Biomedical subjects

Frank Mayer

Publications and source records attributed to Frank Mayer.

24 records · Page 2Linked to original sources

PubMed2002

Microsatellite instability of germ cell tumors is associated with resistance to systemic treatment.

Systemic cisplatin-based chemotherapy cures > or =90% of patients with metastatic germ cell tumors (GCTs). The biological basis of this exquisite chemo-sensitivity and the resistant phenotype encountered in 10-15% of patients with GCT is yet unclear. A defective mismatch repair pathway leading to microsatellite instability (MSI) has been related to resistance to cytotoxic drugs. We investigated 100 unselected GCTs and 11 clinically defined chemotherapy-resistant GCTs for MSI using 8 mono- or dinucleotide markers and the presence of the mismatch repair factors MLH1, MSH2, and MSH6 by immunohistochemistry. The resistant tumors, both chemo-naïve (n = 8) and pretreated (n = 3), showed a significantly higher incidence of MSI compared with the unselected series (45 versus 6% in at least one locus and 36 versus 0% in > or =2 of 8 loci, both P < or = 0.001). In 5 of all 11 unstable tumors, MSI correlated with immunohistochemical findings. This study demonstrates for the first time a positive correlation between MSI and treatment resistance in GCT.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Role of P53 and MDM2 in treatment response of human germ cell tumors.

PURPOSE: Testicular germ cell tumors (TGCTs) of adolescents and adults are very sensitive to systemic treatment. The exquisite chemosensitivity of these cancers has been attributed to a high level of wild-type P53. MATERIALS AND METHODS: To clarify the role of P53 in treatment sensitivity and resistance of TGCTs, we performed immunohistochemistry and Western blotting analysis on a series of 39 fresh-frozen primary TGCTs before therapy (unselected series). In a series of formalin-fixed paraffin-embedded TGCTs of patients with fully documented clinical course, including treatment-sensitive (n = 17) and -resistant (n = 18) tumors, P53 status was assessed by immunohistochemistry and mutation analysis. In addition, the involvement of MDM2, a P53 antagonist, was investigated by immunohistochemistry, reverse transcriptase polymerase chain reaction, and in situ hybridization. RESULTS: Immunohistochemistry demonstrated absence of staining for P53 in 36%, 41%, and 17% of the unselected, responding, and nonresponding TGCTs, respectively. Of the positive TGCTs, most tumors, ie, 49%, 41%, and 33%, showed 1% to 10% positive nuclei. This overall low level of P53 was confirmed by Western blotting. Mutation analysis revealed only one silent P53 mutation in one of the responding patients. All embryonal carcinomas were homogeneously positive for MDM2, encoded by the full length mRNA, while a heterogeneous pattern was found for the other histologic components. Amplification of MDM2 was detected in one out of 12 embryonal carcinomas. CONCLUSION: Although our results are in line with previous findings of the presence of wild-type P53 in TGCTs, they show that a high level of P53 does not relate directly to treatment sensitivity of these tumors, and inactivation of P53 is not a common event in the development of cisplatin resistance.

Blotting, Western↗

PubMed2002

Heart rate prescriptions from performance and anthropometrical characteristics.

PURPOSE: Heart rate (HR) is widely used to adjust exercise intensity in aerobic training. Training HR recommendations are calculated often from simple equations. Because at lactate steady state (LASS) may be an intensity of exercise eliciting similar objective measures of intensity and similar subjective measures of metabolism, it is an appropriate intensity upon which to base aerobic-training prescription. The purpose of this research was to develop regression equations using age and other easily accessible characteristics to estimate the HR associated with LASS (HRLASS). METHODS: The data of 7397 healthy subjects (age >or= 10 yr; 5044 male, 2353 female) with different training habits were analyzed. All participants were tested in an incremental exercise test on the treadmill until subjective exhaustion. The LASS was determined by the concept of blood lactate at the "lactate threshold" plus a net increase of 1.5 mmol.L-1. The interdependence of further characteristics was tested by stepwise multiple regression. RESULTS: Age alone did not allow a precise prediction of lass=hText>HRLASS (r = 0.645 for all participants), regardless of adjustment by sex, training state, body mass, or performance characteristics using ANCOVA. Resting HR (HRrest) decreased steeply within the second life decade but not with further advancing age. The best discrete lactate-independent predictor for HRLASS was HRmax (r = 0.798). Inclusion of age and weight in the model resulted in only a small improvement of the prediction (r = 0.826). Other anthropometrical characteristics could not improve the model further. CONCLUSIONS: The use of age alone seems too imprecise for exactly driven aerobic training prescriptions. A minor improvement can be achieved in this objective by use of HRmax supplemented by age using a multiple regression model.

Adolescent↗

PubMed2002

Regulation of phasin expression and polyhydroxyalkanoate (PHA) granule formation in Ralstonia eutropha H16.

