From developmental disorder to heritable cancer: it's all in the BMP/TGF-beta family

Bone morphogenetic protein signaling in vertebrate motor neurons and neuromuscular communication

An accurate communication between motor neurons and skeletal muscle fibers is required for the proper assembly, growth and maintenance of neuromuscular junctions (NMJs). Several signaling and extracellular matrix molecules play stimulatory and inhibitory roles on the assembly of functional synapses. Studies in Drosophila have revealed crucial functions for early morphogens, such as members of the Wnt and Bone Morphogenetic Proteins (BMP) signaling pathways, during the assembly and maturation of the NMJ. Here, we bring together recent findings that led us to propose that BMPs also work in vertebrate organisms as diffusible cues to communicate motor neurons and skeletal muscles.

PTEN hamartoma tumor syndrome: clinical risk assessment and management protocol

The tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is an important phosphatase that counteracts one of the most critical cancer pathways: the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathways. Clinically, deregulation of PTEN function resulting in reduced PTEN expression and activity is implicated in human diseases. Cowden syndrome (CS) is an autosomal dominant disorder characterized by benign and malignant tumors. CS-related individual features occur commonly in the general population. Approximately 25% of patients diagnosed with CS have pathogenic germline PTEN mutations, which increase lifetime risks of breast, thyroid, uterine, renal and other cancers. PTEN testing and intensive cancer surveillance allow for early detection and treatment of these cancers for mutation positive patients and their relatives. In this review, we highlight our current knowledge of germline PTEN mutations in relation to human disease. We review current clinical diagnosis and management recommendations for PHTS including recent discoveries in understanding PTEN function regulation and how this can be exploited therapeutically.

C-terminal domain (CTD) small phosphatase-like 2 modulates the canonical bone morphogenetic protein (BMP) signaling and mesenchymal differentiation via Smad dephosphorylation

The bone morphogenetic protein (BMP) signaling pathway regulates a wide range of cellular responses in metazoans. A key step in the canonical BMP signaling is the phosphorylation and activation of transcription factors Smad1, Smad5, and Smad8 (collectively Smad1/5/8) by the type I BMP receptors. We previously identified PPM1A as a phosphatase toward dephosphorylation of all receptor-regulated Smads (R-Smads), including Smad1/5/8. Here we report another nuclear phosphatase named SCP4/CTDSPL2, belonging to the FCP/SCP family, as a novel Smad phosphatase in the nucleus. SCP4 physically interacts with and specifically dephosphorylates Smad1/5/8, and as a result attenuates BMP-induced transcriptional responses. Knockdown of SCP4 in multipotent mesenchymal C2C12 cells leads to increased expression of BMP target genes and consequently promotes BMP-induced osteogenic differentiation. Collectively, our results demonstrate that SCP4, as a Smad phosphatase, plays a critical role in BMP-induced signaling and cellular functions.

Structure-activity relationship of 3,5-diaryl-2-aminopyridine ALK2 inhibitors reveals unaltered binding affinity for fibrodysplasia ossificans progressiva causing mutants

There are currently no effective therapies for fibrodysplasia ossificans progressiva (FOP), a debilitating and progressive heterotopic ossification disease caused by activating mutations of ACVR1 encoding the BMP type I receptor kinase ALK2. Recently, a subset of these same mutations of ACVR1 have been identified in diffuse intrinsic pontine glioma (DIPG) tumors. Here we describe the structure–activity relationship for a series of novel ALK2 inhibitors based on the 2-aminopyridine compound K02288. Several modifications increased potency in kinase, thermal shift, or cell-based assays of BMP signaling and transcription, as well as selectivity for ALK2 versus closely related BMP and TGF-β type I receptor kinases. Compounds in this series exhibited a wide range of in vitro cytotoxicity that was not correlated with potency or selectivity, suggesting mechanisms independent of BMP or TGF-β inhibition. The study also highlights a potent 2-methylpyridine derivative 10 (LDN-214117) with a high degree of selectivity for ALK2 and low cytotoxicity that could provide a template for preclinical development. Contrary to the notion that activating mutations of ALK2 might alter inhibitor efficacy due to potential conformational changes in the ATP-binding site, the compounds demonstrated consistent binding to a panel of mutant and wild-type ALK2 proteins. Thus, BMP inhibitors identified via activity against wild-type ALK2 signaling are likely to be of clinical relevance for the diverse ALK2 mutant proteins associated with FOP and DIPG.

Osteoinductive nanohydroxyapatite bone substitute prepared via in situ hydrothermal transformation of cuttlefish bone

The capacity to induce a rapid and controlled healing of bone defects is critical for a bone substitute. Previous studies have reported hydrothermal transformation (HT) of aragonite from cuttlebone (CB) to cuttlebone hydroxyapatite (CBHA). However, the biocompatibility and in vivo characteristic of CBHA have not been fully investigated. We fabricated CBHA via the in situ HT of aragonite from CB. This CBHA exhibited a highly porous structure and nanoscaled surface morphology with a significantly higher protein adsorption rate than CB. Marrow mesenchymal stem cells (MSCs) were seeded and cultured on the CBHA and CB to evaluate their influence on cell proliferation and differentiation. According to scanning electronic microscopy observation and MTT assay, the MSCs adhered and proliferated well on both the CBHA and CB. Compared with the cells on the CB, the MSCs on CBHA exhibited enhanced alkaline phosphatase activity and osteocalcin levels after 13 days of culture. In vivo testing revealed that CBHA could induce ectopic bone formation after implantation, while no bone formation being observed in the CB. These findings demonstrated that a nanoscaled and osteoinductive bone substitute could be produced by hydrothermally transforming an aragonite of CB into a hydroxyapatite.

The DAN family: modulators of TGF-β signaling and beyond

Extracellular binding proteins or antagonists are important factors that modulate ligands in the transforming growth factor (TGF-β) family. While the interplay between antagonists and ligands are essential for developmental and normal cellular processes, their imbalance can lead to the pathology of several disease states. In particular, recent studies have implicated members of the differential screening-selected gene in neuroblastoma (DAN) family in disease such as renal fibrosis, pulmonary arterial hypertension, and reactivation of metastatic cancer stem cells. DAN family members are known to inhibit the bone morphogenetic proteins (BMP) of the TGF-β family. However, unlike other TGF-β antagonist families, DAN family members have roles beyond ligand inhibition and can modulate Wnt and vascular endothelial growth factor (VEGF) signaling pathways. This review describes recent structural and functional advances that have expanded our understanding of DAN family proteins with regards to BMP inhibition and also highlights their emerging roles in the modulation of Wnt and VEGF signaling pathways.

