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Biomedical subjects

B E Black

Publications and source records attributed to B E Black.

18 recordsLinked to original sources
PubMed2001

DNA binding domains in diverse nuclear receptors function as nuclear export signals.

BACKGROUND: The nuclear receptor superfamily of transcription factors directs gene expression through DNA sequence-specific interactions with target genes. Nuclear import of these receptors involves recognition of a nuclear localization signal (NLS) by importins, which mediate translocation into the nucleus. Nuclear receptors lack a leucine-rich nuclear export signal (NES), and export is insensitive to leptomycin B, indicating that nuclear export is not mediated by Crm1. RESULTS: We set out to define the NES in the glucocorticoid receptor (GR) and to characterize the export pathway. We found that the 69 amino acid DNA binding domain (DBD) of GR, which is unrelated to any known NES, is necessary and sufficient for export. Mutational analysis revealed that a 15 amino acid sequence between the two zinc binding loops in the GR-DBD confers nuclear export to a GFP reporter protein, and alanine-scanning mutagenesis was used to identify the residues within this sequence that are critical for export. The DBD is highly related (41%-88% identity) in steroid, nonsteroid, and orphan nuclear receptors, and we found that the DBDs from ten different nuclear receptors all function as export signals. DBD-dependent nuclear export is saturable, and prolonged nuclear localization of the GR increases its transcriptional activity. CONCLUSIONS: Multiple members of the nuclear receptor superfamily use a common pathway to exit the nucleus. We propose that NLS-mediated import and DBD-mediated export define a shuttling cycle that integrates the compartmentalization and activity of nuclear receptors.

Active Transport, Cell Nucleus↗
PubMed2001

RNA export mediated by tap involves NXT1-dependent interactions with the nuclear pore complex.

Nuclear export of ribonucleoprotein complexes requires cis-acting signals and recognition by receptors that mediate translocation through the nuclear pore complex. Translocation is likely to involve a series of physical interactions between the ribonucleoprotein complex and nucleoporins within the nuclear pore complex. Here, we have characterized the function of NXT1 in the context of the Tap-dependent RNA export pathway. Tap has been implicated in the nuclear export of RNA transcripts derived from Mason-Pfizer monkey virus that contain the constitutive transport element. We demonstrate that NXT1 stimulates binding of a Tap-RNA complex to nucleoporins in vitro, and we provide mutational analysis that shows these interactions are necessary for nuclear export of an intron-containing viral mRNA in vivo. Tap contains separate domains for binding to nucleoporins and NXT1, both of which are critical for its export function. RNA export is mediated by a heterodimer of Tap and NXT1, and the function of NXT1 on this pathway is to regulate the affinity of the Tap-RNA complex for nucleoporins within the nuclear pore complex. We propose that NXT1-dependent binding of the Tap-RNA complex to the nucleoporin p62, which we have reconstituted in vitro using recombinant proteins, represents a single step of the translocation reaction.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Calreticulin Is a receptor for nuclear export.

In previous work, we used a permeabilized cell assay that reconstitutes nuclear export of protein kinase inhibitor (PKI) to show that cytosol contains an export activity that is distinct from Crm1 (Holaska, J.M., and B.M. Paschal. 1995. Proc. Natl. Acad. Sci. USA. 95: 14739-14744). Here, we describe the purification and characterization of the activity as calreticulin (CRT), a protein previously ascribed to functions in the lumen of the ER. We show that cells contain both ER and cytosolic pools of CRT. The mechanism of CRT-dependent export of PKI requires a functional nuclear export signal (NES) in PKI and involves formation of an export complex that contains RanGTP. Previous studies linking CRT to downregulation of steroid hormone receptor function led us to examine its potential role in nuclear export of the glucocorticoid receptor (GR). We found that CRT mediates nuclear export of GR in permeabilized cell, microinjection, and transfection assays. GR export is insensitive to the Crm1 inhibitor leptomycin B in vivo, and it does not rely on a leucine-rich NES. Rather, GR export is facilitated by its DNA-binding domain, which is shown to function as an NES when transplanted to a green fluorescent protein reporter. CRT defines a new export pathway that may regulate the transcriptional activity of steroid hormone receptors.

Active Transport, Cell Nucleus↗
PubMed2001

NXT1 is necessary for the terminal step of Crm1-mediated nuclear export.

