Immunostaining for Hu C/D and CD56 is useful for a definitive histopathological diagnosis of congenital and acquired isolated hypoganglionosis.

Isolated hypoganglionosis (IHG) has been proposed as a distinct entity with two subtypes: congenital IHG (CIHG) and acquired IHG (AIHG). However, due to the rarity of the disease and the lack of defining histological criteria, the concept of IHG is not widely accepted. We studied paraffin-embedded intestinal specimens from 79 patients diagnosed with Hirschsprung's disease (HD) (n = 49), CIHG (n = 25), and AIHG (n = 5) collected between January 1996 and December 2015. Histopathological diagnosis of HD, CIHG, and AIHG was confirmed by hematoxylin and eosin staining and immunohistochemical staining using Hu C/D and CD56. We evaluated (immuno)histopathological findings, counted the number of ganglion cells, and measured the size of Auerbach's plexus. Hu C/D labeled neuronal cell bodies, whereas CD56 was detected in all neuronal components. In HD, all ganglion cells in Auerbach's plexus in the normoganglionic segment (NGS) were immunoreactive for Hu C/D, whereas in the aganglionic segment (AGS), these were replaced by CD56-positive extrinsic nerve fibers and bundles. The number of ganglion cells in AIHG and CIHG was significantly lower than in the NGS of HD (p < 0.05). Auerbach's plexus was significantly smaller in CIHG (p < 0.05) but in AIHG equivalent to the NGS in HD. In summary, immunostaining for Hu C/D and CD56 is useful for definitive histopathological diagnosis of IHG.

Analysis of differentially expressed genes in malignant biliary strictures.

Microarray data were collected from bile duct samples from subjects with malignant biliary strictures by endoscopic retrograde cholangiopancreatography to screen for key genes associated with this disease. A predicted interaction network was constructed for these genes to interpret their functions. The gene expression dataset GSE34166 (10 samples: 6 malignant and 4 benign control samples) was downloaded from the Gene Expression Omnibus database. R package scripts were used to process the data and screen for differentially expressed genes. Genes identified were uploaded to the analysis tool String 8.3 to generate a gene interaction network. A hub gene was identified by calculating the node degree. The interaction network of the hub gene with other genes in the human genome was constructed and screened (score >0.9), and pathway-enrichment analysis was performed to elucidate the hub gene function. In total, 377 differentially expressed genes were identified and a network comprising 209 pairs of interactions was constructed. The most critical hub gene was identified as GSTA1, and a GSTA1-based interaction network was constructed consisting of 25 genes (containing the differentially expressed gene GSTA3). The cytochrome P450 (CYP450)-metabolic pathway displayed the most significant enrichment. Additionally, 4 transcription factors and their binding sites were also identified. In conclusion, we have identified the differentially expressed genes GSTA1 (a hub gene) and GSTA3, which may cause abnormal gene expression and tumorigenesis through CYP450-metabolic pathways. The transcription factors and their binding sites in the promoter of the hub gene provide potential directions for future drug design.

Cytoplasmic expression of HuR may be a valuable diagnostic tool for determining the potential for malignant transformation of oral verrucous borderline lesions.

Oral verrucous carcinoma (OVC) is a low grade variant of oral squamous cell carcinoma, and oral verrucous hyperplasia (OVH) is a benign lesion without malignant features. However, pathologists are sometimes presented with borderline lesions and are indecisive as to diagnose them as benign or malignant. Thus, these lesions are tentatively termed oral verrucous lesions (OVLs). HuR is an ARE mRNA-binding protein, normally localized in the nucleus but cytoplasmic exportation is frequently observed in cancer cells. The present study aimed to elucidate whether expression of the HuR protein facilitates the diagnosis of true malignant lesions. Clinicopathological features were evaluated, and immunohistochemical analysis for p53, Ki67 and HuR proteins was performed in 48 cases of OVH, OVC and OVL, and the outcomes were correlated using appropriate statistical analysis. The association of these three proteins in relation to malignant transformation was analyzed after a 3-year follow-up of 25 OVL cases. The basal characteristics (age, gender and location) of all cases had no significant association with the types of lesions. Gingiva (39.4%) was the common site for all lesions. Distribution of the examined proteins had a significant association with the lesions. As compared with the OVLs, the number of immunostained-positive cells was significantly higher in the OVCs and lower in the OVH cases. During follow-up, 24% of the OVLs underwent malignant transformation for which high HuR expression and a diffuse staining pattern in the epithelium were observed. Taken together, the high degree of HuR expression with diffuse staining pattern in the epithelium may be an effective diagnostic tool that determines the potential of OVLs for malignant transformation.