Sertad1 encodes a novel transcriptional co-activator of SMAD1 in mouse embryonic hearts

Despite considerable advances in surgical repairing procedures, congenital heart diseases (CHDs) remain the leading noninfectious cause of infant morbidity and mortality. Understanding the molecular/genetic mechanisms underlying normal cardiogenesis will provide essential information for the development of novel diagnostic and therapeutic strategies against CHDs. BMP signaling plays complex roles in multiple cardiogenic processes in mammals. SMAD1 is a canonical nuclear mediator of BMP signaling, the activity of which is critically regulated through its interaction partners. We screened a mouse embryonic heart yeast two-hybrid library using Smad1 as bait and identified SERTAD1 as a novel interaction partner of SMAD1. SERTAD1 contains multiple potential functional domains, including two partially overlapping transactivation domains at the C terminus. The SERTAD1-SMAD1 interaction in vitro and in mammalian cells was further confirmed through biochemical assays. The expression of Sertad1 in developing hearts was demonstrated using RT-PCR, western blotting and in situ hybridization analyses. We also showed that SERTAD1 was localized in both the cytoplasm and nucleus of immortalized cardiomyocytes and primary embryonic cardiomyocyte cultures. The overexpression of SERTAD1 in cardiomyocytes not only enhanced the activity of two BMP reporters in a dose-dependent manner but also increased the expression of several known BMP/SMAD regulatory targets. Therefore, these data suggest that SERTAD1 acts as a SMAD1 transcriptional co-activator to promote the expression of BMP target genes during mouse cardiogenesis.

Familial juvenile polyposis syndrome with a novel SMAD4 germline mutation

Juvenile polyposis syndrome (JPS) is a dominantly inherited disorder characterized by the development of numerous juvenile polyps (JPs) of the gastrointestinal tract, and associated with a mutation of the SMAD4 or BMPR1A gene. Here, we report a mother-daughter case of familial JPS. A 29-year-old female patient with severe iron deficiency anemia and hypoproteinemia had numerous polyps in the stomach and a few polyps in the ileum and colon that were detected endoscopically. Biopsy specimens from the gastric polyps were diagnosed as JPs. The patient underwent a laparoscopy-assisted total gastrectomy, and her anemia and hypoproteinemia improved. Her mother also had multiple JPs in the stomach, duodenum, jejunum, and colon. We then diagnosed them as having familial JPS. Moreover, germline mutation analysis of the 2 patients presented a novel pathogenic SMAD4 variant.

RNAi screen reveals potentially novel roles of cytokines in myoblast differentiation

Cytokines are cell-secreted signaling molecules that modulate various cellular functions, with the best-characterized roles in immune responses. The expression of numerous cytokines in skeletal muscle tissues and muscle cells has been reported, but their function in skeletal myogenesis, the formation of skeletal muscle, has been largely underexplored. To systematically examine the potential roles of cytokines in skeletal myogenesis, we undertook an RNAi screen of 134 mouse cytokine genes for their involvement in the differentiation of C2C12 myoblasts. Our results have uncovered 29 cytokines as strong candidates for novel myogenic regulators, potentially conferring positive and negative regulation at distinct stages of myogenesis. These candidates represent a diverse collection of cytokine families, including interleukins, TNF-related factors, and chemokines. Our findings suggest the fundamental importance of cytokines in the cell-autonomous regulation of myoblast differentiation, and may facilitate future identification of novel therapeutic targets for improving muscle regeneration and growth in health and diseases.

Beyond TGFβ: roles of other TGFβ superfamily members in cancer

Much of the focus on the transforming growth factor-β (TGFβ) superfamily in cancer has revolved around the TGFβ ligands themselves. However, it is now becoming apparent that deregulated signalling by many of the other superfamily members also has crucial roles in both the development of tumours and metastasis. Furthermore, these signalling pathways are emerging as plausible therapeutic targets. Their roles in tumorigenesis frequently reflect their function in embryonic development or in adult tissue homeostasis, and their influence extends beyond the tumours themselves, to the tumour microenvironment and more widely to complications of cancer such as cachexia and bone loss.

Development of an ALK2-biased BMP type I receptor kinase inhibitor

The bone morphogenetic protein (BMP) signaling pathway has essential functions in development, homeostasis, and the normal and pathophysiologic remodeling of tissues. Small molecule inhibitors of the BMP receptor kinase family have been useful for probing physiologic functions of BMP signaling in vitro and in vivo and may have roles in the treatment of BMP-mediated diseases. Here we describe the development of a selective and potent inhibitor of the BMP type I receptor kinases, LDN-212854, which in contrast to previously described BMP receptor kinase inhibitors exhibits nearly 4 orders of selectivity for BMP versus the closely related TGF-β and Activin type I receptors. In vitro, LDN-212854 exhibits some selectivity for ALK2 in preference to other BMP type I receptors, ALK1 and ALK3, which may permit the interrogation of ALK2-mediated signaling, transcriptional activity, and function. LDN-212854 potently inhibits heterotopic ossification in an inducible transgenic mutant ALK2 mouse model of fibrodysplasia ossificans progressiva. These findings represent a significant step toward developing selective inhibitors targeting individual members of the highly homologous BMP type I receptor family. Such inhibitors would provide greater resolution as probes of physiologic function and improved selectivity against therapeutic targets.

Bioanalytical method development, validation and quantification of dorsomorphin in rat plasma by LC-MS/MS

The present investigation describes the development and validation of a sensitive liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method for the estimation of dorsomorphin in rat plasma. A sensitive LC-MS/MS method was developed using multiple reaction monitoring mode, with the transition of m/z (Q1/Q3) 400.2/289.3 for dorsomorphin and m/z (Q1/Q3) 306.2/236.3 for zaleplon. Chromatographic separation was achieved on a reverse phase Agilent XDB C18 column (100 × 4.6 mm, 5 µm). The mobile phase consisted of acetonitrile and 5 mm ammonium acetate buffer (pH 6.0) 90:10 v/v, at a flow rate of 0.8 mL/min. The effluence was ionized in positive ion mode by electrospray ionization (ESI) and quantitated by mass spectrometry. The retention times of dorsomorphin and internal standard were found to be 2.13 and 1.13 min, respectively. Mean extraction recovery of dorsomorphin and internal standard in rat plasma was above 80%. Dorsomorphin calibration curve in rat plasma was linear (r(2) ≥ 0.99) ranging from 0.005 to 10 µg/mL. Inter-day and intra-day precision and accuracy were found to be within 85-115% (coefficient of variation). This method was successfully applied for evaluation of the oral pharmacokinetic profile of dorsomorphin in male Wistar rats.

