Expression of Stem Cell Markers in High-LET Space Radiation-Induced Intestinal Tumors in Apc1638N/+ Mouse Intestine

Estimation of cancer risk among astronauts planning to undertake future deep-space missions requires understanding the quantitative and qualitative differences in radiogenic cancers after low- and high-LET radiation exposures. Previously, we reported a multifold higher RBE for high-LET radiation-induced gastrointestinal (GI) tumorigenesis in Apc1638N/+ mice. Using the same model system, i.e., Apc1638N/+ mice, here, we report qualitative differences in the cellular phenotype of low- and high-LET radiation-induced GI tumors. Stem cell (SC) phenotypes were identified using BMI1, ALDH1, CD133, DCLK1, MSI1, and LGR5 markers in low (γ-rays)- and high (56Fe)-LET radiation-induced and spontaneous tumors. We also assessed the expression of these markers in the adjacent normal mucosa. All six of these putative SC markers were shown to be overexpressed in tumors compared to the adjacent normal intestinal tissue. A differential SC phenotype for spontaneous and radiogenic intestinal tumors in Apc1638N/+ mice was observed, where the ALDH1, BMI1, CD133, MSI1, and DCLK1 expressing cells were increased, while LGR5 expressing cells were decreased in 56Fe-induced tumors compared to γ-ray-induced and spontaneous tumors. Furthermore, higher β-catenin activation (marked by nuclear localization) was observed in 56Fe-induced tumors compared to γ and spontaneous tumors. Since differential tumor cell phenotype along with activated β-catenin may very well affect malignant progression, our findings are relevant to understanding the higher carcinogenic risk of high-LET radiation. This study has implications for the assessment of GI-cancer risk among astronauts, as well as for the estimation of secondary cancer risk among patients receiving hadron therapy, considering that our results indicate increased stemness properties after radiation.

18F-Fluorodeoxyglucose PET/CT and MRI Imaging Characteristics of Monomorphic Epitheliotropic Intestinal T-cell Lymphoma: A case report

Background Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) is a rare, rapidly progressive, primary intestinal T-cell lymphoma. The most common site of occurrence is on the small intestine. The prognosis of MEITL is extremely poor due to delayed diagnosis and lack of targeted therapy. Case Summary A case of MEITL involving the entire small bowel, part of the colon, rectum, mesenteric lymph nodes, and liver is herein reported. We are presenting the 18F-FDG PET/CT features of MEITL, which showed all involved lesions with increased FDG activity. The MRI and pathological characteristics of MEITL were also described. Furthermore, some malignant diseases and benign diseases should be considered in the differential diagnosis. Conclusion Based on the lesions with a high accumulation of FDG, our case shows the involved extent of MEITL, which is helpful for biopsy and treatment option decisions. We expect more could know about this disease and make an early diagnosis to improve the outcomes of MEITL.

Interstitial deletion of the Apc locus in β-catenin-overexpressing cells is a signature of radiation-induced intestinal tumors in C3B6F1 ApcMin/+ mice†

Recent studies have identified interstitial deletions in the cancer genome as a radiation-related mutational signature, although most of them do not fall on cancer driver genes. Pioneering studies in the field have indicated the presence of loss of heterozygosity (LOH) spanning Apc in a subset of sporadic and radiation-induced intestinal tumors of ApcMin/+ mice, albeit with a substantial subset in which LOH was not detected; whether copy number losses accompany such LOH has also been unclear. Herein, we analyzed intestinal tumors of C3B6F1 ApcMin/+ mice that were either left untreated or irradiated with 2 Gy of γ-rays. We observed intratumor mosaicism with respect to the nuclear/cytoplasmic accumulation of immunohistochemically detectable β-catenin, which is a hallmark of Apc+ allele loss. An immunoguided laser microdissection approach enabled the detection of LOH involving the Apc+ allele in β-catenin-overexpressing cells; in contrast, the LOH was not observed in the non-overexpressing cells. With this improvement, LOH involving Apc+ was detected in all 22 tumors analyzed, in contrast to what has been reported previously. The use of a formalin-free fixative facilitated the LOH and microarray-based DNA copy number analyses, enabling the classification of the aberrations as nondisjunction/mitotic recombination type or interstitial deletion type. Of note, the latter was observed only in radiation-induced tumors (nonirradiated, 0 of 8; irradiated, 11 of 14). Thus, an analysis considering intratumor heterogeneity identifies interstitial deletion involving the Apc+ allele as a causative radiation-related event in intestinal tumors of ApcMin/+ mice, providing an accurate approach for attributing individual tumors to radiation exposure.

