Knock-Down of CD24 in Astrocytes Aggravates Oxyhemoglobin-Induced Hippocampal Neuron Impairment.

Subarachnoid hemorrhage (SAH), as one of the most severe hemorrhagic strokes, is closely related to neuronal damage. Neurogenesis is a promising therapy, however, reliable targets are currently lacking. Increasing evidence has indicated that CD24 is associated with the growth of hippocampal neurons and the regulation of neural stem/precursor cell proliferation. To investigate the potential effect of CD24 in astrocytes on neuron growth in the hippocampus, we used a Transwell co-culture system of hippocampal astrocytes and neurons, and oxyhemoglobin (OxyHb) was added to the culture medium to mimic SAH in vitro. A specific lentivirus was used to knock down CD24 expression in astrocytes, which was verified by western blot, quantitative real-time polymerase chain reaction, and immunofluorescent staining. Astrocyte activation, neurite elongation, neuronal apoptosis, and cell viability were also assessed. We first determined the augmented expression level of CD24 in hippocampal astrocytes after SAH. A similar result was observed in cultured astrocytes exposed to OxyHb, and a corresponding change in SHP2/ERK was also noticed. CD24 in astrocytes was then downregulated by the lentivirus, which led to the impairment of axons and dendrites on the co-cultured neurons. Aggravated neuronal apoptosis was induced by the CD24 downregulation in astrocytes, which might be a result of a lower level of brain derived neurotrophic factor (BDNF). In conclusion, the knock-down of CD24 in astrocytes suppressed hippocampal neuron growth, in which the SHP2-ERK signaling pathway and BNDF were possibly involved.

Mouse HSA+ immature cardiomyocytes persist in the adult heart and expand after ischemic injury.

The assessment of the regenerative capacity of the heart has been compromised by the lack of surface signatures to characterize cardiomyocytes (CMs). Here, combined multiparametric surface marker analysis with single-cell transcriptional profiling and in vivo transplantation identify the main mouse fetal cardiac populations and their progenitors (PRGs). We found that CMs at different stages of differentiation coexist during development. We identified a population of immature heat stable antigen (HSA)/ cluster of differentiation 24 (CD24)+ CMs that persists throughout life and that, unlike other CM subsets, actively proliferates up to 1 week of age and engrafts cardiac tissue upon transplantation. In the adult heart, a discrete population of HSA/CD24+ CMs appears as mononucleated cells that increase in frequency after infarction. Our work identified cell surface signatures that allow the prospective isolation of CMs at all developmental stages and the detection of a subset of immature CMs throughout life that, although at reduced frequencies, are poised for activation in response to ischemic stimuli. This work opens new perspectives in the understanding and treatment of heart pathologies.

Investigation of CD133 and CD24 as candidate azoospermia markers and their relationship with spermatogenesis defects.

