Genetic alterations and their clinical implications in older patients with acute myeloid leukemia.

A number of patient-specific and leukemia-associated factors are related to the poor outcome in older patients with acute myeloid leukemia (AML). However, comprehensive studies regarding the impact of genetic alterations in this group of patients are limited. In this study, we compared relevant mutations in 21 genes between AML patients aged 60 years or older and those younger and exposed their prognostic implications. Compared with the younger patients, the elderly had significantly higher incidences of PTPN11, NPM1, RUNX1, ASXL1, TET2, DNMT3A and TP53 mutations but a lower frequency of WT1 mutations. The older patients more frequently harbored one or more adverse genetic alterations. Multivariate analysis showed that DNMT3A and TP53 mutations were independent poor prognostic factors among the elderly, while NPM1 mutation in the absence of FLT3/ITD was an independent favorable prognostic factor. Furthermore, the status of mutations could well stratify older patients with intermediate-risk cytogenetics into three risk groups. In conclusion, older AML patients showed distinct genetic alterations from the younger group. Integration of cytogenetics and molecular mutations can better risk-stratify older AML patients. Development of novel therapies is needed to improve the outcome of older patients with poor prognosis under current treatment modalities.

TP53 mutations in de novo acute myeloid leukemia patients: longitudinal follow-ups show the mutation is stable during disease evolution.

The TP53 mutation is frequently detected in acute myeloid leukemia (AML) patients with complex karyotype (CK), but the stability of this mutation during the clinical course remains unclear. In this study, TP53 mutations were identified in 7% of 500 patients with de novo AML and 58.8% of patients with CK. TP53 mutations were closely associated with older age, lower white blood cell (WBC) and platelet counts, FAB M6 subtype, unfavorable-risk cytogenetics and CK, but negatively associated with NPM1 mutation, FLT3/ITD and DNMT3A mutation. Multivariate analysis demonstrated that TP53 mutation was an independent poor prognostic factor for overall survival and disease-free survival among the total cohort and the subgroup of patients with CK. A scoring system incorporating TP53 mutation and nine other prognostic factors, including age, WBC counts, cytogenetics and gene mutations, into survival analysis proved to be very useful to stratify AML patients. Sequential study of 420 samples showed that TP53 mutations were stable during AML evolution, whereas the mutation was acquired only in 1 of the 126 TP53 wild-type patients when therapy-related AML originated from different clone emerged. In conclusion, TP53 mutations are associated with distinct clinic-biological features and poor prognosis in de novo AML patients and are rather stable during disease progression.

Knockdown of c-MET induced apoptosis in ABCB1-overexpressed multidrug-resistance cancer cell lines.

Inappropriate c-MET signaling in cancer can enhance tumor cell proliferation, survival, motility, and invasion. Inhibition of c-MET signaling induces apoptosis in a variety of cancers. It has also been recognized as a novel anticancer therapy approach. Furthermore, reports have also indicated that constitutive expression of P-glycoprotein (ABCB1) is involved in the HGF/c-MET-related pathway of multidrug resistance ABCB1-positive human hepatocellular carcinoma cell lines. We previously reported that elevated expression levels of PKCδ and AP-1 downstream genes, and HGF receptor (c-MET) and ABCB1, in the drug-resistant MES-SA/Dx5 cells. Moreover, leukemia cell lines overexpressing ABCB1 have also been shown to be more resistant to the tyrosine kinase inhibitor imatinib mesylate. These findings suggest that chemoresistant cancer cells may also develop a similar mechanism against chemotherapy agents. To circumvent clinical complications arising from drug resistance during cancer therapy, the present study was designed to investigate apoptosis induction in ABCB1-overexpressed cancer cells using c-MET-targeted RNA interference technology in vitro and in vivo. The results showed that cell viability decreased and apoptosis rate increased in c-MET shRNA-transfected HGF/c-MET pathway-positive MES-SA/Dx5 and MCF-7/ADR2 cell lines in a dose-dependent manner. In vivo reduction of tumor volume in mice harboring c-MET shRNA-knockdown MES-SA/Dx5 cells was clearly demonstrated. Our study demonstrated that downregulation of c-MET by shRNA-induced apoptosis in a multidrug resistance cell line.

Management of extensive retrohepatic vena cava defect in recipients of living donor liver transplantation.