Research progress in effects of pyroptosis on intestinal inflammatory injury

Inflammatory injury of the intestine is often accompanied by symptoms such as damage to intestinal mucosa, increased intestinal permeability, and intestinal motility dysfunction. Inflammatory factors spread throughout the body via blood circulation, and can cause multi-organ failure. Pyroptosis is a newly discovered way of programmed cell death, which is mainly characterized by the formation of plasma membrane vesicles, cell swelling until the rupture of the cell membrane, and the release of cell contents, thereby activating a drastic inflammatory response and expanding the inflammatory response cascade. Pyroptosis is widely involved in the occurrence of diseases, and the underlying mechanisms for inflammation are still a hot spot of current research. The caspase-1 mediated canonical inflammasome pathway of pyroptosis and caspase-4/5/8/11-mediated non-canonical inflammasome pathway are closely related to the occurrence and development of intestinal inflammation. Therefore, investigation of the signaling pathways and molecular mechanisms of pyroptosis in intestinal injury in sepsis, inflammatory bowel diseases, infectious enteristic, and intestinal tumor is of great significance for the prevention and treatment of intestinal inflammatory injury.

Establishment of clinical predictive model based on the study of influence factors in patients with colorectal polyps

Background

Colorectal cancer (CRC) is the most common gastrointestinal malignancy and is generally thought to be caused by the transformation of colorectal polyps. It has been shown that early detection and removal of colorectal polyps may reduce the mortality and morbidity of colorectal cancer.

Objective

Based on the risk factors associated with colorectal polyps, an individualized clinical prediction model was built to predict and evaluate the possibility of developing colorectal polyp.

Methods

A case-control study was conducted. Clinical data were collected from 475 patients who underwent colonoscopy at the Third Hospital of Hebei Medical University from 2020 to 2021. All clinical data were then divided into training sets and validation sets by using R software (7:3). A multivariate logistic analysis was performed to identify the factors associated with colorectal polyps according to the training set, and a predictive nomogram was created by R software based on the multivariate analysis. The results were internally validated by receiver operating characteristic (ROC) curves, calibration curves, and externally validated by validation sets.

Results

Multivariate logistic regression analysis showed that age (OR = 1.047, 95% CI = 1.029-1.065), history of cystic polyp (OR = 7.596, 95% CI = 0.976-59.129), and history of colorectal diverticulums (OR = 2.548, 95% CI = 1.209-5.366) were independent risk factors for colorectal polyps. History of constipation (OR = 0.457, 95% CI = 0.268-0.799) and fruit consumption (OR = 0.613, 95% CI 0.350-1.037) were protective factors for colorectal polyps. The nomogram demonstrated good accuracy for predicting colorectal polyps, with both C index and AUC being 0.747 (95% CI = 0.692-0.801). The calibration curves showed good agreement between the predicted risk by the nomogram and real outcomes. Both internal and external validation of the model showed good results.

Conclusion

In our study, the nomogram prediction model is reliable and accurate, which can help early clinical screening of patients with high-risk colorectal polyps, improve polyp detection rate, and reduce the incidence of colorectal cancer (CRC).

A Pediatric Case of Inverted Meckel's Diverticulum Presenting with Cyclic Vomiting-like Symptoms: A Case Report and Literature Review

Asymptomatic Meckel's diverticulum cases are not uncommon, leading to diagnostic difficulties in cases of atypical presentations with only gastrointestinal symptoms other than bloody stool. A nine-year-old boy diagnosed as having cyclic vomiting because of recurrent abdominal pain and vomiting for 6 months was referred to our institute and hospitalized due to worsening symptoms. After admission, abdominal ultrasonography showed the multiple concentric ring sign and a pseudokidney sign at the lower ileum, leading to the diagnosis of ileo-ileal intussusception, but the gastrointestinal symptoms and ultrasonic findings disappeared spontaneously. Transanal, double-balloon, intestinal endoscopy demonstrated a pedunculated polyp-like structure, and surgical resection was performed. An inverted diverticulum was found in the resected intestinal lumen, and ectopic gastric mucosa was identified histologically, leading to the diagnosis of inverted Meckel's diverticulum. In pediatric cases involving periodic attacks of vomiting and abdominal pain, unnecessary emergent surgery could be avoided by cautious imaging evaluation and consideration of ileo-ileal intussusception with advanced lesions of an inverted Meckel's diverticulum as a differential diagnosis, without facilely diagnosing cyclic vomiting. In addition, previous reports of inverted Meckel's diverticulum were reviewed, and the results were compared between adult and pediatric groups in each category.

