Probing the phosphoinositide 4,5-bisphosphate binding site of human profilin I

BACKGROUND

Profilin is a widely and highly expressed 14 kDa protein that binds actin monomers, poly(L-proline) and polyphosphoinositol lipids. It participates in regulating actin-filament dynamics that are essential for many types of cell motility. We sought to investigate the site of interaction of profilin with phosphoinositides.

RESULTS

Human profilin I was covalently modified using three tritium-labeled 4-benzoyldihydrocinnamoyl (BZDC)-containing photoaffinity analogs of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). The P-1-tethered D-myoinositol 1,4,5-trisphosphate (Ins(1,4,5)P3) modified profilin I efficiently and specifically; the covalent labeling could be displaced by co-incubation with an excess of PtdIns(4,5)P2 but not with Ins(1,4,5)P3. The acyl-modified PtdIns(4,5)P2 analog showed little protein labeling even at very low concentrations, whereas the head-group-modified PtdIns(4,5)P2 phosphotriester-labeled monomeric and oligomeric profilin. Mass spectroscopic analyses of CNBr digests of [3H]BZDC-Ins(1,4,5)P3-modified recombinant profilin suggested that modification was in the amino-terminal helical CNBr fragment. Edman degradation confirmed Ala1 of profilin I (residue 4 of the recombinant protein) was modified. Molecular models show a minimum energy conformation in which the hydrophobic region of the ligand contacts the amino-terminal helix whereas the 4,5-bisphosphate interacts with Arg135 and Arg136 of the carboxy-terminal helix.

CONCLUSIONS

The PtdIns(4,5)P2-binding site of profilin I includes a bisphosphate interaction with a base-rich motif in the carboxy-terminal helix and contact between the lipid moiety of PtdIns(4,5)P2 and a hydrophobic region of the aminoterminal helix of profilin. This is the first direct evidence for a site of interaction of the lipid moiety of a phosphoinositide bisphosphate analog with profilin.

Gelsolin is a downstream effector of rac for fibroblast motility

Rac, a member of the rho family of GTPases, when activated transmits signals leading to actin-based membrane ruffling in fibroblasts. Compared with wild-type fibroblasts, gelsolin null (Gsn-) dermal fibroblasts have a markedly reduced ruffling response to serum or EGF stimulation, which signal through rac. Bradykinin-induced filopodial formation, attributable to activation of cdc42, is similar in both cell types. Wild-type fibroblasts exhibit typical lamellipodial extension during translational locomotion, whereas Gsn- cells move 50% slower using structures resembling filopodia. Multiple Gsn- tissues as well as Gsn- fibroblasts overexpress rac, but not cdc42 or rho, 5-fold. Re-expression of gelsolin in Gsn- fibroblasts by stable transfection or adenovirus reverts the ruffling response, translational motility and rac expression to normal. Rac migrates to the cell membrane following EGF stimulation in both cell types. Gelsolin is an essential effector of rac-mediated actin dynamics, acting downstream of rac recruitment to the membrane.

EGF receptor regulation of cell motility: EGF induces disassembly of focal adhesions independently of the motility-associated PLCgamma signaling pathway

