Analyses of micronuclei in exfoliated epithelial cells from individuals chronically exposed to arsenic via drinking water in inner Mongolia, China

The groundwater in Bayingnormen (Ba Men), located in Central West Inner Mongolia, China, is naturally contaminated with arsenic at concentrations ranging from 50 microg/L to 1.8 mg/L. Various adverse health effects in this region, including cancer, have been linked to arsenic exposure via drinking water. A pilot study was undertaken to evaluate frequencies of micronuclei (MN), as measures of chromosomal alterations, in multiple exfoliated epithelial cell types from residents of Ba Men chronically exposed to arsenic via drinking water. Buccal mucosal cells, airway epithelial cells in sputum, and bladder urothelial cells were collected from 19 residents exposed to high levels of arsenic in drinking water (527.5 +/- 24 microg/l), and from 13 control residents exposed to relatively low levels of arsenic in drinking water (4.4 +/- microg/L). Analytical results from these individuals revealed that MN frequencies in the high-exposure group were significantly elevated to 3.4-fold over control levels for buccal and sputum cells, and to 2.7-fold over control for bladder cells (increases in MN frequency significant at p < .001 for buccal cells; p < .01 for sputum cells; p < .05 for bladder cells). When smokers were excluded from high-exposure and control groups the effects of arsenic were observed to be greater, although only in buccal and sputum cells; approximately 6-fold increases in MN frequency occurred in these tissues. The results indicate that residents of Ba Men chronically exposed to high levels of arsenic in drinking water reveal evidence of genotoxicity in multiple epithelial cell types; higher levels of induced MN were observed in buccal and sputum cells than in bladder cells.

Lung tumor KRAS and TP53 mutations in nonsmokers reflect exposure to PAH-rich coal combustion emissions

We determined the TP53 and codon 12 KRAS mutations in lung tumors from 24 nonsmokers whose tumors were associated with exposure to smoky coal. Among any tumors studied previously, these showed the highest percentage of mutations that (a) were G --> T transversions at either KRAS (86%) or TP53 (76%), (b) clustered at the G-rich codons 153-158 of TP53 (33%), and (c) had 100% of the guanines of the G --> T transversions on the nontranscribed strand. This mutation spectrum is consistent with an exposure to polycyclic aromatic hydrocarbons, which are the primary component of the smoky coal emissions. These results show that mutations in the TP53 and KRAS genes can reflect a specific environmental exposure.

Evolutionary dynamics of plant R-genes

Plant R-genes involved in gene-for-gene interactions with pathogens are expected to undergo coevolutionary arms races in which plant specificity and pathogen virulence continually adapt in response to each other. Lending support to this idea, the solvent-exposed amino acid residues of leucine-rich repeats, a region of R-genes involved in recognizing pathogens, often evolve at unusually fast rates. But within-species polymorphism is also common in R-genes, implying that the adaptive substitution process is not simply one of successive selective sweeps. Here we document these features in available data and discuss them in light of the evolutionary dynamics they likely reflect.

[A review on nasopharyngeal carcinoma in ancient Chinese literature]

Based on the clinical characteristics of nasopharyngeal carcinoma (NPC), a receptive standard was set up to screen related information with NPC from ancient literature of traditional Chinese medicine, while a rejection standard was also set up to prevent associated data in these literature with diseases such as lymphatic tuberculosis and lymphoma in the neck etc. Furthermore, a review was made on the etiology, pathogenesis and procedures used in the prevention and treatment of NPC recorded in ancient literature, according to the evaluation as above. The data showed that several hypotheses were present in ancient literature about etiology and pathogenesis of NPC, including healthy qi deficiency, cold in channels, or liver qi stagnation, pyrogenous toxin, phlegm coagulation and blood stasis etc. Therefore, prevention was emphasized and the main therapeutic and preventive methods for NPC were regulating emotions, nourishing qi and harmonizing ying (nutrient).

p53 gene expression in relation to indoor exposure to unvented coal smoke in Xuan Wei, China

