clinical, histopathological, and molecular characteristics of such IDHwt indolent diffuse gliomas (iDGwt), which have not been well documented in the literature. METHODS: Adult patients with IDHwt gliomas admitted between 2011 and 2020 were surveyed. In this particular study, the clinical indolence was defined mainly as having a small enhancing lesion and a stable period for more than 1 month before surgery. The current WHO diagnostic criteria were adapted for the diagnoses. Gene mutations and copy number changes in 43 representative glioma-associated genes, MGMT promoter methylation status, and survival data were compared with those of The Cancer Genome Atlas reference cohort. RESULTS: Nine out of 180 surveyed cases (5.0%) fulfilled the present criteria of the iDGwt. Considering the representative regulatory pathways, 8 (88.9%), 4 (44.4%), and 1 (11.1%) case had genetic alterations in the PI3K/MAPK, TP53, and RB pathways, respectively. The frequency of the RB pathway alteration was significantly lower than that in the reference cohort (281 of 362 cases: 77.6%). Two cases (22.2%) showing EGFR amplification met the diagnostic criteria for glioblastoma, and the frequency was significantly lower than that in the reference cohort (412 of 426 cases: 96.7%). The overall survival (median: 37.5 months) in the present series was significantly longer than that in the reference cohort (n = 426, median: 13.9 months). CONCLUSIONS: iDGwt lacked the molecular features of glioblastoma except for the PI3K/MAPK pathway alteration.

Peritumoral CD16b positive-neutrophil accumulation strongly correlates with regional lymph node metastasis in thoracic esophageal squamous cell cancer.

BACKGROUND: The mechanism underlying cancer cell metastasis from the tumor to regional lymph nodes is not yet fully understood. We hypothesized that peritumoral neutrophil accumulation promotes regional lymph node metastasis in thoracic esophageal squamous cell cancer. METHODS: Between 2010 and 2019, 126 thoracic esophageal squamous cell cancer patients received curative (R0) esophagectomy without preoperative treatment in our hospital. Using paraffin-embedded resected tumors, we performed immunohistochemical analysis of CD16b-positive neutrophil accumulation in the peritumoral area, which was defined as a 1-mm region centered on the border separating the malignant cell nests from the host tissue. The relationship between the density of peritumoral CD16b staining and pathological lymph node metastasis or 5-year overall survival was evaluated. RESULTS: Although the clinicopathological characteristics of CD16b-high and CD16b-low patients did not differ, greater pathological lymph node metastasis (P < .001) and lymphatic invasion by the tumor (P = .024) and a poorer 5-year survival (P = .010) were seen in CD16b-high patients. Moreover, CD16b-positive neutrophil density was generally higher in the peritumoral area than within the tumor itself. Univariate and multivariate analyses showed that CD16b-positive neutrophil accumulation was an independent factor for lymph node metastasis with an odds ratio >25 (P < .001). On the other hand, blood neutrophil counts did not correlate with lymph node metastasis. CONCLUSION: Peritumoral accumulation of CD16b-positive neutrophils is an independent factor strongly correlated with lymph node metastasis in thoracic esophageal squamous cell cancer.

Eosinophil ETosis-Mediated Release of Galectin-10 in Eosinophilic Granulomatosis With Polyangiitis.

OBJECTIVE: Eosinophils are tissue-dwelling immune cells. Accumulating evidence indicates that a type of cell death termed ETosis is an important cell fate involved in the pathophysiology of inflammatory diseases. Although the critical role of eosinophils in eosinophilic granulomatosis with polyangiitis (EGPA; formerly Churg-Strauss syndrome) is well established, the presence of eosinophil ETosis (EETosis) is poorly understood. We undertook this study to better understand the characteristics of EETosis. METHODS: In vitro studies using blood-derived eosinophils were conducted to characterize EETosis. The occurrence of EETosis in tissues from patients with EGPA was studied by immunostaining and electron microscopy. Serum concentrations of eosinophil-derived proteins in healthy controls, patients with asthma, and EGPA patients with active disease or with disease in remission (n = 15 per group) were examined. RESULTS: EETosis was reliant on reactive oxygen species and peptidylarginine deiminase type 4-dependent histone citrullination, resulting in the cytolytic release of net-like eosinophil extracellular traps, free galectin-10, and membrane-bound intact granules. The signature of EETosis, including loss of cytoplasmic galectin-10 and deposition of granules, was observed in eosinophils infiltrating various tissues from EGPA patients. Serum eosinophil granule proteins and galectin-10 levels were increased in EGPA and positively correlated with disease activity as assessed by the Birmingham Vasculitis Activity Score (r = 0.8531, P < 0.0001 for galectin-10). When normalized to blood eosinophil counts, this correlation remained for galectin-10 (r = 0.7168, P < 0.0001) but not for granule proteins. Galectin-10 levels in active EGPA positively correlated with serum interleukin-5 levels. CONCLUSION: Eosinophils infiltrating diseased tissues in EGPA undergo EETosis. Considering the exclusive expression and large pool of cytoplasmic galectin-10 in eosinophils, elevated serum galectin-10 levels in patients with EGPA might reflect the systemic occurrence of cytolytic EETosis.