A current model of growth factor-induced cell motility invokes integration of diverse biophysical processes required for cell motility, including dynamic formation and disruption of cell/substratum attachments along with extension of membrane protrusions. To define how these biophysical events are actuated by biochemical signaling pathways, we investigate here whether epidermal growth factor (EGF) induces disruption of focal adhesions in fibroblasts. We find that EGF treatment of NR6 fibroblasts presenting full-length WT EGF receptors (EGFR) reduces the fraction of cells presenting focal adhesions from approximately 60% to approximately 30% within 10 minutes. The dose dependency of focal adhesion disassembly mirrors that for EGF-enhanced cell motility, being noted at 0.1 nM EGF. EGFR kinase activity is required as cells expressing two kinase-defective EGFR constructs retain their focal adhesions in the presence of EGF. The short-term (30 minutes) disassembly of focal adhesions is reflected in decreased adhesiveness of EGF-treated cells to substratum. We further examine here known motility-associated pathways to determine whether these contribute to EGF-induced effects. We have previously demonstrated that phospholipase C(gamma) (PLCgamma) activation and mobilization of gelsolin from a plasma membrane-bound state are required for EGFR-mediated cell motility. In contrast, we find here that short-term focal adhesion disassembly is induced by a signaling-restricted truncated EGFR (c'973) which fails to activate PLCgamma or mobilize gelsolin. The PLC inhibitor U73122 has no effect on this process, nor is the actin severing capacity of gelsolin required as EGF treatment reduces focal adhesions in gelsolin-devoid fibroblasts, further supporting the contention that focal adhesion disassembly is signaled by a pathway distinct from that involving PLCgamma. Because both WT and c'973 EGFR activate the erk MAP kinase pathway, we additionally explore here this signaling pathway, not previously associated with growth factor-induced cell motility. Levels of the MEK inhibitor PD98059 that block EGF-induced mitogenesis and MAP kinase phosphorylation also abrogate EGF-induced focal adhesion disassembly and cell motility. In summary, we characterize for the first time the ability of EGFR kinase activity to directly stimulate focal adhesion disassembly and cell/substratum detachment, in relation to its ability to stimulate migration. Furthermore, we propose a model of EGF-induced motogenic cell responses in which the PLCgamma pathway stimulating cell motility is distinct from the MAP kinase-dependent signaling pathway leading to disassembly and reorganization of cell-substratum adhesion.

Loss of tuberin in both subependymal giant cell astrocytomas and angiomyolipomas supports a two-hit model for the pathogenesis of tuberous sclerosis tumors

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by seizures, mental retardation, and tumors of skin, brain, heart, and kidney. In this study, we focused on two of the most frequent tumors in TSC patients, renal angiomyolipomas and subependymal giant cell astrocytomas (SEGAs). Two questions were addressed. First, is loss of tuberin, the product of the TSC2 gene, seen in both renal and central nervous system tumors from TSC patients? Second, when loss of tuberin occurs, does it affect each of the cell types seen in these tumors? We used a loss of heterozygosity approach to identify tumors from TSC2 patients. We found loss of tuberin immunostaining in the spindle and epithelioid cells but not in the giant cells of six TSC2 SEGAs. We also found loss of tuberin immunostaining in all three cell types (smooth muscle, fat, and vessels) of six TSC2 angiomyolipomas. Chromosome 16p13 loss of heterozygosity occurred in both spindle and epithelioid cells of a SEGA and in smooth muscle and fat but not the vessels of two angiomyolipomas. These results support a two-hit tumor suppressor model for the pathogenesis of SEGAs and angiomyolipomas. The vascular elements of angiomyolipomas and the giant cells of SEGAs may be reactive rather than neoplastic.

The actin-severing protein gelsolin modulates calcium channel and NMDA receptor activities and vulnerability to excitotoxicity in hippocampal neurons

Calcium influx through NMDA receptors and voltage-dependent calcium channels (VDCC) mediates an array of physiological processes in neurons and may also contribute to neuronal degeneration and death in neurodegenerative conditions such as stroke and severe epileptic seizures. Gelsolin is a Ca2+-activated actin-severing protein that is expressed in neurons, wherein it may mediate motility responses to Ca2+ influx. Primary hippocampal neurons cultured from mice lacking gelsolin exhibited decreased actin filament depolymerization and enhanced Ca2+ influx after exposure to glutamate. Whole-cell patch-clamp analyses showed that currents through NMDA receptors and VDCC were enhanced in hippocampal neurons lacking gelsolin, as a result of decreased current rundown; kainate-induced currents were similar in neurons containing and lacking gelsolin. Vulnerability of cultured hippocampal neurons to glutamate toxicity was greater in cells lacking gelsolin. Seizure-induced damage to hippocampal pyramidal neurons was exacerbated in adult gelsolin-deficient mice. These findings identify novel roles for gelsolin in controlling actin-mediated feedback regulation of Ca2+ influx and in neuronal injury responses. The data further suggest roles for gelsolin and the actin cytoskeleton in both physiological and pathophysiological events that involve activation of NMDA receptors and VDCC.

