ID1 and ID3 are Negative Regulators of TGFß2-Induced Ocular Hypertension and Compromised Aqueous Humor Outflow Facility in Mice.

Purpose: In POAG, elevated IOP remains the major risk factor in irreversible vision loss. Increased TGFß2 expression in POAG aqueous humor and in the trabecular meshwork (TM) amplifies extracellular matrix (ECM) deposition and reduces ECM turnover in the TM, leading to a decreased aqueous humor (AH) outflow facility and increased IOP. Inhibitor of DNA binding proteins (ID1 and ID3) inhibit TGFß2-induced fibronectin and PAI-1 production in TM cells. We examined the effects of ID1 and ID3 gene expression on TGFß2-induced ocular hypertension and decreased AH outflow facility in living mouse eyes. Methods: IOP and AH outflow facility changes were determined using a mouse model of Ad5-hTGFß2C226S/C288S-induced ocular hypertension. The physiological function of ID1 and ID3 genes were evaluated using Ad5 viral vectors to enhance or knockdown ID1/ID3 gene expression in the TM of BALB/cJ mice. IOP was measured in conscious mice using a Tonolab impact tonometer. AH outflow facilities were determined by constant flow infusion in live mice. Results: Over-expressing ID1 and ID3 significantly blocked TGFß2-induced ocular hypertension (P < 0.0001). Although AH outflow facility was significantly decreased in TGFß2-transduced eyes (P < 0.04), normal outflow facility was preserved in eyes injected concurrently with ID1 or ID3 along with TGFß2. Knockdown of ID1 or ID3 expression exacerbated TGFß2-induced ocular hypertension. Conclusions: Increased expression of ID1 and ID3 suppressed both TGFß2-elevated IOP and decreased AH outflow facility. ID1 and/or ID3 proteins thus may show promise as future candidates as IOP-lowering targets in POAG.

ID1 inhibits foot-and-mouth disease virus replication via targeting of interferon pathways.

Inhibitor of DNA-binding 1 (ID1) protein has been studied intensively for its functions in tumorigenesis and maintenance of stem cell-like properties, but its roles in virus infection are less understood. In the present study, we have clearly shown that the foot-and-mouth disease virus (FMDV) promotes ID1 degradation via Cdh1-mediated ubiquitination to facilitate its replication. Mechanistic investigations reveal Forkhead Box O1 (FOXO1) as an ID1 partner, which suppresses interferon regulatory factors 3 expression and interferon (IFN) production. Further investigation identified that ID1 suppresses FOXO1 transcription activity through HDAC4-mediated deacetylation, promoting IFN production and antiviral immune response. These studies establish a prominent role for ID1 in suppressing FDMV replication, which may be extended to other viruses.

Roles of the proteasome and inhibitor of DNA binding 1 protein in myoblast differentiation.

This study was conducted to further understand the mechanism that controls myoblast differentiation, a key step in skeletal muscle formation. RNA sequencing of primary bovine myoblasts revealed many genes encoding the ubiquitin-proteasome system were up-regulated during myoblast differentiation. This up-regulation was accompanied by increased proteasomal activity. Treating myoblasts with the proteasome-specific inhibitor lactacystin impeded myoblast differentiation. Adenovirus-mediated overexpression of inhibitor of DNA binding 1 (ID1) protein inhibited myoblast differentiation too. Further experiments were conducted to determine whether the proteasome promotes myoblast differentiation by degrading ID1 protein. Both ID1 protein and mRNA expression decreased during myoblast differentiation. However, treating myoblasts with lactacystin reversed the decrease in ID1 protein but not in ID1 mRNA expression. Surprisingly, this reversal was not observed when myoblasts were also treated with the mRNA translation inhibitor cycloheximide. Direct incubation of ID1 protein with proteasomes from myoblasts did not show differentiation stage-associated degradation of ID1 protein. Furthermore, ubiquitinated ID1 protein was not detected in lactacystin-treated myoblasts. Overall, the results of this study suggest that, during myoblast differentiation, the proteasomal activity is up-regulated to further myoblast differentiation and that the increased proteasomal activity improves myoblast differentiation partly by inhibiting the synthesis, not the degradation, of ID1 protein.-Leng, X., Ji, X., Hou, Y., Settlage, R., Jiang, H. Roles of the proteasome and inhibitor of DNA binding 1 protein in myoblast differentiation.

