The NeST (Neoadjuvant systemic therapy in breast cancer) study: National Practice Questionnaire of United Kingdom multi-disciplinary decision making.

BACKGROUND: Neoadjuvant systemic therapy (NST) is increasingly used in the treatment of breast cancer, yet it is clear that there is significant geographical variation in its use in the UK. This study aimed to examine stated practice across UK breast units, in terms of indications for use, radiological monitoring, pathological reporting of treatment response, and post-treatment surgical management. METHODS: Multidisciplinary teams (MDTs) from all UK breast units were invited to participate in the NeST study. A detailed questionnaire assessing current stated practice was distributed to all participating units in December 2017 and data collated securely usingREDCap. Descriptive statistics were calculated for each questionnaire item. RESULTS: Thirty-nine MDTs from a diverse range of hospitals responded. All MDTs routinely offered neoadjuvant chemotherapy (NACT) to a median of 10% (range 5-60%) of patients. Neoadjuvant endocrine therapy (NET) was offered to a median of 4% (range 0-25%) of patients by 66% of MDTs. The principal indication given for use of neoadjuvant therapy was for surgical downstaging. There was no consensus on methods of radiological monitoring of response, and a wide variety of pathological reporting systems were used to assess tumour response. Twenty-five percent of centres reported resecting the original tumour footprint, irrespective of clinical/radiological response. Radiologically negative axillae at diagnosis routinely had post-NACT or post-NET sentinel lymph node biopsy (SLNB) in 73.0 and 84% of centres respectively, whereas 16% performed SLNB pre-NACT. Positive axillae at diagnosis would receive axillary node clearance at 60% of centres, regardless of response to NACT. DISCUSSION: There is wide variation in the stated use of neoadjuvant systemic therapy across the UK, with general low usage of NET. Surgical downstaging remains the most common indication of the use of NAC, although not all centres leverage the benefits of NAC for de-escalating surgery to the breast and/or axilla. There is a need for agreed multidisciplinary guidance for optimising selection and management of patients for NST. These findings will be corroborated in phase II of the NeST study which is a national collaborative prospective audit of NST utilisation and clinical outcomes.

Gynaecomastia: a cosmetic concern or a concerning clinical sign?

Gynaecomastia is common and often physiological, leading to frequent dismissal as a cosmetic condition. It can however be a symptom of underlying hormone imbalance, which requires further assessment to exclude underlying sinister pathology. We discuss a rare cause of gynaecomastia that demonstrates the importance of a holistic approach to patient assessment.

The NeST (neoadjuvant systemic therapy in breast cancer) study - Protocol for a prospective multi-centre cohort study to assess the current utilization and short-term outcomes of neoadjuvant systemic therapies in breast cancer.

INTRODUCTION: Neoadjuvant systemic therapy (NST) has several potential advantages in the treatment of breast cancer. However, there is currently considerable variation in NST use across the UK. The NeST study is a national, prospective, multicentre cohort study that will investigate current patterns of care with respect to NST in the UK. METHODS AND ANALYSIS: Phase 1 - a national practice questionnaire (NPQ) to survey current practice.Phase 2 - a multi-centre prospective cohort study of breast cancer patients, undergoing NST.Women undergoing NST as their MDT recommended primary breast cancer treatment between December 2017 and May 2018 will be included. The breast surgery and oncological professional associations and the trainee research collaborative networks will encourage participation by all breast cancer centres.Patient demographics, radiological, oncological, surgical and pathological data will be collected, including complications and the need for further intervention/treatment. Data will be collated to establish current practice in the UK, regarding NST usage and variability of access and provision of these therapies. Prospective data on 600 patients from ~50 centres are anticipated.Trial registration: ISRCTN11160072. ETHICS AND DISSEMINATION: Research ethics approval is not required for this study, as per the online Health Research Authority decision tool. The information obtained will provide valuable insights to help patients make informed decisions about their treatment. These data should establish current practice in the UK concerning NST, inform future service delivery as well as identifying further research questions.This protocol will be disseminated through the Mammary Fold Academic Research Collaborative (MFAC), the Reconstructive Surgery Trials Network and the Association of Breast Surgery. Participating units will have access to their own data and collective results will be presented at relevant conferences and published in appropriate peer-reviewed journals, as well as being made accessible to relevant patient groups.