Caspase-3-generated fragment of gelsolin: effector of morphological change in apoptosis

The caspase-3 (CPP32, apopain, YAMA) family of cysteinyl proteases has been implicated as key mediators of apoptosis in mammalian cells. Gelsolin was identified as a substrate for caspase-3 by screening the translation products of small complementary DNA pools for sensitivity to cleavage by caspase-3. Gelsolin was cleaved in vivo in a caspase-dependent manner in cells stimulated by Fas. Caspase-cleaved gelsolin severed actin filaments in vitro in a Ca2+-independent manner. Expression of the gelsolin cleavage product in multiple cell types caused the cells to round up, detach from the plate, and undergo nuclear fragmentation. Neutrophils isolated from mice lacking gelsolin had delayed onset of both blebbing and DNA fragmentation, following apoptosis induction, compared with wild-type neutrophils. Thus, cleaved gelsolin may be one physiological effector of morphologic change during apoptosis.

Delayed retraction of filopodia in gelsolin null mice

Growth cones extend dynamic protrusions called filopodia and lamellipodia as exploratory probes that signal the direction of neurite growth. Gelsolin, as an actin filament-severing protein, may serve an important role in the rapid shape changes associated with growth cone structures. In wild-type (wt) hippocampal neurons, antibodies against gelsolin labeled the neurite shaft and growth cone. The behavior of filopodia in cultured hippocampal neurons from embryonic day 17 wt and gelsolin null (Gsn-) mice (Witke, W., A.H. Sharpe, J.H. Hartwig, T. Azuma, T.P. Stossel, and D.J. Kwiatkowski. 1995. Cell. 81:41-51.) was recorded with time-lapse video microscopy. The number of filopodia along the neurites was significantly greater in Gsn- mice and gave the neurites a studded appearance. Dynamic studies suggested that most of these filopodia were formed from the region of the growth cone and remained as protrusions from the newly consolidated shaft after the growth cone advanced. Histories of individual filopodia in Gsn- mice revealed elongation rates that did not differ from controls but an impaired retraction phase that probably accounted for the increased number of filopodia long the neutrite shaft. Gelsolin appears to function in the initiation of filopodial retraction and in its smooth progression.

Characterization of gelsolin truncates that inhibit actin depolymerization by severing activity of gelsolin and cofilin

Gelsolin is a calcium-activated actin-binding protein with six subdomains. The N-terminal (G1) domain is essential for actin-filament-severing activity while other domains within G2-3 position the protein on the filament side allowing G1 to sever. In order to generate reagents capable of competitively inhibiting endogenous gelsolin and, potentially, other actin filament regulatory protein, we expressed several truncates of gelsolin in Escherichia coli, and analyzed how they affected the in vitro activity of two different actin-binding proteins, gelsolin and cofilin. A Ca2+-sensitive truncate containing G2-6 inhibited the F-actin-depolymerizing activities of both gelsolin and cofilin, while a G2-3 truncate was less effective. Using two independent assays, our results support the idea that gelsolin truncates inhibit actin filament severing and do not markedly affect actin subunit dissociation kinetics. Cosedimentation assays in the presence of calcium demonstrate that the G2-6 truncate binds to F-actin more strongly than the G2-3 truncate consistent with a protection mechanism by conformational change of F-actin and/or competitive binding to actin filaments which depends upon the presence of actin filament binding domains.

Human XPMC2H: cDNA cloning, mapping to 9q34, genomic structure, and evaluation as TSC1

XPMC2 is a Xenopus gene identified on the basis of its ability to correct a mitotic defect in fission yeast. Here we report the identification of cDNA clones for human XPMC2H, its mapping to the tuberous sclerosis gene TSC1 region on 9q34, determination of genomic structure, and identification of several coding region polymorphisms. The predicted protein has strong sequence similarity to the Xenopus gene. Through SSCP and heteroduplex analysis of genomic DNA, we found two intragenic polymorphisms but no evidence for significant mutations in patients with tuberous sclerosis in this gene.

Identification of the tuberous sclerosis gene TSC1 on chromosome 9q34

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by the widespread development of distinctive tumors termed hamartomas. TSC-determining loci have been mapped to chromosomes 9q34 (TSC1) and 16p13 (TSC2). The TSC1 gene was identified from a 900-kilobase region containing at least 30 genes. The 8.6-kilobase TSC1 transcript is widely expressed and encodes a protein of 130 kilodaltons (hamartin) that has homology to a putative yeast protein of unknown function. Thirty-two distinct mutations were identified in TSC1, 30 of which were truncating, and a single mutation (2105delAAAG) was seen in six apparently unrelated patients. In one of these six, a somatic mutation in the wild-type allele was found in a TSC-associated renal carcinoma, which suggests that hamartin acts as a tumor suppressor.

