Oral Contraceptive Use and Parity Associations with Uncommon Breast Cancer Histologies in the Breast Cancer Family Registry: the Role of Family History

Purpose: The effect of parity and oral contraceptive (OC) use on breast cancer risk differs by cancer subtype as defined by histology. Family history of breast cancer impacts decisions regarding both parity and oral contraceptive use; it is unknown whether reproductive risk factors are related to uncommon histologies in women with and without a strong family history.

Methods: Using population-based data from the Breast Cancer Family Registry, we conducted analyses using unordered polytomous regression to determine the role of family history in associations between parity, OC use, and breast cancer histologic subtype, among 3,260 cases and 2,997 controls. Histologic types examined included ductal and lobular as well as the uncommon histologies of mucinous, tubular, and medullary cancer.

Results: Twenty-eight percent of cases and 9% of controls had a family history (defined as at least 1 first-degree relative with breast cancer). Cases with and without family history were similar in regards to OC use (75% and 73%, respectively were ever-users) and parity (2.08 children in cases with family history, 2.10 in cases without). In a multivariable model, when compared with controls, OC use was inversely associated with tumors of mucinous histology (OR = 0.43, 95% CI 0.23–0.79 for use ≥5 years vs. never use). There was a stronger inverse association with OC use and the mucinous subtype among those without a family history (OR = 0.27, 95% CI 0.13–0.57), and a nonsignificant positive association in those with family history (OR = 2.19, 95% CI 0.40–11.84). High parity (≥3 children) was positively associated with medullary histology (OR = 2.62, 95% CI 1.16–5.91, compared with nulliparity); the association was stronger among women without a family history (OR = 4.31, 95% CI 1.67–11.12), and was not significantly associated among those with a family history (OR = 0.36, 95% CI 0.06–2.29). Parity was inversely associated with the mucinous type (OR = 0.45, 95% CI 0.21–0.96, compared with nulliparity), and this effect remained stable in women with and without family history.

Conclusion: This study suggests that selected reproductive risk factors may only be related to uncommon breast cancer histologies among women without a family history of breast cancer.

Abstract P6-15-14: Inhibit SIAH E3 Ligase, a Downstream Signaling Module Required for the HER2/EGFR/RAS Signal Transduction, To Block Tumorigenesis and Metastasis of Highly Invasive Human Breast Cancers

The central importance of the HER2/Neu/EGFR/RAS signaling pathway has been well established in the growth, invasion and metastasis of human breast cancer, even though oncogenic RAS mutations are rare in breast cancer, activation of the tumor-promoting ERBB/RAS/MEK/MAPK pathway has been consistently documented in high-grade breast tumors. As such, novel approaches to inhibit activated ERBB/RAS signals constitute important measures to block tumor growth and metastasis in mammary tumors. In this study, instead of targeting an upstream signaling component such as HER2/EGFR/RAS, we targeted the most downstream signaling module identified in the RAS pathway — the SIAH proteolytic machinery. SIAH is an evolutionarily conserved RING E3 ligase that is a critical “gatekeeper” required for RAS signal transduction in human cancer cells. SIAH is specifically expressed in tumor cells in 120 human breast cancer patients examined so far. The increased SIAH expression is correlated with increased grades and aggressiveness of human breast cancer. We then asked whether inhibiting the gatekeeper function of SIAH would be effective in blocking mammary tumorigenesis and metastasis in human breast cancer. Our results indicated that SIAH2-deficiency successfully abolished tumor growth of three breast cancer cell lines (MDA-MB-231, MDA-MB-435 and MDA-MB-468) in soft agar assays as well as in athymic nude mice. Importantly, by inhibiting SIAH2 function in highly aggressive human breast cancer cells, we are able to completely block tumorigenesis and metastasis of two highly invasive and metastatic human breast cancer cell lines (MDA-MB-231 and MDA-MB-435). These findings suggest that SIAH2 may be an attractive new therapeutic target for novel breast cancer therapy and developing anti-SIAH molecules will aid in expanding our arsenal of effective anticancer therapies. More effective breast cancer treatments may be obtained by multi-pronged synergistic inhibitions at upstream (HER2/EGFR membrane receptors), midstream (RAS/RAF/MEK/mTOR) and downstream (SIAH E3 ligase) signaling modules in the HER2/EGFR/RAS pathway in parallel. Thus, by attacking the growth-promoting ERBB/RAS pathway at multiple signaling modules simultaneously, we may be in a great position to halt the genesis, progression and metastasis of human breast cancer.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-15-14.