Regulation of expression of the phasin PhaP, which is the major protein at the surface of polyhydroxyalkanoate (PHA) granules in Ralstonia eutropha H16, was studied and analysed at the molecular level. The regulation of PhaP expression is achieved by an autoregulated repressor, which is encoded by phaR in R. eutropha. The occurrence of PhaR homologues and the organization of phaR genes was analysed in detail in 29 different bacteria. Three kinds of molecule to which PhaR binds were identified in cells of R. eutropha, as revealed by gel-mobility-shift assays, DNaseI footprinting, cell fractionation, immunoelectron microscopy studies employing anti-PhaR antibodies raised against purified N-terminal hexahistidine-tagged PhaR and in vitro binding studies employing artificial PHA granules. PhaR binds upstream of phaP at two sites comprising the transcriptional start site plus the -10 region and a region immediately upstream of the -35 region of the sigma(70) promoter of phaP, where two imperfect 12 bp repeat sequences (GCAMMAAWTMMD) were identified on the sense and anti-sense strands. PhaR also binds 86 bp upstream of the phaR translational start codon, where the sigma(54)-dependent promoter was identified. PhaR also binds to the surface of PHA granules. In the cytoplasm of a phaROmegaKm mutant of R. eutropha H16, increased quantities of PhaP were detected and the cells formed by this strain were much smaller and had many more PHA granules present than the wild-type. These data support the following model for the regulation of phaP expression. Under cultivation conditions not permissive for PHA biosynthesis or in mutants defective in PHA biosynthesis, PhaR binds to the phaP promoter region and represses transcription of this gene. After the onset of PHA biosynthesis, under conditions that are permissive for the formation of nascent granules, PhaR binds to PHA granules and phaP is transcribed. At the later stages of PHA accumulation, PhaR no longer binds to the granules and the transcription of phaP is again repressed. In addition to this, phaR expression is subject to autoregulation. Excess PhaR that has not bound to the phaP upstream region or to PHA granules binds to the phaR upstream region, thereby repressing its own transcription.

Bacterial Proteins↗

PubMed1998

Glucoamylase from Thermoanaerobacterium thermosaccharolyticum: Sequence studies and analysis of the macromolecular architecture of the enzyme.

A chromosomal DNA fragment with a length of 2,025 bp, carrying the structural gene coding for glucoamylase in Thermoanaerobacterium thermosaccharolyticum, was cloned and sequenced. It coded for 695 amino acids, representing a polypeptide with a predicted molecular mass of 77.5 kDa. The deduced amino acid sequence exhibited high homologies with the glucoamylase sequence of another bacterial glucoamylase (Clostridium sp. G0005) and with fungal glucoamylases. The catalytic domain (amino acids 271 to 695) of the T. thermosaccharolyticum enzyme shared a high degree of similarity (five conserved regions) with the catalytic domain of Aspergillus awamori glucoamylase. By comparing the secondary structure of the sequence of the catalytic domain of the T. thermosaccharolyticum enzyme with that of glucoamylase from A. awamori, and on the basis of X-ray crystallographic data available for the A. awamori enzyme, it turned out that, most probably, both enzymes have a catalytic domain organized into an "(alpha/alpha)(6)-barrel" and an overall size and shape that is very similar. These findings confirm and extend our working model for the macromolecular architecture of the T. thermosaccharolyticum glucoamylase obtained, in earlier experiments, by electron microscopy of negatively stained isolated enzyme molecules. Antibodies for an enzyme-specific peptide located near the active site were successfully applied for inhibition studies of enzyme activity and for electron microscopic epitope mapping. A study comparing the site of attachment of this kind of antibody to the T. thermosaccharolyticum glucoamylase molecule with the expected attachment site as deduced from the A. awamori enzyme structure confirmed the close similarity of both glucoamylases regarding the macromolecular architecture of that part of the enzyme carrying the catalytic center, though helices H9, H10, and H11 in peripheral parts of the A. awamori enzyme are missing in the T. thermosaccharolyticum enzyme.

Journal Article↗

PubMedDate not supplied

Resistance to platinum-containing chemotherapy in testicular germ cell tumors is associated with downregulation of the protein kinase SRPK1.

Male germ cell tumors (GCTs) are extremely sensitive to platinum-containing chemotherapy, with only 10% of patients showing therapy resistance. However, the biological basis of the high curability of disseminated GCTs by chemotherapy is still unknown. Recently, we demonstrated that the mammalian serine/arginine-rich protein-specific kinase 1 (SRPK1) is a cisplatin-sensitive gene, inactivation of which leads to cisplatin resistance. Because, in mammalians, the expression of SRPK1 is preferentially high in testicular tissues, cisplatin responsiveness of male GCTs might be associated with SRPK1 levels. In the present study, we monitored SRPK1 protein expression in a unique series of nonseminomatous GCTs by immunohistochemistry. Randomly selected GCTs (n = 70) and tumors from patients responding to standard chemotherapy (n = 20) generally showed strong SRPK1 staining. In contrast, expression in refractory GCTs (n = 20) as well as in GCTs from poor-prognosis patients responding to high-dose chemotherapy only (n = 11) was significantly lower (two-sided Wilcoxon rank sum test: P < .001). In conclusion, our data suggest that SRPK1 expression might be an important prognostic indicator for the chemoresponsiveness of nonseminomatous GCTs.

Adolescent↗