Lung cancer mortality rates in Xuan Wei County, which are among the highest in China, have previously been associated with exposure to indoor emissions from burning smoky coal. To determine if this association is stronger among lung cancer patients with abnormal expression of p53, we performed a population-based case-control study. Ninety-seven newly diagnosed lung cancer patients and 97 controls, individually matched by age, sex, and home fuel type, were enrolled. We used immunocytochemical methods to assess p53 protein accumulation in exfoliated tumor cells isolated from sputum samples. As expected, the amount of lifetime smoky coal use was associated with an overall increase in lung cancer risk. Compared with subjects who used less than 130 tons of smoky coal during their lifetime, the odds ratios (OR) for lung cancer were 1.48 (95% confidence interval [CI], 0.73 to 3.02) for subjects exposed to 130 to 240 tons, and 3.21 (95% CI, 1.23 to 9.03) for subjects who used more than 240 tons of smoky coal (P for trend 0.01). The effect was due almost exclusively to the pattern in women, almost all of whom were nonsmokers. Further, among highly exposed women, the association was substantially larger and achieved statistical significance only among patients with sputum samples that were positive for p53 overexpression (OR, 18.72; 95% CI, 1.77 to 383.38 vs OR, 4.80; 95% CI, 0.66 to 43.87 for p53-negative cases). This study suggests that exposure to the combustion products of smoky coal in Xuan Wei is more strongly associated with women who have lung cancer accompanied by p53 protein overexpression in exfoliated tumor cells.

DNA damage in buccal epithelial cells from individuals chronically exposed to arsenic via drinking water in Inner Mongolia, China

The purpose of this pilot study was to assess DNA damage in buccal cells from individuals chronically exposed to arsenic via drinking water in Ba Men, Inner Mongolia. Buccal cells were collected from 19 Ba Men residents exposed to arsenic at 527.5 +/- 23.7 micrograms/L (mean +/- SEM) and 13 controls exposed to arsenic at 4.4 +/- 1.0 micrograms/L. DNA fragmentation by the DNA ladder and TUNEL assay were used to detect DNA damage in buccal cells. In the DNA ladder assay, 89% (17/19) of the arsenic-exposed group showed < 100 bp DNA fragments, in contrast to 15% (2/13) of the controls (p < 0.0001). For the TUNEL assay, the mean frequencies of positive cells were higher in the exposed group (15.1%) than in the controls (2.0%) (p < 0.0001). This study showed that high arsenic exposure via drinking water resulted in DNA damage and DNA fragmentation in buccal cells thus may be an appropriate biomarker for assessing chronic effects of arsenic in humans. A study investigating DNA fragmentation from the individuals with low levels of arsenic exposure in this population is in progress.

Targeting of PYK2 to focal adhesions as a cellular mechanism for convergence between integrins and G protein-coupled receptor signaling cascades

The non-receptor tyrosine kinase PYK2 appears to function at a point of convergence of integrins and certain G protein-coupled receptor (GPCR) signaling cascades. In this study, we provide evidence that translocation of PYK2 to focal adhesions is triggered both by cell adhesion to extracellular matrix proteins and by activation of the histamine GPCR. By using different mutants of PYK2 as green fluorescent fusion proteins, we show that the translocation of PYK2 to focal adhesions is not dependent on its catalytic activity but rather is mediated by its carboxyl-terminal domain. Translocation of PYK2 to focal adhesions was attributed to enhanced tyrosine phosphorylation of PYK2 and its association with the focal adhesion proteins paxillin and p130(Cas). Translocation of PYK2 to focal adhesions, as well as its tyrosine phosphorylation in response to histamine treatment, was abolished in the presence of protein kinase C inhibitors or cytochalasin D treatment, whereas activation of protein kinase C by phorbol ester resulted in focal adhesion targeting of PYK2 and its tyrosine phosphorylation in an integrin-clustering dependent manner. Overexpression of a wild-type PYK2 enhanced ERK activation in response to histamine, whereas a kinase-deficient mutant substantially inhibited this response. Furthermore, inhibition of PYK2 translocation to focal adhesions abolished ERK activation in response to histamine treatment. These results suggest that PYK2 apparently links between GPCRs and focal adhesion-dependent ERK activation and can provide the molecular basis underlying PYK2 function at a point of convergence between signaling pathways triggered by extracellular matrix proteins and certain GPCR agonists.

