Down-regulation of Hox A7 is required for cell adhesion and migration on fibronectin during early HL-60 monocytic differentiation

Magnesium-containing bioceramics stimulate exosomal miR-196a-5p secretion to promote senescent osteogenesis through targeting Hoxa7/MAPK signaling axis

Stem cell senescence is characterized by progressive functional dysfunction and secretory phenotypic changes including decreased proliferation, dysfunction of osteogenic and angiogenic differentiation, increased secretion of the senescence-associated secretory phenotype (SASP), which bring difficulties for bone repair. Rescuing or delaying senescence of aged bone marrow mesenchymal stem cells (O-BMSCs) was considered as effective strategy for bone regeneration in aging microenvironment. Magnesium (Mg) ion released from bioceramics was reported to facilitate bone regeneration via enhancing osteogenesis and alleviating senescence. In this study, Akermanite biocreamics (Akt) containing Mg ion as a model was demonstrated to promote osteogenesis and angiogenesis effects of O-BMSCs by activating the MAPK signaling pathway in vitro. Moreover, the enhanced osteogenesis effects might be attributed to enhanced Mg-containing Akt-mediated exosomal miR-196a-5p cargo targeting Hoxa7 and activation of MAPK signaling pathway. Furthermore, the in vivo study confirmed that 3D-printed porous Mg-containing Akt scaffolds effectively increased bone regeneration in cranial defects of aged rats. The current results indicated that the exosomal-miR-196a-5p/Hoxa7/MAPK signaling axis might be the potential mechanism underlying Akt-mediated osteogenesis. The exosome-meditaed therapy stimulated by the released Mg ion contained in Akt biocreamics or other biomaterials might serve as a candidate strategy for bone repair in aged individuals.

Upregulation of homeobox D10 expression suppresses invasion and migration of clear cell renal cell carcinoma through targeting of E-cadherin

Background

Clear cell renal cell carcinoma (CCRCC) is one of the most common types of renal cell carcinoma. Accumulating evidence indicates that homeobox D10 (HOXD10) acts as a tumor suppressor or oncogene in various carcinomas. However, the regulation and potential mechanisms of HOXD10 in CCRCC remain largely unknown.

Purpose

To explore the effect and potential mechanism of HOXD10 on the invasion and migration of CCRCC cells.

Methods

The expression of HOXD10, E-cadherin and other epithelial mesenchymal transition (EMT)-related proteins was assessed by reverse transcription-quantitative real-time PCR (qRT-PCR) and Western blots. A series of functional assays were performed in RCC cell lines to explore the function of HOXD10 in CCRCC progression. Bioinformatics analysis, ChIP assays, and dual luciferase reporter assays were utilized to identify the interaction between HOXD10 and E-cadherin.

Results

Low expression of HOXD10 and E-cadherin was observed in CCRCC tissues and ACHN and 786-O cells. Downregulation of HOXD10 expression was correlated with the TNM stage of CCRCC patients. Functional experiments demonstrated that malignant biological ability was significantly inhibited by HOXD10 overexpression in RCC cells. Moreover, E-cadherin was a potential target gene of HOXD10, as evidenced by a series of assays. In addition, overexpression of HOXD10 inhibited the progression of CCRCC by regulating the expression of E-cadherin, vimentin, and β-catenin in vitro.

Conclusion

HOXD10 acts as a tumor suppressor and suppresses invasion and migration of CCRCC cells by regulating E-cadherin and EMT processes. Thus, targeting HOXD10 may be a therapeutic strategy for CCRCC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-021-06993-8.

Downregulated lncRNA HOXA11-AS Affects Trophoblast Cell Proliferation and Migration by Regulating RND3 and HOXA7 Expression in PE

The long noncoding RNA HOXA11-AS displays abnormal expression in numerous human diseases. However, its function and biological mechanisms remain unclear in preeclampsia (PE). In this study, we report that HOXA11-AS is significantly downregulated in preeclamptic placental tissues and could contribute to the occurrence and development of PE. Silencing of HOXA11-AS expression could significantly suppress trophoblast cell growth and migration, whereas HOXA11-AS overexpression facilitated cell growth in the HTR-8/SVneo, JEG3, and JAR cell lines. RNA-seq analysis also indicated that HOXA11-AS silencing preferentially regulated numerous genes associated with cell proliferation and cell migration. Mechanistic analyses showed that HOXA11-AS could recruit Ezh2 and Lsd1 protein and regulate RND3 mRNA expression in the nucleus. In the cytoplasm, HOXA11-AS modulates HOXA7 expression by sponged miR-15b-5p, affecting trophoblast cell proliferation. Together, these data confirm that aberrant expression of HOXA11-AS is involved in the occurrence and development of PE and may act as a prospective diagnosis and therapeutic target in PE.

