Glyoxalase I deficiency is associated with an unusual level of advanced glycation end products in a hemodialysis patient

BACKGROUND

Advanced glycation of proteins and their attendant advanced glycation end products (AGEs) contribute to the complications associated with diabetes mellitus or uremia. Regulatory mechanisms of AGE formation in vivo remain an issue of particular interest. We investigated a role of the glyoxalase detoxification system of precursor reactive carbonyl compounds (RCOs) in the in vivo AGE formation.

METHODS

Plasma levels of AGEs [pentosidine and Nepsilon-carboxymethyllysine (CML)], their RCO precursors, d-lactate (the final product resulting from the glyoxalase detoxification pathway), as well as of various compounds known to generate AGE precursors and surrogate markers for oxidative stress (antioxidant enzymes and glutathione), were measured in both hemodialysis (HD) patients and normal subjects. The activity and protein expression of glyoxalase I, an enzyme essential for the detoxification of alpha-oxoaldehydes, in red blood cells (RBC) were also examined.

RESULTS

In one 69-year-old lady who had been on hemodialysis (HD) for three years and had suffered from recurrent cardiovascular complications despite the absence of significant risk factors, plasma levels of pentosidine (77.3 +/- 2.4 pmol/mg protein) and CML (330.8 +/- 8.2 pmol/mg protein) were markedly elevated as compared to other HD patients (N = 20: 26.6 +/- 11.8 pmol/mg protein for pentosidine and 224.4 +/- 51.7 pmol/mg protein for CML). The plasma level of RCO precursors for pentosidine and CML was also higher in this patient than in other HD patients. Further investigation disclosed a very low activity in RBC of glyoxalase I (1.5 +/- 0.4 mU/106 RBC), as compared to other HD patients (3.9 +/- 0.6 mU/106 RBC) or normal subjects (4.0 +/- 0.6 mU/106 RBC). The glyoxalase I protein level, assessed in RBC by immunoblot analysis with a specific antibody, was markedly lower than that observed in HD patients and normal subjects. The causes of this deficiency remain unknown. Nucleotide sequencing of the products of reverse transcription-polymerase chain reaction from the patient's mononuclear cells revealed no genetic mutation within the coding region of the glyoxalase I gene. Plasma d-lactate level was also in the lower range (0.18 +/- 0.03 mg/dL) of the values measured in the other HD patients (0.27 +/- 0.09 mg/dL) and normal subjects (0.35 +/- 0.12 mg/dL). The plasma levels of various compounds known to generate AGE precursors (glucose, lipids and ascorbic acid) were either normal or low. The surrogate markers for oxidative stress such as antioxidant enzymes (glutathione peroxidases and superoxide dismutase) and glutathione were all within the range observed in the other HD patients.

CONCLUSION

The unusually high levels of AGEs in this patient implicate a deficient glyoxalase detoxification of RCO precursors. The present clinical observation implicates, to our knowledge for the first time, the glyoxalase detoxification system and, in particular, glyoxalase in the actual level of AGEs in a uremic patient.

Cloning of human PRP4 reveals interaction with Clk1

Prp4 is a protein kinase of Schizosaccharomyces pombe identified through its role in pre-mRNA splicing, and belongs to a kinase family including mammalian serine/arginine-rich protein-specific kinases and Clks, whose substrates are serine/arginine-rich proteins. We cloned human PRP4 (hPRP4) full-length cDNA and the antiserum raised against a partial peptide of hPRP4 recognized 170-kDa polypeptide in HeLa S3 cell extracts. Northern blot analysis revealed that hPRP4 mRNA was ubiquitously expressed in multiple tissues. The extended NH(2)-terminal region of hPRP4 contains an arginine/serine-rich domain and putative nuclear localization signals. hPRP4 phosphorylated and interacted with SF2/ASF, one of the essential splicing factors. Indirect immunofluorescence analysis revealed that endogenous hPRP4 was distributed in a nuclear speckled pattern and colocalized with SF2/ASF in HeLa S3 cells. Furthermore, hPRP4 interacted directly with Clk1 on its COOH terminus, and the arginine/serine-rich domain of hPRP4 was phosphorylated by Clk1 in vitro. Overexpression of Clk1 caused redistribution of hPRP4, from the speckled to the diffuse pattern in nucleoplasm, whereas inactive mutant of Clk1 caused no change of hPRP4 localization. These findings suggest that the NH(2)-terminal region of hPRP4 may play regulatory roles under an unidentified signal transduction pathway through Clk1.