The expression of CPEB proteins is sequentially regulated during zebrafish oogenesis and embryogenesis.

In many species, there is little transcription in the mature oocyte, and zygotic transcription does not begin immediately after fertilization. In zebrafish, zygotic transcription is not initiated until the mid-blastula transition, thus the production of new proteins during oogenesis and early embryogenesis is dependent on the translation of maternal mRNAs. In a growing number of species, the translation of key maternal transcripts is coupled to their cytoplasmic polyadenylation. One family of RNA-binding proteins implicated in this process is the cytoplasmic polyadenylation element (CPE)-binding proteins (CPEBs), which bind to a sequence in the 3'-untranslated regions of regulated transcripts and mediate their storage/repression or translation. In several species, there is evidence for two classes of CPEBs, a larger oocyte-type and a smaller CPEB that functions during embryogenesis. This appears to be the case in zebrafish as well, and we now provide evidence suggesting that the oocyte-type CPEB (zorba) regulates the translation of the embryonic-type (ElrA) by keeping the ElrA transcript in storage until fertilization. When zorba levels fall, ElrA protein is then produced and available to regulate the translation of additional mRNAs during embryogenesis. We have also identified a potential target of ElrA, the maternal mRNA for hnRNPab, which is a potential homolog of the Drosophila gene squid, whose product plays a role in patterning the Drosophila oocyte and embryo. These data suggest that during zebrafish embryogenesis, cytoplasmic polyadenylation mediates a cascade of translational control whose final targets play central patterning roles during embryogenesis.

Methionine adenosyltransferase 2B, HuR, and sirtuin 1 protein cross-talk impacts on the effect of resveratrol on apoptosis and growth in liver cancer cells.

Resveratrol is growth-suppressive and pro-apoptotic in liver cancer cells. Methionine adenosyltransferase 2B (MAT2B) encodes for two dominant variants V1 and V2 that positively regulate growth, and V1 is anti-apoptotic when overexpressed. Interestingly, crystal structure analysis of MAT2B protein (MATß) protomer revealed two resveratrol binding pockets, which raises the question of the role of MAT2B in resveratrol biological activities. We found that resveratrol induced the expression of MAT2BV1 and V2 in a time- and dose-dependent manner by increasing transcription, mRNA, and protein stabilization. Following resveratrol treatment, HuR expression increased first, followed by SIRT1 and MAT2B. SIRT1 induction contributes to increased MAT2B transcription whereas HuR induction increased MAT2B mRNA stability. MATß interacts with HuR and SIRT1, and resveratrol treatment enhanced these interactions while reducing the interaction between MATß and MATα2. Because MATß lowers the Ki of MATα2 for S-adenosylmethionine (AdoMet), this allowed steady-state AdoMet level to rise. Interaction among MATß, SIRT1, and HuR increased stability of these proteins. Induction of MAT2B is a compensatory response to resveratrol as knocking down MAT2BV1 potentiated the resveratrol pro-apoptotic and growth-suppressive effects, whereas the opposite occurred with V1 overexpression. The same effect on growth occurred with MAT2BV2. In conclusion, resveratrol induces HuR, SIRT1, and MAT2B expression; the last may represent a compensatory response against apoptosis and growth inhibition. However, MATß induction also facilitates SIRT1 activation, as the interaction stabilizes SIRT1. This complex interplay among MATß, HuR, and SIRT1 has not been previously reported and suggests that these proteins may regulate each other's signaling.

HuR cytoplasmic expression is associated with increased cyclin A expression and inferior disease-free survival in patients with gastrointestinal stromal tumours (GISTs).