Soluble factors are required to mediate nuclear export of protein and RNA through the nuclear pore complex (NPC). These soluble factors include receptors that bind directly to the transport substrate and regulators that determine the assembly state of receptor-substrate complexes. We recently reported the identification of NXT1, an NTF2-related export factor that stimulates nuclear protein export in permeabilized cells and undergoes nucleocytoplasmic shuttling in vivo (Black, B.E., L. Lévesque, J.M. Holaska, T.C. Wood, and B.M. Paschal. 1999. Mol. Cell. Biol. 19:8616-8624). Here, we describe the molecular characterization of NXT1 in the context of the Crm1-dependent export pathway. We find that NXT1 binds directly to Crm1, and that the interaction is sensitive to the presence of Ran-GTP. Moreover, mutations in NXT1 that reduce binding to Crm1 inhibit the activity of NXT1 in nuclear export assays. We show that recombinant Crm1 and Ran are sufficient to reconstitute nuclear translocation of a Rev reporter protein from the nucleolus to an antibody accessible site on the cytoplasmic side of the NPC. Further progress on the export pathway, including the terminal step of Crm1 and Rev reporter protein release, requires NXT1. We propose that NXT1 engages with the export complex in the nucleoplasm, and that it facilitates delivery of the export complex to a site on the cytoplasmic side of NPC where the receptor and substrate are released into the cytoplasm.

Active Transport, Cell Nucleus↗
PubMed2001

NXT1 (p15) is a crucial cellular cofactor in TAP-dependent export of intron-containing RNA in mammalian cells.

TAP, the human homologue of the yeast protein Mex67p, has been proposed to serve a role in mRNA export in mammalian cells. We have examined the ability of TAP to mediate export of Rev response element (RRE)-containing human immunodeficiency virus (HIV) RNA, a well-characterized export substrate in mammalian cells. To do this, the TAP gene was fused in frame to either RevM10 or RevDelta78-79. These proteins are nonfunctional Rev mutant proteins that can bind to HIV RNA containing the RRE in vivo but are unable to mediate the export of this RNA to the cytoplasm. However, the fusion of TAP to either of these mutant proteins gave rise to chimeric proteins that were able to complement Rev function. Significantly, cotransfection with a vector expressing NXT1 (p15), an NTF2-related cellular factor that binds to TAP, led to dramatic enhancement of the ability of the chimeric proteins to mediate RNA export. Mutant-protein analysis demonstrated that the domain necessary for nuclear export mapped to the C-terminal region of TAP and required the domain that interacts with NXT1, as well as the region that has been shown to interact with nucleoporins. RevM10-TAP function was leptomycin B insensitive. In contrast, the function of this protein was inhibited by DeltaCAN, a protein consisting of part of the FG repeat domain of CAN/Nup214. These results show that TAP can complement Rev nuclear export signal function and redirect the export of intron-containing RNA to a CRM1-independent pathway. These experiments support the role of TAP as an RNA export factor in mammalian cells. In addition, they indicate that NXT1 serves as a crucial cellular cofactor in this process.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Monoclonal antibodies to NTF2 inhibit nuclear protein import by preventing nuclear translocation of the GTPase Ran.

Nuclear transport factor 2 (NTF2) is a soluble transport protein originally identified by its ability to stimulate nuclear localization signal (NLS)-dependent protein import in digitonin-permeabilized cells. NTF2 has been shown to bind nuclear pore complex proteins and the GDP form of Ran in vitro. Recently, it has been reported that NTF2 can stimulate the accumulation of Ran in digitonin-permeabilized cells. Evidence that NTF2 directly mediates Ran import or that NTF2 is required to maintain the nuclear concentration of Ran in living cells has not been obtained. Here we show that cytoplasmic injection of anti-NTF2 mAbs resulted in a dramatic relocalization of Ran to the cytoplasm. This provides the first evidence that NTF2 regulates the distribution of Ran in vivo. Moreover, anti-NTF2 mAbs inhibited nuclear import of both Ran and NLS-containing protein in vitro, suggesting that NTF2 stimulates NLS-dependent protein import by driving the nuclear accumulation of Ran. We also show that biotinylated NTF2-streptavidin microinjected into the cytoplasm accumulated at the nuclear envelope, indicating that NTF2 can target a binding partner to the nuclear pore complex. Taken together, our data show that NTF2 is an essential regulator of the Ran distribution in living cells and that NTF2-mediated Ran nuclear import is required for NLS-dependent protein import.

Animals↗
PubMed2000

RanGTP-binding protein NXT1 facilitates nuclear export of different classes of RNA in vitro.

To better characterize the mechanisms responsible for RNA export from the nucleus, we developed an in vitro assay based on the use of permeabilized HeLa cells. This new assay supports nuclear export of U1 snRNA, tRNA, and mRNA in an energy- and Xenopus extract-dependent manner. U1 snRNA export requires a 5' monomethylated cap structure, the nuclear export signal receptor CRM1, and the small GTPase Ran. In contrast, mRNA export does not require the participation of CRM1. We show here that NXT1, an NTF2-related protein that binds directly to RanGTP, strongly stimulates export of U1 snRNA, tRNA, and mRNA. The ability of NXT1 to promote export is dependent on its capacity to bind RanGTP. These results support the emerging view that NXT1 is a general export factor, functioning on both CRM1-dependent and CRM1-independent pathways of RNA export.

