Biomedical subjects

N J Wells

Publications and source records attributed to N J Wells.

6 recordsLinked to original sources

PubMed1995

Cell cycle phase-specific phosphorylation of human topoisomerase II alpha. Evidence of a role for protein kinase C.

Type II topoisomerases are essential for faithful cell division in all organisms. In human cells, the alpha isozyme of topoisomerase II has been implicated in catalyzing mitotic chromosome segregation via its action as a DNA unlinking enzyme. Here, we have shown that the enzymatic activity of topoisomerase II alpha protein purified from HeLa cell nuclei was strongly enhanced following phosphorylation by protein kinase C. We have investigated the possibility that this kinase is involved in cell cycle phase-specific phosphorylation of topoisomerase II alpha in HeLa cells. Two-dimensional tryptic phosphopeptide mapping revealed that topoisomerase II alpha protein immunoprecipitated from metabolically labeled HeLa cells was differentially phosphorylated during the G2/M phases of the cell cycle. To identify sites of phosphorylation, and the kinase(s) responsible for this modification, oligohistidine-tagged recombinant domains of topoisomerase II alpha protein were overexpressed in Escherichia coli and purified by affinity chromatography. Phosphorylation of a short fragment of the N-terminal ATPase domain of topoisomerase II alpha by protein kinase C in vitro generated two phosphopeptides that co-migrated with prominent G2/M phase-specific phosphopeptides from the HeLa cell-derived topoisomerase II alpha protein. Site-directed mutagenesis studies indicated that phosphorylation of serine 29 generated both of these phosphopeptides. Our results implicate protein kinase C in the cell cycle phase-dependent modulation of topoisomerase II alpha enzymatic activity in human cells.

Amino Acid Sequence↗

PubMed1995

Human topoisomerase II alpha is phosphorylated in a cell-cycle phase-dependent manner by a proline-directed kinase.

Topoisomerase II is essential for chromosome condensation and segregation at mitosis in eukaryotic cells, but the mechanism of its regulation is not clearly understood. We have investigated whether or not the alpha isozyme of human topoisomerase II is phosphorylated in a cell-cycle phase-dependent manner. Two-dimensional tryptic phosphopeptide mapping revealed that several sites on HeLa topoisomerase II alpha protein were phosphorylated predominantly or exclusively during the G2 and M phases. To identify the protein kinases involved in this cell-cycle phase-specific phosphorylation, oligohistidine-tagged recombinant domains of the topoisomerase II alpha protein were expressed in Escherichia coli, purified by affinity chromatography and phosphorylated in vitro by different protein kinases. Phosphorylation of the C-terminal domain of the topoisomerase II alpha protein by the universal mitotic controller, p34cdc2, generated multiple tryptic phosphopeptides, many of which corresponded to the G2/M-phase-specific phosphorylation sites observed in vivo. The same phosphopeptides were obtained following phosphorylation of the C-terminal domain in vitro by the mitogen-activated protein kinase. Site-directed mutagenesis studies identified five of these sites of phosphorylation, each of which comprised a serine-proline motif. Our data implicate one or more proline-directed kinases in the cell-cycle-dependent regulation of topoisomerase II alpha enzyme activity in human cells.

Amino Acid Sequence↗

PubMed1995

Topoisomerases II alpha and beta as therapy targets in breast cancer.

Topoisomerase II enzymes play an essential role in human DNA metabolism. They are also recognized as primary targets of a number of anti-cancer drugs used in the treatment of breast cancer, which remains a leading cause of cancer-related death in women. While topoisomerase inhibitors have produced significant response rates in this disease, their use has been limited both by toxicity and by the development of resistance. In this article we review the extensive work which has not only increased our understanding of the biochemistry and molecular biology of type II topoisomerases but also enabled more rational drug design. Such knowledge should translate into increased clinical efficacy in the treatment of breast cancer and other malignancies.

Antineoplastic Agents↗

PubMed1995

Lower extremity burns and Unna paste: can we decrease health care costs without compromising patient care?

OBJECTIVE: To compare an alternative treatment for lower extremity burns with the standard in-hospital treatment, in an attempt to shorten hospital stay. DESIGN: A case-control series. SETTING: A university-affiliated hospital. PATIENTS: All patients with a burn isolated to a lower extremity were treated over an 8-month period with split-thickness skin grafting (STSG), Unna paste dressing, immediate mobilization and early discharge. This group was compared with matched controls from the preceding 8 years treated with STSG, occlusive burn gauze dressing, bed rest and hospitalization. MAIN OUTCOME MEASURES: Duration of hospital stay and graft viability. RESULTS: Thirteen patients with an average wound size of 131 cm2 were treated with Unna paste and had a graft viability of greater than 95% and a burn-scar rating equivalent to that of patients treated with the earlier regimen. The duration of hospital stay decreased from a mean of 12.9 days to 1.4 days, with no complications. This translated into a saving of $10,350 per patient. CONCLUSIONS: This alternative treatment is safe, inexpensive and effective and is recommended as the treatment of choice for uncomplicated, noncircumferential lower extremity burns.

Adolescent↗

PubMed1994

Serine 1524 is a major site of phosphorylation on human topoisomerase II alpha protein in vivo and is a substrate for casein kinase II in vitro.

Topoisomerase II protein is essential for cell proliferation and is known to exist as a phosphoprotein in cells from both lower and higher eukaryotic species. In this paper, we have investigated the phosphorylation of the alpha isozyme of human topoisomerase II. The topoisomerase II alpha protein was phosphorylated predominantly on serine residues in the human tumor cell lines HeLa and NSCLC-3. Two-dimensional tryptic phosphopeptide mapping studies revealed several sites of phosphorylation in vivo, including a major site that was common to topoisomerase II alpha protein from both HeLa and NSCLC-3 cells. To identify sites of phosphorylation, the regulatory C-terminal domain of human topoisomerase II alpha protein was overexpressed in Escherichia coli as a hexahistidine-tagged fusion protein and purified by nickel chelate chromatography. Tryptic phosphopeptide mapping revealed that casein kinase II phosphorylated the C-terminal domain primarily on 2 serine residues in vitro, which were shown to be sites of modification in vivo. Site-directed mutagenesis studies identified these casein kinase II-specific phosphorylation sites as serine 1524 and serine 1376.

Base Sequence↗

PubMed1994

Pilomatrixoma: a common, benign childhood skin tumour.

OBJECTIVE: To review recent experience with pilomatrixoma, particularly with respect to diagnosis. DESIGN: Chart review for an 8-year period. SETTING: A university-affiliated children's hospital. PATIENTS: Fifty children with 51 histologically proven pilomatrixomas. INTERVENTION: Excision of the lesion. MAIN OUTCOME MEASURES: Clinical presentation, diagnosis and pathological findings. RESULTS: The clinical presentation was typically that of an asymptomatic superficial mass that increased slowly in size and was located in the head and neck (78%) or chest and upper limbs. In one case the mass increased rapidly over 2 weeks and changed in colour from red to purple with areas of pink and tan. The referring diagnosis was incorrect in 94% of cases, and the preoperative diagnosis was incorrect in 57%. Pathologically the tumours were situated in the dermis or subcutaneous tissue. None were cystic, but several had areas of calcification. None of the tumours recurred after excision, but two patients had multiple lesions at different locations and times. CONCLUSIONS: Pilomatrixomas in children are simple to treat successfully but have variable clinical presentation. Early diagnosis is important so that unnecessary, aggressive surgery can be avoided.

Child↗