Clonal hematopoiesis in adult pure red cell aplasia.

Idiopathic pure red cell aplasia (PRCA) and secondary PRCA associated with thymoma and large granular lymphocyte leukemia are generally considered to be immune-mediated. The PRCA2004/2006 study showed that poor responses to immunosuppression and anemia relapse were associated with death. PRCA may represent the prodrome to MDS. Thus, clonal hematopoiesis may be responsible for treatment failure. We investigated gene mutations in myeloid neoplasm-associated genes in acquired PRCA. We identified 21 mutations affecting amino acid sequences in 11 of the 38 adult PRCA patients (28.9%) using stringent filtering of the error-prone sequences and SNPs. Four PRCA patients showed 7 driver mutations in TET2, DNMT3A and KDM6A, and 2 PRCA patients carried multiple mutations in TET2. Five PRCA patients had mutations with high VAFs exceeding 0.3. These results suggest that clonal hematopoiesis by stem/progenitor cells might be related to the pathophysiology of chronic PRCA in certain adult patients.

B38-CAP is a bacteria-derived ACE2-like enzyme that suppresses hypertension and cardiac dysfunction.

Angiotensin-converting enzyme 2 (ACE2) is critically involved in cardiovascular physiology and pathology, and is currently clinically evaluated to treat acute lung failure. Here we show that the B38-CAP, a carboxypeptidase derived from Paenibacillus sp. B38, is an ACE2-like enzyme to decrease angiotensin II levels in mice. In protein 3D structure analysis, B38-CAP homolog shares structural similarity to mammalian ACE2 with low sequence identity. In vitro, recombinant B38-CAP protein catalyzed the conversion of angiotensin II to angiotensin 1-7, as well as other known ACE2 target peptides. Treatment with B38-CAP suppressed angiotensin II-induced hypertension, cardiac hypertrophy, and fibrosis in mice. Moreover, B38-CAP inhibited pressure overload-induced pathological hypertrophy, myocardial fibrosis, and cardiac dysfunction in mice. Our data identify the bacterial B38-CAP as an ACE2-like carboxypeptidase, indicating that evolution has shaped a bacterial carboxypeptidase to a human ACE2-like enzyme. Bacterial engineering could be utilized to design improved protein drugs for hypertension and heart failure.

Involvement of RSK1 activation in malformin-enhanced cellular fibrinolytic activity.

Pharmacological interventions to enhance fibrinolysis are effective for treating thrombotic disorders. Utilizing the in vitro U937 cell line-based fibrin degradation assay, we had previously found a cyclic pentapeptide malformin A1 (MA1) as a novel activating compound for cellular fibrinolytic activity. The mechanism by which MA1 enhances cellular fibrinolytic activity remains unknown. In the present study, we show that RSK1 is a crucial mediator of MA1-induced cellular fibrinolysis. Treatment with rhodamine-conjugated MA1 showed that MA1 localizes mainly in the cytoplasm of U937 cells. Screening with an antibody macroarray revealed that MA1 induces the phosphorylation of RSK1 at Ser380 in U937 cells. SL0101, an inhibitor of RSK, inhibited MA1-induced fibrinolytic activity, and CRISPR/Cas9-mediated knockout of RSK1 but not RSK2 suppressed MA1-enhanced fibrinolysis in U937 cells. Synthetic active MA1 derivatives also induced the phosphorylation of RSK1. Furthermore, MA1 treatment stimulated phosphorylation of ERK1/2 and MEK1/2. PD98059, an inhibitor of MEK1/2, inhibited MA1-induced phosphorylation of RSK1 and ERK1/2, indicating that MA1 induces the activation of the MEK-ERK-RSK pathway. Moreover, MA1 upregulated the expression of urokinase-type plasminogen activator (uPA) and increased uPA secretion. These inductions were abrogated in RSK1 knockout cells. These results indicate that RSK1 is a key regulator of MA1-induced extracellular fibrinolytic activity.