Cerebral ischemia and seizures induce tyrosine phosphorylation of PYK2 in neurons and microglial cells

The nonreceptor tyrosine kinase PYK2 represents a stress-sensitive mediator of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase (MAPK) signaling pathways in many cell types. In the present study, we assessed the tyrosine phosphorylation of PYK2 under normal and pathological conditions in the CNS. We generated a polyclonal antibody that selectively recognizes tyrosine-phosphorylated PYK2 at its major autophosphorylation site. By using this antibody, we demonstrate that the phosphorylation profile of PYK2 after focal cerebral ischemia is biphasic. The first phase occurs within 1 hr, when most of the phospho-PYK2 immunoreactivity was observed in cortical neurons, whereas 24-72 hr after ischemia, a striking induction of phospho-PYK2 immunoreactivity was evident in microglia around the necrotic infarcted area. Double-immunostaining analysis using both anti-phospho-PYK2 antibody and antibody against the double-phosphorylated active form of p38MAPK revealed that the two phosphorylated protein kinases exhibit strikingly similar distribution patterns after ischemia. A short time after ischemia, phosphorylation of p38MAPK was evident in the cortical neurons as demonstrated by both immunohistochemistry and immunoblotting analysis, whereas 24-72 hr after ischemia, phospho-p38MAPK was found in activated microglia and colocalized with phospho-PYK2. In contrast to cortical neurons, basal phospho-PYK2 immunoreactivity was observed in hippocampal pyramidal neurons, which was markedly decreased after kainate acid-induced status epilepticus. However, 24 hr after the epileptic onset, a pronounced upregulation of PYK2 and phospho-PYK2 immunoreactivities was evident in microglial cells, as demonstrated by double-immunostaining with the microglial marker OX42. These results provide, for the first time, in situ localization of tyrosine-phosphorylated PYK2 in neuronal stress pathways in the adult rat brain and are consistent with the role of PYK2 as an upstream regulator of p38MAPK signaling cascades in response to stress signals.

[Early arthroscopic reconstruction in treatment of acute complete rupture of anterior cruciate ligament]

OBJECTIVE

To early reconstruct acute and complete rupture of anterior cruciate ligament (ACL) and treat combined injuries for the recovery of knee joint stability.

METHODS

Ten cases of acute complete rupture of anterior cruciate ligament and medial collateral ligament were treated arthroscopically by anterior cruciate ligament reconstruction using patellar tendon autograft fixed with interference screw from February 1998 to March 1999.

RESULTS

Follow-up ranged from 5 months to 1 year and 3 months (average 10 months). Clinical results showed that the stability of knee joint was satisfactory in the early stage.

CONCLUSIONS

Acute the ACL rupture can be reconstructed arthroscopically in the early stage and the injuries were moderate, combined injuries could be treated at the same time, and the stability of knee joint could recover in the early stage after operation.

Aplastic anemia is associated with HLA-DRB1*1501 in northern Han Chinese

It has been reported that aplastic anemia (AA) is more common in HLA-DR2-positive individuals than in the general population. We investigated the frequency of some HLA loci of 102 Northern Han Chinese patients with AA and 105 healthy control subjects. Polymerase chain reaction and sequence specific oligonucleotide probe hybridization were used to determine HLA-DR- and HLA-DR2-related DRB1 alleles. The frequency of DR2 is increased in AA patients; the relative risk (RR) was 2.86, and the difference was significant (chi 2 = 11.1, P = .004). The RR of HLA-DRB1*1501 was 3.07, and the difference was significant (chi 2 = 9.42, P = .008). The above results suggest that HLA-DR2 is significantly associated with AA in Northern Han Chinese. HLA-DRB1*1501 is the main subtype of HLA-DR2, and may be the susceptibility gene of AA.

Structural determinants for post-transcriptional stabilization of lactate dehydrogenase A mRNA by the protein kinase C signal pathway

Activation of protein kinase C (PKC) and protein kinase A (PKA) in rat C6 glioma cells increases the half-life of short-lived lactate dehydrogenase (LDH)-A mRNA about 5- and 8-fold, respectively. PKA and PKC act synergistically and prolong LDH-A mRNA half-life more than 21-fold. Similar effects were observed after transfection and transcription of a globin/lactate dehydrogenase minigene consisting of a beta-globin expression vector in which the 3'-untranslated region (UTR) of beta-globin had been replaced with the LDH-A 3'-UTR. Synergism was only obtained by transcription of minigenes containing the entire 3'-UTR and did not occur when truncated 3'-UTR fragments were analyzed. Additional mutational analyses showed that a 20-nucleotide region, named PKC-stabilizing region (PCSR), is responsible for mediating the stabilizing effect of PKC. Previous studies (Tian, D., Huang, D., Short, S., Short, M. L., and Jungmann, R. A. (1998) J. Biol. Chem. 273, 24861-24866) have demonstrated the existence of a cAMP-stabilizing region in LDH-A 3'-UTR. Sequence analysis of PCSR identified a 13-nucleotide AU-rich region that is common to both cAMP-stabilizing region and PCSR. These studies identify a specific PKC-responsive stabilizing element and indicate that interaction of PKA and PKC results in a potentiating effect on LDH-A mRNA stabilization.