Spermatogenesis is initiated when spermatogonial stem cells (SSCs) in the mature testes enter mitosis and trigger differentiation. Thus, spermatogenesis and the ability to maintain a continuous source of spermatogonia relies on the ability to differentiate SSCs. Many studies around the world have been performed to investigate the etiology of male infertility and recent studies have focused on the presence and identification of biomarkers. CD133 and CD24 are stem cell markers locating in the testis and spermatogonia. The aim of this study was to investigate the relationship of the CD133 and CD24 genes with spermatogenesis defects and examine them as a candidate a useful biomarker for azoospermia men. The association of CD133 and CD24 with spermatogenesis defects was investigated in patients with obstructive (O) and non-obstructive azoospermia (NOA). NOA cases were histopathologically classified into Hypospermatogenesis (HS), Maturation Arrest (MA), and Sertoli Cell Only Syndrome (SCO) groups. A qRT-PCR analysis of these genes was performed and protein expression levels were measured by Western blot analysis. CD133 expression in NOA group was found to be significantly different from OA and this was confirmed by immunohistochemistry and immunocytochemical assays. The qRT-PCR analysis revealed that gene expression of CD133 and CD24 had fold changes of 0.80 ±â€¯0.34 and 1.59 ±â€¯0.31 compared to controls, respectively in the HS group (p > 0.05) and 0.04 ±â€¯0.01 and 0.54 ±â€¯0.08 in the MA group (p < 0.05). In the SCO group, CD24 showed a 1.55 ±â€¯0.35-fold increase (p > 0.05). CD133 gene expression was not detected at the transcriptional level in the SCO group. Western blot analysis of CD133 protein expression revealed 1.83, 4.11, and 11.4-fold decreases in the HS, MA and SCO groups, respectively, compared to controls (p < 0.05). CD24 showed fold changes of 1.18, 0.38, (p < 0.05), and 0.89 in the HS, MA, and SCO groups, respectively. Immunohistochemical analysis of CD133 revealed moderate, partial staining in the HS group, compared to substantial, wide-spread staining in the OA group. No staining was detected in either the MA or SCO groups. The localization of CD133 in healthy sperm was determined to be prominent in the tail and partly expressed in the head by confocal laser scanning microscopy analysis. It was also found that the expression of CD133 protein was high in healthy commercially-sourced Sertoli cells as well as in the Sertoli cells of OA individuals. Data from this study show that CD133 exhibits different profiles in infertile patient groups and thus may be considered as a candidate biomarker. CD24 can be associated with blockage of germ cell maturation in the MA group. Curative protocols for spermatogenesis defects may be possible with the use of these markers and thus their identification is extremely valuable in terms of human reproductive health.

CD24 promoted cancer cell angiogenesis via Hsp90-mediated STAT3/VEGF signaling pathway in colorectal cancer.

CD24 is involved in tumor progression of various cancers, but the effects of CD24 on tumor angiogenesis in colorectal cancer are still unknown. We aimed to investigate the underlying mechanism and role of CD24 on colorectal cancer (CRC) angiogenesis. Our data showed that the microvessal density (MVD) was related to the expression of CD24 in primary and metastasis CRC. Silencing of CD24 could dramatically decrease human umbilical vein endothelial cell (HUVEC) migration, invasion and tubule formation, but trivially affected cell proliferation. We also mechanically showed that silencing CD24 could downregulate the expression of VEGF via inhibiting the phosphorylation and translocation of STAT3. Moreover, Hsp90 was identified as the down-interaction protein of CD24 with co-immunoprecipitation assay and systematic mass spectrometry. Immunofluorescence results showed Hsp90 partly co-localized with CD24 in CRC cell membrane and there was a positive correlation between CD24 and Hsp90 expression in CRC tissues. We gradually evidenced that Hsp90 modulated the stability and degradation of CD24 in a proteasome-depended manner, and transferred the signal transmission from CD24 to STAT3. 17-AAG, a specific Hsp90, could abrogate the CD24 induce- HUVEC migration, invasion and tubule formation in vitro and in vivo. Collectively, our results suggested that CD24 induced CRC angiogenesis in Hsp90-dependent manner and activated STAT3-mediated transcription of VEGF. We provided a new insight into the regulation mechanism of tumor angiogenesis by exploring the role of CD24 in angiogenesis.

CD24 Is Not Required for Tumor Initiation and Growth in Murine Breast and Prostate Cancer Models.

CD24 is a small, heavily glycosylated, GPI-linked membrane protein, whose expression has been associated with the tumorigenesis and progression of several types of cancer. Here, we studied the expression of CD24 in tumors of MMTV-PyMT, Apc1572/T+ and TRAMP genetic mouse models that spontaneously develop mammary or prostate carcinoma, respectively. We found that CD24 is expressed during tumor development in all three models. In MMTV-PyMT and Apc1572T/+ breast tumors, CD24 was strongly but heterogeneously expressed during early tumorigenesis, but decreased in more advanced stages, and accordingly was increased in poorly differentiated lesions compared with well differentiated lesions. In prostate tumors developing in TRAMP mice, CD24 expression was strong within hyperplastic lesions in comparison with non-hyperplastic regions, and heterogeneous CD24 expression was maintained in advanced prostate carcinomas. To investigate whether CD24 plays a functional role in tumorigenesis in these models, we crossed CD24 deficient mice with MMTV-PyMT, Apc1572T/+ and TRAMP mice, and assessed the influence of CD24 deficiency on tumor onset and tumor burden. We found that mice negative or positive for CD24 did not significantly differ in terms of tumor initiation and burden in the genetic tumor models tested, with the exception of Apc1572T/+ mice, in which lack of CD24 reduced the mammary tumor burden slightly but significantly. Together, our data suggest that while CD24 is distinctively expressed during the early development of murine mammary and prostate tumors, it is not essential for the formation of tumors developing in MMTV-PyMT, Apc1572T/+ and TRAMP mice.

