The mouse Wnt-10B gene isolated from helper T cells is widely expressed and a possible oncogene in BR6 mouse mammary tumorigenesis

Sequence characterization and comparative expression profile of buffalo WNT10B gene in adult and fetal tissues

In this study, Wingless-type MMTV (mouse mammary tumor virus) integration site family member (WNT10B) gene was sequence characterized in the Indian water buffalo. Sequence analysis revealed an open reading frame of 1176 nucleotides in buffalo, encoding 391 amino acids long protein. Nineteen nucleotide variations were observed between cattle and buffalo resulting in six amino acid changes. Phylogenetic analysis showed the clustering of ruminant species together. Real-time expression analysis of WNT10B in tissues collected from different organs of fetal and adult buffalo, revealed, the gene being abundantly expressed in the rumen and liver of the fetus. The fetal ovary, heart, kidney, lung, testis and mammary gland showed moderate expression, while in adult tissues, expression was high in the ovary, testis, brain, kidney, small intestine and liver, whereas lower expression was observed in the adult rumen. Significant differences in WNT10B expression levels were found for the brain, small intestine, testes, kidney, heart, rumen, and ovary when adult and fetal tissues were compared. A moderate level of genetic variation was found between cattle and buffalo WNT10B and expression patterns in a variety of tissues in adult buffalo implies that in addition to possible roles in adipogenesis and hematopoiesis, the WNT10B gene might be playing a significant role in other regulatory pathways as well.

Mice lacking DKK1 in T cells exhibit high bone mass and are protected from estrogen-deficiency-induced bone loss

The Wnt inhibitor Dickkopf-1 (DKK1) is a negative regulator of bone formation and bone mass and is dysregulated in various bone diseases. How DKK1 contributes to postmenopausal osteoporosis, however, remains poorly understood. Here, we show that mice lacking DKK1 in T cells are protected from ovariectomy-induced bone loss. Ovariectomy activated CD4+ and CD8+ T cells and increased their production of DKK1. Co-culture of activated T cells with osteoblasts inhibited Wnt signaling in osteoblasts, leading to impaired differentiation. Importantly, DKK1 expression in T cells also controlled physiological bone remodeling. T-cell-deficient Dkk1 knock-out mice had a higher bone mass with an increased bone formation rate and decreased numbers of osteoclasts compared with controls, a phenotype that was rescued by adoptive transfer of wild-type T cells. Thus, these findings highlight that T cells control bone remodeling in health and disease via their expression of DKK1.

The Role of T Cells Reactive to the Cathelicidin Antimicrobial Peptide LL-37 in Acute Coronary Syndrome and Plaque Calcification

The human cationic anti-microbial peptide LL-37 is a T cell self-antigen in patients with psoriasis, who have increased risk of cardiovascular events. However, the role of LL-37 as a T cell self-antigen in the context of atherosclerosis remains unclear. The objective of this study was to test for the presence of T cells reactive to LL-37 in patients with acute coronary syndrome (ACS). Furthermore, the role of T cells reactive to LL-37 in atherosclerosis was assessed using apoE-/- mice immunized with the LL-37 mouse ortholog, mCRAMP. Peripheral blood mononuclear cells (PBMCs) from patients with ACS were stimulated with LL-37. PBMCs from stable coronary artery disease (CAD) patients or self-reported subjects served as controls. T cell memory responses were analyzed with flow cytometry. Stimulation of PBMCs with LL-37 reduced CD8+ effector T cell responses in controls and patients with stable CAD but not in ACS and was associated with reduced programmed cell death protein 1 (PDCD1) mRNA expression. For the mouse studies, donor apoE-/- mice were immunized with mCRAMP or adjuvant as controls, then T cells were isolated and adoptively transferred into recipient apoE-/- mice fed a Western diet. Recipient mice were euthanized after 5 weeks. Whole aortas and hearts were collected for analysis of atherosclerotic plaques. Spleens were collected for flow cytometric and mRNA expression analysis. Adoptive transfer experiments in apoE-/- mice showed a 28% reduction in aortic plaque area in mCRAMP T cell recipient mice (P < 0.05). Fifty six percent of adjuvant T cell recipient mice showed calcification in atherosclerotic plaques, compared to none in the mCRAMP T cell recipient mice (Fisher's exact test P = 0.003). Recipients of T cells from mice immunized with mCRAMP had increased IL-10 and IFN-γ expression in CD8+ T cells compared to controls. In conclusion, the persistence of CD8+ effector T cell response in PBMCs from patients with ACS stimulated with LL-37 suggests that LL-37-reactive T cells may be involved in the acute event. Furthermore, studies in apoE-/- mice suggest that T cells reactive to mCRAMP are functionally active in atherosclerosis and may be involved in modulating plaque calcification.