Genome-Wide DNA Methylation Study Identifies Significant Epigenomic Changes in Osteoarthritic Subchondral Bone and Similarity to Overlying Cartilage

OBJECTIVE

To perform a genome-wide DNA methylation study to identify differential DNA methylation patterns in subchondral bone underlying eroded and intact cartilage from patients with hip osteoarthritis (OA) and to compare these with DNA methylation patterns in overlying cartilage.

METHODS

Genome-wide DNA methylation profiling using Illumina HumanMethylation 450 arrays was performed on eroded and intact cartilage and subchondral bone from within the same joint of 12 patients undergoing hip arthroplasty. Genes with differentially methylated CpG sites were analyzed to identify shared pathways, upstream regulators, and overrepresented gene ontologies, and these patterns were compared with those of the overlying cartilage. Histopathology was graded by modified Mankin score and assessed for correlation with DNA methylation.

RESULTS

We identified 7,316 differentially methylated CpG sites in subchondral bone underlying eroded cartilage, most of which (∼75%) were hypomethylated, and 1,397 sites in overlying eroded cartilage, 126 of which were shared. Samples clustered into 3 groups with distinct histopathologic scores. We observed differential DNA methylation of genes including the RNA interference-processing gene AGO2, the growth factor TGFB3, the OA suppressor NFATC1, and the epigenetic effector HDAC4. Among known susceptibility genes in OA, 32 were differentially methylated in subchondral bone, 8 were differentially methylated in cartilage, and 5 were shared. Upstream regulator analysis using differentially methylated genes in OA subchondral bone showed a strong transforming growth factor β1 signature (P = 1 × 10(-40) ) and a tumor necrosis factor family signature (P = 3.2 × 10(-28) ), among others.

CONCLUSION

Our data suggest the presence of an epigenetic phenotype associated with eroded OA subchondral bone that is similar to that of overlying eroded OA cartilage.

Large-scale gene network analysis reveals the significance of extracellular matrix pathway and homeobox genes in acute myeloid leukemia: an introduction to the Pigengene package and its applications

BACKGROUND

The distinct types of hematological malignancies have different biological mechanisms and prognoses. For instance, myelodysplastic syndrome (MDS) is generally indolent and low risk; however, it may transform into acute myeloid leukemia (AML), which is much more aggressive.

METHODS

We develop a novel network analysis approach that uses expression of eigengenes to delineate the biological differences between these two diseases.

RESULTS

We find that specific genes in the extracellular matrix pathway are underexpressed in AML. We validate this finding in three ways: (a) We train our model on a microarray dataset of 364 cases and test it on an RNA Seq dataset of 74 cases. Our model showed 95% sensitivity and 86% specificity in the training dataset and showed 98% sensitivity and 91% specificity in the test dataset. This confirms that the identified biological signatures are independent from the expression profiling technology and independent from the training dataset. (b) Immunocytochemistry confirms that MMP9, an exemplar protein in the extracellular matrix, is underexpressed in AML. (c) MMP9 is hypermethylated in the majority of AML cases (n=194, Welch's t-test p-value <10^-138), which complies with its low expression in AML. Our novel network analysis approach is generalizable and useful in studying other complex diseases (e.g., breast cancer prognosis). We implement our methodology in the Pigengene software package, which is publicly available through Bioconductor.

CONCLUSIONS

Eigengenes define informative biological signatures that are robust with respect to expression profiling technology. These signatures provide valuable information about the underlying biology of diseases, and they are useful in predicting diagnosis and prognosis.

Transglutaminase regulation of cell function

Transglutaminases (TGs) are multifunctional proteins having enzymatic and scaffolding functions that participate in regulation of cell fate in a wide range of cellular systems and are implicated to have roles in development of disease. This review highlights the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression, and function in signal transduction. We also discuss the mechanisms whereby TG level is controlled and how TGs control downstream targets. The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states.