Sphingosine-1-phosphate/sphingosine kinase 1-dependent lymph node metastasis in esophageal squamous cell carcinoma.

PURPOSE: To establish whether Sphingosine-1-phosphate (S1P) and sphingosine kinase 1 (SphK1) contribute to lymph node metastasis in esophageal squamous cell carcinoma. METHODS: Immunohistochemical analysis of SphK1 expression was performed using a tissue microarray containing 177 thoracic squamous cell esophageal cancer specimens resected at surgery, to investigate the association between intratumoral SphK1 expression and lymph node metastasis. Serum S1P levels and intratumoral SphK1 mRNA and protein expression were also evaluated in mice with vs. mice without lymph node metastasis in a murine lymph node metastasis model. RESULTS: Among 177 esophageal cancer patients, 127 (72%) were defined as being SphK1-positive. In univariate and multivariate analyses, SphK1 expression status was a significant factor contributing to lymph node metastasis and poorer 5-year overall survival. In the murine lymph node metastasis model, there was no difference in tumor volume or weight between the lymph node metastasis-negative and lymph node metastasis-positive groups. However, levels of SphK1 mRNA and protein and serum S1P levels were all much higher in the metastasis-positive group. CONCLUSIONS: S1P/SphK1 may be novel targets for inhibiting lymph node metastasis in esophageal squamous cell carcinoma, and may provide the basis for a therapeutic strategy to suppress lymph node metastasis.

Cadmium-coordinated supramolecule suppresses tumor growth of T-cell leukemia in mice.

Cadmium is a toxic pollutant with occupational and environmental significance, due to its diverse toxic effects. Supramolecules that conjugate and decontaminate toxic metals have potential for use in treatment of cadmium intoxication. In addition, metal-coordinating ability has been postulated to contribute to the cytotoxic effects of anti-tumor agents such as cisplatin or bleomycin. Thiacalixarenes, cyclic oligomers of p-alkylphenol bridged by sulfur atoms, are supramolecules known to have potent coordinating ability to metal ions. In this study, we show that cadmium-coordinated thiacalix[4]arene tetrasulfate (TC4ATS-Cd) exhibits an anti-proliferative effect against T-cell leukemia cells. Cadmium exhibited cytotoxicity with IC50 values ranging from 36 to 129 µM against epithelia-derived cancer cell lines, while TC4ATS-Cd elicited no significant cytotoxicity (IC50 > 947 µM). However, a number of T-cell leukemia cell lines exhibited marked sensitivity to TC4ATS-Cd. In Jurkat cells, toxicity of TC4ATS-Cd occurred with an IC50 of 6.9 µM, which is comparable to that of 6.5 µM observed for cadmium alone. TC4ATS-Cd induced apoptotic cell death through activation of caspase-3 in Jurkat cells. In a xenograft model, TC4ATS-Cd (13 mg/kg) treatment significantly suppressed the tumor growth of Jurkat cells in mice. In addition, TC4ATS-Cd-treated mice exhibited significantly less cadmium accumulation in liver and kidney compared to equimolar cadmium-treated mice. These results suggest that cadmium-coordinated supramolecules may have therapeutic potential for treatment of T-cell leukemia.

REG Iα activates c-Jun through MAPK pathways to enhance the radiosensitivity of squamous esophageal cancer cells.

Identification of the key molecules that mediate susceptibility to anticancer treatments would be highly desirable. Based on clinical and cell biological studies, we recently proposed that regenerating gene (REG) Iα may be such a molecule. In the present study, we hypothesized that REG Iα increases radiosensitivity through activation of mitogen-activated protein kinase (MAPK) pathways. To test that idea, we transfected TE-5 and TE-9 squamous esophageal cancer cells with REG Iα and examined its involvement in MAPK signaling and its effect on susceptibility to radiotherapy. We found that REG Iα-expressing cells showed increased expression of c-Jun messenger RNA (mRNA) and phospho-c-Jun protein mediated via the c-Jun N-terminal kinase (JNK) pathway and extracellular signal-regulated kinase (ERK) pathway, as well as increased radiosensitivity. Immunohistochemical analysis confirmed the activation of c-Jun in tumors expressing REG Iα. Collectively, these findings suggest that REG Iα activates c-Jun via the JNK and ERK pathway, thereby enhancing radiosensitivity.