AIMS: HuR is an RNA-binding protein that post-transcriptionally modulates the expression of various target genes involved in carcinogenesis, such as CCNA2, which encodes cyclin A. The aim of this study was to evaluate the significance of HuR expression and subcellular localization in a large cohort of gastrointestinal stromal tumours (GISTs). METHODS AND RESULTS: HuR immunostaining was assessable for nuclear and cytoplasmic expression in 341 cases on tissue microarrays of primary GISTs, of which 318, 296 and 193 cases were also characterized for Ki67 labelling, cyclin A immunoexpression, and KIT and PDGFRA receptor tyrosine kinase (RTK) genotypes, respectively. The results of HuR nuclear and cytoplasmic expression were correlated with disease-free survival (DFS) and clinicopathological, immunohistochemical and RTK genotypic variables. HuR cytoplasmic expression was present in 42% of primary GISTs, and was significantly related to epithelioid histology, larger tumour size, NIH risk category, and nuclear expression of Ki67 and cyclin A. Importantly, HuR cytoplasmic expression (P < 0.001) and cyclin A overexpression (P < 0.001) were strongly associated with worse DFS. Both variables remained independently predictive of adverse outcome [P = 0.020 and risk ratio (RR) 2.605 for cytoplasmic HuR; P = 0.026 and RR 2.763 for cyclin A]. CONCLUSIONS: HuR cytoplasmic expression not only correlates with adverse prognosticators and cyclin A overexpression, but also independently predicts worse DFS, indicating a causative role in conferring tumour aggressiveness.

Melatonin-mediated insulin synthesis during endoplasmic reticulum stress involves HuD expression in rat insulinoma INS-1E cells.

In this study, we investigated how melatonin mediates insulin synthesis through endoplasmic reticulum (ER) via HuD expression in rat insulinoma INS-1E cells. Under ER stress condition (thapsigargin with/without melatonin, tunicamycin with/without melatonin), phosphorylation of AMP-activated protein kinase (p-AMPK) was significantly increased when compared with only with/without melatonin (control/melatonin). Insulin receptor substrate (IRS) two protein was significantly reduced under conditions of ER stress when compared with control/melatonin, but no expression of IRS1 protein was observed. In thapsigargin treatment, melatonin (10, 50 µm) increased IRS2 protein expression in a dose-dependent manner. p-Akt (Ser473) expression significantly decreased under ER stress condition prior to control/melatonin. Melatonin (10, 50 µm) significantly reduced nuclear and cellular p85α expressions in a dose-dependent manner when compared with only thapsigargin or tunicamycin. These results indicate the activation of the aforementioned expressions under regulation of the pathway, AMPK → IRS2 → Akt/PKB → PI3K (p85α). However, mammalian target of rapamycin and raptor protein, mTORC1, was found to be independent of the ER stress response. In thapsigargin treatment, melatonin increased nuclear mammalian RNA-binding protein (HuD) expression and reduced cellular HuD expression and subsequently resulted in a decrease in cellular insulin level and rise in insulin secretion in a dose-dependent manner. In tunicamycin treatment, HuD and insulin proteins showed similar expression tendencies. These results indicate that ER stress/melatonin, especially thapsigargin/melatonin, increased nuclear HuD expression and subsequently resulted in a decrease in intracellular biosynthesis; it is hypothesized that extracellular secretion of insulin may be regulated by melatonin.

Downregulation of ß-actin gene and human antigen R in human keratoconus.

PURPOSE: The purpose of this study was to determine the expression levels and regulation of ß-actin in the stroma of keratoconus (KC) and normal corneas. METHODS: A total of 15 different human corneas from both KC and normal individuals were used for this study. Additionally, 3 Fuch's dystrophic corneas were also used. The ß-actin gene expression was analyzed at the transcriptional and translational levels in the epithelium and stroma of the KC and normal corneas. The human antigen R (HuR) gene expression was analyzed by real-time PCR in the stroma of five KC and five normal corneas. The keratocytes from three normal and three KC corneas were cultured in the presence of serum, and the expression levels of ß-actin and human antigen R (HuR) were analyzed by using confocal imaging in both normal and KC fibroblasts. RESULTS: The expression of the ß-actin gene was downregulated in the stroma of the six KC corneas but not in the stroma of six normal and Fuchs' dystrophic corneas. Immunofluorescence detection of ß-actin showed that it was absent in the KC fibroblast. The real-time PCR analysis of the HuR gene showed a relative 4.7-fold lower expression in KC corneas relative to the normal corneas, which was further confirmed by the immunofluorescence detection of HuR in fibroblasts of KC corneas. CONCLUSIONS: Although ubiquitous ß-actins are essential for cell survival during early embryogenesis, the effects on various stages of development are not well understood. Our results show that ß-actin is downregulated in the corneal stroma of patients with KC, which may be related to reduced levels of a stabilizing factor (HuR) for ß-actin mRNA. We propose that loss of ß-actin in the corneal stroma might be a triggering factor in the development of KC.

The RNA-binding protein human antigen R controls global changes in gene expression during Schwann cell development.