Smad4 expression in hepatocellular carcinoma differs by hepatitis status

AIMS

Primary hepatocellular carcinoma (HCC) is a common malignancy often related to hepatitis viral infection. Smad4 is known to mediate the TGF-β pathway to suppress tumorigenesis. However, the function of Smad4 in HCC is still controversial. In this study we compared levels of Smad4 in HCC tissues with or without hepatitis virus infection and adjacent normal-appearing liver.

METHODS

Samples from HCC patients were analyzed for Smad4 protein and mRNA expression by immunohistochemistry (IHC), RT-PCR and Western blotting.

RESULTS

We found that tumor tissues expressed less Smad4 mRNA and protein than the adjacent tissues. Most HCC tumor tissues were negative for Smad4 in IHC staining, while the majority of adjacent tissues were positively stained. Interestingly, protein levels were higher in HCC tissues with viral hepatitis than those without virus infection. Suppression of expression appeared closely related to HCC, so that Smad4 appears to function as a tumor suppressor gene (TSG).

CONCLUSION

Patients with hepatitis viral infection, at higher risk for HCC, exhibited increased Smad4 protein expression suggesting hepatitis virus may modulate Smad4 expression, which is functionally distinct from its putative role as a TSG. Smad4 expression may thus be an applicable marker for diagnosis and/or a target to develop therapeutic agents for HCC.

Transient treatment of pregnant Merino ewes with modulators of cortisol biosynthesis coinciding with primary wool follicle initiation alters lifetime wool growth

The economically important characteristics of the adult fleece of Merino sheep, such as increases in clean fleece weight, fibre length, fibre diameter and crimp characteristics are determined during critical phases of fetal development of the skin and its appendages. Genetics plays a major role in the development of traits, but the maternal uterine environment could also influence development. Treatment of pregnant ewes with cortisol and its analogues has previously been shown to produce changes in wool follicle morphology. The aim of this study was to determine the effect of transient manipulation of maternal cortisol status during critical phases of wool follicle initiation and development in utero. From Days 55–65 post-conception, singleton-bearing Merino ewes were treated with metyrapone (cortisol inhibitor) or betamethasone (cortisol analogue). Lambs exposed to metyrapone in utero were born with hairier birthcoats than the control or betamethasone treatment groups (P < 0.05), displayed a 10% increase in staple length and a reduction in crimp frequency for the first three shearings (P < 0.05). Co-expression network analysis of microarray data revealed up-regulation of members of the transforming growth factor-β and chemokine receptor superfamilies, gene families known to influence hair and skin development. These experiments demonstrate that presumptive transient manipulation of maternal cortisol status coinciding with the initiation of fetal wool follicle development results in long-term alteration in fleece characteristics, namely fibre length and fibre crimp frequency. These results indicate it is possible to alter the lifetime wool production of Merino sheep with therapeutics targeted to gene expression during key windows of development in utero.

Myocardial Mycn is essential for mouse ventricular wall morphogenesis

MYCN is a highly conserved transcription factor with multifaceted roles in development and disease. Mutations in MYCN are associated with Feingold syndrome, a developmental disorder characterized in part by congenital heart defects. Mouse models have helped elucidate MYCN functions; however its cardiac-specific roles during development remain unclear. We employed a Cre/loxp strategy to uncover the specific activities of MYCN in the developing mouse myocardium. Myocardial deletion of Mycn resulted in a thin-myocardial wall defect with dramatically reduced trabeculation. The mutant heart defects strongly resemble the phenotype caused by disruption of BMP10 and Neuregulin-1 (NRG1) signaling pathways, two central mediators of myocardial wall development. Our further examination showed that expression of MYCN is regulated by both BMP and NRG1 signaling. The thin-wall defect in mutant hearts is caused by a reduction in both cell proliferation and cell size. MYCN promotes cardiomyocyte proliferation through regulating expression of cell cycle regulators (including CCND1, CCND2, and ID2) and promotes cardiomyocyte growth through regulating expression of p70S6K. In addition, expression of multiple sarcomere proteins is altered in Mycn myocardial-inactivation embryos, indicating its essential role for proper cardiomyocyte differentiation. In summary, Mycn acts downstream of BMP and NRG1 cardiogenic signaling pathways to promote normal myocardial wall morphogenesis.

Regulation of the tumor suppressor PTEN by SUMO

The crucial function of the PTEN tumor suppressor in multiple cellular processes suggests that its activity must be tightly controlled. Both, membrane association and a variety of post-translational modifications, such as acetylation, phosphorylation, and mono- and polyubiquitination, have been reported to regulate PTEN activity. Here, we demonstrated that PTEN is also post-translationally modified by the small ubiquitin-like proteins, small ubiquitin-related modifier 1 (SUMO1) and SUMO2. We identified lysine residue 266 and the major monoubiquitination site 289, both located within the C2 domain required for PTEN membrane association, as SUMO acceptors in PTEN. We demonstrated the existence of a crosstalk between PTEN SUMOylation and ubiquitination, with PTEN-SUMO1 showing a reduced capacity to form covalent interactions with monoubiquitin and accumulation of PTEN-SUMO2 conjugates after inhibition of the proteasome. Moreover, we found that virus infection induces PTEN SUMOylation and favors PTEN localization at the cell membrane. Finally, we demonstrated that SUMOylation contributes to the control of virus infection by PTEN.

CCN6 modulates BMP signaling via the Smad-independent TAK1/p38 pathway, acting to suppress metastasis of breast cancer

CCN6 (WISP3) is an extracellular matrix protein that exerts tumor suppressive functions in breast cancer, where its decreased expression is a feature of advanced disease. However, neither its role nor mechanism of action in breast cancer metastasis has been established. Bone morphogenetic proteins (BMPs), which constitute ligands of the TGF-β superfamily, are multifunctional cytokines that induce epithelial-mesenchymal transition, cell invasion, and metastasis. In this study, we identify a CCN6-BMP4-TAK1 kinase signaling pathway that controls the ability of the p38 MAP kinase to regulate acinar morphogenesis and invasion of breast cells. ShRNA-mediated attenuation of CCN6 in human mammary epithelial cells led to BMP4 upregulation as a major response to exposure to the TGF-β superfamily. CCN6 attenuation also induced BMP4-mediated activation of the Smad-independent TAK1 and p38 kinases. Conversely, ectopic expression of CCN6 in breast cancer cells antagonized BMP4-mediated TAK1/p38 activation and invasive capacity, both by binding BMP4 protein as well as decreasing BMP4 protein levels. Effects on BMP4 and p38 were confirmed in vivo where they correlated with decreased metastasis. In clinical specimens, we found that CCN6 expression was inversely associated with BMP4 and phospho-p38 levels in 69% of invasive breast carcinomas examined, consistent with the functional results. Together our findings identify a novel modifier pathway through which CCN6 acts to limit breast cancer invasion and metastasis.