Androgen Receptor Pathway-Independent Prostate Cancer Is Sustained through FGF Signaling.

Androgen receptor (AR) signaling is a distinctive feature of prostate carcinoma (PC) and represents the major therapeutic target for treating metastatic prostate cancer (mPC). Though highly effective, AR antagonism can produce tumors that bypass a functional requirement for AR, often through neuroendocrine (NE) transdifferentiation. Through the molecular assessment of mPCs over two decades, we find a phenotypic shift has occurred in mPC with the emergence of an AR-null NE-null phenotype. These "double-negative" PCs are notable for elevated FGF and MAPK pathway activity, which can bypass AR dependence. Pharmacological inhibitors of MAPK or FGFR repressed the growth of double-negative PCs in vitro and in vivo. Our results indicate that FGF/MAPK blockade may be particularly efficacious against mPCs with an AR-null phenotype.

BMP4 promotes mouse iPS cell differentiation to male germ cells via Smad1/5, Gata4, Id1 and Id2.

Generation of male germ cells from pluripotent cells could provide male gametes for treating male infertility and offer an ideal model for unveiling molecular mechanisms of spermatogenesis. However, the influence and exact molecular mechanisms, especially downstream effectors of BMP4 signaling pathways, in male germ cell differentiation of the induce pluripotent stem (iPS) cells, remain unknown. This study was designed to explore the role and mechanism of BMP4 signaling in the differentiation of mouse iPS cells to male germ cells. Embryoid body (EB) formation and recombinant BMP4 or Noggin were utilized to evaluate the effect of BMP4 on male germ cell generation from mouse iPS cells. Germ cell-specific genes and proteins as well as the downstream effectors of BMP4 signaling pathway were assessed using real-time PCR and Western blots. We found that BMP4 ligand and its multiple receptors, including BMPR1a, BMPR1b and BMPR2, were expressed in mouse iPS cells. Real-time PCR and Western blots revealed that BMP4 could upregulate the levels of genes and proteins for germ cell markers in iPS cells-derived EBs, whereas Noggin decreased their expression in these cells. Moreover, Smad1/5 phosphorylation, Gata4 transcription and the transcripts of Id1 and Id2 were enhanced by BMP4 but decreased when exposed to Noggin. Collectively, these results suggest that BMP4 promotes the generation of male germ cells from iPS cells via Smad1/5 pathway and the activation of Gata4, Id1 and Id2 This study thus offers novel insights into molecular mechanisms underlying male germ cell development.

Inhibitor of DNA binding 1 regulates cell cycle progression of endothelial progenitor cells through induction of Wnt2 expression.

Endothelial injury is a risk factor for atherosclerosis. Endothelial progenitor cell (EPC) proliferation contributes to vascular injury repair. Overexpression of inhibitor of DNA binding 1 (Id1) significantly promotes EPC proliferation; however, the underlying molecular mechanism remains to be fully elucidated. The present study investigated the role of Id1 in cell cycle regulation of EPCs, which is closely associated with proliferation. Overexpression of Id1 increased the proportion of EPCs in the S/G2M phase and significantly increased cyclin D1 expression levels, while knockdown of Id1 arrested the cell cycle progression of EPCs in the G1 phase and inhibited cyclin D1 expression levels. In addition, it was demonstrated that Id1 upregulated wingless­type mouse mammary tumor virus integration site family member 2 (Wnt2) expression levels and promoted ß­catenin accumulation and nuclear translocation. Furthermore, Wnt2 knockdown counteracted the effects of Id1 on cell cycle progression of EPCs. In conclusion, the results of the present study indicate that Id1 promoted Wnt2 expression, which accelerated cell cycle progression from G1 to S phase. This suggests that Id1 may promote cell cycle progression of EPCs, and that Wnt2 may be important in Id1 regulation of the cell cycle of EPCs.