CD40 Accelerates the Antigen-Specific Stem-Like Memory CD8+ T Cells Formation and Human Papilloma Virus (HPV)-Positive Tumor Eradication

Antigen-specific stem-like memory CD8⁺ T cells (Tscm) have a series of stem cell characteristics, including long-term survival, self-renewal, anti-apoptosis and persistent differentiation into cytotoxic T cells. The effective induction of tumor-specific CD8⁺ Tscm could persistently eradicate tumor in pro-tumor hostile microenvironment. This study was to investigate the role of CD40 in HPV16-specific CD8⁺ Tscm induction and its anti-tumor function. We found that CD40 activation accelerated vaccine-induced HPV16 E7-specific CD8⁺ Tscm formation. Comparing to other HPV-specific CD8⁺ T cells, CD8⁺ Tscm were found to be stronger and long-term anti-tumor function, in vivo and in vitro, even in the adoptive cellular transferring model. Furthermore, high frequencies of Tscm might prevent the HPV infection to move on to the development of cancer. And the CD40 effect on Tscm involved Wnt/β-catenin activation. Our study suggest that CD40 activation supports the generation of tumor-specific CD8⁺ Tscm, thus providing new insight into cancer immunotherapy.

Immune Modulation of the T Cell Response in Asthma through Wnt10b

Asthma is a chronic inflammatory disease, which is characterized by activation of CD4(+) T helper 2 cells orchestrating an allergic airway response. Whereas the role of Wnt family members in regulating T cell maintenance and maturation is established, their contribution to T cell activation in allergic asthma is not known. We hypothesized that Wnt10b plays a role in the modulation of the allergic airway response and affects T cell activation and polarization. Using an in vivo house dust mite asthma model, Wnt10b-deficient (Wnt10b(-/-)) mice were allergen-sensitized and inflammation, as well as T cell activation, was studied in vivo and in vitro. Wnt10b(-/-) mice exhibited an augmented inflammatory phenotype with an increase in eosinophils in the bronchoalveolar lavage and IL-4 and IL-13 in the lungs when compared with wild-type mice. In vitro studies confirmed an increased T helper type 2 polarization and increased T cell activation of Wnt10b(-/-) cells. Accordingly, the percentage of naive T cells was elevated by the addition of recombinant Wnt10b protein. Finally, Wnt10b(-/-) mice exhibited an increase in the percentage of effector T cells in the lungs after house dust mite sensitization, which indicated a heightened activation state, measured by an increased percentage of CD69(hi)CD11a(hi) cells. These findings suggest that Wnt10b plays an important role in regulating asthmatic airway inflammation through modification of the T cell response and is a prospective target in the disease process.