[Arthroscopically assisted anterior cruciate ligament reconstruction using patellar tendon autograft fixed with interference screw]

OBJECTIVES

To evaluate the optimal position of bony tunnel, the firmness of tendon graft fixation and the effectiveness of postoperative function recovery in an arthroscopic approach for the minimally invasive reconstruction of anterior cruciate ligament (ACL).

METHODS

In a single arthroscopic approach, the ACL was reconstructed by the bone-tendon-bone compound patellar tendon autograft with the fixation of an interference screw.

RESULTS

ACL reconstruction was performed in 49 patients, of whom 20 were followed up for over one year (average 1 year and 5 months). Among the 20 patients, 13 were rated as excellent, 5 good, and 2 fair. The excellent and good rate went up to 90%. Reconstructed ACLs were reevaluated arthroscopically in 9 patients, in whom, 6 had good remodeling of ACLs.

CONCLUSIONS

Our results indicated that this method has the advantages of less injury, optimal positioning of bone tunnel, firm graft fixation, and early rehabilitation. Compound bone-tendon-bone autograft allows firm fixation and biologic healing with good shape and tension remodeling.

Synthesis and evaluation of furo[3,4-d]pyrimidinones as selective alpha1a-adrenergic receptor antagonists

Furo[3,4-d]pyrimidinones were found to be metabolites of dihydropyrimidinones such as 1a-b that are subtype-selective antagonists of the alpha1a-adrenergic receptor. A versatile synthesis that provides access to furo[3,4-d]pyrimidinones in high yield and in enantiomerically pure forms is described along with structure-activity relationships in the series.

[Study on endothlin and its gene expression in splanchnic vessels in cirrhotic rats]

OBJECTIVE

To investigate the role of endothelin(ET) in the pathogenesis of portal hypertension, ET-1 level and its gene expression in splanchnic vessels from cirrhotic rats were observed.

METHODS

ET levels of both plasma and vascular tissues were determined by radioimmunoassay. ET mRNA in vascular tissues was probed with RT-PCR technique expressed as optical density(OD) value from image analysis.

RESULTS

ET peptide and mRNA in PV and SMA vessels were all significantly higher in cirrhotic rats than those in normal rats, while in cirrhotic rats, ET and its gene expression of PV was dramatically higher than that of SMA(P < 0.05). In addition, the positive correlation was observed in difference between PV and SMA in ET concentration with portal pressure(r = 0.737, P < 0.01).

CONCLUSION

ET may be involved in the mechanisms of the formation of portal hypertension mainly due to constructing portal vein, increasing portal flow resistance.

Design and synthesis of novel alpha(1)(a) adrenoceptor-selective antagonists. 1. Structure-activity relationship in dihydropyrimidinones

Dihydropyrimidinones such as compound 12 exhibited high binding affinity and subtype selectivity for the cloned human alpha(1a) receptor. Systematic modifications of 12 led to identification of highly potent and subtype-selective compounds such as (+)-30 and (+)-103, with high binding affinity (K(i) = 0.2 nM) for alpha(1a) receptor and greater than 1500-fold selectivity over alpha(1b) and alpha(1d) adrenoceptors. The compounds were found to be functional antagonists in human, rat, and dog prostate tissues. Compound (+)-103 exhibited excellent selectively to inhibit intraurethral pressure (IUP) as compared to lowering diastolic blood pressure (DBP) in mongrel dogs (K(b)(DBP)/K(b)(IUP) = 40) suggesting uroselectivity for alpha(1a)-selective compounds.

Design and synthesis of novel alpha(1)(a) adrenoceptor-selective antagonists. 3. Approaches to eliminate opioid agonist metabolites by using substituted phenylpiperazine side chains

Dihydropyrimidinones, such as 1, represent a novel class of alpha(1a) adrenoceptor antagonists with potential for the treatment of benign prostatic hyperplasia (BPH) (see part 1 of this series). Analysis of the metabolites of 1 revealed that 4-methoxycarbonyl-4-phenylpiperidine is formed as the major metabolite and is an agonist at the mu-opioid receptor. To circumvent any potential liability resulting from the metabolite, we decided to identify alternate templates devoid of agonist activity at the mu-opioid receptor to replace the 4-methoxycarbonyl-4-phenylpiperidine moiety. The present study describes the synthesis and SAR of dihydropyrimidinones linked to substituted 4-phenylpiperazine containing side chains. Compound (+)-38 was identified as a lead compound with a binding and functional profile comparable to that of 1. The putative metabolite 2-carboxamidophenylpiperazine has negligible affinity for the mu-opioid receptor.