Animals↗
PubMed1999

Identification of an NTF2-related factor that binds Ran-GTP and regulates nuclear protein export.

Active transport of macromolecules between the nucleus and cytoplasm requires signals for import and export and their recognition by shuttling receptors. Each class of macromolecule is thought to have a distinct receptor that mediates the transport reaction. Assembly and disassembly reactions of receptor-substrate complexes are coordinated by Ran, a GTP-binding protein whose nucleotide state is regulated catalytically by effector proteins. Ran function is modulated in a noncatalytic fashion by NTF2, a protein that mediates nuclear import of Ran-GDP. Here we characterize a novel component of the Ran system that is 26% identical to NTF2, which based on its function we refer to as NTF2-related export protein 1 (NXT1). In contrast to NTF2, NXT1 preferentially binds Ran-GTP, and it colocalizes with the nuclear pore complex (NPC) in mammalian cells. These properties, together with the fact that NXT1 shuttles between the nucleus and the cytoplasm, suggest an active role in nuclear transport. Indeed, NXT1 stimulates nuclear protein export of the NES-containing protein PKI in vitro. The export function of NXT1 is blocked by the addition of leptomycin B, a compound that selectively inhibits the NES receptor Crm1. Thus, NXT1 regulates the Crm1-dependent export pathway through its direct interaction with Ran-GTP.

Amino Acid Sequence↗
PubMed1997

The cerebral palsied hip.

Controversy exists regarding the role of pelvic obliquity in hip dysplasia and cerebral palsy. Earlier authors noted such a relationship but did not confirm its existence by scientific study. The current study confirms the association of pelvic obliquity to hip dysplasia in spastic cerebral palsy. At presentation of subluxation or dislocation before surgery, 80 patients were indexed into 5 body alignment types. Reclassifications were performed with passage of time to study the natural history and effects of surgery. Hip dysplasia was found in all cases to be consistent with the forces related to pelvic obliquity.

Cerebral Palsy↗
PubMed1997

Shortening in femoral shaft fractures in children treated with spica cast.

Early spica cast treatment is one method used for children's femoral shaft fractures; it is increasingly advocated as treatment that allows early hospital discharge. The outcome of early spica cast treatment in 100 children, ages 2 to 10 years, with uncomplicated and isolated closed femoral shaft fractures treated at Johns Hopkins Hospital between October 1987 and March 1994 were analyzed. The objective was to identify those children who can be treated safely and dependably with early spica casting without excessive shortening of the fracture fragments. Eighty-one (81%) children had an acceptable outcome and 19 (19%) had an unacceptable outcome by the definition of more than 25 mm of fracture fragment overlap after clinical healing. A new clinical test, the telescope test, was statistically significant for correlation with spica cast outcome. Age, gender, fracture, location, mechanism of injury, fracture type, and resting radiograph of fracture fragment overlap were not statistically significant. The telescope test had a sensitivity of 80% and a specificity of 85% for predicting outcome. The relative risk for failure of spica cast treatment with a positive telescope test was 20.4 (95% confidence limits = 2.7-225.1). Children 2 to 10 years of age with uncomplicated femoral shaft fractures and a negative telescope test can be treated appropriately in most cases with early application of a spica cast.

Casts, Surgical↗
PubMed1997

Tibial opening greenstick osteotomy for Blount's disease.

Tibial opening wedge greenstick osteotomy with fibular interposition, for infantile Blount's disease (Langenskiöld II through IV) and moderate-to-severe adolescent Blount's disease, achieved intraoperative stability with accurate correction of angular, longitudinal, and rotational deformities and rapid healing in 10 patients. There were no complications.

Bone Diseases, Developmental↗
PubMed1994

Hip dysplasia in spastic cerebral palsy.

Previous reports have noted a relationship between pelvic obliquity and hip dysplasia in spastic cerebral palsy but did not confirm its existence by scientific study. A study is reported that confirms the association of pelvic obliquity with hip dysplasia in spastic cerebral palsy. At presentation of subluxation or dislocation prior to surgery, 80 patients were indexed into five body alignment types. Reclassifications were performed with passage of time in order to study the natural history and effects of surgery. In all cases, hip dysplasia was found to be consistent with the forces related to pelvic obliquity.

Adolescent↗
PubMed1994

Thoracic and lumbar spine injuries in children: different than in adults.