Ifosfamide/carboplatin/etoposide/paclitaxel in advanced lung cancer: update and preliminary survival analysis

The primary objective of this study was to define the maximum tolerated dose and toxicity profile of paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ), given as a 24-hour infusion, in conjunction with ifosfamide/carboplatin/etoposide (ICE) chemotherapy in patients with advanced lung cancer. Paclitaxel was escalated from 75 to 225 mg/m2 in 25-mg/m2 increments. All patients received granulocyte colony-stimulating factor 5 microg/kg/d from day 4 until the neutrophil count was > or = 10,000/microL. The study population consisted of 41 patients with a median age of 60 years and a median follow-up of 20.7 months. Stage distribution included 5% stage IIIA, 46% stage IIIB, and 49% stage IV. Histology consisted of 61% adenocarcinoma, 12% squamous cell carcinoma, 10% large cell carcinoma, 15% small cell carcinoma, and 2% mixed. The predominant toxicity was hematologic; 63% of patients experienced grade 4 neutropenia and 49% developed grade 4 thrombocytopenia. Fever and neutropenia occurred in 34% of patients. Hematologic toxicity was, in all cases, short-term and reversible and was not dose related. With few exceptions, nonhematologic toxicity was not clinically important. Among 39 patients evaluable for response, 36% achieved a remission (8% complete, 28% partial, 41% had stable disease, and 23% experienced disease progression). Among 33 patients with non-small cell lung cancer, the response rate was 27% (one complete response, eight partial responses, 15 had stable disease, and nine had progressive disease). Among six patients with small cell carcinoma, the response rate was 83% (two complete responses, three partial responses, and one had stable disease). The median survival of all 41 patients was 13.6 months. Survival was almost identical between stage IIIA and stage IV subsets. We conclude that it is possible to safely administer full-dose single-agent paclitaxel with granulocyte colony-stimulating factor support in conjunction with full-dose ifosfamide/carboplatin/etoposide chemotherapy. While response rates observed were not particularly notable, median survival is considerably longer than that usually achieved with combination chemotherapy in advanced lung cancer.

Cloning and evaluation of RALGDS as a candidate for the tuberous sclerosis gene TSC1

RALGDS is a 115 kDa protein which was identified by its ability to enhance guanine nucleotide exchange for the ras family member ral. It also binds to activated ras and rap1, and appears to function as part of a signalling complex in downstream events following rap1 activation. Here we report the identification of full-length cDNA clones for human RALGDS, isolated from a brain cDNA library. The predicted protein has strong sequence homology to rat and murine isoforms of RALGDS in the N- and C-terminal regions, but an internal region (aa 250-380) shows relatively high divergence with only 42% identical amino acid residues. The human RALGDS gene is contained within a 30 kb region of 9q34, approximately 200 kb proximal to the ABO gene, within the current critical region for the tuberous sclerosis gene TSC1. Partial genomic structure was determined; it consists of at least 11 exons. Based upon analysis of Southern blots from 110 TSC patients, genomic DNA SSCP analysis, and RT-PCR analysis which demonstrated RNA expression of both alleles in patients from 9q34-linked TSC families using intragenic polymorphisms, we conclude that RALGDS is not likely to be TSC1.

Report on the Fifth International Workshop on Chromosome 9 held at Eynsham, Oxfordshire, UK, September 4-6, 1996