Loss of the xeroderma pigmentosum group B protein binding site impairs p210 BCR/ABL1 leukemogenic activity.

Previous studies have demonstrated that p210 BCR/ABL1 interacts directly with the xeroderma pigmentosum group B (XPB) protein, and that XPB is phosphorylated on tyrosine in cells that express p210 BCR/ABL1. In the current study, we have constructed a p210 BCR/ABL1 mutant that can no longer bind to XPB. The mutant has normal kinase activity and interacts with GRB2, but can no longer phosphorylate XPB. Loss of XPB binding is associated with reduced expression of c-MYC and reduced transforming potential in ex-vivo clonogenicity assays, but does not affect nucleotide excision repair in lymphoid or myeloid cells. When examined in a bone marrow transplantation (BMT) model for chronic myelogenous leukemia, mice that express the mutant exhibit attenuated myeloproliferation and lymphoproliferation when compared with mice that express unmodified p210 BCR/ABL1. Thus, the mutant-transplanted mice show predominantly neutrophilic expansion and altered progenitor expansion, and have significantly extended lifespans. This was confirmed in a BMT model for B-cell acute lymphoblastic leukemia, wherein the majority of the mutant-transplanted mice remain disease free. These results suggest that the interaction between p210 BCR/ABL1 and XPB can contribute to disease progression by influencing the lineage commitment of lymphoid and myeloid progenitors.

Contributions of the RhoGEF activity of p210 BCR/ABL to disease progression.

We have previously identified a tyrosine kinase-independent, guanine nucleotide exchange factor (GEF) activity, which is contained within the region of p210 no expansion BCR/ABL that distinguishes it from p190 BCR/ABL. In the current study, we have compared the transforming activity of p190 BCR/ABL, p210 BCR/ABL and a mutant that lacks GEF activity (p210 BCR/ABL(S509A)). In cell-based, ex vivo, and murine bone marrow transplantation (BMT) assays the transforming activity of p210 BCR/ABL(S509A) mimics p190 BCR/ABL, and is distinct from p210 BCR/ABL. Thus, in the BMT assay, the p190 BCR/ABL- and p210 BCR/ABL(S509A)-transplanted mice exhibit a more rapid onset of disease than mice transplanted with p210 BCR/ABL. The reduced disease latency is associated with erythroid hyperplasia in the absence of anemia, and expansion of the megakaryocyte-erythrocyte progenitor (MEP), common myeloid progenitor (CMP) and granulocyte-macrophage progenitor (GMP) populations, producing a phenotype that is similar to acute myeloid leukemia (AML-M6). The disease phenotype is readily transplantable into secondary recipients. This is consistent with ex vivo clonogenicity assays, where p210 BCR/ABL preferentially supports the growth of colony forming unit (CFU)-granulocyte-macrophage (GM), whereas p190 BCR/ABL and the mutant preferentially support the growth of burst forming unit-erythroid (BFU-E). These results suggest that the GEF activity that distinguishes p210 BCR/ABL from p190 BCR/ABL actively regulates disease progression.

The RhoGEF domain of p210 Bcr-Abl activates RhoA and is required for transformation.