Intestinal CD8+ tissue-resident memory T cells: From generation to function

Tissue-resident memory T cells (Trm), and particularly the CD8⁺ subset, have been shown to play a pivotal role in protection against infections and tumors. Studies in animal models and human tissues have highlighted that, while a core functional program is shared by Trm at all anatomical sites, distinct tissues imprint unique features through specific molecular cues. The intestinal tissue is often the target of pathogens for local proliferation and penetration into the host systemic circulation, as well as a prominent site of tumorigenesis. Therefore, promoting the formation of Trm at this location is an appealing therapeutic option. The various segments composing the gastrointestinal tract present distinctive histological and functional characteristics, which may reflect on the imprinting of unique functional features in the respective Trm populations. What these features are, and whether they can effectively be harnessed to promote local and systemic immunity, is still under investigation. Here, we review how Trm are generated and maintained in distinct intestinal niches, analyzing the required molecular signals and the models utilized to uncover them. We also discuss evidence for a protective role of Trm against infectious agents and tumors. Finally, we integrate the knowledge obtained from animal models with that gathered from human studies.

Lipopolysaccharides Enhance Epithelial Hyperplasia and Tubular Adenoma in Intestine-Specific Expression of krasV12 in Transgenic Zebrafish

Intestinal carcinogenesis is a multistep process that begins with epithelial hyperplasia, followed by a transition to an adenoma and then to a carcinoma. Many etiological factors, including KRAS mutations and inflammation, have been implicated in oncogenesis. However, the potential synergistic effects between KRAS mutations and inflammation as well as the potential mechanisms by which they promote intestinal carcinogenesis remain unclear. Thus, the objective of this study was to investigate the synergistic effects of kras^V12, lipopolysaccharides (LPS), and/or dextran sulfate sodium (DSS) on inflammation, tumor progression, and intestinal disorders using transgenic adults and larvae of zebrafish. Histopathology and pathological staining were used to examine the intestines of kras^V12 transgenic zebrafish treated with LPS and/or DSS. LPS and/or DSS treatment enhanced intestinal inflammation in kras^V12 transgenic larvae with concomitant increases in the number of neutrophils and macrophages in the intestines. The expression of kras^V12, combined with LPS treatment, also enhanced epithelial hyperplasia and tubular adenoma, demonstrated by histopathological examinations and by increases in cell apoptosis, cell proliferation, and downstream signaling of phosphorylated AKT serine/threonine kinase 1 (AKT), extracellular-signal-regulated kinase (ERK), and histone. We also found that kras^V12 expression, combined with LPS treatment, significantly enhanced changes in intestinal morphology, specifically (1) decreases in goblet cell number, goblet cell size, villi height, and intervilli space, as well as (2) increases in villi width and smooth muscle thickness. Moreover, kras^V12 transgenic larvae cotreated with DSS and LPS exhibited exacerbated intestinal inflammation. Cotreatment with DSS and LPS in kras^V12-expressing transgenic adult zebrafish also enhanced epithelial hyperplasia and tubular adenoma, compared with wild-type fish that received the same cotreatment. In conclusion, our data suggest that kras^V12 expression, combined with LPS and/or DSS treatment, can enhance intestinal tumor progression by activating the phosphatidylinositol-3-kinase (PI3K)/AKT signaling pathway and may provide a valuable in vivo platform to investigate tumor initiation and antitumor drugs for gastrointestinal cancers.