Identification of recurrent SMO and BRAF mutations in ameloblastomas.

Here we report the discovery of oncogenic mutations in the Hedgehog and mitogen-activated protein kinase (MAPK) pathways in over 80% of ameloblastomas, locally destructive odontogenic tumors of the jaw, by genomic analysis of archival material. Mutations in SMO (encoding Smoothened, SMO) are common in ameloblastomas of the maxilla, whereas BRAF mutations are predominant in tumors of the mandible. We show that a frequently occurring SMO alteration encoding p.Leu412Phe is an activating mutation and that its effect on Hedgehog-pathway activity can be inhibited by arsenic trioxide (ATO), an anti-leukemia drug approved by the US Food and Drug Administration (FDA) that is currently in clinical trials for its Hedgehog-inhibitory activity. In a similar manner, ameloblastoma cells harboring an activating BRAF mutation encoding p.Val600Glu are sensitive to the BRAF inhibitor vemurafenib. Our findings establish a new paradigm for the diagnostic classification and treatment of ameloblastomas.

Ameloblastin in Hertwig's epithelial root sheath regulates tooth root formation and development.

Tooth root formation begins after the completion of crown morphogenesis. At the end edge of the tooth crown, inner and outer enamel epithelia form Hertwig's epithelial root sheath (HERS). HERS extends along with dental follicular tissue for root formation. Ameloblastin (AMBN) is an enamel matrix protein secreted by ameloblasts and HERS derived cells. A number of enamel proteins are eliminated in root formation, except for AMBN. AMBN may be related to tooth root formation; however, its role in this process remains unclear. In this study, we found AMBN in the basal portion of HERS of lower first molar in mice, but not at the tip. We designed and synthesized small interfering RNA (siRNA) targeting AMBN based on the mouse sequence. When AMBN siRNA was injected into a prospective mandibular first molar of postnatal day 10 mice, the root became shorter 10 days later. Furthermore, HERS in these mice revealed a multilayered appearance and 5-bromo-2'-deoxyuridine (BrdU) positive cells increased in the outer layers. In vitro experiments, when cells were compared with and without transiently expressing AMBN mRNA, expression of growth suppressor genes such as p21(Cip1) and p27(Kip1) was enhanced without AMBN and BrdU incorporation increased. Thus, AMBN may regulate differentiation state of HERS derived cells. Moreover, our results suggest that the expression of AMBN in HERS functions as a trigger for normal root formation.

Anti-melanogenesis effect of Glechoma hederacea L. extract on B16 murine melanoma cells.

Glechoma hederacea L. (Labiatae) has been used in folk medicine to treat various ailments for centuries. We investigated the effects of G. hederacea extract on melanogenesis in B16 melanoma cells. It significantly reduced both the cellular melanin content and tyrosinase activity in a concentration-dependent manner. An MTT assay did not reveal any obvious cytotoxicity. Furthermore, we found that G. hederacea extract decreased tyrosinase and microphthalmia-associated transcription factor protein expression, but did not inhibit tyrosinase-related protein-1 and tyrosinase-related protein-2 expression. RT-PCR analysis indicated that the antimelanogenic effect of G. hederacea extract might be due to inhibition of tyrosinase gene transcription. Moreover, this effect is regulated via suppression of microphthalmia-associated transcription factor protein expression. Our data indicate that G. hederacea extract inhibits melanin synthesis in B16 melanoma cells but is not cytotoxic. Hence it might prove a useful therapeutic agent for treating hyperpigmentation and an effective component of whitening cosmetics.

Generation of intracellular single-chain antibodies directed against polypeptide GalNAc-transferase using a yeast two-hybrid system.

Mucin-type O-glycosylation is initiated by a large number of UDP-GalNAc: polypeptide N-acetylgalactosaminyltransferases (GalNAc-T). Although extensive in vitro studies using synthetic peptides as substrates suggest that most GalNAc-Ts exhibit overlapping substrate specificities, many studies have shown that individual GalNAc-Ts play an important role in both animals and humans. Further investigations of the functions of individual GalNAc-Ts including in vivo substrate proteins and O-glycosylation sites are necessary. In this study, we attempted to generate single-chain variable fragment (scFv) antibodies to bind to GalNAc-T1, T2, T3, and T4 using a yeast two-hybrid system for screening a naive chicken scFv library. Several different scFvs were isolated against a single target GalNAc-T isoform specifically under expressed in yeast and were confirmed to be expressed in mammalian cells and to retain binding activity inside the cells. Generation of these specific antibodies provides an opportunity to modify and exploit antibodies for specific applications in investigations of GalNAc-T functions.