The BCR-ABL oncogene encodes an in-frame fusion protein containing N-terminal sequences derived from Bcr and C-terminal sequences derived from Abl. Bcr contains a centrally located Rho-specific guanine nucleotide exchange factor (RhoGEF) domain that is retained within p210 Bcr-Abl. Although this domain is subject to autoinhibition in the context of Bcr, here we show that it is constitutively activated in p210 Bcr-Abl. p210 Bcr-Abl can stimulate RhoA activation independently of its tyrosine kinase activity, and mutations within the RhoGEF domain that are predicted to eliminate RhoGEF activity inhibit RhoA activation. The RhoGEF mutant of p210 Bcr-Abl does not affect the tyrosine kinase activity of the molecule, nor the ability of p210 Bcr-Abl to interact with XPB through the RhoGEF domain. Despite retaining normal levels of tyrosine kinase activity, the RhoGEF mutant of p210 Bcr-Abl is impaired in transforming activity as measured by anchorage-independent growth. However, the mutant is still able to confer the phenotype of growth factor independence in myeloid cells, suggesting that some, but not all parameters of p210 Bcr-Abl transformation, are dependent upon a catalytically active RhoGEF domain. Collectively, these observations identify a gain-of-function activity attributable to the RhoGEF domain of p210 Bcr-Abl that is required to support the transformed phenotype.

The thrombin receptor, PAR-1, causes transformation by activation of Rho-mediated signaling pathways.

We utilized a cDNA expression library derived from the B6SutA(1) mouse myeloid progenitor cell line to search for novel oncogenes that promote growth transformation of NIH3T3 cells. A 2.2 kb transforming cDNA was recovered that encodes the wild type thrombin-stimulated G protein-coupled receptor PAR-1. In addition to its potent focus forming activity, constitutive overexpression of PAR-1 in NIH3T3 cells promoted the loss of anchorage- and serum-dependent growth. Although inhibitors of thrombin failed to block PAR-1 transforming activity, a PAR-1 mutant that cannot be cleaved by thrombin was nontransforming. Since the foci of transformed cells induced by PAR-1 bear a striking resemblance to those induced by activated RhoA, we determined if PAR-1 transformation was due to the aberrant activation of a specific Rho family member. Like RhoA, PAR-1 cooperated with activated Raf-1 and caused synergistic enhancement of transforming activity, induced stress fibers when microinjected into porcine aortic endothelial cells, stimulated the activity of the serum response factor and NF-kappaB transcription factors, and PAR-1 transformation was blocked by co-expression of dominant negative RhoA. Finally, PAR-1 transforming activity was blocked by pertussis toxin and by co-expression of the RGS domain of Lsc, implicating Galpha(i) and Galpha(12)/Galpha(13) subunits, respectively, as mediators of PAR-1 transformation. Taken together, these observations suggest that PAR-1 growth transformation is mediated, in part, by activation of RhoA.

Rho GTPase-dependent transformation by G protein-coupled receptors.

G protein coupled receptors (GPCRs) constitute the largest family of cell surface receptors, with more than 1000 members, and are responsible for converting a diverse array of extracellular stimuli into intracellular signaling events. Most members of the family have defined roles in intermediary metabolism and generally perform these functions in well-differentiated cells. However, there is an increasing awareness that some GPCRs can also regulate proliferative signaling pathways and that chronic stimulation or mutational activation of receptors can lead to oncogenic transformation. Activating mutations in GPCRs are associated with several types of human tumors and some receptors exhibit potent oncogenic activity due to agonist overexpression. Additionally, expression screening analyses for novel oncogenes identified GPCRs whose expression causes the oncogenic transformation of NIH3T3 mouse fibroblasts. These include Mas, G2A, and the PAR-1 thrombin receptor. In this review we summarize the signaling and transforming properties of these GPCR oncoproteins. What has emerged from these studies is the delineation of a GTPase cascade where transforming GPCRs cause aberrant growth regulation via activation of Rho family small GTPases.

Purification, molecular cloning, and expression of the gene encoding fatty acid 13-hydroperoxide lyase from guava fruit (Psidium guajava).