SCN2A mutation associated with neonatal epilepsy, late-onset episodic ataxia, myoclonus, and pain

BACKGROUND

Inherited and de novo mutations in sodium channel genes underlie a variety of channelopathies. Mutations in SCN2A, encoding the brain sodium channel Na(V)1.2, have previously been reported to be associated with benign familial neonatal infantile seizures, febrile seizures plus, and intractable epilepsy of infancy.

METHODS

We evaluated the clinical characteristics in a patient with a neonatal-onset complex episodic neurologic phenotype. We screened SCN2A for mutations and carried out in vitro electrophysiologic analyses to study the consequences of the identified mutation. We studied the developmental expression of Na(V)1.2 in cerebellum by immunohistochemical analysis.

RESULTS

The patient presented with neonatal-onset seizures and variable episodes of ataxia, myoclonia, headache, and back pain after 18 months of age. The patient carries a de novo missense mutation (p.Ala263Val) in SCN2A, which leads to a pronounced gain-of-function, in particular an increased persistent Na(+) current. Immunohistochemical studies suggest a developmentally increasing expression of Na(V)1.2 in granule cell axons projecting to Purkinje neurons.

CONCLUSIONS

These results can explain a neuronal hyperexcitability resulting in seizures and other episodic symptoms extending the spectrum of SCN2A-associated phenotypes. The developmentally increasing expression of Na(V)1.2 in cerebellum may be responsible for the later onset of episodic ataxia.

The glycoprotein Ibalpha-von Willebrand factor interaction induces platelet apoptosis

BACKGROUND

The interaction of glycoprotein (GP) Ibalpha with von Willebrand factor (VWF) initiates platelet adhesion, and simultaneously triggers intracellular signaling cascades leading to platelet aggregation and thrombus formation. Some of the signaling events are similar to those occurring during apoptosis, however, it is still unclear whether platelet apoptosis is induced by the GPIbalpha-VWF interaction.

OBJECTIVES

To investigate whether the GPIbalpha-VWF interaction induces platelet apoptosis and the role of 14-3-3zeta in apoptotic signaling.

METHODS

Apoptotic events were assessed in platelets or Chinese hamster ovary (CHO) cells expressing wild-type (1b9) or mutant GPIb-IX interacting with VWF by flow cytometry or western blotting.

RESULTS

Ristocetin-induced GPIbalpha-VWF interaction elicited apoptotic events in platelets, including phosphatidylserine exposure, elevations of Bax and Bak, gelsolin cleavage, and depolarization of mitochondrial inner transmembrane potential. Apoptotic events were also elicited in platelets exposed to pathologic shear stresses in the presence of VWF; however, the shear-induced apoptosis was eliminated by the anti-GPIbalpha antibody AK2. Furthermore, apoptotic events occurred in 1b9 cells stimulated with VWF and ristocetin, but were significantly diminished in two CHO cell lines expressing mutant GPIb-IX with GPIbalpha truncated at residue 551 or a serine-to-alanine mutation at the 14-3-3zeta-binding site in GPIbalpha.

CONCLUSIONS

This study demonstrates that the GPIbalpha-VWF interaction induces apoptotic events in platelets, and that the association of 14-3-3zeta with the cytoplasmic domain of GPIbalpha is essential for apoptotic signaling. This finding may suggest a novel mechanism for platelet clearance or some thrombocytopenic diseases.