Dual effects of heparin on BMP-2-induced osteogenic activity in MC3T3-E1 cells

Heparin displays several types of biological activities by binding to various extracellular molecules, including pivotal roles in bone metabolism. We have previously reported that heparin competitively inhibits the binding activity of bone morphogenic protein-2 (BMP-2) to BMP and the BMP receptor (BMPR) and suppresses BMP-2 osteogenic activity. In the present study, we examined whether heparin affects osteoblast differentiation induced by BMP-2 at various time points in vitro. We found that 72 h of treatment with heparin inhibited alkaline phosphatase (ALP) activity. However, 144 h of treatment enhanced the ALP activity in BMP-2-stimulated MC3T3-E1 cells. Although heparin decreased the phosphorylation of Smad1/5/8 after 0.5 h of culture, prolonged periods of culture with heparin enhanced the Smad phosphorylation. In addition, 72 h of treatment with heparin enhanced the mRNA expression of runx2 and osterix in BMP-2-stimulated MC3T3-E1 cells. Furthermore, the mRNA expression of BMP antagonists and inhibitory Smads induced by BMP-2 was preferentially blocked by heparin at the 24 and 48 h time points. These findings indicate biphasic effects of heparin on BMP-2 activity and suggest that heparin has complex effects on the BMP-2 osteogenic bioactivities. Prolonged culture with heparin stimulated BMP-2-induced osteogenic activity via down-regulation of BMP-2 antagonists and inhibitory Smads.

Bone induction through controlled release of novel BMP-2-related peptide from PTMC₁₁-F127-PTMC₁₁ hydrogels

Bone morphogenetic protein 2 (BMP-2) is the most powerful osteogenic factor; its effectiveness in enhancing osteoblastic activation has been confirmed both in vitro and in vivo. We developed a novel peptide (designated P24) derived from the 'knuckle' epitope of BMP-2 and found it also had osteogenic bioactivity to some extent. The main objective of this study was to develop a controlled release system based on poly(trimethylene carbonate)-F127-poly(trimethylene carbonate) (PTMC₁₁-F127-PTMC₁₁) hydrogels for the P24 peptide, to promote bone formation. By varying the copolymer concentrations, we demonstrated that P24/PTMC₁₁-F127-PTMC₁₁ hydrogels were an efficient system for the sustained release of P24 over 21-35 days. The P24-loaded hydrogels elevated alkaline phosphatase activity and promoted the expression of osteocalcin mRNA in bone marrow stromal cells (BMSCs) in vitro. Radiographic and histological examination showed that P24-loaded hydrogels could induce more effective ectopic bone formation in vivo than P24-free hydrogels. These results indicate that the PTMC₁₁-F127-PTMC₁₁ hydrogel is a suitable carrier for the controlled release of P24, and is a promising injectable biomaterial for the induction of bone regeneration.

Small bowel polyposis syndromes

Intestinal polyposis syndromes are relatively rare. However, it is important for clinicians to recognize the potential risks of these syndromes. Based on histology, these syndromes can be classified mainly into hamartomatous polyposis syndromes and familial adenomatous polyposis (FAP), which affects mainly the large intestine. This review discusses the clinical manifestations and underlying genetics of the most common small intestinal polyposis syndromes: Peutz-Jeghers syndrome (PJS), juvenile polyposis (JP), PTEN hamartoma tumor syndrome (PHTS), and the small intestinal implications of familial adenomatous polyposis (FAP).

Nonmyelinating Schwann cells maintain hematopoietic stem cell hibernation in the bone marrow niche

Hematopoietic stem cells (HSCs) reside and self-renew in the bone marrow (BM) niche. Overall, the signaling that regulates stem cell dormancy in the HSC niche remains controversial. Here, we demonstrate that TGF-β type II receptor-deficient HSCs show low-level Smad activation and impaired long-term repopulating activity, underlining the critical role of TGF-β/Smad signaling in HSC maintenance. TGF-β is produced as a latent form by a variety of cells, so we searched for those that express activator molecules for latent TGF-β. Nonmyelinating Schwann cells in BM proved responsible for activation. These glial cells ensheathed autonomic nerves, expressed HSC niche factor genes, and were in contact with a substantial proportion of HSCs. Autonomic nerve denervation reduced the number of these active TGF-β-producing cells and led to rapid loss of HSCs from BM. We propose that glial cells are components of a BM niche and maintain HSC hibernation by regulating activation of latent TGF-β.

A restricted spectrum of mutations in the SMAD4 tumor-suppressor gene underlies Myhre syndrome

Myhre syndrome is a developmental disorder characterized by reduced growth, generalized muscular hypertrophy, facial dysmorphism, deafness, cognitive deficits, joint stiffness, and skeletal anomalies. Here, by performing exome sequencing of a single affected individual and coupling the results to a hypothesis-driven filtering strategy, we establish that heterozygous mutations in SMAD4, which encodes for a transducer mediating transforming growth factor β and bone morphogenetic protein signaling branches, underlie this rare Mendelian trait. Two recurrent de novo SMAD4 mutations were identified in eight unrelated subjects. Both mutations were missense changes altering Ile500 within the evolutionary conserved MAD homology 2 domain, a well known mutational hot spot in malignancies. Structural analyses suggest that the substituted residues are likely to perturb the binding properties of the mutant protein to signaling partners. Although SMAD4 has been established as a tumor suppressor gene somatically mutated in pancreatic, gastrointestinal, and skin cancers, and germline loss-of-function lesions and deletions of this gene have been documented to cause disorders that predispose individuals to gastrointestinal cancer and vascular dysplasias, the present report identifies a previously unrecognized class of mutations in the gene with profound impact on development and growth.

Inhibition of BMP signaling in P-Cadherin positive hair progenitor cells leads to trichofolliculoma-like hair follicle neoplasias

BACKGROUND

Skin stem cells contribute to all three major lineages of epidermal appendages, i.e., the epidermis, the hair follicle, and the sebaceous gland. In hair follicles, highly proliferative committed progenitor cells, called matrix cells, are located at the base of the follicle in the hair bulb. The differentiation of these early progenitor cells leads to specification of a central hair shaft surrounded by an inner root sheath (IRS) and a companion layer. Multiple signaling molecules, including bone morphogenetic proteins (BMPs), have been implicated in this process.