Id1 modulates endothelial progenitor cells function through relieving the E2-2-mediated repression of FGFR1 and VEGFR2 in vitro.

The migration and proliferation of EPCs are crucial for re-endothelialization in vascular repair and development. Id1 has a regulatory role in the regulation of EPCs migration and proliferation. Based on these findings, we hypothesized that Id1 plays a regulatory role in modulating the migration and proliferation of EPCs by interaction with other factors. Herein, we report that the Id1 protein and E-box protein E2-2 regulate EPCs function with completely opposite effects. Id1 plays a positive role in the regulation of EPC proliferation and migration, while endogenous E2-2 appears to be a negative regulator. Immunoprecipitation and immunofluorescence assay revealed that the Id1 protein interacts and co-localizes with the E2-2 protein in EPCs. Further, endogenous E2-2 protein was found to block EPCs function via the inhibition of FGFR1 and VEGFR2 expression. The overexpression and silencing of Id1 have no direct regulatory role on VEGFR2 and FGFR1 expression. On the other hand, Id1 relieves the E2-2-mediated repression of FGFR1 and VEGFR2 expression to modulate EPCs proliferation, migration, and tube formation in vitro. In summary, we demonstrated that Id1 and E2-2 are critical regulators of EPCs function in vitro. Id1 interacts with E2-2 and relieves the E2-2-mediated repression of FGFR1 and VEGFR2 expression to modulate EPCs functions. Id1 and E2-2 may represent novel therapeutic targets for re-endothelialization in vascular damage and repair.

Scleroderma dermal microvascular endothelial cells exhibit defective response to pro-angiogenic chemokines.

OBJECTIVES: Angiogenesis plays a critical role in SSc (scleroderma). The aim of this study was to examine the expression of growth-regulated protein-γ (Gro-γ/CXCL3), granulocyte chemotactic protein 2 (GCP-2/CXCL6) and their receptor CXCR2 in endothelial cells (ECs) isolated from SSc skin and determine whether these cells mount an angiogenic response towards pro-angiogenic chemokines. The downstream signalling pathways as well as the pro-angiogenic transcription factor inhibitor of DNA-binding protein 1 (Id-1) were also examined. METHODS: Skin biopsies were obtained from patients with dcSSc. ECs were isolated via magnetic positive selection. Angiogenesis was measured by EC chemotaxis assay. RESULTS: Gro-γ/CXCL3 and GCP-2/CXCL6 were minimally expressed in both skin types but elevated in SSc serum. Pro-angiogenic chemokine mRNA was greater in SSc ECs than in normal ECs. SSc ECs did not migrate to vascular endothelial growth factor (VEGF), Gro-γ/CXCL3, GCP-2/CXCL6 or CXCL16. The signalling pathways stimulated by these chemokines were also dysregulated. Id-1 mRNA in SSc ECs was lower compared with normal ECs, and overexpression of Id-1 in SSc ECs increased their ability to migrate towards VEGF and CXCL16. CONCLUSION: Our results show that SSc ECs are unable to respond to pro-angiogenic chemokines despite their increased expression in serum and ECs. This might be due to the differences in the signalling pathways activated by these chemokines in normal vs SSc ECs. In addition, the lower expression of Id-1 also decreases the angiogenic response. The inability of pro-angiogenic chemokines to promote EC migration provides an additional mechanism for the impaired angiogenesis that characterizes SSc.

Id1 suppresses anti-tumour immune responses and promotes tumour progression by impairing myeloid cell maturation.