Certain complexities, such as extensive vena caval injury, unexpected dense adhesions between liver and retrohepatic vena cava, and liver tumor abutting retrohepatic vena cava, sometimes warrant resection of vena cava during living-donor liver transplantation. Because the donor graft is devoid of vena cava, reconstruction of the retrohepatic cava is required, which can be done with the use of either a cryopreserved venous graft or an artificial conduit. With only a few published reports, the experience in vena cava reconstruction with the use of expanded polytetrafluoroethylene (ePTFE) during living-donor liver transplantation remains limited. We present our experience of 4 patients who successfully underwent vena caval resection during liver transplantation for various indications, which was subsequently reconstructed with the use of ePTFE grafts. All of these patients except 1 recovered well without any undue complications, such as thrombosis or outflow inadequacies, thus proving this extensive surgical treatment to be a successful and life-saving procedure, though meticulous skills are prerequisite.

Experience of using everolimus in the early stage of living donor liver transplantation.

OBJECTIVES: The aim of our study was to review the experience of early use of everolimus for recipients after adult-to-adult living donor liver transplantation. METHODS: From February 2012 to December 2012, 80 recipients underwent living donor liver transplantation. Forty-three of them used everolimus as an adjunct to the calcineurin inhibitors (CNIs) in the early postoperative period. Thirty-nine patients had hepatocellular carcinoma (HCC) and poor renal function was noted in 9 patients. Ten of them were females and 33 were males. The age varied from 39 to 75 years old. The starting date of use was within 1 week in 33 patients, 2 weeks in 9 patients, and 1 patient was administered on postoperative day 20. The initial doses of everolimus were 0.25 mg every 12 hours and increased to 0.5 mg every 12 hours to target the level at 3-5 ng/mL. Doppler ultrasound was performed regularly postoperative days 1, 4, and 14. RESULTS: The mean time between liver transplantation and everolimus treatment was 12 ± 8 days. The maximum dose of everolimus used was 1 mg/d with a target trough level between 3 and 5 ng/mL. At 3 months, a target trough level of 3 ng/mL was achieved. Six of 9 renal failure patients showed significant recovery of renal function, whereas 3 of them showed further deterioration and 1 required hemodialysis. During the follow-up period of 9 ± 6 months, all showed good patency of hepatic artery without thrombosis. Three patients (7%) developed HCC recurrence, whereas 1 patient died at the 10th month postoperative due to sepsis. Elevation of lipid profile was noted in 5 patients. Stomatitis was the most frequent side effect and occurred in 15 patients. CONCLUSIONS: The early use of everolimus was safe and feasible. Also, it can be safely used in patients with prior renal failure while reducing the doses of CNIs. Although the recurrence rate of HCC was reduced, further study is ongoing to evaluate the long-term impact of everolimus on prevention of HCC recurrence.

A tryptophan metabolite, kynurenine, promotes mast cell activation through aryl hydrocarbon receptor.

BACKGROUND: Tryptophan metabolites have been suggested to play a role in immune modulation, wherein those have recently been shown to be endogenous ligands of aryl hydrocarbon receptor (AhR; a unique cellular chemical sensor). However, the involvement of tryptophan metabolites and AhR in modulating mast cell function remains to be fully defined. We therefore investigated that the functional impacts of tryptophan metabolites on human and mouse mast cell responses in vitro and their functional importance in vivo. METHODS: Three tryptophan metabolites, kynurenine (KYN), kynurenic acid (KA) and quinolinic acid (QA), were examined in terms of their effect on IgE-mediated responses in mouse bone marrow-derived mast cells (BMMCs) and in human peripheral blood-derived cultured mast cells (HCMCs) and on in vivo anaphylactic responses. For evaluation of AhR involvement, we examined the responses of mast cells from AhR-null or AhR-wild-type mice with the use of a known AhR antagonist, CH223191. RESULTS: Kynurenine, but not KA and QA, enhanced IgE-mediated responses, including degranulation, LTC4 release, and IL-13 production in BMMCs through the activation of PLCγ1, Akt, MAPK p38, and the increase of intracellular calcium. KYN also enhanced cutaneous anaphylaxis in vivo. These enhancing effects of KYN were not observed in AhR-deficient BMMCs and could be inhibited by CH223191 in BMMCs. Further, KYN had similar enhancing effects on HCMCs, which were inhibited by CH223191. CONCLUSION: The AhR-KYN axis is potentially important in modulating mast cell responses and represents an example of AhR's critical involvement in the regulation of allergic responses.

Dynamics of ASXL1 mutation and other associated genetic alterations during disease progression in patients with primary myelodysplastic syndrome.