The Fifth International workshop on chromosome 9 comprised a gathering of 36 scientists from seven countries and included a fairly even distribution of interests along chromosome 9 as well as a strong input from more global activities and from comparative mapping. At least eight groups had participated in the goal set at the previous workshop which was to improve the fine genetic mapping in different regions of chromosome 9 by meiotic breakpoint mapping in allocated regions and this has resulted in some greatly improved order information. Excellent computing facilities were available and all contributed maps were entered not only into SIGMA (and thence submitted to GDB) but also into a dedicated version of ACEDB which can be accessed on the Web in the form of one of 28 slices into which the chromosome has been arbitrarily divided. It was generally agreed that the amount of data is now overwhelming and that the integration and validation of all data is not only unrealistic in a short meeting but probably impossible until the whole chromosome has been sequenced and fully annotated. Sequence-ready contigs presented at the meeting totalled about 3 MB which is about one fiftieth of the estimated length. The single biggest barrier to integration of maps is the problem of non-standard nomenclature of loci. In the past 2 workshops efforts have been made to compare traditional 'consensus' maps made by human insight (still probably best for small specific regions) with those generated with some computer assistance (such as SIGMA) and those generated objectively by defined computer algorithms such as ldb. Since no single form of map or representation is entirely satisfactory for all purposes the maps reproduced in the published version of the report are confined to one of the genetic maps, in which Genethon and older markers have been incorporated, a Sigma map of the genes as symbols together with a listing of known 'disease' genes on chromosome 9, and a revised assessment of the mouse map together with a list of mouse loci predicted to be on human chromosome 9. One of the 28 ACEDB slices is also shown to illustrate strengths and weaknesses of this approach. Workshop files include not only all maps available at the time but also details of loci and details of the meiotic breakpoints in the CEPH families (http:/(/)www.gene.ucl.ac.uk/scw9db.shtml) .

Fine mapping of the nail-patella syndrome locus at 9q34

Nail-patella syndrome (NPS), or onychoosteodysplasia, is an autosomal dominant, pleiotropic disorder characterized by nail dysplasia, absent or hypoplastic patellae, iliac horns, and nephropathy. Previous studies have demonstrated linkage of the nail-patella locus to the ABO and adenylate kinase loci on human chromosome 9q34. As a first step toward isolating the NPS gene, we present linkage analysis with 13 polymorphic markers in five families with a total of 69 affected persons. Two-point linkage analysis with the program MLINK showed tight linkage of NPS and the anonymous markers D9S112 (LOD = 27.0; theta = .00) and D9S315 (LOD = 22.0; theta = .00). Informative recombination events place the NPS locus within a 1-2-cM interval between D9S60 and the adenylate kinase gene (AK1).

Genomic organization and chromosomal location of murine Cdc42

cdc42 is a member of the rho family of small GTPases, which are implicated as regulators of cellular morphology. To date, one murine and two human cdc42 isoforms have been identified. Here we report the cloning of a second murine isoform and provide evidence that the two isoforms arise from a single gene by alternative splicing. In contrast with the previously identified murine cdc42 sequence, which is expressed in a wide variety of tissues, the second isoform appears to be expressed exclusively in brain. Using single-strand conformation polymorphism analysis of a mouse backcross panel, the gene encoding cdc42 has been localized to distal chromosome 4.

Tuberous sclerosis-associated renal cell carcinoma. Clinical, pathological, and genetic features

The tuberous sclerosis complex (TSC) is a multisystem autosomal dominant disorder characterized by seizures, mental retardation, and hamartomas. Patients with TSC have been reported to develop renal cell carcinomas (RCC) with increased frequency, an observation that is supported by the Eker rat model. To address the role of the tuberous sclerosis tumor suppressor genes in the pathogenesis of RCC, we studied six TSC-associated RCCs. Our findings suggest that some TSC-associated RCCs have clinical, pathological, or genetic features distinguishing them from sporadic RCC. Clinically, the TSC-associated tumors occurred at a younger age (mean, 36 years) than sporadic tumors and occurred primarily in women. Four of the six patients died of metastatic disease. Pathologically, five tumors displayed clear cell morphology. Of those five, two had high-grade spindle cell areas and one had granular cell histology in addition to the clear cell areas. A sixth tumor was anaplastic throughout. Four of the six tumors immunostained positively for a melanocyte-associated marker, HMB-45. HMB-45 positivity has been seen in two other TSC lesions: renal angiomyolipomas and pulmonary lymphangiomyomatosis. Five tumors were analyzed for loss of heterozygosity. Two had loss of heterozygosity on chromosome 9q34 and one had loss of heterozygosity on chromosome 16p13. We conclude that TSC-associated RCCs occur at an earlier age than sporadic RCCs, that some TSC-associated renal carcinomas have a different immunophenotype than sporadic RCCs, and that the TSC tumor suppressor genes may play a specific pathogenic role in these tumors.