A central mechanism of tumour progression and metastasis involves the generation of an immunosuppressive 'macroenvironment' mediated in part through tumour-secreted factors. Here we demonstrate that upregulation of the Inhibitor of Differentiation 1 (Id1), in response to tumour-derived factors, such as TGFß, is responsible for the switch from dendritic cell (DC) differentiation to myeloid-derived suppressor cell expansion during tumour progression. Genetic inactivation of Id1 largely corrects the myeloid imbalance, whereas Id1 overexpression in the absence of tumour-derived factors re-creates it. Id1 overexpression leads to systemic immunosuppression by downregulation of key molecules involved in DC differentiation and suppression of CD8 T-cell proliferation, thus promoting primary tumour growth and metastatic progression. Furthermore, advanced melanoma patients have increased plasma TGFß levels and express higher levels of ID1 in myeloid peripheral blood cells. This study reveals a critical role for Id1 in suppressing the anti-tumour immune response during tumour progression and metastasis.

Id1 Deficiency Protects against Tumor Formation in Apc(Min/+) Mice but Not in a Mouse Model of Colitis-Associated Colon Cancer.

Different mechanisms contribute to the development of sporadic, hereditary and colitis-associated colorectal cancer. Inhibitor of DNA binding/differentiation (Id) proteins act as dominant-negative antagonists of basic helix-loop-helix transcription factors. Id1 is a promising target for cancer therapy, but little is known about its role in the development of colon cancer. We used immunohistochemistry to demonstrate that Id1 is overexpressed in human colorectal adenomas and carcinomas, whether sporadic or syndromic. Furthermore, elevated Id1 levels were found in dysplasia and colon cancer arising in patients with inflammatory bowel disease. Because levels of PGE2 are also elevated in both colitis and colorectal neoplasia, we determined whether PGE2 could induce Id1. PGE2 via EP4 stimulated protein kinase A activity resulting in enhanced pCREB-mediated Id1 transcription in human colonocytes. To determine the role of Id1 in carcinogenesis, two mouse models were used. Consistent with the findings in humans, Id1 was overexpressed in tumors arising in both Apc(Min) (/+) mice, a model of familial adenomatous polyposis, and in experimental colitis-associated colorectal neoplasia. Id1 deficiency led to significant decrease in the number of intestinal tumors in Apc(Min) (/+) mice and prolonged survival. In contrast, Id1 deficiency did not affect the number or size of tumors in the model of colitis-associated colorectal neoplasia, likely due to exacerbation of colitis associated with Id1 loss. Collectively, these results suggest that Id1 plays a role in gastrointestinal carcinogenesis. Our findings also highlight the need for different strategies to reduce the risk of colitis-associated colorectal cancer compared with sporadic or hereditary colorectal cancer.

Id1 Expression Level Determines the Differentiation of Human Dental Pulp Stem Cells.

TWIST1 plays a crucial role in dentinogenesis, and its activity depends on both a dimerization partner selection and phosphorylation. Other factors, like Id proteins, can affect the availability of dimerization partners for TWIST1, subsequently leading to diverse biological outcomes. The purpose of this study was to evaluate an impact of Id1 expression on differentiation of dental pulp stem cells (DPSCs). The altered expression of Id1 was achieved by transfection of human DPSCs with lentiviral vectors either driving an entire sequence of Id1, hence leading to Id1 overexpression, or carrying the Id1 silencing sequence. We observed that both overexpression and silencing of Id1 modulated human DPSC differentiation. Id1 overexpression resulted in a prevailing formation of TWIST1 homodimer and increased expression of genes encoding dentin sialophosphoprotein and dentin matrix protein 1, which confirm an enhanced odontogenic differentiation of DPSCs. Concurrently, Id1 silencing produced an opposite effect, slowing DPSC differentiation. These results highlight Id1 as an important modulator of molecular events during DPSC commitment and differentiation, which should be considered in dental research on tissue engineering. Moreover, we assume that the balance between TWIST1 dimerization forms in DPSCs might function in a cell-type-specific manner.