T cells, osteoblasts, and osteocytes: interacting lineages key for the bone anabolic and catabolic activities of parathyroid hormone

Osteoimmunology is a field of research dedicated to the study of the interactions between the immune system and bone. Among the cells of the immune system that regulate bone turnover and the responsiveness of bone cells to calciothropic hormones are bone marrow T lymphocytes. T cells secrete osteoclastogenic cytokines such as RANKL and TNF-α, as well as factors that stimulate bone formation, one of which is Wnt10b. In addition, T cells regulate the differentiation and life span of stromal cells (SCs) and their responsiveness to parathyroid hormone (PTH) via costimulatory molecules expressed on their surface. The conditioning effect of T cells on SCs is inherited by the osteoblastic and osteocytic progeny of SCs. As a result, osteoblastic cells of T cell-deficient mice have functional characteristics different from corresponding cells of T cell-replete mice. These differences include the ratio of RANKL/OPG produced in response to continuous PTH treatment, and the osteoblastogenic response to intermittent PTH treatment. This article reviews the evidence indicating that the effects of PTH are mediated not only by osteoblasts and osteocytes but also by T cells.

T cell-expressed CD40L potentiates the bone anabolic activity of intermittent PTH treatment

T cells are known to potentiate the bone anabolic activity of intermittent parathyroid hormone (iPTH) treatment. One of the involved mechanisms is increased T cell secretion of Wnt10b, a potent osteogenic Wnt ligand that activates Wnt signaling in stromal cells (SCs). However, additional mechanisms might play a role, including direct interactions between surface receptors expressed by T cells and SCs. Here we show that iPTH failed to promote SC proliferation and differentiation into osteoblasts (OBs) and activate Wnt signaling in SCs of mice with a global or T cell-specific deletion of the T cell costimulatory molecule CD40 ligand (CD40L). Attesting to the relevance of T cell-expressed CD40L, iPTH induced a blunted increase in bone formation and failed to increase trabecular bone volume in CD40L(-/-) mice and mice with a T cell-specific deletion of CD40L. CD40L null mice exhibited a blunted increase in T cell production of Wnt10b and abrogated CD40 signaling in SCs in response to iPTH treatment. Therefore, expression of the T cell surface receptor CD40L enables iPTH to exert its bone anabolic activity by activating CD40 signaling in SCs and maximally stimulating T cell production of Wnt10b.

Ovariectomy expands murine short-term hemopoietic stem cell function through T cell expressed CD40L and Wnt10B

Estrogen deficiency expands hemopoietic stem and progenitor cells (HSPCs) and mature blood lineages, but the involved mechanism and the affected HSPC populations are mostly unknown. Here we show that ovariectomy (ovx) expands short-term HSPCs (ST-HSPCs) and improves blood cell engraftment and host survival after bone marrow (BM) transplantation through a dual role of the T-cell costimulatory molecule CD40 ligand (CD40L). This surface receptor is required for ovx to stimulate T-cell production of Wnt10b, a Wnt ligand that activates Wnt signaling in HSPCs and stromal cells (SCs). Moreover, CD40L is required for ovx to increase SC production of the hemopoietic cytokines interleukin (IL)-6, IL-7, and granulocyte macrophage-colony-stimulating factor. Attesting to the relevance of CD40L and Wnt10b, ovx fails to expand ST-HSPCs in CD40L-null mice and in animals lacking global or T-cell expression of Wnt10b. In summary, T cells expressed CD40L, and the resulting increased production of Wnt10b and hemopoietic cytokines by T cells and SCs, respectively, plays a pivotal role in the mechanism by which ovx regulates hemopoiesis. The data suggest that antiestrogens may represent pharmacological targets to improve ST-HSPC function through activation of the microenvironment.