Pre- and postoperative bone metabolism of primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a well-known indicator of severe bone loss. However, the recovery process of bone mineral density after surgery in PHPT patients is not sufficiently clear. We examined postoperative bone metabolism in 24 PHPT patients.

PATIENTS AND METHODS

Subjects were 24 patients with PHPT upon whom we performed parathyroidectomy in the Department of Surgery II, Fukushima Medical University. Mean age was 54.2 years and the male-to-female ratio was 10:14; mean time of follow-up was 27.3 months. Patients were divided histopathologically into 16 adenomas and eight hyperplasias, and classified by heredity into seven familial (six, MEN 1; one, MEN 2) and 17 sporadic types. Bone mineral density was measured by dual energy X-ray absorptometry (DXA) and digital image processing (DIP). Age-matched values of these parameters were obtained. Serum bone metabolic parameters; ionized calcium (CaF), phosphorus, intact PTH (iPTH), c-PTH, ALP, osteocalcin (OC) and PTHrP were measured.

RESULTS

PHPT patient preoperative bone mineral densities were significantly lower than those of healthy controls. Those by DIP method were lower than those by DXA. High CaF, iPTH, OC and ALP levels were indicated before surgery, but all parameters immediately became normal. Longitudinal bone mineral density changes of asymptomatic cases increased more than those of patients with renal stone and/or ostitis fibrosa. In adenoma cases, tumor weights were significantly inversely, which correlated with preoperative DIP bone density measurements.

CONCLUSION

Preoperative PHPT patients showed decreased bone density; bone loss in symptomatic cases was especially prominent compared to asymptomatic cases. Most PHPT patients had not completed the BMD recovery after surgery, so even asymptomatic and mild PHPT patients should undergo parathyroidectomy to minimize irreversible bone loss.

Fatty acid synthase expression in Japanese breast carcinoma patients

Fatty acid synthase (FAS) is the key enzyme required for the conversion of dietary carbohydrates to fatty acids. Recent studies have demonstrated that high levels of FAS expression occur in a variety of cancers, including breast cancer. We evaluated 243 primary breast cancer patients in the period between 1989 and 1996. Immunohistochemical staining for FAS was performed on formaline-fixed, paraffin-embedded sections. FAS staining intensity was graded as low or high. The expression of FAS was high in 145 (60%) and low in 98 cases (40%). A weak correlation between FAS expression and nodal status was noted in premenopausal patients (p=0. 01). FAS was associated with estrogen receptor (p=0.0022) and progesterone receptor (p=0.0085) status. We found that a low expression of FAS was significantly related to a shorter disease-free survival (DFS) rate in estrogen receptor positive patients (p=0.024) and a similar trend was recognized in progesterone receptor positive patients (p=0.083). The low FAS group showed better DFS and OS in all but ER-/PgR- cases (p=0.011, 0.076). This study showed close correlations between immunohistochemical FAS expression and steroid hormone receptors in premenopausal patients. The use of FAS expression may increase the diagnostic utility of ER and PgR in premenopausal patients. FAS may be able to predict the responsiveness of tumors to endocrine therapy.

The subcellular localization of SF2/ASF is regulated by direct interaction with SR protein kinases (SRPKs)