Cellular functions of tissue transglutaminase

Transglutaminase 2 (TG2 or tissue transglutaminase) is a highly complex multifunctional protein that acts as transglutaminase, GTPase/ATPase, protein disulfide isomerase, and protein kinase. Moreover, TG2 has many well-documented nonenzymatic functions that are based on its noncovalent interactions with multiple cellular proteins. A vast array of biochemical activities of TG2 accounts for its involvement in a variety of cellular processes, including adhesion, migration, growth, survival, apoptosis, differentiation, and extracellular matrix organization. In turn, the impact of TG2 on these processes implicates this protein in various physiological responses and pathological states, contributing to wound healing, inflammation, autoimmunity, neurodegeneration, vascular remodeling, tumor growth and metastasis, and tissue fibrosis. TG2 is ubiquitously expressed and is particularly abundant in endothelial cells, fibroblasts, osteoblasts, monocytes/macrophages, and smooth muscle cells. The protein is localized in multiple cellular compartments, including the nucleus, cytosol, mitochondria, endolysosomes, plasma membrane, and cell surface and extracellular matrix, where Ca(2+), nucleotides, nitric oxide, reactive oxygen species, membrane lipids, and distinct protein-protein interactions in the local microenvironment jointly regulate its activities. In this review, we discuss the complex biochemical activities and molecular interactions of TG2 in the context of diverse subcellular compartments and evaluate its wide ranging and cell type-specific biological functions and their regulation.

CALM/AF10-positive leukemias show upregulation of genes involved in chromatin assembly and DNA repair processes and of genes adjacent to the breakpoint at 10p12

The t(10;11)(p12;q14) is a recurring chromosomal translocation that gives rise to the CALM/AF10 fusion gene, which is found in acute myeloid leukemia, acute lymphoblastic leukemia and malignant lymphoma. We analyzed the fusion transcripts in 20 new cases of CALM/AF10-positive leukemias, and compared the gene expression profile of 10 of these to 125 patients with other types of leukemia and 10 normal bone marrow samples. Based on gene set enrichment analyses, the CALM/AF10-positive samples showed significant upregulation of genes involved in chromatin assembly and maintenance and DNA repair process, and downregulation of angiogenesis and cell communication genes. Interestingly, we observed a striking upregulation of four genes located immediately centromeric to the break point of the t(10;11)(p12;q14) on 10p12 (COMMD3 (COMM domain containing 3), BMI1 (B lymphoma Mo-MLV insertion region 1 homolog), DNAJC1 (DnaJ (Hsp40) homolog subfamily C member 1) and SPAG6 (sperm associated antigen 6)). We also conducted semiquantitative reverse transcriptase-PCR analysis on leukemic blasts from a murine CALM/AF10 transplantation model that does not have the translocation. Commd3, Bmi1 and Dnajc1, but not Spag6 were upregulated in these samples. These results strongly indicate that the differential regulation of these three genes is not due to the break point effect but as a consequence of the CALM/AF10 fusion gene expression, though the mechanism of regulation is not well understood.

HOX gene expression in phenotypic and genotypic subgroups and low HOXA gene expression as an adverse prognostic factor in pediatric ALL

BACKGROUND

HOX genes play an important role in both normal lymphopoiesis and leukemogenesis. However, HOX expression patterns in leukemia cells compared to normal lymphoid progenitors have not been systematically studied in acute lymphoblastic leukemia (ALL) subtypes.

PROCEDURE

The RNA expression levels of HOXA, HOXB, and CDX1/2 genes were analyzed by qRT-PCR in a cohort of 61 diagnostic pediatric ALL samples and FACS-sorted subpopulations of normal lymphoid progenitors.

RESULTS

The RNA expression of HOXA7-10, HOXA13, and HOXB2-4 genes was exclusively detected in leukemic cells and immature progenitors. The RNA expression of HOXB6 and CDX2 genes was exclusively detected in leukemic cells but not in B-lineage cells at any of the studied developmental stages. HOXA3-4, HOXA7, and HOXB3-4 genes were differentially expressed between BCP-ALL and T-ALL subgroups, and among genotypically defined MLL/AF4, TEL/AML1, BCR/ABL, hyperdiploid and normal karyotype subgroups. However, this differential expression did not define specific clusters in hierarchical cluster analysis. HOXA7 gene was low expressed at the RNA level in patients with hyperdiploid leukemia, whereas HOXB7 and CDX2 genes were low expressed in TEL/AML1-positive and BCR/ABL-positive cases, respectively. In contrast to previous findings in acute myeloid leukemia, high HOXA RNA expression was associated with an excellent prognosis in Cox's regression model (P = 0.03). In MLL/AF4-positive ALL, lower HOXA RNA expression correlated with the methylation status of their promoters.