Stress-associated erythropoiesis initiation is regulated by type 1 conventional dendritic cells.

Erythropoiesis is an important response to certain types of stress, including hypoxia, hemorrhage, bone marrow suppression, and anemia, that result in inadequate tissue oxygenation. This stress-induced erythropoiesis is distinct from basal red blood cell generation; however, neither the cellular nor the molecular factors that regulate this process are fully understood. Here, we report that type 1 conventional dendritic cells (cDC1s), which are defined by expression of CD8α in the mouse and XCR1 and CLEC9 in humans, are critical for induction of erythropoiesis in response to stress. Specifically, using murine models, we determined that engagement of a stress sensor, CD24, on cDC1s upregulates expression of the Kit ligand stem cell factor on these cells. The increased expression of stem cell factor resulted in Kit-mediated proliferative expansion of early erythroid progenitors and, ultimately, transient reticulocytosis in the circulation. Moreover, this stress response was triggered in part by alarmin recognition and was blunted in CD24 sensor- and CD8α+ DC-deficient animals. The contribution of the cDC1 subset to the initiation of stress erythropoiesis was distinct from the well-recognized role of macrophages in supporting late erythroid maturation. Together, these findings offer insight into the mechanism of stress erythropoiesis and into disorders of erythrocyte generation associated with stress.

Regulatory B Cell Function Is Suppressed by Smoking and Obesity in H. pylori-Infected Subjects and Is Correlated with Elevated Risk of Gastric Cancer.

Helicobacter pylori infection occurs in more than half of the world's population and is the main cause for gastric cancer. A series of lifestyle and nutritional factors, such as tobacco smoking and obesity, have been found to elevate the risk for cancer development. In this study, we sought to determine the immunological aspects during H. pylori infection and gastric cancer development. We found that B cells from H. pylori-infected patients presented altered composition and function compared to uninfected patients. IL-10-expressing CD24+CD38+ B cells were upregulated in H. pylori-infected patients, contained potent regulatory activity in inhibiting T cell pro-inflammatory cytokine secretion, and responded directly to H. pylori antigen stimulation. Interestingly, in H. pylori-infected smoking subjects and obese subjects, the number of IL-10+ B cells and CD24+CD38+ B cells were reduced compared to H. pylori-infected asymptomatic subjects. Regulatory functions mediated by CD24+CD38+ B cells were also impaired. In addition, gastric cancer positive patients had reduced IL-10-producing B cell frequencies after H. pylori-stimulation. Altogether, these data suggest that in H. pylori-infection, CD24+CD38+ B cell is upregulated and plays a role in suppressing pro-inflammatory responses, possibly through IL-10 production, a feature that was not observed in smoking and obese patients.

Siglec-10 is associated with survival and natural killer cell dysfunction in hepatocellular carcinoma.