The relationship between plasma level of adiponectin and coronary lesion complexity in the population of north-east China

The relationship between plasma adiponectin and severity of coronary artery disease (CAD) in 683 cases of suspected CAD from north-east China was determined. Cases were divided into four groups, as follows: group 1, no stenosis; group 2, > 50% stenosis of one vessel; group 3, > 50% stenosis of two vessels; group 4, > 50% stenosis of three or more vessels. Group 1 was classified as a non-CAD group (control) and groups 2, 3 and 4 were classified as CAD groups. Plasma adiponectin levels were significantly correlated with coronary artery stenosis and were lower in the CAD groups than in the non-CAD group. Adiponectin concentration decreased from group 2 to group 4, but this difference was not significant. Adiponectin levels among females were also lower than for males in the CAD groups. There was a significant difference between plasma adiponectin levels in patients with coronary stenoses versus those without, but there were no significant differences between the three CAD groups in terms of plasma adiponectin levels.

Differential expression of candidate genes for lignin biosynthesis under drought stress in maize leaves

In order to provide information for the development of molecular selection markers for drought tolerance improvement, the methods of prometric analysis, quantitative real-time PCR and field evaluation were employed for the identification of the differential expression of candidate genes under drought stress in maize. At seventeen, twenty-four and forty-eight hours of polyethylene glycol-simulated drought stress at the seventh leaf stage, leaf samples were collected from two drought-tolerant inbred lines for prometric analysis by two-dimensional electrophoresis and peptide mass fingerprinting. Fifty-eight proteins out of more than 500 were found in response to drought stress. Three drought-induced spots 2506, 3507 and 4506 showed sequence similarity with cinnamyl alcohol dehydrogenase, cytochrome protein 96A8 and S-adenosyl-L-methionine synthase, respectively. The expression of two key enzymes to lignin biosynthesis was quantified by quantitative real-time PCR among three drought-tolerant and one drought-sensitive inbred lines under drought stress and well-watered control conditions. After a decrease at the beginning of drought stress, the expression of cinnamyl alcohol dehydrogenase and caffeate O-methyltransferase recovered at twenty-four hours of the drought stress in the three drought-tolerant lines, but not in the drought-sensitive lines. Leaf lignin content, anthesis-silking interval and grain weight per plant were investigated with six inbred lines of varying drought tolerance under drought stress and well-watered control. Drought tolerance coefficients of these three characters were calculated and the correlation coefficients among these drought tolerance coefficients were estimated. Significant difference in leaf lignin content was found among the inbred lines and in response to drought stress. Close correlations were observed between the drought tolerant coefficients for leaf lignin content and grain weight per plant, and between the drought tolerant coefficients for leaf lignin content and anthesis-silking interval. These results indicate that leaf lignin content is a useful index for evaluation of drought tolerance in maize. Molecular selection markers can be developed on the basis of differential expression of the candidate genes and applied to maize improvement for drought tolerance.

miR-584 mediates post-transcriptional expression of lactoferrin receptor in Caco-2 cells and in mouse small intestine during the perinatal period

MicroRNAs function as gene expression modulators that are critical for mammalian development. Lactoferrin receptor on the apical membrane of enterocytes has been suggested to play key roles in the absorption of lactoferrin-bound iron from breast milk. The objective of this study was to identify mechanisms of microRNA mediated post-transcriptional regulation of the lactoferrin receptor. Sequence analyses revealed that the miR-584 sequence is identical in human, mouse and rat, and there is a conserved region complementary to the seed region (5' nucleotides 2-8) of miR-584 within the lactoferrin receptor mRNA-3'-untranslated region. miR-584 was further found to co-localize with lactoferrin receptor mRNA in mouse small intestine. The 3'-untranslated region of human lactoferrin receptor mRNA was cloned into pGL3-control luciferase reporter vector. By luciferase reporter assays in HEK293 cells, miR-584 mimic specifically repressed the reporter activity in a dose-dependent manner. miR-584 mimic reduced endogenous lactoferrin receptor protein expression in Caco-2 cells, without significantly affecting the mRNA level. We also determined that miR-584 expression is inversely correlated with lactoferrin receptor mRNA and protein expression. Taken together, we propose that miR-584 contributes to the post-transcriptional expression of lactoferrin receptor during the perinatal period. These findings demonstrate a novel example of how microRNAs may be involved in regulation of nutrient metabolism in the newborn.