E47 and Id1 interplay in epithelial-mesenchymal transition.

E12/E47 proteins (encoded by E2A gene) are members of the class I basic helix-loop-helix (bHLH) transcription factors (also known as E proteins). E47 has been described as repressor of E-cadherin and inducer of epithelial-mesenchymal transition (EMT). We reported previously that EMT mediated by E47 in MDCK cells occurs with a concomitant overexpression of Id1 and Id3 proteins. Id proteins belong to class V of HLH factors that lack the basic domain; they dimerise with E proteins and prevent their DNA interaction, thus, acting as dominant negative of E proteins. Here, we show that E47 interacts with Id1 in E47 overexpressing MDCK cells that underwent a full EMT as well as in mesenchymal breast carcinoma and melanoma cell lines. By conducting chromatin immunoprecipitation assays we demonstrate that E47 binds directly to the endogenous E-cadherin promoter of mesenchymal MDCK-E47 cells in a complex devoid of Id1. Importantly, our data suggest that both E47 and Id1 are required to maintain the mesenchymal phenotype of MDCK-E47 cells. These data support the collaboration between E47 and Id1 in the maintenance of EMT by mechanisms independent of the dominant negative action of Id1 on E47 binding to E-cadherin promoter. Finally, the analysis of several N0 breast tumour series indicates that the expression of E47 and ID1 is significantly associated with the basal-like phenotype supporting the biological significance of the present findings.

Id-1 is a key transcriptional regulator of glioblastoma aggressiveness and a novel therapeutic target.

Glioblastoma is the most common form of primary adult brain tumors. A majority of glioblastomas grow invasively into distant brain tissue, leading to tumor recurrence, which is ultimately incurable. It is, therefore, essential to discover master regulators that control glioblastoma invasiveness and target them therapeutically. We show here that the transcriptional regulator Id-1 plays a critical role in modulating the invasiveness of glioblastoma cell lines and primary glioblastoma cells. Id-1 expression levels positively correlate with glioma cell invasiveness in culture and with histopathologic grades in patient biopsies. Id-1 knockdown dramatically reduces glioblastoma cell invasion that is accompanied by profound morphologic changes and robust reduction in expression levels of "mesenchymal" markers, as well as inhibition of self-renewal potential and downregulation of glioma stem cell markers. Importantly, genetic knockdown of Id-1 leads to a significant increase in survival in an orthotopic model of human glioblastoma. Furthermore, we show that a nontoxic compound, cannabidiol, significantly downregulates Id-1 gene expression and associated glioma cell invasiveness and self-renewal. In addition, cannabidiol significantly inhibits the invasion of glioblastoma cells through an organotypic brain slice and glioma progression in vivo. Our results suggest that Id-1 regulates multiple tumor-promoting pathways in glioblastoma and that drugs targeting Id-1 represent a novel and promising strategy for improving the therapy and outcome of patients with glioblastoma.

The expression and modulation of CEACAM1 and tumor cell transformation.

BACKGROUND: In this review, we focus our discussion on one class of carcinoembryonic antigen- related cell adhesion molecules, Carcinoembryonic antigen-related cell adhesion molecules 1 (CEACAM1). This has been observed in several malignant transformations to be subjected to complex mechanisms of modulation and dysregulation. AIMS: Restoration of CEACAM1 expression in tumor cell lines often abolishes their oncogenicity in vivo, and therefore, this adhesion molecule has been regarded as a tumor suppressor. In contrast, de novo expression of CEACAM1 is found with the progression of malignancy and metastatic spread in a large array of cancer tissues which include melanoma, Non Small Cell Lung Carcinoma (NSCLC) as well as bladder, prostate, thyroid, breast, colon and gastric carcinomas. DISCUSSION: We report and discuss the most significant findings confirming at immunohistochemical and clinical level the correlation between poor prognosis and expression of CEACAM1 on the cell surface of tumors.