The Role of Inflammatory Cytokines, the RANKL/OPG Axis, and the Immunoskeletal Interface in Physiological Bone Turnover and Osteoporosis

Although it has long been recognized that inflammation, a consequence of immune-driven processes, significantly impacts bone turnover, the degree of centralization of skeletal and immune functions has begun to be dissected only recently. It is now recognized that formation of osteoclasts, the bone resorbing cells of the body, is centered on the key osteoclastogenic cytokine, receptor activator of NF- κ B ligand (RANKL). Although numerous inflammatory cytokines are now recognized to promote osteoclast formation and skeletal degradation, with just a few exceptions, RANKL is now considered to be the final downstream effector cytokine that drives osteoclastogenesis and regulates osteoclastic bone resorption. The biological activity of RANKL is moderated by its physiological decoy receptor, osteoprotegerin (OPG). New discoveries concerning the sources and regulation of RANKL and OPG in physiological bone turnover as well as under pathological (osteoporotic) conditions continue to be made, opening a window to the complex regulatory processes that control skeletal integrity and the depth of integration of the skeleton within the immune response. This paper will examine the interconnection between bone turnover and the immune system and the implications thereof for physiological and pathological bone turnover.

The role of WNT10B in physiology and disease

Wnt10b is a member of the Wnt ligand gene family that encodes for secreted proteins, which activate the ancient and highly conserved Wnt signalling cascade. The Wnt pathway has been shown to be essential for embryonic development, tissue integrity, and stem cell activity, but if deregulated, also causes disease such as cancer. Although the 19 different Wnt ligands found in both human and mouse can activate several branches of the Wnt pathway, WNT10B specifically activates canonical Wnt/β-catenin signalling and thus triggers β-catenin/LEF/TCF-mediated transcriptional programs. In this review, we highlight the unique functions of WNT10B and mechanisms of how WNT10B acts in the immune system, mammary gland, adipose tissue, bone and skin. In these organs, WNT10B has been well established to be involved in signalling networks controlling stemness, pluripotency and cell fate decisions. Deregulation of these processes causes diseases such as breast cancer, obesity and osteoporosis. Compelling evidence suggests that WNT10B is a valuable candidate for the development of therapeutic regimens for human diseases.

Effects of Wnt-10b on proliferation and differentiation of adult murine skin-derived CD34 and CD49f double-positive cells

Although mouse Wnt-10b has been shown to play various roles in a wide range of biological actions, the effects on epithelial stem/progenitor cells in the skin have not been reported. In the present study, we investigated the effects of Wnt-10b on proliferation and differentiation of murine skin-derived CD34 and CD49f double-positive (CD34(+)CD49f(+)) cells, a supposed fraction as enriched epithelial stem/progenitor cells. The cells were prepared from dorsal skin samples obtained from young adult mice as alpha6 integrin (CD49f) and CD34 double-positive cells by fluorescent activated cell sorting (FACS), and they were cultured with or without Wnt-10b to investigate its effects on proliferation and differentiation. Involvement of canonical Wnt signaling pathway was confirmed by TOPFLASH assay, and differentiation of the CD34(+)CD49f(+) cells was assessed by RT-PCR analysis and immunocytochemical examinations. The skin-derived CD34(+)CD49f(+) cells were immunopositive for Lhx2 and expressed mRNA of classical markers for bulge stem cells, including Lhx2, keratin15, Sox9, S100a6, and NFATc1. Their proliferation was suppressed by Wnt-10b, and the markers for differentiated epithelial cells became to be expressed in the culture with Wnt-10b. These results suggest that Wnt-10b promotes differentiation of epithelial stem/progenitor cells in the skin.

T lymphocytes amplify the anabolic activity of parathyroid hormone through Wnt10b signaling

Intermittent administration of parathyroid hormone (iPTH) is used to treat osteoporosis because it improves bone architecture and strength, but the underlying cellular and molecular mechanisms are unclear. Here, we show that iPTH increases the production of Wnt10b by bone marrow CD8+ T cells and induces these lymphocytes to activate canonical Wnt signaling in preosteoblasts. Accordingly, in responses to iPTH, T cell null mice display diminished Wnt signaling in preosteoblasts and blunted osteoblastic commitment, proliferation, differentiation, and life span, which result in decreased trabecular bone anabolism and no increase in strength. Demonstrating the specific role of lymphocytic Wnt10b, iPTH has no anabolic activity in mice lacking T-cell-produced Wnt10b. Therefore, T-cell-mediated activation of Wnt signaling in osteoblastic cells plays a key permissive role in the mechanism by which iPTH increases bone strength, suggesting that T cell osteoblast crosstalk pathways may provide pharmacological targets for bone anabolism.