Recently, mutations of the additional sex comb-like 1 (ASXL1) gene were identified in patients with myelodysplastic syndrome (MDS), but the interaction of this mutation with other genetic alterations and its dynamic changes during disease progression remain to be determined. In this study, ASXL1 mutations were identified in 106 (22.7%) of the 466 patients with primary MDS based on the French-American-British (FAB) classification and 62 (17.1%) of the 362 patients based on the World Health Organization (WHO) classification. ASXL1 mutation was closely associated with trisomy 8 and mutations of RUNX1, EZH2, IDH, NRAS, JAK2, SETBP1 and SRSF2, but was negatively associated with SF3B1 mutation. Most ASXL1-mutated patients (85%) had concurrent other gene mutations at diagnosis. ASXL1 mutation was an independent poor prognostic factor for survival. Sequential studies showed that the original ASXL1 mutation remained unchanged at disease progression in all 32 ASXL1-mutated patients but were frequently accompanied with acquisition of mutations of other genes, including RUNX1, NRAS, KRAS, SF3B1, SETBP1 and chromosomal evolution. On the other side, among the 80 ASXL1-wild patients, only one acquired ASXL1 mutation at leukemia transformation. In conclusion, ASXL1 mutations in association with other genetic alterations may have a role in the development of MDS but contribute little to disease progression.

Phenethyl isothiocyanate triggers apoptosis in human malignant melanoma A375.S2 cells through reactive oxygen species and the mitochondria-dependent pathways.

We have reported previously that phenethyl isothiocyanate (PEITC) induces apoptosis in human osteosarcoma U-2 OS cells. Cytotoxic activity of PEITC towards other cancer cells such as human malignant melanoma and skin cancer cells has not been reported. In this study, the anticancer activity of PEITC towards human malignant melanoma cancer A375.S2 cells was investigated. To determine the mechanisms of PEITC inhibition of cell growth, the following end points were determined in A375.S2 cells: cell morphological changes, cell cycle arrest, DNA damage and fragmentation assays and morphological assessment of nuclear change, reactive oxygen species (ROS) and Ca(2+) generations, mitochondrial membrane potential disruption, and nitric oxide and 10-N-nonyl acridine orange productions, expression and activation of caspase-3 and -9, B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax), Bcl-2, poly (adenosine diphosphate-ribose) polymerase, and cytochrome c release, apoptosis-inducing factor and endonuclease G. PEITC induced morphological changes in time- and dose-dependent manner. PEITC induced G2/M phase arrest and induced apoptosis via endoplasmic reticulum stress-mediated mitochondria-dependent pathway. Western blot analysis showed that PEITC promoted Bax expression and inhibited Bcl-2 expression associated with the disintegration of the outer mitochondrial membrane causing cytochrome c release, and activation of caspase-9 and -3 cascade leading to apoptosis. We conclude that PEITC-triggered apoptotic death in A375.S2 cells occurs through ROS-mediated mitochondria-dependent pathways.

Integration of cytogenetic and molecular alterations in risk stratification of 318 patients with de novo non-M3 acute myeloid leukemia.

Conventionally, acute myeloid leukemia (AML) patients are categorized into good-, intermediate- and poor-risk groups according to cytogenetic changes. However, patients with intermediate-risk cytogenetics represent a largely heterogeneous population regarding treatment response and clinical outcome. In this study, we integrated cytogenetics and molecular mutations in the analysis of 318 patients with de novo non-M3 AML who received standard chemotherapy. According to the mutation status of eight genes, including NPM1, CEBPA, IDH2, RUNX1, WT1, ASXL1, DNMT3A and FLT3, that had prognostic significance, 229 patients with intermediate-risk cytogenetics could be refinedly stratified into three groups with distinct prognosis (P<0.001); patients with good-risk genotypes had a favorable outcome (overall survival, OS, not reached) similar to those with good-risk cytogenetics, whereas those with poor-risk genotypes had an unfavorable prognosis (OS, 10 months) similar to those with poor-risk cytogenetics (OS, 13.5 months), and the remaining patients with other genotypes had an intermediate outcome (OS, 25 months). Integration of cytogenetic and molecular profiling could thus reduce the number of intermediate-risk AML patients from around three-fourth to one-fourth. In conclusion, integration of cytogenetic and molecular changes improves the prognostic stratification of AML patients, especially those with intermediate-risk cytogenetics, and may lead to better decision on therapeutic strategy.