An important prerequisite to myelination in peripheral nerves is the establishment of one-to-one relationships between axons and Schwann cells. This patterning event depends on immature Schwann cell proliferation, apoptosis, and morphogenesis, which are governed by coordinated changes in gene expression. Here, we found that the RNA-binding protein human antigen R (HuR) was highly expressed in immature Schwann cells, where genome-wide identification of its target mRNAs in vivo in mouse sciatic nerves using ribonomics showed an enrichment of functionally related genes regulating these processes. HuR coordinately regulated expression of several genes to promote proliferation, apoptosis, and morphogenesis in rat Schwann cells, in response to NRG1, TGFß, and laminins, three major signals implicated in this patterning event. Strikingly, HuR also binds to several mRNAs encoding myelination-related proteins but, contrary to its typical function, negatively regulated their expression, likely to prevent ectopic myelination during development. These functions of HuR correlated with its abundance and subcellular localization, which were regulated by different signals in Schwann cells.

Sex hormone-dependent attenuation of EAE in a transgenic mouse with astrocytic expression of the RNA regulator HuR.

In experimental autoimmune encephalomyelitis (EAE) and other neurodegenerative diseases, astrocytes play an important role in promoting or attenuating the inflammatory response through induction of different cytokines and growth factors. HuR plays a major role in regulating many of these factors by modulating RNA stability and translational efficiency. Here, we engineered transgenic mice to express HuR in astrocytes using the human glial fibrillary acidic protein promoter and found that female transgenic mice had significantly less clinical disability and histopathological changes in the spinal cord. Ovariectomy prior to EAE induction abrogated the protective effect. Our findings support a role for the astrocyte and posttranscriptional regulation in hormonally-mediated attenuation of EAE.

The RNA-binding protein RNPC1 stabilizes the mRNA encoding the RNA-binding protein HuR and cooperates with HuR to suppress cell proliferation.

The RNA-binding protein HuR, a member of the embryonic lethal abnormal vision/Hu protein family, plays a critical role in many cellular processes, including cell proliferation, angiogenesis, and inflammatory response. Despite significant progresses in understanding how HuR functions, the mechanism by which HuR expression is controlled is still poorly understood. Here, we showed that RNA-binding protein RNPC1 post-transcriptionally regulates HuR expression via mRNA stability. Specifically, we showed that overexpression of RNPC1 increases, whereas knockdown or knock-out of RNPC1 decreases, the level of HuR transcript and protein. Moreover, we showed that RNPC1, but not mutant RNPC1 deficient in RNA binding, stabilizes HuR transcript via binding to its 3'-untranslated region. Furthermore, to determine the biological significance of RNPC1-enhanced HuR expression, we showed that HuR, by repressing c-Myc expression, facilitates RNPC1-mediated growth suppression. Together, we have uncovered a novel mechanism by which HuR is regulated by RNPC1 via mRNA stability and HuR is a mediator of RNPC1-induced growth suppression.

Neuron-specific ELAV/Hu proteins suppress HuR mRNA during neuronal differentiation by alternative polyadenylation.

The ubiquitously expressed RNA-binding protein HuR increases the stability and translation of mRNAs encoding growth regulatory proteins that promote proliferation in a variety of cell types. However, the three neuron-specific ELAV/Hu proteins, HuB, HuC and HuD, while binding to the same types of mRNAs, are required instead for neuronal differentiation, and it becomes difficult to reconcile these contrary functions when all four Hu proteins are expressed in the same neuron. HuR mRNA exists as three alternatively polyadenylated variants, a 1.5-kb testes-specific mRNA isoform, a ubiquitous 2.4-kb isoform and a 6.0-kb isoform that we now show is induced during neuronal differentiation and appears to be neuron-specific. This 6.0-kb neuron-specific mRNA isoform is inherently less stable and produces less HuR protein than the ubiquitous 2.4-kb mRNA. Furthermore, we show that neuronal HuB, HuC and HuD, as well as HuR itself, can bind at the 2.4-kb mRNA polyadenylation site, and when overexpressed can affect alternative polyadenylation to generate an extended HuR 3'-UTR that is translationally suppressed. We propose that the regulation of HuR protein expression by alternative polyadenylation allows neurons to post-transcriptionally regulate mRNAs-encoding factors required for proliferation versus differentiation to facilitate neuronal differentiation.

The role of translational regulation in ultraviolet C light-induced cyclooxygenase-2 expression.