Guava fruit was identified as a particularly rich source of 13-hydroperoxide lyase activity. The enzyme proved stable to chromatographic procedures and was purified to homogeneity. Based on gel filtration and gel electrophoresis, the native enzyme appears to be a homotetramer with subunits of 55 kD. Starting with primers based on the peptide sequence, the enzyme was cloned by polymerase chain reaction with 3' and 5' rapid amplification of cDNA ends. The sequence shows approximately 60-70% identity to known 13-hydroperoxide lyases and is classified in cytochrome P450 74B subfamily as CYP74B5. The cDNA was expressed in Escherichia coli (BL21 cells), with optimal enzyme activity obtained in the absence of isopropyl-beta-D-thiogalactopyranoside and delta-aminolevulinic acid. The expressed enzyme metabolized 13(S)-hydroperoxylinolenic acid over 10-fold faster than 13(S)-hydroperoxylinoleic acid and the 9-hydroperoxides of linoleic and linolenic acids. 13(S)-Hydroperoxylinolenic acid was converted to 12-oxododec-9(Z)-enoic acid and 3(Z)-hexenal, as identified by gas chromatography-mass spectrometry. The turnover number with this substrate, with enzyme concentration estimated from the Soret absorbance, was approximately 2000/s, comparable to values reported for the related allene oxide synthases. Distinctive features of the guava 13-hydroperoxide lyase and related cytochrome P450 are discussed.

Functional interaction between the cytoplasmic leucine-zipper domain of HIV-1 gp41 and p115-RhoGEF.

The long cytoplasmic tail of the human immunodeficiency virus (HIV)-1 transmembrane protein gp41 (gp41C) is implicated in the replication and cytopathicity of HIV-1 [1]. Little is known about the specific functions of gp41C, however. HIV-1 or simian immunodeficiency virus (SIV) mutants with defective gp41C have cell-type- or species-dependent phenotypes [2] [3] [4] [5] [6]. Thus, host factors are implicated in mediating the functions of gp41C. We report here that gp41C interacted with the carboxy-terminal regulatory domain of p115-RhoGEF [7], a specific guanine nucleotide exchange factor (GEF) and activator of the RhoA GTPase, which regulates actin stress fiber formation, activation of serum response factor (SRF) and cell proliferation [8] [9]. We demonstrate that gp41C inhibited p115-mediated actin stress fiber formation and activation of SRF. An amphipathic helix region with a leucine-zipper motif in gp41C is involved in its interaction with p115. Mutations in gp41C leading to loss of interaction with p115 impaired HIV-1 replication in human T cells. These findings suggest that an important function of gp41C is to modulate the activity of p115-RhoGEF and they thus reveal a new potential anti-HIV-1 target.

Dependence of Dbl and Dbs transformation on MEK and NF-kappaB activation.

Dbs was identified initially as a transforming protein and is a member of the Dbl family of proteins (>20 mammalian members). Here we show that Dbs, like its rat homolog Ost and the closely related Dbl, exhibited guanine nucleotide exchange activity for the Rho family members RhoA and Cdc42, but not Rac1, in vitro. Dbs transforming activity was blocked by specific inhibitors of RhoA and Cdc42 function, demonstrating the importance of these small GTPases in Dbs-mediated growth deregulation. Although Dbs transformation was dependent upon the structural integrity of its pleckstrin homology (PH) domain, replacement of the PH domain with a membrane localization signal restored transforming activity. Thus, the PH domain of Dbs (but not Dbl) may be important in modulating association with the plasma membrane, where its GTPase substrates reside. Both Dbs and Dbl activate multiple signaling pathways that include activation of the Elk-1, Jun, and NF-kappaB transcription factors and stimulation of transcription from the cyclin D1 promoter. We found that Elk-1 and NF-kappaB, but not Jun, activation was necessary for Dbl and Dbs transformation. Finally, we have observed that Dbl and Dbs regulated transcription from the cyclin D1 promoter in a NF-kappaB-dependent manner. Previous studies have dissociated actin cytoskeletal activity from the transforming potential of RhoA and Cdc42. These observations, when taken together with those of the present study, suggest that altered gene expression, and not actin reorganization, is the critical mediator of Dbl and Rho family protein transformation.