[Suppressive effects for osteoclastogenesis regulated by RANKL signal].

RANKL signal promotes osteoclast differentiation through a transcriptional activation of responsible genes for osteoclast formation and functions. Recent works revealed that RANKL signal plays a role to repress transcription of suppressive factors for osteoclastogenesis. Some transcriptional repressors actively inhibit expressions of osteoclast-specific genes in the precursors through canceling the functions of transcription activators to prevent uncontrollable osteoclast formation and pathological bone resorption. The mouse models lacking those transcriptional repressors exhibited accelerated osteoclast differentiation and bone loss. Although the suppressive factors are important for maintaining bone homeostasis, they have to be removed for osteoclast formation in the presence of RANKL. The transcriptional repressor Blimp1 was identified as a new target of RANKL signal and strongly attenuated expressions of various suppressive factors including Bcl6. The osteoclast-specific Blimp1 knockout mice exhibited defect of osteclast formation and loss of bone resorption. Thus, RANKL signal regulates osteoclast differentiation by inducing transcriptional activators such as NFATc1 as well as transcriptional repressors such as Blimp1.The former is essential for expressions of osteclast-specific genes, while the latter is required for terminating suppressions of osteoclast differentiation.

Id1 promotes lung cancer cell proliferation and tumor growth through Akt-related pathway.

Overexpression of Id family proteins inhibits cell differentiation and enhances cell proliferation and invasiveness. Although Id1 is the Id family member mostly linked to tumorigenesis, its role in lung cancer is unclear. An elevated Id1 expression was observed in lung cancer cell lines as well as lung cancer tissues. Id1 overexpression increased cell proliferation while Id1 knockdown decreased cell proliferation, mostly through Akt-related pathway. Nude mice study further confirmed an increased tumor growth in Id1-overexpressing cells and a decreased tumor growth in Id1-knockdowned cells. In conclusion, inactivation of Id1 may provide a novel strategy for treatment of lung cancer patients.

Expression of Id-1 is regulated by MCAM/MUC18: a missing link in melanoma progression.

The acquisition of the metastatic melanoma phenotype is associated with increased expression of the melanoma cell adhesion molecule MCAM/MUC18 (CD146). However, the mechanism by which MUC18 contributes to melanoma metastasis remains unclear. Herein, we stably silenced MUC18 expression in two metastatic melanoma cell lines, A375SM and C8161, and conducted cDNA microarray analysis. We identified and validated that the transcriptional regulator, inhibitor of DNA binding-1 (Id-1), previously shown to function as an oncogene in several malignancies, including melanoma, was downregulated by 5.6-fold following MUC18 silencing. Additionally, we found that MUC18 regulated Id-1 expression at the transcriptional level via ATF-3, which itself was upregulated by 6.9-fold in our cDNA microarray analysis. ChIP analysis showed increased binding of ATF-3 to the Id-1 promoter after MUC18 silencing. To complement these studies, we rescued the expression of MUC18, which reversed the expression patterns of Id-1 and ATF-3. Moreover, we showed that MUC18 promotes melanoma invasion through Id-1, as overexpression of Id-1 in MUC18-silenced cells resulted in increased MMP-2 expression and activity. To our knowledge, this is the first demonstration that MUC18 is involved in cell signaling regulating the expression of Id-1 and ATF-3, thus contributing to melanoma metastasis.

Silencing Id-1 with RNA interference inhibits adenoid cystic carcinoma in mice.