AIMS: The role of ultraviolet C light (UVC)-induced phosphorylation of the eukaryotic initiation factor 2 (eIF2) in the regulation of cyclooxygenase-2 (COX-2) expression at both transcriptional and translational levels is investigated. MAIN METHODS: Western analysis was used to determine COX expressions. Immunoprecipitation after [(35)S]-Met/Cys metabolic labeling was used to determine the rate for COX-2 synthesis and turnover. Quantitative real-time PCR was used to determine COX-2 mRNA levels. Ingenuity Pathways Analysis 6 was used for mapping COX-2 activation network. KEY FINDINGS: UVC induces COX-2 expression in wild-type mouse embryo fibroblasts (MEF(S/S)) and that the inducibility is reduced in MEF(A/A) cells in which the phosphorylation site, Ser-51 in the eIF2alpha, is replaced with a nonphosphorylatable Ala (S51A). UVC-induced transcription of COX-2 is delayed in MEF(A/A) cells, which correlates with NF-kappaB activation as previously reported (Wu, S, Tan, M, Hu, Y, Wang, JL, Scheuner, D, Kaufman, RJ, Ultraviolet light activates NFkappaB through translational inhibition of IkappaBalpha synthesis. The Journal of Biological Chemistry, 279, 34898-34902, 2004). The translational efficiency of COX-2 is higher in MEF(A/A) cells than in MEF(S/S) cells at 4 h, but not at 24 h post-UVC. The translation efficiency is correlated to the ratio of activated COX-2 binding protein HuR/TIAR. In addition, the newly synthesized COX-2 protein is more stable in MEF(A/A) cells than in MEF(S/S) cells. The results demonstrated a complex and dynamic regulation of COX-2 expression. SIGNIFICANCE: UVC induces a prolonged expression of COX-2. While transcriptional regulation of COX-2 expression is intensively studied, the role of translational regulation of COX-2 synthesis upon UVC-irradiation is not yet clear. This study elucidated a novel eIF2alpha phosphorylation-centered network for the regulation of COX-2 expression after UVC-irradiation.

Characterisation of calcitonin gene-related peptide-immunoreactive neurons in the myenteric plexus of rat colon.

A mechanical or chemical stimulus applied to the intestinal mucosa induces motility reflexes in the rat colon. Enteric neurons containing calcitonin gene-related peptide (CGRP) have been suggested as intrinsic primary afferent neurons responsible for mediating such reflexes. In the present study, immunohistochemistry was performed on whole-mount stretch preparations to investigate chemical profiles, morphological characteristics and projections of CGRP-containing neurons in the myenteric plexus of the rat colon. CGRP-positive neuronal cell bodies were detected in preparations incubated with colchicine-containing medium, whereas CGRP-positive nerve fibres were found in colchicine-untreated preparations. These neurons had large oval or round cell bodies that were also immunoreactive for the calcium-binding protein calretinin and neurofilament 200. Myenteric neurons positive for both calretinin and neurofilament 200 had several long processes that emerged from the cell body, consistent with Dogiel type II morphology. Application of the neural tracer DiI to the intestinal mucosa revealed that DiI-labelled myenteric neurons each had an oval or round cell body immunoreactive for calretinin. Thus, CGRP-containing myenteric neurons are Dogiel type II neurons and are immunoreactive for calretinin and neurofilament 200 in the rat colon. These neurons probably project to the intestinal mucosa.

Useful markers for detecting minimal residual disease in cases of neuroblastoma.

Neuroblastoma (NB), which is a malignant tumor of young children derived from neural crest cells that occurs in children, exhibits a wide range of clinical behaviors, from spontaneous regression to rapid progression. Advanced NB patients have a poor prognosis, and recently, autologous bone marrow transplantation (BMT) and autologous peripheral blood stem cell transplantation (PBSCT) have been attempted to improve the prognosis of these patients. In this study, we attempted to detect the expression of tyrosine hydroxylase (TH), neuroendocrine protein gene product (PGP) 9.5, ELAVL-4 and GD2 synthetase (GALGT), all of which are highly expressed in NBs, by the reverse transcription-polymerase chain reaction (RT-PCR) technique in order to detect minimal residual disease (MRD) in the bone marrow (BM) and peripheral blood (PB). Analysis of various tumor cell lines (Ewing's sarcoma, hepatoma, leukemias, and breast cancer cell lines in addition to NBs), and human normal samples (BM and PB cells) revealed that TH was the most specific marker for the detection of NB. On the other hand, PGP9.5 was the most sensitive marker, and was detected even when there was only one positive cell per 10(7) negative cells. We concluded that TH is a better marker before the diagnosis of NB while PGP9.5 is a better marker to detect MRD after the diagnosis. Here, we describe our results on useful markers to detect MRD in patients with NB.