High bone marrow angiopoietin-1 expression is an independent poor prognostic factor for survival in patients with myelodysplastic syndromes.

BACKGROUND: Angiogenic factors have an essential role in normal and pathologic angiogenesis. However, the clinical implication of angiogenic factor expression in myelodysplastic syndromes (MDS) remains unclear. METHODS: In this study, we sought to investigate the prognostic impact of the expression of genes encoding angiopoietin-1 (Ang-1), Ang-2, the receptor Tie2, vascular endothelial growth factor-A (VEGF-A) and VEGF-C in the bone marrow (BM) in 208 patients with newly diagnosed primary MDS. RESULTS: BM Ang-1 expression was significantly higher in MDS patients, especially those with higher-risk subtypes, than in normal controls. With a median follow-up time of 32.9 months, the disease transformed to acute leukaemia more frequently in the patients bearing higher Ang-1 expression than in those with lower expression (31.5% vs 18.6%, P=0.023). The MDS patients with higher Ang-1 expression had shorter overall survival than those with lower expression (median 20.8±4.5 months vs 63.3±17.8 months, P<0.001). Multivariate analyses showed that higher Ang-1 expression was an independent unfavourable prognostic factor for overall survival. There was no impact of the expression of other angiogenic factors on survival. CONCLUSION: BM Ang-1 expression may serve as a new biomarker to predict clinical outcome in MDS patients.

The prognostic impact and stability of Isocitrate dehydrogenase 2 mutation in adult patients with acute myeloid leukemia.

Although the clinical features of the Isocitrate dehydrogenase 2 (IDH2) mutation in acute myeloid leukemia (AML) have been characterized, its prognostic significance remains controversial and its stability has not been investigated. We analyzed 446 adults with primary non-M3 AML and found IDH2 R172, R140 and IDH1 R132 mutations occurred at a frequency of 2.9, 9.2 and 6.1%, respectively. Compared with wild-type IDH2, mutation of IDH2 was associated with higher platelet counts, intermediate-risk or normal karyotype and isolated +8, but was inversely correlated with expression of HLA-DR, CD34, CD15, CD7 and CD56, and was mutually exclusive with WT1 mutation and chromosomal translocations involving core-binding factors. All these correlations became stronger when IDH1 and IDH2 mutations were considered together. Multivariate analysis revealed IDH2 mutation as an independent favorable prognostic factor. IDH2(-)/FLT3-ITD(+) genotype conferred especially negative impact on survival. Compared with IDH2 R140 mutation, IDH2 R172 mutation was associated with younger age, lower white blood cell count and lactate dehydrogenase level, and was mutually exclusive with NPM1 mutation. Serial analyses of IDH2 mutations at both diagnosis and relapse in 121 patients confirmed high stability of IDH2 mutations. In conclusion, IDH2 mutation is a stable marker during disease evolution and confers favorable prognosis.

Acute myeloid leukemia bearing t(7;11)(p15;p15) is a distinct cytogenetic entity with poor outcome and a distinct mutation profile: comparative analysis of 493 adult patients.

Acute myeloid leukemia (AML) with t(7;11)(p15;p15), which results in a NUP98-HOXA9 fusion, is a distinct entity, but this subtype has not been characterized in detail. In a comprehensive study comparing 11 such patients with another 482 adult patients, we found that those with t(7;11) were younger (P=0.0076) and female (P=0.0111), with almost all having the M2-subtype of AML (P<0.0001). Even when those with low-risk karyotypes were excluded, patients with t(7;11) had poorer overall survival than the other AML group (median 13.5 and 20 months, respectively, P=0.045) and poorer relapse-free survival (median 6 and 12 months, respectively, P=0.003). The NUP98-HOXA9 fusion was strongly associated with KRAS and WT1 mutations (P=0.015 and P=0.0018, respectively). We characterized four varieties of this fusion, among which NUP98 exon 12/HOXA9 exon 1b was present in all 11 patients. We developed a highly sensitive and specific assay to quantify the abundance of leukemic cells, and found that the fusion remained detectable in morphological complete remission, even after allogeneic stem cell transplantation, suggesting that this disease was highly refractory to very intensive treatment. AML with NUP98-HOXA9 fusion therefore appears to have a distinct clinical and biological profile, and should be regarded as a poor prognostic group.

Apoptosis modulatory activities of transiently expressed Bcl-2: roles in cytochrome C release and Bax regulation.