Decreasing disparity in cholesterol screening in minority communities--findings from the racial and ethnic approaches to community health 2010

BACKGROUND

Highly controlled research projects demonstrated success in preventing and controlling cardiovascular diseases. Community-based programs have yet to demonstrate significant influence. Data on large-scale community-level interventions targeting minority communities are limited. The aim of this study is to measure the impact of the Racial and Ethnic Approaches to Community Health (REACH 2010) project, a community-based intervention to eliminate racial/ethnic disparities in blood cholesterol screening in minority communities.

METHODS

Annual survey data from 2001 to 2006 were gathered in 22 communities. Trends in the prevalence of age-standardised blood cholesterol screening were examined for four racial/ethnic groups (black, Hispanic, Asian and American Indian/Alaska Native), stratified by education level, and compared with national data from the Behavioral Risk Factor Surveillance System.

RESULTS

The prevalence of cholesterol screening increased among persons in black, Hispanic and Asian REACH communities (p<0.001), whereas prevalence decreased in the total US and Hispanic populations (p<0.001) and remained similar among blacks and Asians nationwide. The relative disparity between the total US population and most REACH communities decreased (p<0.05). Relative disparity in cholesterol screening related to education level decreased (p<0.05) within REACH communities, whereas relative disparity related to education level nationwide remained similar in blacks and increased (p<0.001) in Hispanics.

CONCLUSION

The REACH project decreased racial and ethnic disparities in cholesterol screening between REACH communities and the total US population, as well as disparities related to education level within REACH communities.

Coronavirus envelope protein: a small membrane protein with multiple functions

Coronavirus envelope protein is a small membrane protein and minor component of the virus particles. It plays important roles in virion assembly and morphogenesis, alteration of the membrane permeability of host cells and virus-host cell interaction. Here we review recent progress in characterization of the biochemical properties, membrane topology and functions of the protein.

Biochemical evidence for the presence of mixed membrane topologies of the severe acute respiratory syndrome coronavirus envelope protein expressed in mammalian cells

Coronavirus envelope (E) protein is a small integral membrane protein with multi‐functions in virion assembly, morphogenesis and virus–host interaction. Different coronavirus E proteins share striking similarities in biochemical properties and biological functions, but seem to adopt distinct membrane topology. In this report, we study the membrane topology of the SARS‐CoV E protein by immunofluorescent staining of cells differentially permeabilized with detergents and proteinase K protection assay. It was revealed that both the N‐ and C‐termini of the SARS‐CoV E protein are exposed to the cytoplasmic side of the membranes (N_cytoC_cyto). In contrast, parallel experiments showed that the E protein from infectious bronchitis virus (IBV) spanned the membranes once, with the N‐terminus exposed luminally and the C‐terminus exposed cytoplasmically (N_exo(lum)C_cyto). Intriguingly, a minor proportion of the SARS‐CoV E protein was found to be modified by N‐linked glycosylation on Asn 66 and inserted into the membranes once with the C‐terminus exposed to the luminal side. The presence of two distinct membrane topologies of the SARS‐CoV E protein may provide a useful clue to the pathogenesis of SARS‐CoV.