Functions of Dendritic Cells and Its Association with Intestinal Diseases

Dendritic cells (DCs), including conventional DCs (cDCs) and plasmacytoid DCs (pDCs), serve as the sentinel cells of the immune system and are responsible for presenting antigen information. Moreover, the role of DCs derived from monocytes (moDCs) in the development of inflammation has been emphasized. Several studies have shown that the function of DCs can be influenced by gut microbes including gut bacteria and viruses. Abnormal changes/reactions in intestinal DCs are potentially associated with diseases such as inflammatory bowel disease (IBD) and intestinal tumors, allowing DCs to be a new target for the treatment of these diseases. In this review, we summarized the physiological functions of DCs in the intestinal micro-environment, their regulatory relationship with intestinal microorganisms and their regulatory mechanism in intestinal diseases.

Assessment of Mechanistic Data for Hexavalent Chromium-Induced Rodent Intestinal Cancer Using the Key Characteristics of Carcinogens

Oral exposure to hexavalent chromium (Cr[VI]) induces intestinal tumors in mice. Mutagenic and nonmutagenic modes of action (MOAs) have been accepted by different regulatory bodies globally, the latter involving cytotoxicity-induced regenerative cell proliferation. However, concerns persist that all possible MOAs have not been fully considered. To address the potential for alternative MOAs, mechanistic data not represented in the existing two MOAs were evaluated. Relevant data were identified and organized by key characteristics of carcinogens (KCCs); literature related to epigenetics, immunosuppression, receptor-mediated effects, and immortalization were reviewed to identify potential key events associated with an alternative MOA. Over 200 references were screened for these four KCCs and further prioritized based on relevance to the research objective (ie, in vivo, oral exposure, gastrointestinal tissue). Minimal data were available specific to the intestine for these KCCs, and there was no evidence of any underlying mechanisms or key events that are not already represented in the two proposed MOAs. For example, while epigenetic dysregulation of DNA repair genes has been demonstrated, epigenetic effects were not measured in intestinal tissue, and it has been shown that Cr(VI) does not cause DNA damage in intestinal tissue. High-throughput screening data related to the KCCs were also evaluated, with activity generally limited to the two recognized MOAs. Collectively, no plausible alternative MOAs (or key events) were identified in addition to those previously proposed for Cr(VI) small intestine tumors.

A histopathological study on spontaneous gastrointestinal epithelial tumors in dogs

The present study evaluated the histopathological features, biological nature, anatomical location, sex, age and breeds of dogs affected by spontaneous gastrointestinal epithelial tumor. Biopsy samples of gastrointestinal tumors, from 95 dogs were examined and classified according to the WHO histological classification. A total of 131 samples, including 38 gastric, 13 small intestinal, and 80 large intestinal tumors were examined. The study observed that Jack Russell Terriers and Miniature Dachshunds were the breeds with the highest predisposition for gastrointestinal tumors. Gastric tumors included 5 adenomas, 30 adenocarcinomas (12 tubular, 2 papillary, 4 tubulopapillary and 12 signet-ring cell carcinomas) and 3 undifferentiated carcinomas. Intestinal tumors included 35 adenomas, 57 adenocarcinomas (43 acinar, 4 papillary, 7 mucinous and 3 signet-ring cell carcinomas), and 1 undifferentiated carcinoma. The study did not detect any difference among the incidence rates of invasion/metastasis in the tubular (44%), papillary (33%) and tubulopapillary (25%) adenocarcinomas. Additionally, the tubular (acinar), papillary and tubulopapillary adenocarcinomas were further divided into 48 polypoid and 17 non-polypoid types, based on their growth patterns. Invasion/metastasis was detected in 21% of the polypoid type and 100% of the non-polypoid type of adenocarcinomas. A correlation was detected between the occurrence of invasion/metastasis and the type of histopathological growth pattern in adenocarcinomas. The study demonstrated that Jack Russell terriers and Miniature Dachshunds are the most common breeds affected by gastrointestinal tumors and the entire group of the canine adenocarcinomas with non-polypoid growth pattern has greater malignant potentials, compared to the adenocarcinomas with polypoid growth patterns.