BACKGROUND: The interaction between Siglec-10 and its ligand, CD24, selectively represses tissue damage-caused immune responses. However, the nature of Siglec-10 and CD24 in human hepatocellular carcinoma (HCC) is still poorly defined. Hereon, the expression, function, and regulation of CD24 and Siglec-10 in HCC were investigated in the present study. METHODS: Flow cytometry was performed to examine the expression of Siglec-10 in HCC tissues and adjacent non-tumor tissues of HCC patients. To further determine whether Siglec-10 expression is associated with the clinical characteristics and survival, conventional immunohistochemistry was performed in 96 HCC patients. Additionally, the role of Siglec-10 in the regulation of natural killer (NK) cell dysfunction was evaluated. Finally, CD24 expression in HCC was also assessed. RESULTS: Siglec-10 was expressed most on NK cells in HCC (40.7 ± 4.5%). Compared with surrounding non-tumor tissues, tumor tissues had higher Siglec-10 expression (31.0 ± 1.7% versus 40.7 ± 4.5%, n = 10, P < 0.05), and the expression was negatively associated with patient survival. Siglec-10(+)CD56(+) NK cells exhibited reduced effector function, as shown by decreased granules and cytokine expressions compared with Siglec-10(-)CD56(+) NK cells. Moreover, the number of CD24(+)CD45(-) cells in HCC tissues was higher than that in adjacent non-tumor tissues (9.4 ± 0.9% versus 3.1 ± 0.9%, n = 15, P < 0.05). CONCLUSIONS: These findings suggest that Siglec-10 is associated with decreased survival and impaired NK cell function in human HCC. This process may function via the CD24-Siglec-10 interaction, which may represent a therapeutic target in HCC patients.

Impaired function of CD19(+) CD24(hi) CD38(hi) regulatory B cells in patients with pemphigus.

BACKGROUND: Pemphigus is an organ-specific autoimmune bullous disease. OBJECTIVES: To determine the role of regulatory B cells (Bregs) in patients with pemphigus. METHODS: The frequency of the occurrence of CD19(+) CD24(hi) CD38(hi) Bregs was detected from 34 patients with pemphigus and 20 healthy controls. Interleukin (IL)-10 secretion was processed after stimulating B cells. Specific antidesmoglein antibody (Ab) titres and their subclasses were also measured. Ab response and cytokine production from peripheral blood mononuclear cells (PBMCs) with or without Bregs were analysed. RESULTS: The number of Bregs was significantly increased in patients with pemphigus compared with healthy controls (15 ± 7% vs. 9 ± 3%; P < 0·01) and the proportion of Bregs in the active groups (newly diagnosed and chronic active patients) was significantly higher than in remittent individuals (16 ± 7% vs. 13 ± 8%; P = 0·04). The IL-10-producing B cells were significantly increased upon stimulation both in patients and in healthy controls. However, the increase ratio of IL-10-producing B cells between short- and long-term stimulation was significantly lower in patients with pemphigus (1·0-fold vs. 2·6-fold increase in control group; P < 0·01). Strikingly, Bregs from the controls were able to suppress interferon (IFN)-γ expression and T helper cell 1 (Th1) immune response (26% inhibition rate), while the suppressive function of Bregs from patients with pemphigus was significantly decreased (9% inhibition rate). There was no difference in Ab levels from PBMCs with or without Bregs after stimulation. CONCLUSIONS: Bregs in patients with pemphigus are elevated but with defective regulatory function on Th1 cells.

Twist2 promotes self-renewal of liver cancer stem-like cells by regulating CD24.

Twist2 is a highly conserved basic helix-loop-helix transcription factor that plays a critical role in embryogenesis. Recent evidence has revealed that aberrant Twist2 expression contributes to tumor progression; however, the role of Twist2 in human hepatocellular carcinoma (HCC) and its underlying mechanisms remain undefined. In this report, we demonstrate that Twist2 is overexpressed in human HCC tumors. We show that ectopic expression of Twist2 induces epithelial-mesenchymal transition phenotypes, augments cell migration and invasion and colony-forming abilities in human HCC cells in vitro, and promotes tumor growth in vivo. Moreover, we found a higher percentage of CD24(+) liver cancer stem-like cells in Twist2-transduced HCC cells. Twist2-expressing cells exhibited an increased expression of stem cell markers Bmi-1, Sox2, CD24 and Nanog and an increased capacity for self-renewal. Knockdown of CD24 in HepG2/Twist2 cells decreased the levels of Sox2, pSTAT3 and Nanog, and reversed the cancer stem-like cell phenotypes induced by ectopic expression of Twist2. Furthermore, Twist2 regulated the CD24 expression by directly binding to the E-box region in CD24 promoter. Therefore, our data demonstrated that Twist2 augments liver cancer stem-like cell self-renewal in a CD24-dependent manner. Twist2-CD24-STAT3-Nanog pathway may play a critical role in regulating liver cancer stem-like cell self-renewal. The identification of the Twist2-CD24 signaling pathway provides a potential therapeutic approach to target cancer stem cells in HCCs.