Biochemical and functional characterization of the membrane association and membrane permeabilizing activity of the severe acute respiratory syndrome coronavirus envelope protein

A diverse group of cytolytic animal viruses encodes small, hydrophobic proteins to modify host cell membrane permeability to ions and small molecules during their infection cycles. In this study, we show that expression of the SARS-CoV E protein in mammalian cells alters the membrane permeability of these cells. Immunofluorescent staining and cell fractionation studies demonstrate that this protein is an integral membrane protein. It is mainly localized to the ER and the Golgi apparatus. The protein can be translocated to the cell surface and is partially associated with lipid rafts. Further biochemical characterization of the protein reveals that it is posttranslationally modified by palmitoylation on all three cysteine residues. Systematic mutagenesis studies confirm that the membrane permeabilizing activity of the SARS-CoV E protein is associated with its transmembrane domain.

Optical modulation and detection in slotted Silicon waveguides

We demonstrate a novel mechanism for low power optical detection and modulation in a slotted waveguide geometry filled with nonlinear electro-optic polymers. The nanoscale confinement of the optical mode, combined with its close proximity to electrical contacts, enables the direct conversion of optical energy to electrical energy, without external bias, via optical rectification, and also enhances electro-optic modulation. We demonstrate this process for power levels in the sub-milliwatt regime, as compared to the kilowatt regime in which optical nonlinear effects are typically observed at short length scales. Our results suggest that a new class of detectors based on nonlinear optics may be practical.

Expression of SARS-coronavirus envelope protein in Escherichia coli cells alters membrane permeability

To promote viral entry, replication, release, and spread to neighboring cells, many cytolytic animal viruses encode proteins responsible for modification of host cell membrane permeability and for formation of ion channels in host cell membranes during their life cycles. In this study, we show that the envelope (E) protein of severe acute respiratory syndrome-associated coronavirus can induce membrane permeability changes when expressed in Escherichia coli. E protein expressed in bacterial and mammalian cells under reducing conditions existed as monomers, but formed homodimer and homotrimer under non-reducing conditions. Site-directed mutagenesis studies revealed that two cysteine residues of the E protein were essential for oligomerization, leading to induction of membrane permeability. This is the first report demonstrating that a coronavirus-encoded protein could modify membrane permeability in E. coli cells.

Comments on “Bubble motion in aqueous surfactant solutions”

The numerical simulations of bubble motion in dilute surfactant solutions reported previously by two of the authors contained a serious numerical inaccuracy. In agreement with experiments, single bubbles released from rest were predicted to reach a maximum speed before slowing to a terminal speed. However, subsequent experiments demonstrated that, in the simulations, the bubbles reached their terminal speed too quickly. The source of the discrepancy is an inaccuracy associated with the numerical algorithm used to solve the surfactant transport equation on the bubble surface. After correcting the problem, the simulations agree much better with the experiments.

Myosin-induced autoimmune myocarditis in BALB/C mice

Experimental mice were immunized with cardiac myosin and complete Freund's adjuvant (CFA) on days 0, 7 and 30 and control mice were immunized with CFA. Sera and myocardium samples were harvested on days 15, 21 and 120 after the first immunization. Pathological findings demonstrated that there were necrosis and inflammatory infiltration in acute stage and fibrosis mainly in chronic stage of experimental group. Anti-myosin antibodies were also found in sera of experimental mice, but not in control group. Our study showed that cardiac myosin served as an autoantigen to provoke autoimmunity and lead to the transformation of VMC into DCM.

[Determination of shrinkage and bending strength of GI-II infiltrated ceramic]

OBJECTIVE

To determine the shrinkage and strength of GI-II Infiltrated Ceramic for providing scientific basis of its clinical use.

METHODS

The adobes by slip-casting alumina powder of GI-II Infiltrated Ceramic were sintered at 1125 degrees C for 2 hours. The sintered alumina bodies were then divided into two groups and infiltrated by melt glass at 1125 degrees C and 1100 degrees C respectively for 6 hours. The length of the infiltrated ceramic specimens before and after fabrication was determined to calculate shrinkage. Their strength values were obtained by 3-point bending test.