Allelic loss is frequent in tuberous sclerosis kidney lesions but rare in brain lesions

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by seizures, mental retardation, and hamartomatous lesions. Although hamartomas can occur in almost any organ, they are most common in the brain, kidney, heart, and skin. Allelic loss or loss of heterozygosity (LOH) in TSC lesions has previously been reported on chromosomes 16p13 and 9q34, the locations of the TSC2 and TSC1 genes, respectively, suggesting that the TSC genes act as tumor-suppressor genes. In our study, 87 lesions from 47 TSC patients were analyzed for LOH in the TSC1 and TSC2 chromosomal regions. Three findings resulted from this analysis. First, we confirmed that the TSC1 critical region is distal to D9S149. Second, we found LOH more frequently on chromosome 16p13 than on 9q34. Of the 28 patients with angiomyolipomas or rhabdomyomas, 16p13 LOH was detected in lesions from 12 (57%) of 21 informative patients, while 9q34 LOH was detected in lesions from only 1 patient (4%). This could indicate that TSC2 tumors are more likely than TSC1 tumors to require surgical resection or that TSC2 is more common than TSC1 in our patient population. It is also possible that small regions of 9q34 LOH were missed. Lastly, LOH was found in 56% of renal angiomyolipomas and cardiac rhabdomyormas but in only 4% of TSC brain lesions. This suggests that brain lesions can result from different pathogenic mechanisms than kidney and heart lesions.

Coordinated regulation of platelet actin filament barbed ends by gelsolin and capping protein

Exposure of cryptic actin filament fast growing ends (barbed ends) initiates actin polymerization in stimulated human and mouse platelets. Gelsolin amplifies platelet actin assembly by severing F-actin and increasing the number of barbed ends. Actin filaments in stimulated platelets from transgenic gelsolin-null mice elongate their actin without severing. F-actin barbed end capping activity persists in human platelet extracts, depleted of gelsolin, and the heterodimeric capping protein (CP) accounts for this residual activity. 35% of the approximately 5 microM CP is associated with the insoluble actin cytoskeleton of the resting platelet. Since resting platelets have an F-actin barbed end concentration of approximately 0.5 microM, sufficient CP is bound to cap these ends. CP is released from OG-permeabilized platelets by treatment with phosphatidylinositol 4,5-bisphosphate or through activation of the thrombin receptor. However, the fraction of CP bound to the actin cytoskeleton of thrombin-stimulated mouse and human platelets increases rapidly to approximately 60% within 30 s. In resting platelets from transgenic mice lacking gelsolin, which have 33% more F-actin than gelsolin-positive cells, there is a corresponding increase in the amount of CP associated with the resting cytoskeleton but no change with stimulation. These findings demonstrate an interaction between the two major F-actin barbed end capping proteins of the platelet: gelsolin-dependent severing produces barbed ends that are capped by CP. Phosphatidylinositol 4,5-bisphosphate release of gelsolin and CP from platelet cytoskeleton provides a mechanism for mediating barbed end exposure. After actin assembly, CP reassociates with the new actin cytoskeleton.

Novel mutations detected in the TSC2 gene from both sporadic and familial TSC patients

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by hamartomas in one or more organs, including the brain, skin, heart and kidneys. Linkage studies have shown locus heterogeneity with one TSC gene mapped to chromosome 9q34 and a second to 16p13.3. The gene on 16p13.3, TSC2, has been cloned and shown to encode a 5.5 kb transcript that is widely expressed. To facilitate the search for mutations in the TSC2 gene product, tuberin, we have designed an RT-PCR-based assay system to scan the expressed coding region of the TSC2 gene in lymphoblasts. Using 34 overlapping PCR assays we performed single-strand conformation polymorphism analysis of DNA from 26 apparently sporadic TSC cases, two TSC families non-informative for linkage analysis and two confirmed chromosome 16-linked TSC families. Of the 60 chromosomes scanned, 14 showed abnormal SSCP mobility shifts. Using direct PCR sequencing we have identified five missense mutations, one 3 bp in-frame deletion and one 2 bp frameshift deletion, one nonsense mutation, one 29 bp tandem duplication and five silent nucleotide changes that are likely to be polymorphisms. There is no apparent clustering of mutations within TSC2. The diversity of mutation types argues that TSC2 may not act in a classic tumor suppressor fashion. In addition, we saw no specific correlation between the different mutations and clinical severity or expression. These data confirm that TSC2 is indeed the relevant gene, and that a substantial number of sporadic cases arise from mutations in the TSC2 gene.