Determination of 35 cell surface antigen levels in malignant pleural effusions identifies CD24 as a marker of disseminated tumor cells.

Many targets have been identified in solid tumors for antibody therapy but it is less clear what surface antigens may be most commonly expressed on disseminated tumor cells. Using malignant pleural effusions as a source of disseminated tumor cells, we compared a panel of 35 antigens for their cancer specificity, antigen abundance and functional significance. These antigens have been previously implicated in cancer metastasis and fall into four categories: (i) cancer stem cell, (ii) epithelial-mesenchymal transition, (iii) metastatic signature of in vivo selection and (iv) tyrosine kinase receptors. We determined the antigen density of all 35 antigens on the cell surface by flow cytometry, which ranges from 3 × 10(3) -7 × 10(6) copies per cell. Comparison between the malignant and benign pleural effusions enabled us to determine the antigens specific for cancer. We further chose six antigens and examined the correlation between their expression levels and tumor formation in immunocompromised mice. We concluded that CD24 is one of the few antigens that could simultaneously meet all three criteria of an ideal target. It was specifically and abundantly expressed in malignant pleural effusions; CD24(high) tumor cells formed tumors in mice at a faster rate than CD24(low) tumor cells, and shRNA-mediated knockdown of CD24 in HT29 cells confirmed a functional requirement for CD24 in the colonization of the lung. Concomitant consideration of antigen abundance, specificity and functional importance can help identify potentially useful markers for disseminated tumor cells.

Cluster of differentiation 24 expression is an independent prognostic factor of adverse outcome in cervical carcinoma.

OBJECTIVE: Cluster of differentiation (CD) 24 is a cell adhesion molecule that has been implicated in tumor invasion and metastasis of various solid tumors. The aim of this study was to explore the expression patterns of CD24 as a predictive marker for long-term survival in cervical carcinomas. METHODS: A total of 144 patients diagnosed with International Federation of Gynecology and Obstetrics stage I to IV cervical carcinoma were studied, and 95 patients underwent surgical intervention. The expression of CD24 protein was studied by immunohistochemistry using tissue microarrays. RESULTS: Overexpression of CD24 was observed in 50 (34.7%) of 144 invasive carcinomas. Patients with CD24 overexpression had poorer survival compared with that of patients with CD24 underexpression (5-year survival rate, 52.0% vs 72.3%; log rank P = 0.014). Importantly, in multivariate analysis, CD24 overexpression proved to be a significant independent predictor of short-term survival (relative risk, 1.814; P = 0.043). CONCLUSIONS: The present study suggests that CD24 overexpression is a predictor of decreased long-term survival in patients with cervical carcinoma. Therefore, immunohistochemical evaluation of CD24 expression is a potential prognostic biomarker for cervical carcinomas.

Involvement of CD24 in angiogenesis in a mouse model of oxygen-induced retinopathy.