Effects of Wnt-10b on hair shaft growth in hair follicle cultures

Wnts are deeply involved in the proliferation and differentiation of skin epithelial cells. We previously reported the differentiation of cultured primary skin epithelial cells toward hair shaft and inner root sheath (IRS) of the hair follicle via beta-catenin stabilization caused by Wnt-10b, however, the effects of Wnt-10b on cultured hair follicles have not been reported. In the present study, we examined the effects of Wnt-10b on shaft growth using organ cultures of whisker hair follicles in serum-free conditions. No hair shaft growth was observed in the absence of Wnt-10b, whereas its addition to the culture promoted elongation of the hair shaft, intensive incorporation of BrdU in matrix cells flanking the dermal papilla (DP), and beta-catenin stabilization in DP and IRS cells. These results suggest a promoting effect of Wnt-10b on hair shaft growth that is involved with stimulation of the DP via Wnt-10b/beta-catenin signalling, proliferation of matrix cells next to the DP, and differentiation of IRS cells by Wnt-10b.

Wnt-10b promotes differentiation of skin epithelial cells in vitro

To evaluate the role of Wnt-10b in epithelial differentiation, we investigated the effects of Wnt-10b on adult mouse-derived primary skin epithelial cells (MPSEC). Recombinant Wnt-10b protein (rWnt-10b) was prepared using a gene engineering technique and MPSEC were cultured in its presence, which resulted in morphological changes from cuboidal to spindle-shaped and inhibited their proliferation. Further, involvement of the canonical Wnt signal pathway was also observed. MPSEC treated with rWnt-10b showed characteristics of the hair shaft and inner root sheath of the hair follicle, in results of Ayoub Shklar staining and immunocytochemistry. Further, the cells expressed mRNA for differentiated epithelial cells, including keratin 1, keratin 2, loricrin, mHa5, and mHb5, in association with a decreased expression of the basal cell marker keratin 5. These results suggest that Wnt-10b promotes the differentiation of MPSEC.

Wnt-10b secreted from lymphocytes promotes differentiation of skin epithelial cells

Wnt-10b was originally isolated from lymphoid tissue and is known to be involved in a wide range of biological actions, while recently it was found to be expressed early in the development of hair follicles. However, few studies have been conducted concerning the role of Wnt-10b with the differentiation of skin epithelial cells. To evaluate its role in epithelial differentiation, we purified Wnt-10b from the supernatant of a concanavalin A-stimulated lymphocyte culture using an affinity column and investigated its effects on the differentiation of adult mouse-derived primary skin epithelial cells (MPSEC). MPSEC cultured with Wnt-10b showed morphological changes from cuboidal to spindle-shaped with inhibited proliferation, and also obtained characteristics of the hair shaft and inner root sheath of the hair follicle, represented by red-colored Ayoub Shklar staining, and reactions to AE-13 and AE-15 as seen with immunocytology. Further, RT-PCR analysis demonstrated the expression of mRNA for keratin 1, keratin 2, loricrin, mHa5, and mHb5, in association with a decreased expression of the basal cell marker keratin 5, in Wnt-10b-treated MPSEC. In addition, involvement of the canonical Wnt signal pathway was demonstrated by a TCF reporter (pTOPFLASH) assay. These results suggest that Wnt-10b promotes the differentiation of MPSEC and may play an important role in hair follicle development by promoting differentiation of epithelial cells.