Inhibition of dendritic cell migration by transforming growth factor-ß1 increases tumor-draining lymph node metastasis.

BACKGROUND: Transforming growth factor (TGF)-ß is known to be produced by progressor tumors and to immobilize dendritic cells (DCs) within those tumors. Moreover, although TGF-ß1 has been shown to promote tumor progression, there is still no direct, in vivo evidence as to whether TGF-ß1 is able to directly induce distant metastasis. METHODS: To address that issue and investigate the mechanism by which TGF-ß1 suppresses DC activity, we subdermally inoculated mouse ears with squamous cell carcinoma cells stably expressing TGF-ß1 or empty vector (mock). RESULTS: The numbers of DCs within lymph nodes draining the resultant TGF-ß1-expressing tumors was significantly lower than within nodes draining tumors not expressing TGF-ß1. We then injected fluorescently labeled bone marrow-derived dendritic cells into the tumors, and subsequent analysis confirmed that the tumors were the source of the DCs within the tumor-draining lymph nodes, and that there were significantly fewer immature DCs within the nodes draining TGF-ß1-expressing tumors than within nodes draining tumors not expressing TGF-ß1. In addition, 14 days after tumor cell inoculation, lymph node metastasis occurred more frequently in mice inoculated with TGF-ß1 transfectants than in those inoculated with the mock transfectants. CONCLUSIONS: These findings provide new evidence that tumor-derived TGF-ß1 inhibits migration of DCs from tumors to their draining lymph nodes, and this immunosuppressive effect of TGF-ß1 increases the likelihood of metastasis in the affected nodes.

In vitro prominent bone regeneration by release zinc ion from Zn-modified implant.

Zinc is one of the trace elements which induce the proliferation and the differentiation of the osteoblast. In the previous study, we found that zinc ions (Zn(2+) ion)-releasing titanium implants had excellent bone fixation using a rabbit femurs model. In this study, we isolated the Zn(2+) ions (eluted Zn(2+) ion; EZ) released from the implant surface, and evaluated the effect of EZ on the osteogenesis of human bone marrow-derived mesenchymal cells (hBMCs). In the result, it was found that the EZ stimulated cell viability, osteoblast marker gene (type I collagen, osteocalcin (OC), alkaline phosphatase (ALP) and bone sialoprotein (BSP)) expressions and calcium deposition in hBMCs.

A novel monoclonal antibody identified hepatic stem-like cells in rats.

Both liver epithelial and oval cells are believed to be liver stem cells. We investigated the identification by producing monoclonal antibodies against liver epithelial cells. Monoclonal antibodies against hepatic stem-like cells (HSL cells) have been selected to follow the hepatic stem cells during hepatic regeneration and developmental changes in the liver. Monoclonal antibodies were induced by immunization of BALB/c mice with HSL cells established from the epithelial cells of the adult rat liver. The hybridomas were screened by indirect immunofluorescence staining of HSL cells. We produced a unique monoclonal antibody against HSL cells, MabH, which specifically recognizes liver epithelial cells. MabH did not react with liver parenchymal cells but did react with bile ductule cells under normal conditions in the adult liver. This antibody also reacted with oval cell lines and with the oval cells that appeared during liver regeneration. In addition, fetal liver cells showed immunoreactivity with MabH. Although the level of staining decreased after birth, some cells in the portal area remained highly reactive. These results suggested that liver epithelial cells, oval cells, and fetal liver cells possess a common cell marker of liver stem cells.

Sexual dimorphism in LEC rat liver: suppression of carbonic anhydrase III by copper accumulation during hepatocarcinogenesis.