PURPOSE: To investigate a possible involvement of CD24 in vascular remodeling and angiogenesis in retinopathy of prematurity (ROP) in a mouse model of oxygen-induced retinopathy. MATERIALS AND METHODS: 17 CD24 knockout (KO) and 12 wild-type (WT) C57BL/6 mice were used. Group 1 mice were exposed to oxygen concentrations of 75 ± 2% from postnatal day (P) 7 to P12. Group 2 mice were raised in room air. At P17, all mice underwent fluorescein-conjugated-dextran perfusion and were sacrificed. The flat-mounted retinas were scored manually and digitally by a new computerized algorithm, according to blood vessel obliteration, tortuosity, vascular tufts and neovascularization formation. RESULTS: Fifty four retinal whole mounts were available for analysis and scoring. Group 1 retinas had significantly higher values of vaso-obliteration, tufts, neovascularization, vessel tortuosity and higher mean retinopathy scores than Group 2 retinas (KO mice: 9.0 ± 0.27 vs. 0.74 ± 0.2, respectively, P < 0.0001; WT mice: 7.58 ± 0.40 vs. 1.17 ± 0.27, respectively, P < 0.0001). Manual scoring in Group 1 revealed higher values of neovascularization, tortuosity and mean retinopathy scores in KO mice vs. WT mice (9.0 ± 0.27 vs. 7.58 ± 0.40, respectively, P = 0.009). Digital scoring revealed a higher neovascularization score in KO mice as well (13.72 ± 0.82% vs. 8.06 ± 0.27%, P < 0.0001). All mice had similar vaso-obliteration areas. There were no significant differences between KO and WT mice in Group 2. CONCLUSIONS: Absence of CD24 may have a deleterious effect on angiogenesis occurring in the second stage of ROP development, though its role in vessel obliteration during the first stage of ROP is probably limited.

Pten loss and RAS/MAPK activation cooperate to promote EMT and metastasis initiated from prostate cancer stem/progenitor cells.

PTEN loss or PI3K/AKT signaling pathway activation correlates with human prostate cancer progression and metastasis. However, in preclinical murine models, deletion of Pten alone fails to mimic the significant metastatic burden that frequently accompanies the end stage of human disease. To identify additional pathway alterations that cooperate with PTEN loss in prostate cancer progression, we surveyed human prostate cancer tissue microarrays and found that the RAS/MAPK pathway is significantly elevated in both primary and metastatic lesions. In an attempt to model this event, we crossed conditional activatable K-ras(G12D/WT) mice with the prostate conditional Pten deletion model. Although RAS activation alone cannot initiate prostate cancer development, it significantly accelerated progression caused by PTEN loss, accompanied by epithelial-to-mesenchymal transition (EMT) and macrometastasis with 100% penetrance. A novel stem/progenitor subpopulation with mesenchymal characteristics was isolated from the compound mutant prostates, which was highly metastatic upon orthotopic transplantation. Importantly, inhibition of RAS/MAPK signaling by PD325901, a mitogen-activated protein (MAP)-extracellular signal-regulated (ER) kinase (MEK) inhibitor, significantly reduced the metastatic progression initiated from transplanted stem/progenitor cells. Collectively, our findings indicate that activation of RAS/MAPK signaling serves as a potentiating second hit to alteration of the PTEN/PI3K/AKT axis, and cotargeting both the pathways is highly effective in preventing the development of metastatic prostate cancers.

Lessons from common markers of tumor-initiating cells in solid cancers.

Tumor-initiating cells (TICs) have emerged as the driving force of carcinomas, which appear as hierarchically structured. TICs as opposed to the tumor bulk display tumor forming potential, which is linked to a certain degree of self-renewal and differentiation, both major features of stem cells. Markers such as CD44, CD133, CD24, EpCAM, CD166, Lgr5, CD47, and ALDH have been described, which allow for the prospective enrichment of TICs. It is conspicuous that the same markers allow for an enrichment of TICs in various entities and, on the other hand, that different combinations of these markers were independently reported for the same tumor entity. Potential functions of these markers in the regulation of TIC phenotypes remained somewhat neglected although they might give insights in common molecular themes of TICs. The present review discusses major TIC markers with respect to their function and potential contributions to the tumorigenic phenotype of TICs.

NFAT5 regulates T lymphocyte homeostasis and CD24-dependent T cell expansion under pathologic hypernatremia.