Gene expression array analyses predict increased proto-oncogene expression in MMTV induced mammary tumors

Exogenous infection by milk-borne mouse mammary tumor viruses (MMTV) typically induce mouse mammary tumors in genetically susceptible mice at a rate of 90-95% by 1 year of age. In contrast to other transforming retroviruses, MMTV acts as an insertional mutagen and under the influence of steroid hormones induces oncogenic transformation after insertion into the host genome. As these events correspond with increases in adjacent proto-oncogene transcription, we used expression array profiling to determine which commonly associated MMTV insertion site proto-oncogenes were transcriptionally active in MMTV induced mouse mammary tumors. To verify our gene expression array results we developed real-time quantitative RT-PCR assays for the common MMTV insertion site genes found in RIII/Sa mice (int-1/wnt-1, int-2/fgf-3, int-3/Notch 4, and fgf8/AIGF) as well as two genes that were consistently up regulated (CCND1, and MAT-8) and two genes that were consistently down regulated (FN1 and MAT-8) in the MMTV induced tumors as compared to normal mammary gland. Finally, each tumor was also examined histopathologically. Our expression array findings support a model whereby just one or a few common MMTV insertions into the host genome sets up a dominant cascade of events that leave a characteristic molecular signature.

Human breast epithelial stem cells and their regulation

This review summarizes the current evidence for the existence of human breast stem cells and the pathways involved in their regulation, and discusses how the disruption of these pathways may result in the generation of a population of cells with the capacity for unlimited self-renewal. Relevant data from mouse model systems are also discussed where appropriate. By understanding the molecular pathways that regulate self-renewal of normal mammary stem cells, it may be possible to target the activation of these pathways in breast tumours.

The Wnts

SUMMARY

The Wnt genes encode a large family of secreted protein growth factors that have been identified in animals from hydra to humans. In humans, 19 WNT proteins have been identified that share 27% to 83% amino-acid sequence identity and a conserved pattern of 23 or 24 cysteine residues. Wnt genes are highly conserved between vertebrate species sharing overall sequence identity and gene structure, and are slightly less conserved between vertebrates and invertebrates. During development, Wnts have diverse roles in governing cell fate, proliferation, migration, polarity, and death. In adults, Wnts function in homeostasis, and inappropriate activation of the Wnt pathway is implicated in a variety of cancers.

Langerhans' cell histiocytosis is caused by dysregulation of the E-cadherin-beta-catenin cascade: a hypothesis

Langerhans' cell histiocytosis (LCH) is a proliferative disease of cells of the dendritic cell lineage, closely resembling activated Langerhans' cells. The clinical picture of LCH is greatly variable, suggesting a scale of aberrancies at the cellular level. Despite progress in clinical treatment, the aetiology and pathogenesis of this disease remain unknown. In the present paper, we present the hypothesis that dysregulation of the E-cadherin-beta-catenin-Wnt cascade, which has both adhesive and transcriptional functions, may be fundamental to the development of LCH. This hypothesis is founded upon two notions: (i) careful regulation of this cascade is essential in normal Langerhans cell activation; and (ii) abnormalities in the E-cadherin-beta-catenin cascade are a major cause of epithelial neoplastic proliferation. On the basis of this hypothesis, we present three alternative scenarios that may describe the initial steps in the pathogenesis of LCH.

Identification of a Wnt-responsive signal transduction pathway in primary endothelial cells

The beta-catenin signal transduction pathway, which can be activated by secreted Wnt proteins, plays a key role in normal embryonic development and in malignant transformation of the mammary gland and colon. Here we demonstrate, for the first time, that Wnt and beta-catenin signaling also function in cells of the vasculature. RT-PCR analysis showed that primary endothelial and smooth muscle cell cultures, of both mouse and human origin, express members of the Wnt and Wnt receptor (Frizzled) gene families. Transfection of an expression vector for Wnt-1 into primary endothelial cells increased both the free pool of beta-catenin and the transcription from a Lef/tcf-dependent reporter gene construct. Expression of Wnt-1, but not Wnt-5a, also stimulated proliferation of primary endothelial cell cultures. These data show that Wnt and Frizzled proteins can regulate signal transduction, via beta-catenin, in endothelial cells. These findings suggest that Wnt signaling may feature in normal differentiation of the vasculature as well as in pathological settings where endothelial and smooth muscle proliferation is disturbed.