We examined age-related changes in the protein expression of carbonic anhydrase III (CAIII) in livers of Long-Evans with a cinnamon-like color (LEC) rats using an agouti color (LEA) rats as controls. The levels of the protein of CAIII in the liver of LEC male rats increased before 20 weeks of age, at the stage of acute hepatitis, and were decreased at 54 weeks of age, while those of CAIII in the liver of LEA male rats were highly expressed at all ages. In the normal LEA rats, CAIII showed sexual dimorphism. The level of CAIII in LEA male rat liver relative to female was four times higher. On the other hand, young LEC rat (at 4-12 weeks) showed a higher protein level of CAIII than LEA rats, and then decreased during development of hepatitis. CAIII mRNA also decreased in the LEC rat liver during hepatocarcinogenesis. The level of CAIII in the tumor region was lower than that in the tumor-free region. Immunohistochemical analysis showed that glutathione S-transferase P (GST-P) was positive and CAIII was negative in the precancerous region. The expression of CAIII was suppressed in cancerous lesions in hepatoma-bearing LEC rat liver compared to uninvolved surrounding tissues. These results indicated that suppression of CAIII accompanied hepatocarcinogenesis and it is a secondary consequence of the high copper levels in the liver.

IGFBP3 and BAG1 enhance radiation-induced apoptosis in squamous esophageal cancer cells.

Identification of reliable markers of radiosensitivity and the key molecules that enhance the susceptibility of esophageal cancer cells to anticancer treatments would be highly desirable. To identify molecules that confer radiosensitivity to esophageal squamous carcinoma cells, we assessed the radiosensitivities of the TE-5, TE-9 and TE-12 cloneA1 cell lines. TE-12 cloneA1 cells showed significantly greater susceptibility to radiotherapy at 5 and 10Gy than either TE-5 or TE-9 cells. Consistent with that finding, 24h after irradiation (5Gy), TE-12 cloneA1 cells showed higher levels of caspase 3/7 activity than TE-5 or TE-9 cells. When we used DNA microarrays to compare the gene expression profiles of TE-5 and TE-12 cloneA1 cells, we found that the mRNA and protein expression of insulin-like growth factor binding protein 3 (IGFBP3) and Bcl-2-associated athanogene 1 (BAG1) was five or more times higher in TE-12 cloneA1 cells than TE-5 cells. Conversely, knocking down expression of IGFBP3 and BAG1 mRNA in TE-12 cloneA1 cells using small interfering RNA (siRNA) significantly reduced radiosensitivity. These data suggest that IGFBP3 and BAG1 may be key markers of radiosensitivity that enhance the susceptibility of squamous cell esophageal cancer to radiotherapy. IGFBP3 and BAG1 may thus be useful targets for improved and more individualized treatments for patients with esophageal squamous cell carcinoma.

Regenerating gene I regulates interleukin-6 production in squamous esophageal cancer cells.

Regenerating gene (REG) I plays important roles in cancer cell biology. The purpose of this study was to determine whether REG I affects cytokine production in cancer cells. We transfected TE-5 and TE-9 squamous esophageal cancer cells with REG Ialpha and Ibeta and examined its effects on cytokine expression. We found that transfecting TE-5 and TE-9 cells with REG I Ialpha and Ibeta led to significantly increased expression of interleukin (IL)-6 mRNA and protein, but it had little or no effect on expression of IL-2, IL-4, IL-5, IL-10, IL-12, IL-13, IL-17A, interferon-gamma, tumor necrosis factor-alpha, granulocyte-colony stimulating factor or transforming growth factor-beta1. The elevated IL-6 expression seen in REG Ialpha transfectants was silenced by small interfering RNA-mediated knockdown. These finding suggest that REG I may act through IL-6 to exert effects on squamous esophageal cancer cell biology.

Expression and localization of regenerating gene I in a rat liver regeneration model.

Regenerating gene (Reg) I has been identified as a regenerative/proliferative factor for pancreatic islet cells. We examined Reg I expression in the regenerating liver of a rat model that had been administered 2-acetylaminofluorene and treated with 70% partial hepatectomy (2-AAF/PH model), where hepatocyte and cholangiocyte proliferation was suppressed and the hepatic stem cells and/or hepatic progenitor cells were activated. In a detailed time course study of activation of hepatic stem cells in the 2-AAF/PH model, utilizing immunofluorescence staining with antibodies of Reg I and other cell-type-specific markers, we found that Reg I-expressing cells are present in the bile ductules and increased during regeneration. Reg I-expressing cells were colocalized with CK19, OV6, and AFP. These results demonstrate that Reg I is significantly upregulated in the liver of the 2-AAF/PH rat model, accompanied by the formation of bile ductules during liver regeneration.