Serine/arginine-rich (SR) proteins play an important role in constitutive and alternative pre-mRNA splicing. The C-terminal arginine-serine domain of these proteins, such as SF2/ASF, mediates protein-protein interactions and is phosphorylated in vivo. Using glutathione S-transferase (GST)-SF2/ASF-affinity chromatography, the SF2/ASF kinase activity was co-purified from HeLa cells with a 95-kDa protein, which was recognized by an anti-SR protein kinase (SRPK) 1 monoclonal antibody. Recombinant SRPK1 and SRPK2 bound to and phosphorylated GST-SF2/ASF in vitro. Phosphopeptide mapping showed that identical sites were phosphorylated in the pull-down kinase reaction with HeLa extracts and by recombinant SRPKs. Epitope-tagged SF2/ASF transiently expressed in COS7 cells co-immunoprecipitated with SRPKs. Deletion analysis mapped the phosphorylation sites to a region containing an (Arg-Ser)8 repeat beginning at residue 204, and far-Western analysis showed that the region is required for binding of SRPKs to SF2/ASF. Further binding studies showed that SRPKs bound unphosphorylated SF2/ASF but did not bind phosphorylated SF2/ASF. Expression of an SRPK2 kinase-inactive mutant caused accumulation of SF2/ASF in the cytoplasm. These results suggest that the formation of complexes between SF2/ASF and SRPKs, which is influenced by the phosphorylation state of SF2/ASF, may have regulatory roles in the assembly and localization of this splicing factor.

cdc2 kinase-mediated phosphorylation of splicing factor SF2/ASF

SR proteins are a family of splicing factors which are important components of spliceosomes. Recent studies suggested that phosphorylation of SR protein might be a key event for the regulation of pre-mRNA splicing and is prevalent in metaphase cells. To investigate the role of cdc2 kinase in cell cycle-dependent phosphorylation of SR protein, we examined its phosphorylation of SF2/ASF, a representative SR protein. SF2/ASF was phosphorylated both by recombinant cdc2 kinase, a cdc2-cyclin B complex, and by cdc2 kinase immunoprecipitated from G2/M phase HeLa cells. In vitro phosphorylation and phosphopeptide mapping of several mutant proteins revealed that cdc2 kinase specifically phosphorylates the RS domain of SF2/ASF with serines 227, 238 and presumably 199 as major phosphorylation sites. These findings suggest the possibility that cdc2 kinase takes part in the cell cycle-dependent phosphorylation of SR protein which regulates the function of spliceosomes.

Novel SR-protein-specific kinase, SRPK2, disassembles nuclear speckles

SR-protein-specific kinase 1 (SRPK1) is first identified as a specific kinase for SR splicing factors. By RT-PCR of a conserved kinase domain, novel SR-protein-specific kinase clones were isolated from mouse brain. The cloned cDNAs encode a 106 kDa protein (648 amino acids, 92% identical to human SRPK1) and a 120 kDa protein (681 amino acids, 58% identical to human SRPK1). Therefore, they were designated mSRPK1 and mSRPK2, respectively. Northern blotting revealed the ubiquitous expression of mSRPK1 in all tissues examined and the tissue-specific expression of mSRPK2 in testis, lung, and brain. Both kinases phosphorylated SF2/ASF, a member of SR proteins in vitro and the phosphopeptide mappings were identical, indicating that these kinases phosphorylate the same site of SF2/ASF. Overexpression of mSRPK2 caused disassembly of cotransfected SF2/ASF and endogenous SC35. Our results indicate that SRPK family members may regulate the disassembly of the SR proteins in a tissue-specific manner.

Dymple, a novel dynamin-like high molecular weight GTPase lacking a proline-rich carboxyl-terminal domain in mammalian cells

We have cloned human dymple, a novel dynamin family member. The full-length cDNA sequence encodes a protein composed of 736 amino acids with a molecular mass of 80 kDa. This amino acid sequence most resembles yeast DNM1P and VPS1P. Dymple lacks a proline-rich carboxyl-terminal domain through which dynamin binds to SH3 domains to be activated. Northern blot analysis revealed two transcript sizes of 2.5 and 4.2 kilobases with alternative polyadenylation at the highest levels in brain, skeletal muscle, and testis. It was further established that there are three patterns of alternative splicing producing in-frame deletions in the coding sequence of dymple in a tissue-specific manner. When overexpressed, wild-type dymple exhibited a punctate perinuclear cytoplasmic pattern, whereas an amino-terminal deletion mutant formed large aggregates bounded by a trans-Golgi network marker. Since dynamin participates in clathrin-mediated endocytosis through a well-characterized mechanism, the existence of a dynamin-like molecule in each specific vesicle transport pathway has been predicted. Our findings suggest that dymple may be the first example of such a subfamily in mammalian cells other than dynamin itself, although its precise role and membrane localization remain to be resolved.