Role of Members of the Wnt Gene Family in Human Hematopoiesis

The hematopoietic system is derived from ventral mesoderm. A number of genes that are important in mesoderm development have been identified including members of the transforming growth factor-β (TGF-β) superfamily, the fibroblast growth factor (FGF) family, and the Wnt gene family. Because TGF-β plays a pleiotropic role in hematopoiesis, we wished to determine if other genes that are important in mesoderm development, specifically members of theWnt gene family, may play a role in hematopoiesis. Three members of the Wnt gene family (Wnt-5A, Wnt-2B, and Wnt-10B) were identified and cloned from human fetal bone stromal cells. These genes are expressed to varying levels in hematopoietic cell lines derived from T cells, B cells, myeloid cells, and erythroid cells; however, only Wnt-5A was expressed in CD34+Lin− primitive progenitor cells. The in vitro biological activity of these Wnt genes on CD34+Lin− hematopoietic progenitors was determined in a feeder cell coculture system and assayed by quantitating progenitor cell numbers, CD34+ cell numbers, and numbers of differentiated cell types. The number of hematopoietic progenitor cells was markedly affected by exposure to stromal cell layers expressing Wnt genes with 10- to 20-fold higher numbers of mixed colony-forming units (CFU-MIX), 1.5- to 2.6-fold higher numbers of CFU-granulocyte macrophage (CFU-GM), and greater than 10-fold higher numbers of burst-forming units-erythroid (BFU-E) in the Wnt-expressing cocultures compared with the controls. Colony formation by cells expanded on theWnt-expressing cocultures was similar for each of the three genes, indicating similar action on primitive progenitor cells; however, Wnt-10B showed differential activity on erythroid progenitors (BFU-E) compared with Wnt-5A and Wnt-2B. Cocultures containing Wnt-10B alone or in combination with all three Wnt genes had threefold to fourfold lower BFU-E colony numbers than the Wnt-5A– or Wnt-2B–expressing cocultures. The frequency of CD34+ cells was higher inWnt-expressing cocultures and cellular morphology indicated that coculture in the presence of Wnt genes resulted in higher numbers of less differentiated hematopoietic cells and fewer mature cells than controls. These data indicate that the gene products of theWnt family function as hematopoietic growth factors, and that they may exhibit higher specificity for earlier progenitor cells.

© 1998 by The American Society of Hematology.

Role of Members of the Wnt Gene Family in Human Hematopoiesis

The hematopoietic system is derived from ventral mesoderm. A number of genes that are important in mesoderm development have been identified including members of the transforming growth factor-β (TGF-β) superfamily, the fibroblast growth factor (FGF) family, and the Wnt gene family. Because TGF-β plays a pleiotropic role in hematopoiesis, we wished to determine if other genes that are important in mesoderm development, specifically members of theWnt gene family, may play a role in hematopoiesis. Three members of the Wnt gene family (Wnt-5A, Wnt-2B, and Wnt-10B) were identified and cloned from human fetal bone stromal cells. These genes are expressed to varying levels in hematopoietic cell lines derived from T cells, B cells, myeloid cells, and erythroid cells; however, only Wnt-5A was expressed in CD34+Lin− primitive progenitor cells. The in vitro biological activity of these Wnt genes on CD34+Lin− hematopoietic progenitors was determined in a feeder cell coculture system and assayed by quantitating progenitor cell numbers, CD34+ cell numbers, and numbers of differentiated cell types. The number of hematopoietic progenitor cells was markedly affected by exposure to stromal cell layers expressing Wnt genes with 10- to 20-fold higher numbers of mixed colony-forming units (CFU-MIX), 1.5- to 2.6-fold higher numbers of CFU-granulocyte macrophage (CFU-GM), and greater than 10-fold higher numbers of burst-forming units-erythroid (BFU-E) in the Wnt-expressing cocultures compared with the controls. Colony formation by cells expanded on theWnt-expressing cocultures was similar for each of the three genes, indicating similar action on primitive progenitor cells; however, Wnt-10B showed differential activity on erythroid progenitors (BFU-E) compared with Wnt-5A and Wnt-2B. Cocultures containing Wnt-10B alone or in combination with all three Wnt genes had threefold to fourfold lower BFU-E colony numbers than the Wnt-5A– or Wnt-2B–expressing cocultures. The frequency of CD34+ cells was higher inWnt-expressing cocultures and cellular morphology indicated that coculture in the presence of Wnt genes resulted in higher numbers of less differentiated hematopoietic cells and fewer mature cells than controls. These data indicate that the gene products of theWnt family function as hematopoietic growth factors, and that they may exhibit higher specificity for earlier progenitor cells.