Involvement of NH(2)-terminal sequences in the negative regulation of Vav signaling and transforming activity.

Deletion of the NH(2)-terminal 65 amino acids of proto-Vav (to form onco-Vav) activates its transforming activity, suggesting that these sequences serve a negative regulatory role in Vav function. However, the precise role of these NH(2)-terminal sequences and whether additional NH(2)-terminal sequences are also involved in negative regulation have not been determined. Therefore, we generated additional NH(2)-terminal deletion mutants of proto-Vav that lack the NH(2)-terminal 127, 168, or 186 amino acids, and assessed their abilities to cause focus formation in NIH 3T3 cells and to activate different signaling pathways. Since Vav mutants lacking 168 or 186 NH(2)-terminal residues showed a several 100-fold greater focus forming activity than that seen with deletion of 65 residues, residues spanning 66 to 187 also contribute significantly to negative regulation of Vav transforming activity. The increase in Vav transforming activity correlated with the activation of the c-Jun, Elk-1, and NF-kappaB transcription factors, as well as increased transcription from the cyclin D1 promoter. Tyrosine 174 is a key site of phosphorylation by Lck in vitro and Lck-mediated phosphorylation has been shown to be essential for proto-Vav GEF function in vitro. However, we found that an NH(2)-terminal Vav deletion mutant lacking this tyrosine residue (DeltaN-186 Vav) retained the ability to be phosphorylated by Lck in vivo and Lck still caused enhancement of DeltaN-186 Vav signaling and transforming activity. Thus, Lck can stimulate Vav via a mechanism that does not involve Tyr(174) or removal of NH(2)-terminal regulatory activity. Finally, we found that NH(2)-terminal deletion enhanced the degree of Vav association with the membrane-containing particulate fraction and that an isolated NH(2)-terminal fragment (residues 1-186) could impair DeltaN-186 Vav signaling. Taken together, these observations suggest that the NH(2) terminus may serve as a negative regulator of Vav by intramolecular interaction with COOH-terminal sequences to modulate efficient membrane association.

The Dbl-related protein, Lfc, localizes to microtubules and mediates the activation of Rac signaling pathways in cells.

The possibility that the Dbl family member Lfc can activate Rac1 in cells is investigated in this study. Previously, we demonstrated that both Lfc and Lsc, like their closest relative Lbc, can act catalytically in stimulating the guanine nucleotide exchange activity of RhoA in vitro. Neither Lfc nor Lsc stimulated the in vitro exchange activity of Cdc42 or Rac1; however, Lfc was capable of forming a tight complex with Rac1 in vitro. We show here that Lfc stimulates c-Jun kinase (JNK) activity in COS-7 cells. This stimulation was blocked by a dominant negative mutant of Rac1 and somewhat less effectively by dominant negative RhoA, but not by dominant negative Cdc42. Overexpression of Lfc in NIH 3T3 cells induced the formation of actin stress fibers and membrane ruffles, consistent with the activation of both RhoA and Rac1 signaling pathways, whereas overexpression of Lsc led exclusively to well developed stress fibers. Using a recently developed assay for measuring the cellular activation of Rac, we did not find that expression of Lfc increased the levels of GTP-bound Rac1. However, an examination of the cellular localization of Lfc showed that it was localized to microtubules, similar to what has been reported for activated Rac1, the mixed lineage kinase (MLK) and JNK. Moreover, we have found that the Pleckstrin homology (PH) domain of Lfc specifically associates with tubulin. Taken together, these findings suggest a model where the PH domain-mediated localization of Lfc to microtubules enables the recruitment of Rac to a site proximal to its signaling targets, resulting in JNK activation and actin cytoskeletal changes.

Regulation of RasGRP via a phorbol ester-responsive C1 domain.