A study of 38 patients, ages birth through 17 years, is reported that was performed to identify patterns of thoracic and lumbar spine injuries and healing in children in order to make appropriate treatment recommendations and avoid unnecessary surgery. This retrospective/prospective study, which is the largest review of children's thoracic and lumbar spine injuries in the orthopaedic literature, supports several accepted concepts regarding children's spine fractures. In addition, the periosteal sleeve fracture mimicking lumbar dislocations in small children, which has not been reported previously in the clinical setting, is described. Thoracic and lumbar spine injuries in children have distinct differences from these injuries in adults, and the treatment should take these differences into consideration.

Adolescent↗
PubMed1989

Promotion of differentiation in human colon carcinoma cells by vasoactive intestinal polypeptide.

The effects of vasoactive intestinal polypeptide (VIP) and dibutyryl cyclic adenosine 3':5'monophosphate (dbcAMP) on two human colon carcinoma cell lines, HCT 116 and GEO, were investigated. VIP and dbcAMP inhibited the growth of both cell lines in monolayer culture in a dose-dependent manner. Within 6 h of treatment with 1 mM dbcAMP or 0.3 microM VIP, numerous mucin-like droplets were secreted by GEO cells. VIP and dbcAMP also increased carcinoembryonic antigen (CEA) secretion. In both cell lines, a 9-fold increase in conditioned medium CEA levels was observed at 1 mM dbcAMP and a 2.6-fold increase at 1.5 microM VIP. Time- and concentration-dependent evaluation in cAMP levels were elicited by VIP in the two cell lines. Immunocytochemical studies for cell-surface glycoprotein detection in GEO cells showed that VIP induced a morphological and functional organization of mucin-secreting cells. These results indicate that VIP and dbcAMP have antiproliferative and strong differentiation-promoting effects in colon cancer cells. This is the first report of VIP-induced mucin secretion in colon tumor cells.

Carcinoembryonic Antigen↗
PubMed1982

A phase I study of misonidazole and pelvic irradiation in patients with carcinoma of cervix.

A Phase I study of oral daily misonidazole (MISO) with conventional pelvic irradiation, has been conducted in patients with carcinoma of the cervix Stages IB, IIB, IIIB and IVA. MISO was administered in daily dosages to sequential groups of patients at doses of 0.15 g/m2, 0.30 g/m2 or 0.45 g/m2 for 22 days over 5 weeks. Sixteen patients were assigned to each dose level. Using a double-blind randomization, they received either placebo (3/16) or MISO (13/16). The major dose-limiting toxicity was peripheral neuropathy (PN). None of the 13 patients receiving 0.15 g/m2 or the 13 receiving 0.3 g/m2 developed PN. However, 6/13 at the 0.45 g/m2 level (total dose less than or equal to 9.9 g/m2) developed PN. Additional patients were entered at this level and a total of 13/26 developed PN, which was considered of clinically significant severity in 9. Symptoms of PN have persisted from 1 week to 10 months, and have been completely reversed in 9/13 patients. Pharmacological parameters were examined for correlation with clinically evident toxicities. Although peak plasma MISO levels and half-lives did not correlate significantly with PN, there was a significant correlation between the calculated "area under the curve" (AUC) and PN. No correlation exists between PN and total urinary excretion of MISO or the O-demethylation product. A daily dose of 0.45 g/m2; MISO (total dose less than or equal to 9.9 g/m2) is considered to produce an acceptable level of toxicity for this patient population.

Double-Blind Method↗
PubMedDate not supplied

A prospective study of early spica casting outcomes in the treatment of femoral shaft fractures in children.

We analyzed the early spica casting outcomes of 50 children age 2 to 10 years with uncomplicated femoral shaft fractures treated at Johns Hopkins Hospital between October 1987 and October 1990. Our objective was to develop criteria for the prospective identification of patients who can be safely and dependably treated with early spica casting without excessive shortening of the fracture fragments. Forty-one (82%) children had an acceptable outcome and nine (18%) had an unacceptable outcome according to our definition of > 25 mm of fracture fragment overlap at 3 to 4 weeks follow-up. A new clinical test, the telescope test, was statistically significant (p < 0.001) for association with spica casting outcome. Age, sex, fracture location, mechanism of injury, fracture type, and resting roentgenogram fracture fragment overlap were not statistically significant (p > 0.10). The telescope test had a sensitivity of 78%, a specificity of 85%, and a negative predictive value of 95% for predicting spica casting outcome. The relative risk of failing spica casting after a positive telescope test was 20.4 (95% CI, 2.74-225.10). We conclude that children 2 to 10 years of age with uncomplicated femoral shaft fractures and a negative telescope test can be safely treated with early spica casting and have a 95% change of having a successful outcome with this treatment.

Casts, Surgical↗