Bcl-2 and Bcl-X(L) are pro-survival members of the Bcl-2 family. These proteins have been shown to antagonize the pro-apoptotic activity of Bax and promote cell survival through blocking Bax translocation from the cytosol to mitochondria and by preventing the release of cytochrome c. However, it has been recently reported that transiently expressed Bcl-2 unexpectedly leads to significant cell toxicity. To study this intriguing phenomenon, we have carried out further analyses into the properties of transiently expressed Bcl-2. We found that various isoforms of human and different species of Bcl-2 were equally capable of inducing apoptosis. In addition, we discovered that transient expression of Bcl-2, unlike its pro-survival homolog Bcl-X(L), can lead to the release of cytochrome c from mitochondria and that the resulting cell death can be inhibited by caspase and calpain inhibitors. Moreover, we have shown that unlike the pro-apoptotic protein Bid, the toxicity associated with the transient expression of Bcl-2 occurs independent of the activity of the endogenous Bax. Finally, we found that in spite of its intrinsic toxicity, transiently expressed Bcl-2 is fully capable of blocking the ectopically expressed Bax from localizing to mitochondria. Taken together, these studies demonstrate that transiently expressed Bcl-2 displays opposing functional properties.

Changes in vesicourethral function following laparoscopic hysterectomy versus abdominal hysterectomy.

OBJECTIVE: To assess whether total hysterectomy is associated with increased postoperative vesicourethral abnormalities. SAMPLE: Forty-five patients had a laparoscopic hysterectomy and 36 patients had a total abdominal hysterectomy. DESIGN: Before and after hysterectomy, patients underwent a urinalysis, a personal interview, and an urodynamic study. RESULTS: Of the laparoscopic hysterectomy group, 27 patients (60%) exhibited urinary symptoms preoperatively, and 22 patients (48.9%) remained symptomatic following surgery. There was no significant change in the number of women with one or more urinary symptoms, but the incidence of urinary frequency and stress incontinence decreased significantly following hysterectomy (p < 0.05). Of the total abdominal hysterectomy group, preoperative voiding symptoms were present in 22 patients (61.1%). After surgery, urinary symptoms were present in 19 patients (52.8%). Some patients did not complain of any urinary frequency or stress incontinence following hysterectomy, but this figure did not differ significantly (p > 0.05). Maximal urethral closure pressure and maximal cystometric capacity demonstrated significant increases for both groups following surgery. CONCLUSIONS: The results indicated that total hysterectomy, either laparoscopic or total abdominal hysterectomy, did not significantly increase the subjective and objective incidence of vesicourethral dysfunction. On the contrary, some patients experience a substantial improvement of pre-existing urinary frequency or stress incontinence, partly as a result of an increase in the maximal urethral closure pressure and total bladder capacity following hysterectomy.

Effect of hormone replacement therapy on uterine fibroids in postmenopausal women--a 3-year study.

OBJECTIVE: The aim of this prospective 3-year clinical study was to examine the effect of hormone replacement therapy (HRT) on uterine fibroid growth among postmenopausal women. METHODS: Thirty-seven postmenopausal women with uterine solitary fibroids were recruited randomly for HRT in a 3-year program. All participants received 0.625 mg conjugated equine estrogen (CEE) and 5 mg medroxyprogesterone (MPA) daily. Fibroid volume was measured by transvaginal ultrasonography at baseline and then at 12-month intervals for 3 times. Clinically, significant fibroid growth was defined as an increase in volume of more than 25% compared with baseline. Also, 35 postmenopausal women with uterine fibroid were studied as control who did not receive HRT during the study period. RESULTS: Fibroid volume had increased significantly after 1 year both in HRT users and non-users. These increases continued to the second year significantly in HRT users but not in non-users. However, the volumes declined significantly at the third year to similar levels as those measured at baseline in control. In HRT users, fibroid volume though significantly increased at the third year (vs. baseline) but declined insignificantly in comparison with the second year. Clinically, at end of the third year study, one of 34 and three of 34 women increased fibroid volume over 25% compared with baseline in HRT non-users and users, respectively. CONCLUSIONS: HRT does increase uterine fibroid volume statistically. However, its effect appears in the first 2 years of use. The increased fibroid volume begins to decline at the third year both in HRT users and non-users. Clinically, the increased effect of HRT on uterine fibroid of postmenopausal women should be not over-emphasized at least for 3 years of usage.

Systemic lupus erythematosus presented as non-inflammatory necrotizing vasculopathy-induced ischemic glomerulopathy and small vessels-related ischemic cardiomyopathy.