PP2A Deficiency Enhances Carcinogenesis of Lgr5+ Intestinal Stem Cells Both in Organoids and In Vivo

In most cancers, cellular origin and the contribution of intrinsic and extrinsic factors toward transformation remain elusive. Cell specific carcinogenesis models are currently unavailable. To investigate cellular origin in carcinogenesis, we developed a tumorigenesis model based on a combination of carcinogenesis and genetically engineered mouse models. We show in organoids that treatment of any of three carcinogens, DMBA, MNU, or PhIP, with protein phosphatase 2A (PP2A) knockout induced tumorigenesis in Lgr5⁺ intestinal lineage, but not in differentiated cells. These transformed cells increased in stem cell signature, were upregulated in EMT markers, and acquired tumorigenecity. A mechanistic approach demonstrated that tumorigenesis was dependent on Wnt, PI3K, and RAS-MAPK activation. In vivo combination with carcinogen and PP2A depletion also led to tumor formation. Using whole-exome sequencing, we demonstrate that these intestinal tumors display mutation landscape and core driver pathways resembling human intestinal tumor in The Cancer Genome Atlas (TCGA). These data provide a basis for understanding the interplay between extrinsic carcinogen and intrinsic genetic modification and suggest that PP2A functions as a tumor suppressor in intestine carcinogenesis.

Dietary Lipids Modulate Notch Signaling and Influence Adult Intestinal Development and Metabolism in Drosophila

Tissue homeostasis involves a complex balance of developmental signals and environmental cues that dictate stem cell function. We found that dietary lipids control enteroendocrine cell production from Drosophila posterior midgut stem cells. Dietary cholesterol influences new intestinal cell differentiation in an Hr96-dependent manner by altering the level and duration of Notch signaling. Exogenous lipids modulate Delta ligand and Notch extracellular domain stability and alter their trafficking in endosomal vesicles. Lipid-modulated Notch signaling occurs in other nutrient-dependent tissues, suggesting that Delta trafficking in many cells is sensitive to cellular sterol levels. These diet-mediated alterations in young animals contribute to a metabolic program that persists after the diet changes. A low-sterol diet also slows the proliferation of enteroendocrine tumors initiated by Notch pathway disruption. Thus, a specific dietary nutrient can modify a key intercellular signaling pathway to shift stem cell differentiation and cause lasting changes in tissue structure and physiology.

Dietary feeding of freeze-dried whole cranberry inhibits intestinal tumor development in Apcmin/+ mice

It is increasingly perceived that dietary components have been linked with the prevention of intestinal cancer. Cranberry is a rich source of phenolic constituents and non-digestible fermentable dietary fiber, which shows anti-proliferation effect in colorectal cancer cells. Herein, we investigated the efficacy of long-term cranberry diet on intestinal adenoma formation in Apc^min/+ mice. Apc^min/+ mice were fed a basal diet or a diet containing 20% (w/w) freeze-dried whole cranberry powder for 12 weeks, and the number and size of tumors were recorded after sacrifice. Our results showed that cranberry strongly prevented the growth of intestinal tumors by 33.1%. Decreased cell proliferation and increased apoptosis were observed in tumors of cranberry-fed mice. Cranberry diet reduced the expression profile of colonic inflammatory cytokines (IFN-γ, IL-1β and TNF-α) accompanied with increased levels of anti-inflammatory cytokines (IL-4 and IL-10). Moreover, the number of colonic goblet cells and MUC2 production were increased, and the intestinal barrier function was also improved. In addition, cranberry diet increased caecal short chain fatty acids concentrations, and down-regulated epidermal growth factor receptor signaling pathway. These data firstly show the efficacy and associated mechanisms of cranberry diet on intestinal tumor growth in Apc^min/+ mice, suggesting its chemopreventive potential against intestinal cancer.

Decreased RXRα is Associated with Increased β-Catenin/TCF4 in (56)Fe-Induced Intestinal Tumors

Although it is known that accumulation of oncogenic β-catenin is critical for intestinal tumorigenesis, the underlying mechanisms have not yet been fully explored. Post-translational β-catenin level is regulated via the adenomatous polyposis coli (APC)-dependent as well as the APC-independent ubiquitin–proteasome pathway (UPP). Employing an APC-mutant mouse model (APC^Min/+) the present study aimed to investigate the status of RXRα, an APC-independent factor involved in targeting β-catenin to UPP for degradation, in tumor-bearing and tumor-free areas of intestine after exposure to energetic ⁵⁶Fe ions. APC^Min/+ mice were exposed to energetic ⁵⁶Fe ions (4 or 1.6 Gy) and intestinal tumor samples and tumor-free normal intestinal samples were collected 100–110 days after exposure. The status of TCF4, β-catenin, cyclin D1, and RXRα was examined using immunohistochemistry and immunoblots. We observed increased accumulation of the transcription factor TCF4 and its co-activator β-catenin as well as their downstream oncogenic target protein cyclin-D1 in ⁵⁶Fe ion-induced intestinal tumors. Further, decreased expression of RXRα in tumors as well as in adjacent normal epithelium was indicative of perturbations in β-catenin proteasomal-targeting machinery. This indicates that decreased UPP targeting of β-catenin due to downregulation of RXRα can contribute to further accumulation of β-catenin and to ⁵⁶Fe-induced tumorigenesis.