RESULTS

The infiltrated ceramic infiltrated at 1125 degrees C was 0.289 +/- 0.155% in shrinkage, 367.7 +/- 76.1 MPa in strength, and 4.79 in Weibull modulus; that infiltrated at 1100 degrees C was 0.253 +/- 0.043%, 377.5 +/- 64.4 MPa, and 5.52, respectively. There was no statistically significant difference between those two groups. But their strength values were statistically high, compared with 300 MPa.

CONCLUSION

The shrinkage of GI-II Infiltrated Ceramic could be compensated by brushing spacer on dies and expansion of die stone. Its strength satisfied the requirement for clinical use of all-ceramic bridge materials. This kind of high-strength and low-shrinkage ceramic could be used for fabricating all ceramic crown and bridge core.

[The influences of crystallized compositions in the porcelain on bonding strength of titanium to porcelain]

OBJECTIVE

Sufficient porcelain-titanium bond is a vital factor determining the clinical performance of titanium-porcelain restorations. The purpose of this study was to investigate the effects of self-preparation La-porcelain composition on the porcelain-titanium bonding strength and to compare with the Vita Titankeramik.

METHODS

The present study examines 5 different recipes of porcelain by weight%: SiO2, 12%-17%; LaO2, 7%-10%; Al2O3, 9%-14%; B2O3, 23%-31%; CaO, 6%-8%; K2O, 2%-3%; SrO, 2%-4%; Na2O, 1%-3%; SnO2, 8%-10%; ZrO2, 3%-5%; TiO2, 6%-8%. Specimens were tested in push type shear with a universal testing machine. Scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA) were employed to reveal the microstructures and diffusion of elements in the interfacial regions between the porcelain coating and titanium to the bond strength when fired at 800 degrees C.

RESULTS

The ratios of crystallized compositions had significant influences on the porcelain-titanium bond strength (P < 0.05). La-porcelain had the highest shear bond strength (37.76 MPa). The shear bond strength of the Vita Titankeramik to titanium was 20.18 MPa. The results of SEM revealed integrity of porcelain-titanium joints in La-porcelain and a greater amount of porosity in the interface of Vita Titankeramik to titanium. EPMA analysis demonstrated the aggregation of Si and Sn in the interfacial regions and their diffusion into the titanium.

CONCLUSION

Chemical compositions of porcelain and ratios of crystallized compositions play the important role in the titanium porcelain bond. La-porcelain had the highest shear bond strength and good porcelain-titanium joints. La-porcelain is a new-style low fusing porcelain/titanium system.

Coronary angiographic findings in African-American and white patients from a single institution

No data exist comparing clinical and angiographic findings in large numbers of contemporary African-American and white patients from the same hospital. Limited angiographic data on African Americans were obtained from hospitals serving predominantly minority patients, making the valid African-American:white comparisons difficult. The study included 2,624 consecutive white and 1,793 African-American patients who had angiography for diagnostic evaluation of presumed coronary artery disease at the Louisiana State University Medical Center in Shreveport between 1990 and 1997. Compared to whites of the same sex, a greater proportion of African-American patients had a history of hypertension, stroke, and heart failure. African Americans also had significantly higher systemic and left ventricular pressure, lower ejection fraction, greater echocardiographic left ventricular mass index, and more concentric hypertrophy. The overall proportion of patients with normal or minimal stenosis of coronary artery (<50% narrowing in the luminal diameter) was greater in African Americans than in whites for both men and women. This difference was predominately found in men aged > or = 55 years or older. Except among older men, African-American patients with coronary heart disease had a similar distribution of 1-, 2-, 3-vessel disease and mean stenosis score compared to whites. In conclusion, a higher frequency of normal coronaries and less frequent coronary stenosis were found in older African-American men. The African-American:white differences in angiographic findings were minimal in younger men and in women. However, African Americans had worse clinical profiles than whites.