Characterization of fetal and postnatal enteric neuronal cell lines with improvement in intestinal neural function.

BACKGROUND & AIMS: The isolation and culture of primary enteric neurons is a difficult process and yields a small number of neurons. We developed fetal and postnatal enteric neuronal cell lines using H-2K(b)-tsA58 transgenic mice (immortomice) that have a temperature-sensitive mutation of the SV40 large tumor antigen gene under the control of an interferon gamma-inducible H-2K(b) promoter element. METHODS: Enteric neuronal precursors were isolated from the intestines of E13-mouse fetuses and second day postnatal mice using magnetic immunoselection with a p75NTR antibody. The cells were maintained at the permissive temperature, 33 degrees C, and interferon-gamma for 24 or 48 hours, and then transferred to 39 degrees C in the presence of glial cell line-derived neurotrophic factor for 7 days for further differentiation. Neuronal markers were assessed by reverse-transcription polymerase chain reaction, Western blot, and immunocytochemistry. Neuronal function was assessed by transplanting these cells into the colons of Piebald or nNOS(-/-) mice. RESULTS: Expression analysis of cells showed the presence of neuronal markers peripherin, PGP9.5, HuD, tau, synaptic marker synaptophysin, characteristic receptors of enteric neurons, Ret, and 5-hydroxytryptamine-receptor subtypes at 33 degrees C and 39 degrees C. Nestin, S-100beta, and alpha-smooth muscle actin were expressed minimally at 39 degrees C. Glial cell line-derived neurotrophic factor resulted in increased phosphorylation of Akt in these cells, similar to primary enteric neurons. Transplantation of cells into the piebald or nNOS(-/-) mice colon improved colonic motility. CONCLUSIONS: We have developed novel enteric neuronal cell lines that have neuronal characteristics similar to primary enteric neurons. These cells can help us in understanding newer therapeutic options for Hirschsprung's disease.

Coordinated expression of HuD and GAP-43 in hippocampal dentate granule cells during developmental and adult plasticity.

Previous work from our laboratory demonstrated that the RNA-binding protein HuD binds to and stabilizes the GAP-43 mRNA. In this study, we characterized the expression of HuD and GAP-43 mRNA in the hippocampus during two forms of neuronal plasticity. During post-natal development, maximal expression of both molecules was found at P5 and their levels steadily decreased thereafter. At P5, HuD was also present in the subventricular zone, where it co-localized with doublecortin. In the adult hippocampus, the basal levels of HuD and GAP-43 were lower than during development but were significantly increased in the dentate gyrus after seizures. The function of HuD in GAP-43 gene expression was confirmed using HuD-KO mice, in which the GAP-43 mRNA was significantly less stable than in wild type mice. Altogether, these results demonstrate that HuD plays a role in the post-transcriptional control of GAP-43 mRNA in dentate granule cells during developmental and adult plasticity.

HuD distribution changes in response to heat shock but not neurotrophic stimulation.

Cellular stress leads to a change in distribution of RNA-binding proteins. HuR, a member of the ELAV/Hu family of RNA-binding proteins, is nuclear in distribution and following heat shock is found in large cytoplasmic stress granules where translation is inhibited. HuD, another ELAV/Hu RNA-binding protein, stabilizes the GAP-43 mRNA in response to nerve growth factor (NGF) stimulation in PC12 cells. We were interested in determining the nuclear distribution of HuD and if neurotrophic stimulation induced changes in the distribution of HuD. In PC12 cells, we found, as expected, that HuR translocates from the nucleus to the cytoplasm in response to heat shock. In response to heat shock, HuD forms large cytoplasmic stress granules, consistent with a role for HuD in the cessation of translation. In unstimulated cells, HuD is distributed in small granules in the cytoplasm and is consistently present at low levels in the nucleus. Stimulation of PC12 cells with NGF induces neuronal differentiation including outgrowth of neurites and increased levels of GAP-43 protein, whereas HuD remains localized in small cytoplasm granules and is still present in the nucleus. These results suggest that, following neurotrophic stimulation, the lack of changes in HuD distribution are due to continued steady state of HuD nuclear shuttling in PC12 cells, or that HuD is not normally shuttled from the nucleus in response to NGF.