The clinical significance of lupus non-inflammatory necrotizing vasculopathy (NINV) is not well established. For example, since lupus renal NINV is usually reported to coexist with proliferative and active glomerulonephritis, it is difficult to demonstrate the role of NINV on renal pathophysiology. Here we report a 16-year-old SLE boy with renal NINV presenting as ischemic glomerulopathy and small vessels-related ischemic heart failure. The renal biopsy demonstrated mild proliferative glomerulonephritis and NINV initially, and one month later repeated renal biopsy showed NINV with ischemic glomerulopathy. These findings established that NINV, but not proliferative glomerulonephritis, was responsive for his acute renal failure (ARF). Another interesting question is about the pathophysiology of his myocardial dysfunction. This patient presented typical angina and congestive heart failure (CHF). Echocardiograms and ventriculography revealed dilatation of four chambers and low ejection fraction. Serial electrocardiograms demonstrated evolutionary ischemic changes. Coronary angiography revealed no abnormality of large vessels. These findings suggested small vascular lesions-induced myocardial ischemia was the underlying mechanism of dilated cardiomyopathy. As myocardial biopsy was not done in our case, we could only speculate, but not prove, that the NINV observed in renal biopsy may also involve in cardiac microvascular beds. Nevertheless, this interesting case emphasized the role of obliterative small vascular lesions in the pathophysiology of ARF and myocardial dysfunction. The patient was treated with high-dose corticosteroid, plasma infusion and hemodialysis. His cardiac function improved gradually, however the renal function did not recover.

Weekly and monthly regimens of paclitaxel and carboplatin in the management of advanced ovarian cancer. A preliminary report on side effects.

This preliminary study was carried out over 18 months to evaluate whether the side effects in patients with advanced ovarian cancer receiving chemotherapy using paclitaxel-carboplatin differed between weekly (98 cycles in 14 patients) and monthly (102 cycles in 15 patients) administrations. We used paclitaxel (60 mg/m2) and carboplatin (AUC of 2) in the weekly regimen and 175 mg/m2 of paclitaxel and carboplatin (AUC of 6) in the monthly regimen. All eligible patients received at least four cycles of treatment in both regimens. The results revealed significantly decreased hematological toxicity in weekly regimens relative to monthly ones, ie, 7.1% vs. 18.6% of anemia (> or = grade 2), 7.1% vs. 32.3% of grade 3/4 granulocytopenia, and 0% vs. 15.7% of >grade 2 thrombocytopenia. There was no significant difference in nonhematological toxicities between the two regimens. The incidence of unscheduled events was much less in the weekly regimen than in the monthly one; ie, delayed treatment (3 vs. 18 events), unanticipated hospitalizations (3 vs. 15 times), and supplemental support with G-CSF (7 vs. 33 times). Complete responses were observed in 6 of 14 patients in the weekly regimen and in five of 15 patients in the monthly regimen, while partial responses were seen in four and five patients in the weekly and monthly regimens, respectively. The present results demonstrate that the weekly regimen can achieve the benefits of tolerable toxicity with significantly reduced myelosuppression and improved cost-effectiveness in terms of unscheduled events.

The exocyst complex associates with microtubules to mediate vesicle targeting and neurite outgrowth.

During neuronal development, vesicles are targeted to the growth cone to promote neurite outgrowth and synaptogenesis. The Exocyst complex is an essential macromolecule in the secretory pathway that may play a role in vesicle targeting. Although it has been shown that this complex is enriched in rat brain, the molecular mechanism underlying its function is largely unknown. Here, we report that the Exocyst complex coimmunoprecipitates with microtubules from total rat brain lysate. Additionally, the Exocyst complex subcellular localization changes on neuronal differentiation. In undifferentiated pheochromocytoma (PC12) cells, this complex is associated with microtubules at the microtubule organizing center. However, in differentiated PC12 cells and cultured hippocampal neurons, the Exocyst complex and microtubules extend to the growing neurite and colocalize at the growth cone with synaptotagmin. Inhibition of the NGF-activated MAP kinase pathway blocks the Exocyst complex and microtubule redistribution, abolishing neurite outgrowth and promoting cytosolic accumulation of secretory vesicles. Consistently, the overexpression of Exocyst sec10 subunit mutant blocks neurite outgrowth. These results indicate that the Exocyst complex targets secretory vesicles to specific domains of the plasma membrane through its association with the microtubules, promoting neurite outgrowth.