Locating acoustic emission with an amplitude-multiplexed acoustic sensor array based on a modified mach-zehnder interferometer

We report on an amplitude-division-multiplexed interferometric sensor array for locating acoustic emission. Preliminary experiments were carried out with a modified Mach-Zehnder interferometer consisting of two sensing arms and a reference arm and demonstrated a one-dimensional location accuracy of a few centimeters. The system can be extended for two- and three-dimensional location of acoustic emissions by the addition of one or two more sensing arms, respectively, in the interferometer.

Statins as antioxidant therapy for preventing cardiac myocyte hypertrophy

Cardiac hypertrophy is a major cause of morbidity and mortality worldwide. The hypertrophic process is mediated, in part, by small G proteins of the Rho family. We hypothesized that statins, inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, inhibit cardiac hypertrophy by blocking Rho isoprenylation. We treated neonatal rat cardiac myocytes with angiotensin II (AngII) with and without simvastatin (Sim) and found that Sim decreased AngII-induced protein content, [3H] leucine uptake, and atrial natriuretic factor (ANF) promoter activity. These effects were associated with decreases in cell size, membrane Rho activity, superoxide anion (O2*-) production, and intracellular oxidation, and were reversed with L-mevalonate or geranylgeranylpyrophosphate, but not with farnesylpyrophosphate or cholesterol. Treatments with the Rho inhibitor C3 exotoxin and with cell-permeable superoxide dismutase also decreased AngII-induced O2*- production and myocyte hypertrophy. Overexpression of the dominant-negative Rho mutant N17Rac1 completely inhibited AngII-induced intracellular oxidation and ANF promoter activity, while N19RhoA partially inhibited it, and N17Cdc42 had no effect. Indeed, Sim inhibited cardiac hypertrophy and decreased myocardial Rac1 activity and O2*- production in rats treated with AngII infusion or subjected to transaortic constriction. These findings suggest that statins prevent the development of cardiac hypertrophy through an antioxidant mechanism involving inhibition of Rac1.

Identification and characterization of RA-GEF-2, a Rap guanine nucleotide exchange factor that serves as a downstream target of M-Ras

The Ras family small GTPase Rap is regulated by an array of specific guanine nucleotide exchange factors (GEFs) in response to upstream stimuli. RA-GEF-1 was identified as a novel Rap GEF, which possesses a Ras/Rap1-associating (RA) domain. Here we report a protein closely related to RA-GEF-1, named RA-GEF-2. Like RA-GEF-1, a putative cyclic nucleotide monophosphate-binding domain, a Ras exchanger motif, a PSD-95/DlgA/ZO-1 domain, and an RA domain in addition to the GEF catalytic domain are found in RA-GEF-2. However, RA-GEF-2 displays a different tissue distribution profile from that of RA-GEF-1. RA-GEF-2 stimulates guanine nucleotide exchange of both Rap1 and Rap2, but not Ha-Ras. The RA domain of RA-GEF-2 binds to M-Ras in a GTP-dependent manner, but not to other Ras family GTPases tested, including Ha-Ras, N-Ras, Rap1A, Rap2A, R-Ras, RalA, Rin, Rit, and Rheb, in contrast to the RA domain of RA-GEF-1, which specifically binds to Rap1. In accordance with this, RA-GEF-2 colocalizes with activated M-Ras in the plasma membrane in COS-7 cells, suggesting a role of RA-GEF-2 in the regulation of Rap1 and Rap2, particularly in the plasma membrane. In fact, an increase in the level of the GTP-bound form of plasma membrane-located Rap1 was observed when coexpressed with RA-GEF-2 and activated M-Ras. Thus, RA-GEF-2 acts as a GEF for Rap1 and Rap2 downstream of M-Ras in the plasma membrane, whereas RA-GEF-1 exerts Rap GEF function in perinuclear compartments including the Golgi apparatus.