© 1998 by The American Society of Hematology.

Differential expression of Wnt genes in normal and flat variants of PC12 cells, a cell line responsive to ectopic Wnt1 expression

Wnt genes encode secreted growth factor-like proteins that participate in growth regulation, differentiation and tumorigenesis. Ectopic expression of Wnt1 converts the PC12 neural crest-derived rat pheochromocytoma cell line from a round phenotype that express chromaffin markers to flat adherent cells (termed PC12/Wnt1) that do not express them. A pool of spontaneously flat variants of PC12 cells (PC12/flat) is phenotypically similar to the PC12/Wnt1 cells, but does not express Wnt1. Here we describe the expression of 13 Wnt genes in wild type PC12, PC12/flat and PC12/Wnt1 cells. Wild type PC12 expressed Wnt3, Wnt3a, Wnt4, Wnt5a, Wnt6, Wnt10a and Wnt11. Compared with expression in wild type cells, both PC12/flat and PC12/Wnt1 cells lost most or all expression of Wnt3a and Wnt4 and gained expression of Wnt7b. Wnt5a and Wnt6 expression was higher in PC12/Wnt1 cells than in PC12 or PC12/flat. Wnt3 was expressed at low levels in both PC12 and PC12/flat, but was absent in PC12/Wnt1 cells. Wnt10a and Wnt11 were approximately equally expressed in the three groups, and Wnt2, Wnt5b, Wnt7a, Wnt10b and endogenous Wnt1 mRNAs were not detected. These results demonstrate that the expression of some Wnt genes changes in PC12 cells upon conversion to the flat phenotype, and suggest that Wnt1 may modulate expression of several other Wnt genes in these cells.

Genetic structure and chromosomal mapping of MyD88

The myeloid differentiation (MyD) marker MyD88 was initially characterized as a primary response gene, upregulated in mouse M1 myeloleukemic cells in response to differentiation induced by interleukin-6. Subsequent analysis revealed that MyD88 possesses a unique modular structure, which consists of an N-terminal "death domain," similar to the intracellular segments of TNF receptor 1 and Fas, and a C-terminal region related to the cytoplasmic domains of the Drosophila morphogen Toll and vertebrate interleukin-1 receptors. In this report we describe the cloning and gene structure of mouse MyD88. The complete coding sequence of mouse MyD88 spans five exons, with the first exon encoding the complete death domain. Zooblot analysis revealed that MyD88 is an evolutionarily conserved gene. MyD88 was localized to the distal region of mouse chromosome 9 by interspecific backcross mapping. The human homolog (hMyD88) was mapped to chromosome 3p22-p21.3 by PCR analysis of a human chromosome 3 somatic cell hybrid mapping panel. Northern blot analysis revealed widespread expression of MyD88 in many adult mouse tissues, and RT-PCR studies detected MyD88 mRNA in T and B cell lines and differentiating embryonic stem cells. The broad expression pattern demonstrates that mouse MyD88 expression is not restricted to cells of myeloid lineage as was originally believed.