METHODS

To further probe the contribution of BMP signaling to hair follicle development and maintenance we employed a transgenic mouse that expresses the BMP inhibitor, Noggin, to disrupt BMP signaling specifically in subset of hair follicle progenitors under the control of neuron specific enolase (Nse) promoter. We then studied the skin tumor phenotypes of the transgenic mice through histology, immunohistochemistry and Western Blotting to delineate the underlying mechanisms. Double transgenic mice expressing BMP as well as noggin under control of the Nse promoter were used to rescue the skin tumor phenotypes.

RESULTS

We found that the transgene is expressed specifically in a subpopulation of P-cadherin positive progenitor cells in Nse-Noggin mice. Blocking BMP signaling in this cell population led to benign hair follicle-derived neoplasias resembling human trichofolliculomas, associated with down-regulation of E-cadherin expression and dynamic regulation of CD44.

CONCLUSIONS

These observations further define a critical role for BMP signaling in maintaining the homeostasis of hair follicles, and suggest that dysregulation of BMP signaling in hair follicle progenitors may contribute to human trichofolliculoma.

Overexpression of Evi-1 oncoprotein represses TGF-β signaling in colorectal cancer

Human colorectal cancer (CRC) cells are resistant to the anti-proliferative effect of transforming growth factor-β (TGF-β), suggesting that disruption of TGF-β signaling plays an important role in colorectal carcinogenesis. Ecotropic virus integration site-1 (Evi-1) oncoprotein represses TGF-β signaling by interacting with Smads, but its role in CRC has not been established. The purpose of this study is to determine whether Evi-1 plays role(s) in CRCs and to characterize Evi-1 transcript(s) in CRCs. Evi-1 was overexpressed in 53% of human CRC samples, 100% of colon adenoma samples, and 100% of human colon cancer cell lines tested. Using 5' RACE, we cloned a novel Evi-1 transcript (Evi-1e) from a human CRC tissue and found that this novel transcript was expressed at a higher level in CRC tissues than in normal tissues and was the major Evi-1 transcript in CRCs. Transient Evi-1 transfection inhibited TGF-β-induced transcriptional activity and reversed the growth inhibitory effect of TGF-β in MC-26 mouse colon cancer cells. In conclusion, we have identified overexpression of Evi-1 oncoprotein as a novel mechanism by which a subset of human CRCs may escape TGF-β regulation. We have also identified a novel Evi-1 transcript, Evi-1e, as the major Evi-1 transcript expressed in human CRCs.

Human ovarian carcinoma–associated mesenchymal stem cells regulate cancer stem cells and tumorigenesis via altered BMP production

Accumulating evidence suggests that mesenchymal stem cells (MSCs) are recruited to the tumor microenvironment; however, controversy exists regarding their role in solid tumors. In this study, we identified and confirmed the presence of carcinoma-associated MSCs (CA-MSCs) in the majority of human ovarian tumor samples that we analyzed. These CA-MSCs had a normal morphologic appearance, a normal karyotype, and were nontumorigenic. CA-MSCs were multipotent with capacity for differentiating into adipose, cartilage, and bone. When combined with tumor cells in vivo, CA-MSCs promoted tumor growth more effectively than did control MSCs. In vitro and in vivo studies suggested that CA-MSCs promoted tumor growth by increasing the number of cancer stem cells. Although CA-MSCs expressed traditional MSCs markers, they had an expression profile distinct from that of MSCs from healthy individuals, including increased expression of BMP2, BMP4, and BMP6. Importantly, BMP2 treatment in vitro mimicked the effects of CA-MSCs on cancer stem cells, while inhibiting BMP signaling in vitro and in vivo partly abrogated MSC-promoted tumor growth. Taken together, our data suggest that MSCs in the ovarian tumor microenvironment have an expression profile that promotes tumorigenesis and that BMP inhibition may be an effective therapeutic approach for ovarian cancer.

Aberrant TGFβ/SMAD4 signaling contributes to epigenetic silencing of a putative tumor suppressor, RunX1T1 in ovarian cancer

Aberrant TGFβ signaling pathway may alter the expression of down-stream targets and promotes ovarian carcinogenesis. However, the mechanism of this impairment is not fully understood. Our previous study has identified RunX1T1 as a putative SMAD4 target in an immortalized ovarian surface epithelial cell line, IOSE. In this study, we report that transcription of RunX1T1 was confirmed to be positively regulated by SMAD4 in IOSE cells and epigenetically silenced in a panel of ovarian cancer cell lines by promoter hypermethylation and histone methylation at H3 lysine 9. SMAD4 depletion increased repressive histone modifications of RunX1T1 promoter without affecting promoter methylation in IOSE cells. Epigenetic treatment can restore RunX1T1 expression by reversing its epigenetic status in MCP3 ovarian cancer cells. When transiently treated with a demethylating agent, the expression of RunX1T1 was partially restored in MCP3 cells, but gradual re-silencing through promoter re-methylation was observed after the treatment. Interestingly, SMAD4 knockdown accelerated this re-silencing process, suggesting that normal TGF-beta signaling is essential for the maintenance of RunX1T1 expression. In vivo analysis confirmed that hypermethylation of RunX1T1 was detected in 35.7% (34/95) of ovarian tumors with high clinical stages (P=0.035) and in 83% (5/6) of primary ovarian cancer-initiating cells. Additionally, concurrent methylation of RunX1T1 and another SMAD4 target, FBXO32 which was previously found to be hypermethylated in ovarian cancer was observed in this same sample cohort (P< 0.05). Restoration of RunX1T1 inhibited cancer cell growth. Taken together, dysregulated TGFβ/SMAD4 signaling may lead to epigenetic silencing of a putative tumor suppressor, RunX1T1, during ovarian carcinogenesis.

Transforming growth factor-β and the hallmarks of cancer

Tumorigenesis is in many respects a process of dysregulated cellular evolution that drives malignant cells to acquire six phenotypic hallmarks of cancer, including their ability to proliferate and replicate autonomously, to resist cytostatic and apoptotic signals, and to induce tissue invasion, metastasis, and angiogenesis. Transforming growth factor-β (TGF-β) is a potent pleiotropic cytokine that functions as a formidable barrier to the development of cancer hallmarks in normal cells and tissues. Paradoxically, tumorigenesis counteracts the tumor suppressing activities of TGF-β, thus enabling TGF-β to stimulate cancer invasion and metastasis. Fundamental gaps exist in our knowledge of how malignant cells overcome the cytostatic actions of TGF-β, and of how TGF-β stimulates the acquisition of cancer hallmarks by developing and progressing human cancers. Here we review the molecular and cellular mechanisms that underlie the ability of TGF-β to mediate tumor suppression in normal cells, and conversely, to facilitate cancer progression and disease dissemination in malignant cells.