Immune cells rely on the transcription factor NFAT5 to adapt to hypertonic stress. The hypertonicity-dependent role of NFAT5 in T cells in vivo remains unclear because mouse models of NFAT5 deficiency have produced substantially different T cell phenotypes. In this study, we analyzed the T cell compartment in NFAT5-null and T cell-specific NFAT5 knockout mice. We found that NFAT5-null mice had constitutive, pronounced hypernatremia and suffered a severe immunodeficiency, with T cell lymphopenia, altered CD8 naive/memory homeostasis, and inability to reject allogeneic tumors. By contrast, T cell-specific NFAT5 knockout mice had normal plasma tonicity, rejected allogeneic tumors, and exhibited only a mild, low-penetrance memory bias in CD8 cells. Notably, when T cells from these mice were cultured ex vivo in hypernatremic media, they exhibited features found in NFAT5-null mice, with pronounced naive/memory imbalance and impaired homeostatic survival in response to IL-7, as well as a severe inhibition of their mitogen-induced proliferation. By analyzing surface receptors whose expression might be affected in NFAT5-deficient cells, we identified CD24 as a novel NFAT5 target induced by hypertonicity both in vitro and in vivo, and required to sustain T cell expansion under osmostress. NFAT5 bound to the Cd24 promoter in response to hypertonicity facilitated the local derepression of chromatin and enhanced the expression of CD24 mRNA and protein. Altogether, our results indicate that the systemic hypernatremia of NFAT5-null mice is a major contributor to their immunodeficiency, and highlight the role of NFAT5 and CD24 in the homeostasis of T cells under osmostress in vivo.

CD24-dependent MAPK pathway activation is required for colorectal cancer cell proliferation.

CD24 is a glycosylphosphatidylinositol-anchored membrane protein reported to be overexpressed in human tumorigenesis and progression. Our purpose was to determine the role of CD24 in the proliferation of colorectal cancer cells and the potential mechanisms in this process. Our data showed that CD24 promoted cell growth and induced activation of extracellular signal-regulated kinases, Raf-1, and p38 mitogen-activated protein kinase. Furthermore, suppression of extracellular signal-regulated kinases and p38 mitogen-activated protein kinase activity by their specific inhibitors, U0126 and SB203580, abrogated CD24-induced proliferation in vitro. By tumorigenicity assay in female BALB/c nude mice, we further demonstrated that CD24 promoted tumor growth in vivo. Immunohistochemical analysis revealed that CD24 expression occurred in 92.5% of human colorectal cancer tissue, and increased with tumor progression. More importantly, the stainings of phospho-extracellular signal-regulated kinases and phospho-p38 mitogen-activated protein kinase were strongly correlated with CD24 expression. Taken together, our data suggest that CD24-dependent extracellular signal-regulated kinases and p38 mitogen-activated protein kinase activations are required for colorectal cancer cell proliferation in vitro and in vivo. The linkage of CD24 and the mitogen-activated protein kinase pathway may unravel a novel mechanism in the regulation of colorectal cancer proliferation.

Regenerative potentials of the murine thyroid in experimental autoimmune thyroiditis: role of CD24.

Hashimoto thyroiditis can be partially reproduced in mice by immunization with thyroglobulin or, more recently, thyroperoxidase. This experimental autoimmune thyroiditis (EAT) model has been extensively characterized during early disease phases (up to d 35 after immunization). By extending the analysis of EAT to 100 d after immunization, we noted a remarkable regenerative capacity of the thyroid and the expression of Oct-4, suggesting in vivo the existence of adult thyroid stem cells. After an almost complete destruction of the follicular architecture, occurring between d 21 and 28, the thyroid was capable of restoring its follicles and reducing the mononuclear infiltration, so that by d 100 after immunization, it regained its normal morphology and function. During this regeneration process, thyrocytes expressed high levels of CD24. We therefore assessed the role of CD24 in thyroid regeneration by inducing EAT in mice lacking CD24. Regeneration was faster in the absence of CD24, likely a consequence of the effect of CD24 on the infiltrating lymphocytes. The study suggests that the EAT model can also be used as a tool to investigate adult thyroid stem cells.