Design and synthesis of novel alpha(1)(a) adrenoceptor-selective antagonists. 4. Structure-activity relationship in the dihydropyrimidine series

We have previously disclosed dihydropyridines such as 1a,b as selective alpha(1a) antagonists as a potential treatment for benign prostatic hyperplasia (BPH). The propensity of dihydropyridines toward an oxidation led us to find suitable replacements of the core unit. The accompanying papers describe the structure-activity relationship (SAR) of dihydropyrimidinones 2a,b as selective alpha(1a) antagonists. We report herein the SAR of dihydropyrimidines such as 4 and highlight the similarities and differences between the dihydropyrimidine and dihydropyrimidinone series of compounds.

Design and synthesis of novel alpha(1)(a) adrenoceptor-selective antagonists. 2. Approaches to eliminate opioid agonist metabolites via modification of linker and 4-methoxycarbonyl-4-phenylpiperidine moiety

We have previously described compound 1a as a high-affinity subtype selective alpha(1a) antagonist. In vitro and in vivo evaluation of compound 1a showed its major metabolite to be a mu-opioid agonist, 4-methoxycarbonyl-4-phenylpiperidine (3). Several dihydropyrimidinone analogues were synthesized with the goal of either minimizing the formation of 3 by modification of the linker or finding alternative piperidine moieties which when cleaved as a consequence of metabolism would not give rise to mu-opioid activity. Modification of the linker gave several compounds with good alpha(1a) binding affinity (K(i) = < 1 nM) and selectivity (>300-fold over alpha(1b) and alpha(1d)). In vitro analysis in the microsomal assay revealed these modifications did not significantly affect N-dealkylation and the formation of the piperidine 3. The second approach, however, yielded several piperidine replacements for 3, which did not show significant mu-opioid activity. Several of these compounds maintained good affinity at the alpha(1a) adrenoceptor and selectivity over alpha(1b) and alpha(1d). For example, the piperidine fragments of (+)-73 and (+)-83, viz. 4-cyano-4-phenylpiperidine and 4-methyl-4-phenylpiperidine, were essentially inactive at the mu-opioid receptor (IC(50) > 30 microM vs 3 microM for 3). Compounds (+)-73 and (+)-83 were subjected to detailed in vitro and in vivo characterization. Both these compounds, in addition to their excellent selectivity (>880-fold) over alpha(1b) and alpha(1d), also showed good selectivity over several other recombinant human G-protein coupled receptors. Compounds (+)-73 and (+)-83 showed good functional potency in isolated human prostate tissues, with K(b)s comparable to their in vitro alpha(1a) binding data. In addition, compound (+)-73 also exhibited good uroselectivity (DBP K(b)/IUP K(b) > 20-fold) in the in vivo experiments in dogs, similar to 1a.

[Acute rupture of anterior cruciate ligament: diagnosis and treatment by early arthroscopy]

OBJECTIVE

To early diagnose and treat acute rupture of anterior cruciate ligament (ACL).

METHODS

23 patients with acute rupture of ACL were examined and treated by early arthroscopy.

RESULTS

The preoperative diagnosis of ACL rupture was similar to that of in 18 patients. Three patients were confirmed by early arthroscopy and 2 patients were found to have ACL rupture, 16 patients were combined with meniscus injuries and 6 patients with cartilaginous injuries. Patholanatomical type of ACL were rupture of parenchymal part (21 patients) and avulsion rupture of attachment point (2 patients). In 6 patients ACL was reconstructed under arthroscope.

CONCLUSIONS

Early arthroscopy in the treatment of acute ACL rupture has advantages of minor injury, correct diagnosis, visible location of injury or combined injury and timely treatment. Early arthroscopy for acute ACL rupture is an important measure for diagnosis, treatment, and stabilization of the knee joint.