The neuronal influence on tumor progression

Nerve fibers accompany blood and lymphatic vessels all over the body. An extensive amount of knowledge has been obtained with regard to tumor angiogenesis and tumor lymphangiogenesis, yet little is known about the potential biological effects of "neoneurogenesis". Cancer cells can exploit the advantage of the factors released by the nerve fibers to generate a positive microenvironment for cell survival and proliferation. At the same time, they can stimulate the formation of neurites by secreting neurotrophic factors and axon guidance molecules. The neuronal influence on the biology of a neoplasm was initially described several decades ago. Since then, an increasing amount of experimental evidence strongly suggests the existence of reciprocal interactions between cancer cells and nerves in humans. Moreover, researchers have been able to demonstrate a crosstalk between cancer cells and nerve fibers as a strategy for survival. Despite all these evidence, a lot remains to be done in order to clarify the role of neurotransmitters, neuropeptides, and their associated receptor-initiated signaling pathways in the development and progression of cancer, and response to therapy. A global-wide characterization of the neurotransmitters or neuropeptides present in the tumor microenvironment would provide insights into the real biological influences of the neuronal tissue on tumor progression. This review is intended to discuss our current understanding of neurosignaling in cancer and its potential implications on cancer prevention and therapy. The review will focus on the soluble factors released by cancer cells and nerve endings, their biological effects and their potential relevance in the treatment of cancer.

SMAD4 mutation segregating in a family with juvenile polyposis, aortopathy, and mitral valve dysfunction

Juvenile polyposis syndrome (JPS) is caused by heterozygous mutations in either SMAD4 or BMPR1A. Individuals with JPS due to mutations in SMAD4 are at greater risk to manifest signs of hereditary hemorrhagic telangiectasia (HHT). HHT is caused by either mutations in SMAD4 or other genes that modulate transforming growth factor-beta (TGFβ) signaling. Additional genes in the TGFβ network include FBN1, TGFBR1, and TGFBR2, mutations of which cause either Marfan syndrome (MFS) or Loeys-Dietz syndrome (LDS), respectively. As SMAD4, FBN1, and TGFBR1/2 map to different regions of the genome, disorders associated with mutations in these genes are not expected to co-segregate in a family. We report an individual whose family history was positive for aortopathy, mitral valve dysfunction, and JPS. Mutation analysis of SMAD4 implicates this gene for these phenotypes in this family. Although SMAD4 is among several genes in the TGFβ network, and although prior single case reports have described large vessel aneurysms in HHT, this is the first description of aortic and mitral disease presenting with JPS. This observation suggests that, in addition to HHT, individuals with SMAD4 mutations may be at risk for aortic dilation and mitral valve dysfunction. We emphasize the importance of comprehensive review of the medical history prior to molecular testing, especially in an asymptomatic patient.

Bone morphogenetic protein 4 induces differentiation of colorectal cancer stem cells and increases their response to chemotherapy in mice

BACKGROUND & AIMS

The limited clinical response observed in many patients with colorectal cancer may be related to the presence of chemoresistant colorectal cancer stem cells (CRC-SCs). Bone morphogenetic protein 4 (BMP4) promotes the differentiation of normal colonic stem cells. We investigated whether BMP4 might be used to induce differentiation of CRC-SCs and for therapeutic purposes.

METHODS

CRC-SCs were isolated from 25 tumor samples based on expression of CD133 or using a selection culture medium. BMP4 expression and activity on CRC-SCs were evaluated in vitro; progeny of the stem cells were evaluated by immunofluorescence, immunoblot, and flow cytometry analyses. The potential therapeutic effect of BMP4 was assessed in immunocompromised mice after injection of CRC-SCs that responded to chemotherapy (n = 4) or that did not (n = 2).

RESULTS

CRC-SCs did not express BMP4 whereas differentiated cells did. Recombinant BMP4 promoted differentiation and apoptosis of CRC-SCs in 12 of 15 independent experiments; this effect did not depend on Small Mothers against decapentaplegic (Smad)4 expression level or microsatellite stability. BMP4 activated the canonical and noncanonical BMP signaling pathways, including phosphoInositide 3-kinase (PI3K) and PKB (protein kinase B)/AKT. Mutations in PI3K or loss of Phosphatase and Tensin homolog (PTEN) in Smad4-defective tumors made CRC-SCs unresponsive to BMP4. Administration of BMP4 to immunocompromised mice with tumors that arose from CRC-SCs increased the antitumor effects of 5-fluorouracil and oxaliplatin.

CONCLUSIONS

BMP4 promotes terminal differentiation, apoptosis, and chemosensitization of CRC-SCs in tumors that do not have simultaneous mutations in Smad4 and constitutive activation of PI3K. BMP4 might be developed as a therapeutic agent against cancer stem cells in advanced colorectal tumors.

Mesenchymal cells of the intestinal lamina propria

The mesenchymal elements of the intestinal lamina propria reviewed here are the myofibroblasts, fibroblasts, mural cells (pericytes) of the vasculature, bone marrow-derived stromal stem cells, smooth muscle of the muscularis mucosae, and smooth muscle surrounding the lymphatic lacteals. These cells share similar marker molecules, origins, and coordinated biological functions previously ascribed solely to subepithelial myofibroblasts. We review the functional anatomy of intestinal mesenchymal cells and describe what is known about their origin in the embryo and their replacement in adults. As part of their putative role in intestinal mucosal morphogenesis, we consider the intestinal stem cell niche. Lastly, we review emerging information about myofibroblasts as nonprofessional immune cells that may be important as an alarm system for the gut and as a participant in peripheral immune tolerance.