CONCLUSIONS

HOX gene RNA expression cannot discriminate leukemia subgroups or relative maturity of leukemic cells. However, HOXA RNA expression correlates with prognosis, and particular HOX genes are expressed in specific genotypically characterized subgroups.

Hip geometry variation is associated with bone mineralization pathway gene variants: The Framingham Study

Mineralization of bone matrix is an important process in bone formation; thus defects in mineralization have been implicated in bone mineral density (BMD) and bone structure alterations. Three central regulators of phosphate balance, ALPL, ANKH, and ENPP1, are central in the matrix mineralization process; therefore, the genes encoding them are considered important candidates genes for BMD and bone geometry. To test for an association between these three candidate genes and BMD and bone geometry traits, 124 informative singlenucleotide polymorphisms (SNPs) were selected and genotyped in 1513 unrelated subjects from the Framingham offspring cohort. Initial results showed that SNP rs1974201 in the gene ENPP1 was a susceptibility variant associated with several hip geometric indices, with the strongest p value of 3.8 × 10(7) being observed for femoral neck width. A few modest associations were observed between SNPs in or near ALPL and several bone traits, but no association was observed with ANKH. The association signals observed for SNPs around rs1974201 were attenuated after conditional analysis on rs1974201. Transcription factor binding-site prediction revealed that the HOXA7 binding site was present in the reference sequence with the major allele, whereas this potential binding site is lost in the sequence with the minor allele of rs1974201. In conclusion, we found evidence for association of bone geometry variation with an SNP in ENPP1, a gene in the mineralization pathway. The alteration of a binding site of the deregulator of extracellular matrix HOXA7 warrants further investigation.

DNA replication, development and cancer: a homeotic connection?

The homeotic proteins are transcription factors, highly conserved in metazoan organisms, exerting a pivotal role in development and differentiation. They individually display a loose specificity for the DNA sequence they can bind, but operate mainly in multi-molecular associations that assure their target and function specificity. Homeotic proteins are known to play a role in the positive or negative regulation of cell proliferation. Furthermore, many homeotic proteins are actually proto-oncogenes, since different translocations involving their genes cause tumors, particularly in the hematopoietic system. A one-hybrid screen to detect proteins with affinity for the lamin B2 replication origin identified three homeotic proteins, namely HoxA13, HoxC10 and HoxC13. Recent data demonstrate that the HoxC13 oncoprotein specifically associates with replication foci and binds in vitro and in vivo to several human DNA replication origins. Moreover, Hox proteins interact with geminin, a regulator of cell cycle progression, and control the interaction of this protein with the DNA replication licensing factor Ctd1. Thus, the homeotic proteins, by participating directly in the function of DNA replication origins, may provide a direct link between the accurate regulation of DNA replication required by the morphogenetic program and the deregulation of this process typical of cancer.

HOX gene analysis of endothelial cell differentiation in human bone marrow-derived mesenchymal stem cells

Human bone marrow-derived mesenchymal stem cells (hMSCs) have been shown to possess multilineage differentiation potential. HOX genes function in transcriptional regulators, and are involved in stem cell differentiation. The aim of the present study was to demonstrate HOX genes that are related to angiogenesis. To identify the expression patterns of 37 HOX genes in the endothelial cell differentiation of hMSCs, we analyzed HOX genes through profiling with multiplex RT-PCR. The results showed that the expression patterns of four HOX genes, HOXA7, HOXB3, HOXA3, and HOXB13, significantly changed during angiogenesis. The expression levels of HOXA7 and HOXB3 were dramatically increased, whereas those of HOXA3 and HOXB13 were decreased during endothelial cell differentiation. When further analysis of the expressions of these HOX genes was performed with real-time PCR and an immunoblot assay, the expression patterns were also found to be well-matched with the results of multiplex RT-PCR. Here, we report that HOXA7, HOXB3, HOXA3, and HOXB13 might be involved in the angiogenesis of hMSCs.

Slug is required for cell survival during partial epithelial-mesenchymal transition of HGF-induced tubulogenesis

Transcription factors of the Snail family are key regulators of epithelial-mesenchymal transition (EMT). In many processes during development or disease, cells do not acquire all the characteristics associated with EMT, leading to what we refer to as partial EMT (p-EMT). However, little is known of the implications of the Snail transcription factors in processes that only involve a p-EMT. To assess this, we used the hepatocyte growth factor (HGF)-induced Madin-Darby canine kidney tubulogenesis system, which provides a three-dimensional culture model of a morphogenetic process including a p-EMT. We found that although Slug (Snail2) is highly and transitory up-regulated during the p-EMT phase of tubulogenesis, it is not a repressor of E-cadherin during this process. Using inducible knockdown of Slug, we demonstrate that Slug is not an inducer of cell movement and instead is required for survival during p-EMT. We conclude that in epithelial cells, promoting cell survival can be a primary function of Slug, rather than being acquired concomitantly with EMT.