Loss of heterozygosity in the tuberous sclerosis (TSC2) region of chromosome band 16p13 occurs in sporadic as well as TSC-associated renal angiomyolipomas

Angiomyolipomas (AMLs) are renal tumors that occur both sporadically and in association with tuberous sclerosis (TSC). TSC is an autosomal dominant disorder characterized by hamartomatous lesions in multiple organs. Two TSC loci are recognized: TSC1 on 9q34 and TSC2 on 16p13. Loss of heterozygosity (LOH) at the TSC1 and TSC2 loci in lesions from TSC patients has recently been reported. Lesions that are not associated with TSC have not been previously examined for LOH at the TSC loci. We analyzed 29 renal angiomyolipomas from patients without a history of TSC. Three tumors demonstrated LOH on 16p13. This is the first report indicating that mutations in TSC2 occur in tumors of patients who do not have TSC. We also found LOH on 16p13 in 5 of 8 TSC-associated AMLs. Two of these tumors were from a single patient and demonstrated different regions of LOH. These findings support the hypothesis that the TSC2 gene functions as a tumor suppressor.

A phase I study of ifosfamide/carboplatin/etoposide/paclitaxel in advanced lung cancer

A phase I study was conducted to define the maximally tolerated dose and toxicity profile of the ifosfamide/carboplatin/etoposide/paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) (ICE-T) regimen in advanced lung cancer. This chemotherapy program uses paclitaxel given as a 24-hour continuous infusion in conjunction with full-dose ICE chemotherapy with growth factor support. The dosage of paclitaxel was escalated from 75 to 225 mg/m2. Thirty-four patients have been accrued to date onto this study. Because hematologic dose-limiting toxicity was defined in terms of neutropenia and/or thrombocytopenia exceeding 7 days' duration, no patient demonstrated what was defined by the protocol as dose-limiting toxicity. Nonetheless, substantial hematologic toxicity was observed. Overall, 26% had fever and neutropenia, 56% had grade 4 neutropenia, and 26% had grade 4 thrombocytopenia. In all cases, hematologic toxicity was short term and reversible. While grade 3 and 4 myelosuppression was frequently observed, it was not dose related (in terms of paclitaxel dosage). Nonhematologic toxicity also was not dose related and, with only a few exceptions, was not clinically significant. Among 27 patients evaluable for response, 41% achieved an objective response, including 15% with a complete response. All of five patients with small cell lung cancer responded (including two with a complete response). Among 22 patients with non-small cell lung cancer, 27% achieved an objective response (also including two with a complete response). The results of this study suggest that with growth factor support, it is possible to safely administer full-dose, single-agent paclitaxel in conjunction with full-dose ICE chemotherapy. We will soon be initiating a phase II study of the ICE-T regimen using paclitaxel at 225 mg/m2 as a 24-hour continuous infusion in advanced lung cancer. We will also conduct a phase I study of ICE-T, with paclitaxel administered as a 3-hour continuous infusion.

A 37-marker PCR-based genetic linkage map of human chromosome 9: observations on mutations and positive interference

Refinement of an "index" marker genetic linkage map of human chromosome 9 using the CEPH reference pedigrees has been achieved through the addition of 11 markers to the previous map of 26 markers. Five of the 11 markers added to the map are new markers of the GATA repeat type, 1 is a complex repeat, and the remaining 5 as well as the original 26 markers are all GT/CA repeats. Twelve definite and five probable mutations were detected in this analysis and were more common for the GATA repeats than the GT/CA repeats. Strong evidence for positive interference was seen over the length of the chromosome, but there were significantly more double recombination events in the pericentromeric region than elsewhere, suggesting that interference is less strong in that region.