A sensitive immunofluorescence assay for detection of p53 protein accumulation in sputum

p53 mutations are common genetic alterations in lung cancers and usually result in p53 protein accumulation in tumor cells. Sputum is noninvasive to collect and ideal for screening p53 abnormalities. This study was to determine the feasibility of detecting p53 protein accumulation in sputum cells using an immunofluorescence assay. Sputum samples were collected from 58 Chinese subjects, including 16 lung cancer cases from Xuan Wei (XW) County exposed to coal smoke, 25 mostly tobacco smoke-related cases from Zhengzhou City, and 17 XW controls. The p53 protein accumulation in tumor cells and some atypical cells was detected in 56% (9/16) of the coal smoke-exposed XW cases, 44% (11/25) of the Zhengzhou cases and none (0/17) in controls. The p53+ tumor cells were confirmed morphologically by Papanicolaou staining after the p53 immunofluorescence assay. This is the first report of successfully using an immunofluorescence assay to detect p53 protein accumulation in sputum.

Detection of p53 protein accumulation in sputum and lung adenocarcinoma associated with indoor exposure to unvented coal smoke in China

Lung cancer in Xuan Wei (XW), China has been linked to exposure to unvented coal smoke and adenocarcinoma, especially bronchioloalveolar carcinoma, is most common. p53 mutations occur commonly in lung cancers and usually generate detectable levels of p53 protein accumulation. Sputum is noninvasive to collect and ideal for screening p53 abnormalities. p53 protein accumulation was detected by immunohistochemistry in lung tumors and sputa from XW lung cancer patients to determine (1) the role of p53 in lung pathogenesis, and (2) feasibility of detecting p53 protein accumulation in sputum, p53 protein accumulation was detected in 73% (22/30) of lung adenocarcinomas from XW females exposed to coal emissions and significantly higher than the control cases (33%, p < 0.05). In sputum, we detected p53 overexpression in tumor cells in 54% (13/24) of XW cases and also in dysplastic cells (50% or 4/8). These findings suggest that p53 abnormalities is important in XW lung cancer etiology.

Multifocal accumulation of p53 protein in esophageal carcinoma: evidence for field cancerization

A systematic characterization of the cancerization field of esophageal carcinoma based on p53 protein accumulation has not been reported previously. The present report presents such a study based on 50 specimens of esophageal squamous-cell carcinoma from northern China. To gain insight into the etiology of this disease among the 50 subjects, DNA was analyzed for a polymorphism of the aldehyde dehydrogenase-2 (ALDH2) gene, which has been associated with increased risk for esophageal cancer among alcohol-consuming patients in Japan. However, the frequency of this polymorphism among our subjects, 30% (15/50), was within published control frequencies for this allele, suggesting that this allele may not play a role in the etiology of esophageal cancer in this northern Chinese population. Immuno-histochemical staining showed that 66% of the tumors were p53+. Of 420 pieces near or adjacent to p53+ tumors, p53+ cells were present among 64% of basal-cell hyperplasia (BCH), 70% of dysplasia (DYS) and 88% of carcinoma in situ (CIS). Of 216 pieces near or adjacent to p53- tumors, p53+ frequencies were 25% of BCH, 25% of DYS and 0% of CIS. The proportion of BCH cells that were p53+ decreased at increasing distance from the tumor (p = 0.006). The sporadic distribution of p53+ cells and the distribution and frequency of p53+ precursor lesions support the view that accumulation of p53 protein is multifocal and occurs in precursor lesions in early stages of esophageal carcinogenesis.

Protein kinase A stimulates binding of multiple proteins to a U-rich domain in the 3'-untranslated region of lactate dehydrogenase A mRNA that is required for the regulation of mRNA stability

We have explored the molecular basis of the cAMP-induced stabilization of lactate dehydrogenase A (LDH-A) mRNA and identified four cytoplasmic proteins of 96, 67, 52, and 50 kDa that specifically bind to a 30-nucleotide uridine-rich sequence in the LDH 3'-untranslated region with a predicted stem-loop structure. Mutational analysis revealed that specific protein binding is dependent upon an intact primary nucleotide sequence in the loop as well as integrity of the adjoining double-stranded stem structure, thus indicating a high degree of primary and secondary structure specificity. The critical stem-loop region is located between nucleotides 1473 and 1502 relative to the mRNA cap site and contains a previously identified cAMP-stabilizing region (CSR) required for LDH-A mRNA stability regulation by the protein kinase A pathway. The 3'-untranslated region binding activity of the proteins is up-regulated after protein kinase A activation, whereas protein dephosphorylation is associated with a loss of binding activity. These results imply a cause and effect relationship between LDH-A mRNA stabilization and CSR-phosphoprotein binding activity. We propose that the U-rich CSR is a recognition signal for CSR-binding proteins and for an mRNA processing pathway that specifically stabilizes LDH mRNA in response to activation of the protein kinase A signal transduction pathway.