Tissue transglutaminase expression promotes cell attachment, invasion and survival in breast cancer cells

Distant metastasis is frequently observed in patients with breast cancer and is a major cause of cancer-related deaths in these patients. Currently, very little is known about the mechanisms that underlie the development of the metastatic phenotype in breast cancer cells. We previously found that metastatic breast cancer cells express high levels of tissue transglutaminase (TG2), but established no direct link between TG2 and metastasis. In this study, we hypothesized that TG2 plays a role in conferring the metastatic phenotype to breast cancer cells. The results obtained suggested that increased expression of TG2 in breast cancer cells contributes to their increased survival, invasion and motility. We further found that TG2 protein in a metastatic breast cancer MDA-MB231 cells was present on the cell surface in close association with integrins beta1, beta4 and beta5. Downregulation of endogenous TG2 by small interfering RNA inhibited fibronectin (Fn)-mediated cell attachment, survival and invasion. Conversely, ectopic expression of TG2 augmented invasion of breast cancer cells and attachment to Fn-coated surfaces. We conclude that TG2 expression in breast cancer cells plays an important role in the development of the metastatic phenotype.

Differential expression of HOX genes in neoplastic and non-neoplastic human astrocytes

HOX genes are a large family of regulatory genes implicated in the control of developmental processes. HOX genes are involved in malignant transformation and progression of different types of tumour. Despite intensive efforts to delineate the expression profiles of HOX genes in other cell types, nothing is known regarding the global expression profile of these genes in normal human astrocytes and astrocytomas. The present study has analysed the expression profile of the 39 class I HOX genes in normal human astrocytes (NHA and E6/E7), two well-established glioblastoma cell lines (U-87 MG and U-1242-MG), as well as neoplastic (WHO grades II/III and IV) and non-neoplastic temporal lobe specimens with hippocampal sclerosis and medically intractable epilepsy. RT-PCR, quantitative real-time PCR, immunocytochemistry, and western blot analyses revealed differential expression of nine HOX genes (A6, A7, A9, A13, B13, D4, D9, D10, and D13) in normal human astrocytic cell lines and non-neoplastic temporal lobe specimens. The data show that HOX genes are differentially expressed in neoplastic and non-neoplastic astrocytes and that multiple HOX genes are overexpressed in glioblastoma cell lines, astrocytomas (II/III), and glioblastoma multiforme. The differential expression of HOX genes in normal and neoplastic astrocytes suggests a role for these genes in brain tumourigenesis.

Cell type- and stage-specific changes in HOXA7 protein expression in human ovarian folliculogenesis: possible role of GDF-9

Homeobox (HOX) genes are important transcriptional regulators in development and in adult tissues. A major obstacle to the understanding of their roles in humans has been the lack of well-defined anti-human HOX antibodies. We generated a thoroughly characterized polyclonal rabbit antibody against human HOXA7 and used it to study the distribution, role, and regulation of HOXA7 in human ovarian folliculogenesis and in granulosa cell tumors. Immunohistochemically, follicles were strongly HOXA7-positive compared with stroma. Oocytes expressed little HOXA7. Granulosa cells were predominantly negative in primordial follicles, had uniformly HOXA7-positive nuclei in primary follicles, and, as follicles matured, the subcellular localization of HOXA7 changed from nuclear to predominantly cytoplasmic. HOXA7 was mainly cytoplasmic in theca interna, but completely absent in theca externa. Granulosa cell tumors were mainly HOXA7 positive and, like in preovulatory follicles and theca interna, staining was predominantly cytoplasmic. The change in HOXA7 expression from negative primordial to positive primary follicles suggested a relationship with granulosa cell proliferation. To test this hypothesis, SV40 Tag-immortalized human granulosa cells (SVOG) were double stained with anti-HOXA7 antibody and with Ki-67 as proliferation marker. HOXA7 expression was highest in mitotic cells. In addition, growth differentiation factor-9 (GDF-9), known to be secreted by oocytes in primary human follicles, up-regulated HOXA7 protein, and stimulated proliferation of SVOG, while TGF-beta1 inhibited HOXA7 expression and proliferation. This is the first report on the expression of any HOX gene in human ovarian follicles and granulosa cell tumors. It shows that HOXA7 undergoes cell type- and stage-specific changes during ovarian folliculogenesis, likely regulates granulosa cell proliferation, and in subcellular location differs between proliferating and secretory cells. The increase in HOXA7 protein in response to GDF-9 represents the first demonstration of a possible regulatory role of oocytes in ovarian follicular HOX gene expression.