As part of a cDNA library screen for clones that induce transformation of NIH 3T3 fibroblasts, we have isolated a cDNA encoding the murine homolog of the guanine nucleotide exchange factor RasGRP. A point mutation predicted to prevent interaction with Ras abolished the ability of murine RasGRP (mRasGRP) to transform fibroblasts and to activate mitogen-activated protein kinases (MAP kinases). MAP kinase activation via mRasGRP was enhanced by coexpression of H-, K-, and N-Ras and was partially suppressed by coexpression of dominant negative forms of H- and K-Ras. The C terminus of mRasGRP contains a pair of EF hands and a C1 domain which is very similar to the phorbol ester- and diacylglycerol-binding C1 domains of protein kinase Cs. The EF hands could be deleted without affecting the ability of mRasGRP to transform NIH 3T3 cells. In contrast, deletion of the C1 domain or an adjacent cluster of basic amino acids eliminated the transforming activity of mRasGRP. Transformation and MAP kinase activation via mRasGRP were restored if the deleted C1 domain was replaced either by a membrane-localizing prenylation signal or by a diacylglycerol- and phorbol ester-binding C1 domain of protein kinase C. The transforming activity of mRasGRP could be regulated by phorbol ester when serum concentrations were low, and this effect of phorbol ester was dependent on the C1 domain of mRasGRP. The C1 domain could also confer phorbol myristate acetate-regulated transforming activity on a prenylation-defective mutant of K-Ras. The C1 domain mediated the translocation of mRasGRP to cell membranes in response to either phorbol ester or serum stimulation. These results suggest that the primary mechanism of activation of mRasGRP in fibroblasts is through its recruitment to diacylglycerol-enriched membranes. mRasGRP is expressed in lymphoid tissues and the brain, as well as in some lymphoid cell lines. In these cells, RasGRP has the potential to serve as a direct link between receptors which stimulate diacylglycerol-generating phospholipase Cs and the activation of Ras.

Suppressors of position-effect variegation in Drosophila melanogaster affect expression of the heterochromatic gene light in the absence of a chromosome rearrangement.

Suppressors of position-effect variegation (Su(var)s) in Drosophila melanogaster are usually studied in the presence of chromosomal rearrangements, which exhibit variegated expression of euchromatic genes moved near to, or heterochromatic genes moved away from, centromeric heterochromatin. However, the effects of Su(var) mutations on heterochromatic gene expression in the absence of a variegating re-arrangement have not yet been defined. Here we present a number of results which suggest that Su(var) gene products can interact to affect the expression of the light gene in its normal heterochromatic location. We initially observed that eye pigment was reduced in several Su(var) double mutants; the phenotype resembled that of light mutations and was more severe when only one copy of the light gene was present. This reduced pigmentation could be alleviated by a duplication for the light gene or by a reduction in the amount of cellular heterochromatin. In addition, the viability of most Su(var) double mutant combinations tested was greatly reduced in a genetic background of reduced light gene dosage, when extra heterochromatin is present. We conclude that Su(var) gene products can affect expression of the heterochromatic light gene in the absence of any chromosomal rearrangements. However, it is noteworthy that mutations in any single Su(var) gene have little effect on light expression; we observe instead that different pairings of Su(var) mutations are required to show an effect on light expression. Interestingly, we have obtained evidence that at least two of the second chromosome Su(var) mutations are gain-of-function lesions, which also suggests that there may be different modes of interaction among these genes. It may therefore be possible to use this more sensitive assay of Su(var) effects on heterochromatic genes to infer functional relationships among the products of the 50 or more known Su(var) loci.

CDC42 and FGD1 cause distinct signaling and transforming activities.