Transforming growth factor beta2 is negatively regulated by endogenous retinoic acid during early heart morphogenesis

Vitamin A-deficient (VAD) quail embryos lack the vitamin A-active form, retinoic acid (RA) and are characterized by a phenotype that includes a grossly abnormal cardiovascular system that can be rescued by RA. Here we report that the transforming growth factor, TGFbeta2 is involved in RA-regulated cardiovascular development. In VAD embryos TGFbeta2 mRNA and protein expression are greatly elevated. The expression of TGFbeta receptor II is also elevated in VAD embryos but is normalized by treatment with TGFbeta2-specific antisense oligonucleotides (AS). Administration of this AS or an antibody specific for TGFbeta2 to VAD embryos normalizes posterior heart development and vascularization, while the administration of exogenous active TGFbeta2 protein to normal quail embryos mimics the excessive TGFbeta2 status of VAD embryos and induces VAD cardiovascular phenotype. In VAD embryos pSmad2/3 and pErk1 are not activated, while pErk2 and pcRaf are elevated and pSmad1/5/8 is diminished. We conclude that in the early avian embryo TGFbeta2 has a major role in the retinoic acid-regulated posterior heart morphogenesis for which it does not use Smad2/3 pathways, but may use other signaling pathways. Importantly, we conclude that retinoic acid is a critical negative physiological regulator of the magnitude of TGFbeta2 signals during vertebrate heart formation.

Peptide ligands that use a novel binding site to target both TGF-β receptors

The transforming growth factor beta (TGF-β) signaling pathway plays myriad roles in development and disease. TGF-β isoforms initiate signaling by organizing their cell surface receptors TβRI and TβRII. Exploration and exploitation of the versatility of TGF-β signaling requires an enhanced understanding of structure-function relationships in this pathway. To this end, small molecule, peptide, and antibody effectors that bind key signaling components would serve as valuable probes. We focused on the extracellular domain of TβR1 (TβRI-ED) as a target for effector screening. The observation that TβRI-ED can bind to a TGF-β coreceptor (endoglin) suggests that the TβRI-ED may have multiple interaction sites. Using phage display, we identified two peptides LTGKNFPMFHRN (Pep1) and MHRMPSFLPTTL (Pep2) that bind the TβRI-ED (K(d)≈ 10(-5) M). Although our screen focused on TβRI-ED, the hit peptides interact with the TβRII-ED with similar affinities. The peptide ligands occupy the same binding sites on TβRI and TβRII, as demonstrated by their ability to compete with each other for receptor binding. Moreover, neither interferes with TGF-β binding. These results indicate that both TβRI and TβRII possess hot spots for protein-protein interactions that are distinct from those used by their known ligand TGF-β. To convert these compounds into high affinity probes, we exploited the observation that TβRI and TβRII exist as dimers on the cell surface; therefore, we assembled a multivalent ligand. Specifically, we displayed one of our receptor-binding peptides on a dendrimer scaffold. We anticipate that the potent multivalent ligand that resulted can be used to probe the role of receptor assembly in TGF-β function.

Enhancement of bone morphogenetic protein-2-induced ectopic bone formation by transforming growth factor-β1

Bone morphogenetic proteins (BMPs) possess osteoinductive activities and are useful for clinical treatments, including bone regeneration. We found that transforming growth factor (TGF)-β1 strongly enhances the osteoinductive activity of BMP-2. Collagen sponges containing 5 μg of BMP-2 were implanted into mouse muscle tissues, after which lump-like masses appeared and grew until day 7. Subsequently, calcification occurred in the lump-like masses by day 14. Addition of 50 ng of TGF-β1 to the BMP-2-containing sponges markedly accelerated the growth of the lump-like masses and resulted in a fivefold increase in total bone volume as compared with BMP-2 alone. The number of osteoblasts in ectopic bone tissues at 14 days after implantation induced by BMP-2+TGF-β1 was twofold greater than that with BMP-2 alone, whereas the number of osteoclasts was decreased by half. On the other hand, TGF-β1 accelerated the differentiation of both osteoblasts and osteoclasts in the early stage (2-7 days after implantation) of ectopic bone formation. We also implanted collagen sponges into bone defects surgically created in mouse calvaria. Sponges containing 2.5 μg of BMP-2 and 25 ng of TGF-β1 caused complete filling of the defects with orthotopic bone, whereas those containing 2.5 μg of BMP-2 alone caused only partial filling. These results suggest that TGF-β1 enhances BMP-2-induced ectopic bone formation by accelerating the growth of lump-like masses, and regulates osteoblast and osteoclast generation. Our findings may contribute to the development of a new treatment method for skeletal disorders.

[Cancer genetic predisposition: current events and perspectives in 2010]

Studies performed during these last 30 years have had a major impact on the understanding of carcinogenesis. They have opened a new field: cancer genetic predisposition. At the present time, most of the cancer predispositions linked to the alteration of one gene, associated with a high risk of cancer and with a specific phenotype have been identified. About 70 genes have been identified and have led to genetic testing. The indication of genetic testing, the management of at risk patients require the establishment of guidelines. The next challenge is the identification of cancer susceptibility genes associated with low risk or modifying the effect of treatment.

[Tumor stem cell research - basis and challenge for diagnosis and therapy]

Biological features of tumor cells relevant to progression, metastasis, and prognosis in cancer patients have been investigated for many years. During the past few years, the concept of tumor stem cells has gained widespread acceptance. The cancer stem cell (CSC) model is based on the observation that continuous growth of tumors depends on a small population of immature neoplastic cells with unlimited proliferative potential. In contrast to these CSC, more mature clonal cells in the same neoplasm undergo apoptosis and die after a variable number of cell divisions. The self-renewal capacity of CSC plays a central role in this scenario and enables permanent tumor cell repopulation in vivo in patients as well as in experimental animals, e.g., immunodeficient mice. Based on the stem cell concept, it is clear that the success of an anti-neoplastic approach depends on efficient targeting and elimination of CSC. An important aspect of CSC is their intrinsic resistance against conventional drugs. Therefore, a major focus in current research is molecular targets and their expression in CSC, with the goal to use targeted drugs for CSC elimination. It is the hope for the future that therapeutic approaches involving CSC-targeting concepts will lead to sustained remission and thus improvement of prognosis in leukemia and cancer patients.

N-cadherin can structurally substitute for E-cadherin during intestinal development but leads to polyp formation

We conditionally substituted E-cadherin (E-cad; cadherin 1) with N-cadherin (N-cad; cadherin 2) during intestine development by generating mice in which an Ncad cDNA was knocked into the Ecad locus. Mutant mice were born, demonstrating that N-cad can structurally replace E-cad and establish proper organ architecture. After birth, mutant mice gradually developed a mutant phenotype in both the small and large intestine and died at ~2-3 weeks of age, probably due to malnutrition during the transition to solid food. Molecular analysis revealed an extended domain of cells from the crypt into the villus region, with nuclear localization of β-catenin (β-cat; Ctnnb1) and enhanced expression of several β-cat target genes. In addition, the BMP signaling pathway was suppressed in the intestinal epithelium of the villi, suggesting that N-cad might interfere with BMP signaling in the intestinal epithelial cell layer. Interestingly, mutant mice developed severe dysplasia and clusters of cells with neoplastic features scattered along the crypt-villus axis in the small and large intestine. Our experimental model indicates that, in the absence of E-cad, the sole expression of N-cad in an epithelial environment is sufficient to induce neoplastic transformations.