Homeobox D10 Induces Phenotypic Reversion of Breast Tumor Cells in a Three-Dimensional Culture Model

Homeobox (Hox) genes are master regulatory genes that direct organogenesis and maintain differentiated tissue function. We previously reported that HoxD10 helps to maintain a quiescent, differentiated phenotype in endothelial cells by suppressing expression of genes involved in remodeling the extracellular matrix and cell migration. Here we investigated whether HoxD10 could also promote or maintain a differentiated phenotype in epithelial cells. We observed that HoxD10 expression is progressively reduced in epithelial cells as malignancy increases in both breast and endometrial tumors. Retroviral gene transfer to restore expression of HoxD10 in the malignant breast tumor cells MDA-MB-231 significantly impaired migration, and when these cells were cultured in a three-dimensional laminin-rich basement membrane (3DlrBM) model, they formed polarized, acinar structures. This phenotypic reversion was accompanied by decreased alpha3 integrin expression and reduced proliferation. Importantly, expression of HoxD10 in the MDA-MB-231 cells inhibited their ability to form tumors in mouse xenografts. Taken together, our results suggest that HoxD10 has tumor-suppressive functions for mammary epithelial cells.

The pathophysiology of HOX genes and their role in cancer

The HOM-C clustered prototype homeobox genes of Drosophila, and their counterparts, the HOX genes in humans, are highly conserved at the genomic level. These master regulators of development continue to be expressed throughout adulthood in various tissues and organs. The physiological and patho-physiological functions of this network of genes are being avidly pursued within the scientific community, but defined roles for them remain elusive. The order of expression of HOX genes within a cluster is co-ordinated during development, so that the 3' genes are expressed more anteriorly and earlier than the 5' genes. Mutations in HOXA13 and HOXD13 are associated with disorders of limb formation such as hand-foot-genital syndrome (HFGS), synpolydactyly (SPD), and brachydactyly. Haematopoietic progenitors express HOX genes in a pattern characteristic of the lineage and stage of differentiation of the cells. In leukaemia, dysregulated HOX gene expression can occur due to chromosomal translocations involving upstream regulators such as the MLL gene, or the fusion of a HOX gene to another gene such as the nucleoporin, NUP98. Recent investigations of HOX gene expression in leukaemia are providing important insights into disease classification and prediction of clinical outcome. Whereas the oncogenic potential of certain HOX genes in leukaemia has already been defined, their role in other neoplasms is currently being studied. Progress has been hampered by the experimental approach used in many studies in which the expression of small subsets of HOX genes was analysed, and complicated by the functional redundancy implicit in the HOX gene system. Attempts to elucidate the function of HOX genes in malignant transformation will be enhanced by a better understanding of their upstream regulators and downstream target genes.

Beta1-integrin orients epithelial polarity via Rac1 and laminin

Epithelial cells polarize and orient polarity in response to cell-cell and cell-matrix adhesion. Although there has been much recent progress in understanding the general polarizing machinery of epithelia, it is largely unclear how this machinery is controlled by the extracellular environment. To explore the signals from cell-matrix interactions that control orientation of cell polarity, we have used three-dimensional culture systems in which Madin-Darby canine kidney (MDCK) cells form polarized, lumen-containing structures. We show that interaction of collagen I with apical beta1-integrins after collagen overlay of a polarized MDCK monolayer induces activation of Rac1, which is required for collagen overlay-induced tubulocyst formation. Cysts, comprised of a monolayer enclosing a central lumen, form after embedding single cells in collagen. In those cultures, addition of a beta1-integrin function-blocking antibody to the collagen matrix gives rise to cysts that have defects in the organization of laminin into the basement membrane and have inverted polarity. Normal polarity is restored by either expression of activated Rac1, or the inclusion of excess laminin-1 (LN-1). Together, our results suggest a signaling pathway in which the activation of beta1-integrins orients the apical pole of polarized cysts via a mechanism that requires Rac1 activation and laminin organization into the basement membrane.