P-Selectin-Mediated Adhesion between Platelets and Tumor Cells Promotes Intestinal Tumorigenesis in Apc(Min/+) Mice

Studies have indicated that platelets play an important role in tumorigenesis, and an abundance of platelets accumulate in the ovarian tumor microenvironment outside the vasculature. However, whether cancer cells recruit platelets within intestinal tumors and how they signal adherent platelets to enter intestinal tumor tissues remain unknown. Here, we unexpectedly found that large numbers of platelets were deposited within human colorectal tumor specimens using immunohistochemical staining, and these platelets were fully associated with tumor development. We further report the robust adhesion of platelet aggregates to tumor cells within intestinal tumors, which occurs via a mechanism that is dependent on P-selectin (CD62P), a cell adhesion molecule that is abundantly expressed on activated platelets. Using spontaneous intestinal tumor mouse models, we determined that the genetic deletion of P-selectin suppressed intestinal tumor growth, which was rescued by the infusion of wild-type platelets but not P-selectin^-/- platelets. Mechanistically, platelet adhesion to tumor cells induced the secretion of vascular endothelial growth factor (VEGF) to promote angiogenesis and accelerate intestinal tumor cell proliferation. Our results indicate that the adherence of platelets to tumor cells could promote tumor growth and metastasis. By targeting this platelet-tumor cell interaction, recombinant soluble P-selectin may have therapeutic value for the treatment of intestinal tumors.

Induction of intestinal tumors and lymphomas in C57BL/6N mice by a food-borne carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is the most abundant heterocyclic amine contained in cooked meat and fish. Although PhIP has been demonstrated to induce various types of tumors in rats, lymphomas predominated in mice using the CDF1 strain. To investigate the carcinogenic activity of PhIP on other organs in mice with a different genetic background, PhIP was administered to C57BL / 6N mice. After a 40-week administration of 300 ppm of PhIP in a high-fat diet followed by continuous feeding with a high fat diet, C57BL / 6N mice developed adenomas and adenocarcinomas in the small intestine, the incidences being 52% in males and 68% in females at weeks 95 and 70, respectively. Lymphomas of B-cell origin also developed in both sexes as frequently as in the CDF1 strain, incidences being 48% in males and 32% in females. Although the incidence in PhIP-treated female mice did not differ from that in the control mice, lymphomas developed significantly earlier in the PhIP-treated mice. The present study demonstrated that the intestinal tract is another potential target of PhIP-induced carcinogenesis in mice, and that the carcinogenic activity of PhIP could be affected by the genetic background of the animals.

Identification of a protein increasing in serum of Nagase analbuminemic rats bearing intestinal tumors as an isotype of T-kininogen

Increase in an unidentified protein was observed in serum of Nagase analbuminemic rats (NAR) bearing intestinal tumors induced by azoxymethane. This protein seemed to be a polymer of a protein of 73 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and so was tentatively named 73K-protein. The serum concentration of 73K-protein in NAR bearing intestinal tumors was 11.9 +/- 2.2 mg/ml (mean +/- SD, n = 5), whereas that in control NAR was 2.0 +/- 0.2 mg/ml. Increase of the serum 73K-protein level was also observed in Sprague-Dawley rats bearing intestinal tumors, skin tumors, subcutaneous sarcomas, or mammary tumors and in ACI rats bearing urinary bladder tumors. On double immunodiffusion analysis, the 73K-protein was not detected in mouse, guinea pig, pig, horse, or human serum. A cDNA clone bearing the sequence encoding 73K-protein was isolated from a cDNA library constructed from rat liver mRNA. The nucleotide sequence of the 73K-protein showed 98.8% and 96.9% homologies with the sequences of the 3'-proximal domains of the cDNAs for TI- and TII-kininogen, respectively. Therefore, the 73K-protein was concluded to be an isotype of T-kininogen.