[Malformation syndromes associated with childhood cancer: an update]

Biology, genetics and environment of childhood solid tumours set them apart from adult solid tumours. The nature of the progenitor cells from which these tumours arise, and their immature tissue environment, allows childhood solid tumours to develop with fewer defects in cell regulatory processes. Constitutional molecular defects are known to play a role in childhood solid tumours, as shown by the increased incidence of embryonic cancers in children carrying malformations associated with childhood cancer. These rare diagnoses are commonly missed. In this article, we reviewed the spectrum of these tumour predisposition syndromes.

Soluble repulsive guidance molecule c/hemojuvelin is a broad spectrum bone morphogenetic protein (BMP) antagonist and inhibits both BMP2- and BMP6-mediated signaling and gene expression

Inactivating mutations in hemojuvelin/repulsive guidance molecule c (HJV/RGMc) cause juvenile hemochromatosis (JH), a rapidly progressive iron overload disorder in which expression of hepcidin, a key liver-derived iron-regulatory hormone, is severely diminished. Several growth factors in the bone morphogenetic protein (BMP) family, including BMP2 and BMP6, can stimulate production of hepcidin, a biological effect that may be modified by RGMc. Here we demonstrate that soluble RGMc proteins are potent BMP inhibitors. We find that 50- and 40-kDa RGMc isoforms, when added to cells as highly purified IgG Fc fusion proteins, are able to block the acute effects of both BMP2 and BMP6 at the levels of Smad induction and gene activation, and thus represent a potentially unique class of broad-spectrum BMP antagonists. Whole transcript microarray analysis revealed that BMP2 and BMP6 each stimulated expression of a nearly identical cohort of approximately 40 mRNAs in Hep3B cells and demonstrated that 40-kDa RGMc was an effective inhibitor of both growth factors, although its potency was less than that of the known BMP2-selective antagonist, Noggin. We additionally show that JH-linked RGMc mutant proteins that retain the ability to bind BMPs are also able to function as BMP inhibitors, and like the wild type soluble RGMc species, can block BMP-activated hepcidin gene expression. The latter results raise the question of whether disease severity in JH will vary depending on the ability of a given mutant RGMc protein to interact with BMPs.

Transforming growth factor-beta: a target for cancer therapy

Transforming growth factor-beta (TGF-beta) is a pleiotropic growth factor that regulates cell growth and differentiation, apoptosis, cell motility, extracellular matrix production, angiogenesis, and cellular immune responses. TGF-beta demonstrates paradoxical action whereby it can function to suppress early tumorigenesis; however, it can also facilitate malignant transformation and stimulate tumor growth by manipulating a more hospitable environment for tumor invasion and the development of metastases. Given the integral role of TGF-beta in transformation and cancer progression, various components of the TGF-beta signaling pathway offer potentially attractive therapeutic targets for cancer treatment. This review focuses on the role of TGF-beta in cancer and discusses both small and large molecule drugs currently in development that target TGF-beta, its receptor and important down stream steps along its signaling pathway.

The long-range activity of Hedgehog is regulated in the apical extracellular space by the glypican Dally and the hydrolase Notum

Cell fate determination during developmental patterning is often controlled by concentration gradients of morphogens. In the epithelial field, morphogens like the Hedgehog (Hh) peptides diffuse both apically and basolaterally; however, whether both pools of Hh are sensed at the cellular level is unclear. Here, we show that interfering with the amount of apical Hh causes a dramatic change in the long-range activation of low-threshold Hh target genes, without similar effect on short-range, high-threshold targets. We provide genetic evidence that the glypican Dally upregulates apical Hh levels, and that the release of Dally by the hydrolase Notum promotes apical Hh long-range activity. Our data suggest that several pools of Hh are perceived in epithelial tissues. Thus, we propose that the overall gradient of Hh is a composite of pools secreted by different routes (apical and basolateral), and that a cellular summation of these components is required for appropriate developmental patterning.

Tumor angiogenesis: insights and innovations

Angiogenesis is a vital process resulting in the formation of new blood vessels. It is normally a highly regulated process that occurs during human development, reproduction, and wound repair. However, angiogenesis can also become a fundamental pathogenic process found in cancer and several other diseases. To date, the inhibition of angiogenesis has been researched at both the bench and the bedside. While several studies have found moderate improvements when treating with angiogenesis inhibitors, greater success is being seen when the inhibition of angiogenesis is combined with other traditional forms of available therapy. This review summarizes several important angiogenic factors, examines new research and ongoing clinical trials for such factors, and attempts to explain how this new knowledge may be applied in the fight against cancer and other angiogenic-related diseases.

Granulosa cell-expressed BMPR1A and BMPR1B have unique functions in regulating fertility but act redundantly to suppress ovarian tumor development

Bone morphogenetic proteins (BMPs) have diverse roles in development and reproduction. Although several BMPs are produced by oocytes, thecal cells, and granulosa cells of developing follicles, the in vivo functions of most of these ligands are unknown. BMP signals are transduced by multiple type I and type II TGFbeta family receptors, and of the type I receptors, BMP receptor 1A (BMPR1A) and BMP receptor 1B (BMPR1B) are known to be expressed in rodent granulosa cells. Female mice homozygous null for Bmpr1b are sterile due to compromised cumulus expansion, but the function of BMPR1A in the ovary is unknown. To further decipher a role for BMP signaling in mouse granulosa cells, we deleted Bmpr1a in the granulosa cells of the ovary and found Bmpr1a conditional knockout females to be subfertile with reduced spontaneous ovulation. To explore the redundant functions of BMP receptor signaling in the ovary, we generated Bmpr1a Bmpr1b double-mutant mice, which developed granulosa cell tumors that have evidence of increased TGFbeta and hedgehog signaling. Thus, similar to SMAD1 and SMAD5, which have redundant roles in suppressing granulosa cell tumor development in mice, two type I BMP receptors, BMPR1A and BMPR1B, function together to prevent ovarian tumorigenesis. These studies support a role for a functional BMP signaling axis as a tumor suppressor pathway in the ovary, with BMPR1A and BMPR1B acting downstream of BMP ligands and upstream of BMP receptor SMADs.