A 5.4-Mb continuous pulsed-field gel electrophoresis map of human 9q34.1 between ABL and D9S114, including the tuberous sclerosis (TSC1) region

We constructed a long-range restriction map of the tuberous sclerosis (TSC1) region of human chromosome 9q34, extending from ABL (T39-2-2) to D9S114. The physical map includes five genes and seven anonymous markers. The maximum distance between ABL and D9S114 is 5.4 Mb. The TSC1 critical region, between D9S149 and D9S114, has a maximum distance of 2.7 Mb. The ratio of genetic and physical distance in the region is 1 cM:600 kb. We also used Southern blot analysis and a radiation hybrid cell line, E6B, to exclude 3 genes--PBX3A, RXR alpha, and TAN1--from the AK1 to D9S114 interval. This excludes them as disease genes for tuberous sclerosis.

Molecular and pathologic markers in stage I non-small-cell carcinoma of the lung

PURPOSE

Although standard treatment of stage I non-small-cell lung cancer (NSCLC) consists of surgical resection alone, approximately 50% of clinical stage I and 30% to 40% of pathologic stage I patients have disease recurrence and die following curative resection. A large number of traditional pathologic and newer molecular markers have been identified, which appear to have important prognostic significance in this population. This review attempts to summarize these data comprehensively.

METHODS

Criteria for study selection were English-language reports, identified using Medline and Cancerline, through the fall of 1994. Abstracts from the American Society of Clinical Oncology (ASCO) and the International Association for the Study of Lung Cancer (IASLG) were also reviewed.

RESULTS

Molecular markers are classified as molecular genetic markers, differentiation markers, proliferation markers, and markers of metastatic propensity. A number of these markers have been reported to be highly predictive of outcome in stage I NSCLC, and several reports conclude that a specific biomarker may be, aside from clinical stage, the most powerful determinant of prognosis in NSCLC. However, little has been done to clarify the relationships between these newer biologic markers, classic clinicopathologic variables, and clinical outcome.

CONCLUSION

At present, a firm conclusion regarding which biomarkers are most important in predicting outcome is not possible, and a model that reliably integrates all independent prognostic variables cannot be developed. A prospective trial is mandatory to address this issue, and a study design is suggested that would facilitate the development of a prognostic index, while simultaneously asking a therapeutic question. The development of a prognostic index would facilitate future trials in which only high-risk stage I patients could be targeted for investigation of postresection adjuvant treatment strategies.

Functions of [His321]gelsolin isolated from a flat revertant of ras-transformed cells

A mutant gelsolin, [His321]gelsolin, was isolated from R1, a flat revertant of human activated c-Ha-ras oncogene-transformed NIH/3T3 cells (EJ-NIH/3T3) produced by ethylmethanesulfonate treatment. [His321]Gelsolin has a histidine instead of a proline residue at position 321 and suppresses the tumorigenicity of EJ-NIH/3T3 cells when it is constitutively expressed [Müllauer, L., Fujita, H., Ishizaki, A. & Kuzumaki, N. (1993) Oncogene 8, 2531-2536]. To investigate the biochemical consequences of the amino acid substitution of His321, we expressed the [His321]gelsolin and wild-type gelsolin in Escherichia coli, purified them, and analyzed their effects on actin, polyphosphoinositol lipids and phospholipase C. [His321]Gelsolin has decreased actin-filament-severing activity and increased nucleating activity compared with wild-type gelsolin in vitro. Furthermore, compared to wild-type gelsolin both nucleation and severing by [His321]gelsolin are inhibited more strongly by the phosphoinositol lipids phosphatidylinositol 4-phosphate (PtdInsP) and phosphatidylinositol 4,5-bisphosphate (PtdInsP2). In addition, [His321]gelsolin inhibits PtdInsP2 hydrolysis by phospholipase C gamma 1 more strongly than wild-type gelsolin in vitro because of its higher binding capacity for phosphoinositol lipid. Gelsolin has six homologous amino acid repeats called S1-S6. Our results suggest that the segment S3 which contains the mutation is functionally relevant for regulation of gelsolin's activities even though the relevant actin-binding domains are in segments 1, 2, and 4-6, and that the region around the residue 321 may contain a phosphoinositol-lipid-binding site. Altered functions of [His321]gelsolin might be important for the loss of tumorigenicity of the ras-transformed cells.