Activated forms of different Rho family members (CDC42, Rac1, RhoA, RhoB, and RhoG) have been shown to transform NIH 3T3 cells as well as contribute to Ras transformation. Rho family guanine nucleotide exchange factors (GEFs) (also known as Dbl family proteins) that activate CDC42, Rac1, and RhoA also demonstrate oncogenic potential. The faciogenital dysplasia gene product, FGD1, is a Dbl family member that has recently been shown to function as a CDC42-specific GEF. Mutations within the FGD1 locus cosegregate with faciogenital dysplasia, a multisystemic disorder resulting in extensive growth impairments throughout the skeletal and urogenital systems. Here we demonstrate that FGD1 expression is sufficient to cause tumorigenic transformation of NIH 3T3 fibroblasts. Although both FGD1 and constitutively activated CDC42 cooperated with Raf and showed synergistic focus-forming activity, both quantitative and qualitative differences in their functions were seen. FGD1 and CDC42 also activated common nuclear signaling pathways. However, whereas both showed comparable activation of c-Jun, CDC42 showed stronger activation of serum response factor and FGD1 was consistently a better activator of Elk-1. Although coexpression of FGD1 with specific inhibitors of CDC42 function demonstrated the dependence of FGD1 signaling activity on CDC42 function, FGD1 signaling activities were not always consistent with the direct or exclusive stimulation of CDC42 function. In summary, FGD1 and CDC42 signaling and transformation are distinct, thus suggesting that FGD1 may be mediating some of its biological activities through non-CDC42 targets.

Transforming potential of Dbl family proteins correlates with transcription from the cyclin D1 promoter but not with activation of Jun NH2-terminal kinase, p38/Mpk2, serum response factor, or c-Jun.

The dbl family of oncogenes encodes a large, structurally related, family of growth-regulatory molecules that possess guanine nucleotide exchange factor activity for specific members of the Rho family of Ras-related GTPases. We have evaluated matched sets of weakly and strongly transforming versions of five Dbl family proteins (Lfc, Lsc, Ect2, Dbl, and Dbs) to determine their ability to stimulate signaling pathways that are activated by Rho family proteins. We found that the transforming potential of this panel did not correlate directly with their ability to activate Jun NH2-terminal kinase, p38/Mpk2, serum response factor, or c-Jun. In contrast, transient stimulation of transcription from the cyclin D1 promoter provided a strong correlation with transforming potential, and we found constitutive up-regulation of cyclin D1 protein in Dbl family protein-transformed cells. In addition, we observed that at least two Dbl family members (Lfc and Ect2) induced changes in the actin cytoskeleton and exhibited nuclear signaling profiles that are consistent with a broader range of in vivo substrate utilization than is predicted from their in vitro exchange specificities. In summary, although Dbl family proteins exhibit signaling profiles that are consistent with their in vivo activation of Rho proteins, stimulation of cyclin D1 transcription is the only activity that correlates with transforming potential, thus suggesting that deregulated cell cycle progression may be important for Dbl family protein transformation.

Cdc42 and Rac1 induce integrin-mediated cell motility and invasiveness through PI(3)K.

Transformation of mammary epithelial cells into invasive carcinoma results in alterations in their integrin-mediated responses to the extracellular matrix, including a loss of normal epithelial polarization and differentiation, and a switch to a more motile, invasive phenotype. Changes in the actin cytoskeleton associated with this switch suggest that the small GTPases Cdc42 and Rac, which regulate actin organization, might modulate motility and invasion. However, the role of Cdc42 and Rac1 in epithelial cells, especially with respect to integrin-mediated events, has not been well characterized. Here we show that activation of Cdc42 and Rac1 disrupts the normal polarization of mammary epithelial cells in a collagenous matrix, and promotes motility and invasion. This motility does not require the activation of PAK, JNK, p70 S6 kinase, or Rho, but instead requires phosphatidylinositol-3-OH kinase (PI(3)K). Further, direct PI(3)K activation is sufficient to disrupt epithelial polarization and induce cell motility and invasion. PI(3)K inhibition also disrupts actin structures, suggesting that activation of PI(3)K by Cdc42 and Rac1 alters actin organization, leading to increased motility and invasiveness.