BACKGROUND: The helix-loop-helix (HLH) protein Id-1 (inhibitor of DNA binding/differentiation) has been demonstrated to play an important role in tumor development. Our previous in vitro research has shown that Id-1 is a potential target in the treatment of human adenoid cystic carcinoma (ACCM). The purpose of this study was to analyze the influence of Id inhibition on ACCM in mice. MATERIALS AND METHODS: To suppress the expression of Id-1 gene, we used lentivirus-mediated RNA interference to silence the Id-1 gene post-transcriptionally in ACCM models that stably express GFP in mice. Tumor development was evaluated by size measurement. Effects of Id-1 siRNA on mRNA and protein expression of Id-1 were analyzed using quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting respectively. Ki-67 expression was measured by immunohistochemistry. In vitro studies of Hoechst staining for cell apoptosis, Boyden-chamber assay for cell invasion, and MTT-tests for cell growth were performed as well. RESULTS: Id-1 knockdown resulted in inhibition of tumor growth in mice. Id-1 siRNA significantly decreased not only Id-1 in mRNA and protein level, but also Ki-67 expression. In addition, apoptosis was induced and cell proliferation activity and invasion were significantly reduced. CONCLUSIONS: Lentivirus-mediated gene knockdown by silencing Id-1 constitute a valid methodological approach, which may represent an attractive, potent and specific therapeutic tool for the treatment of ACCM.

The expression and roles of inhibitor of DNA binding helix-loop-helix proteins in the developing and adult mouse retina.

Inhibitor of DNA binding (Id) proteins bind to and inhibit the function of basic helix-loop-helix (bHLH) transcription factors including those that regulate retinal development. However, little is known about the role of Id proteins in the growth and differentiation of the retina during development. The purpose of this study is to observe the expression of Id proteins in the developing and adult mouse retinas as the first step in investigating the functions of Id family members in the eye. The expression of Id1-4 was examined by real-time PCR, Western blot, and immunohistochemistry in wild-type and Id1/Id3 double-knockout mice. Id1-4 genes and proteins showed high expression levels in the retina at embryonic and early postnatal stages, whereas declined in the adult. Expression of Id proteins was observed in the inner neuroblastic layer (NBL) at embryonic (E) day 13.5 through 16.5. Id4 expression began at E18.5. By E18.5 and postnatal day 1, the expression of Id1-4 exhibited distinct yet overlapping patterns in the ganglion cell layer and inner part of NBL. In the adult, Ids were expressed in retinal ganglion cells, amacrine cells, bipolar cells, and horizontal cells. No Id expression was found in Müller cells. Id1 and Id3 double-knockout mice (Id1(-/-)/Id3(-/-)) showed smaller retinal size compared to wild-type or heterozygous littermates. However, histological analyses in Id1 and Id3 single-knockout retinas revealed no obvious defects in developmental phenotype. Our results indicate that the expression of the Id family may play an important role in regulating retinal progenitor cell proliferation and differentiation.

Inhibitor of DNA binding-1 induces mesenchymal features and promotes invasiveness in thyroid tumour cells.

Characterisation of molecular mechanisms that control tumour invasion is a crucial step for the identification of molecular markers to apply in cancer diagnosis and treatment. In this work, we have investigated the role of Id1 in thyroid tumours. We demonstrate that Id1 participates to tumour progression by powering the invasion capacity of cancer cells. We prove that the overexpression of Id1 in thyroid tumour cells profoundly alters cell morphology and growth, increasing migration and invasion properties of the cells. Analysis in human thyroid tumours reveals that Id1 is expressed in invading cells and its expression is associated with an increased metastatic potential of non-anaplastic tumours. The gene expression study supports these observations demonstrating that Id1 modulates a number of genes known to control invasion, aggressiveness and pharmacological resistance in different type of human tumours. Finally, we demonstrate that the pro-invasive effect of Id1 is accompanied by the acquisition of mesenchymal features in thyroid tumour cells. This suggests that the trans-differentiation towards a more immature condition is the mechanism through which Id1 promotes thyroid tumour metastatic spreading. This study identifies Id1 as part of the pro-metastatic programme of thyroid cancer and suggests its possible utilisation as a prognostic marker.