Actin binding proteins: regulation of cytoskeletal microfilaments.

The actin cytoskeleton is a complex structure that performs a wide range of cellular functions. In 2001, significant advances were made to our understanding of the structure and function of actin monomers. Many of these are likely to help us understand and distinguish between the structural models of actin microfilaments. In particular, 1) the structure of actin was resolved from crystals in the absence of cocrystallized actin binding proteins (ABPs), 2) the prokaryotic ancestral gene of actin was crystallized and its function as a bacterial cytoskeleton was revealed, and 3) the structure of the Arp2/3 complex was described for the first time. In this review we selected several ABPs (ADF/cofilin, profilin, gelsolin, thymosin beta4, DNase I, CapZ, tropomodulin, and Arp2/3) that regulate actin-driven assembly, i.e., movement that is independent of motor proteins. They were chosen because 1) they represent a family of related proteins, 2) they are widely distributed in nature, 3) an atomic structure (or at least a plausible model) is available for each of them, and 4) each is expressed in significant quantities in cells. These ABPs perform the following cellular functions: 1) they maintain the population of unassembled but assembly-ready actin monomers (profilin), 2) they regulate the state of polymerization of filaments (ADF/cofilin, profilin), 3) they bind to and block the growing ends of actin filaments (gelsolin), 4) they nucleate actin assembly (gelsolin, Arp2/3, cofilin), 5) they sever actin filaments (gelsolin, ADF/cofilin), 6) they bind to the sides of actin filaments (gelsolin, Arp2/3), and 7) they cross-link actin filaments (Arp2/3). Some of these ABPs are essential, whereas others may form regulatory ternary complexes. Some play crucial roles in human disorders, and for all of them, there are good reasons why investigations into their structures and functions should continue.

Heart failure and apoptosis: electrophoretic methods support data from micro- and macro-arrays. A critical review of genomics and proteomics.

The multiple causes and multiple consequences of mammalian heart failure make it an attractive proposition for analysis using gene array technology, especially where the failure is idiopathic in nature. However, gene arrays also hold potential artefacts, particularly when gene expression levels are low, and where changes in expression levels are modest. Also, at present, the number of genes available on arrays is not large enough to prevent potential sampling deficiencies. Thus, it may not be wise to place too much reliance on quantitative interpretations of gene array data. Also, recently doubts were raised about the qualitative reliability of array genes. Electrophoretic methods are slow, cumbersome and complex but they can provide confirmation that the trends and numbers arising from the new gene arrays are reliable. In this overview, we compare gene array data with data from protein activity assays such as zymograms, Western blots, two-dimensional electrophoresis, and immunohistochemistry. Similar or complementary data from the same heart tissues analyzed by either microarrays or macroarrays can be reassuring to those interested in reliable molecular analyses of normal and failing hearts. Similar principles will apply to other tissues and cells.

[Leukoencephalopathy in a patient being treated for small cell lung cancer].

A 62-year-old man was given a diagnosis of small cell lung cancer, and received 6 courses of combination chemotherapy (PE therapy) composed of cisplatin (80 mg/m2, day 1) and etoposide (100 mg/m2, days 1, 2, 3). Multiple brain metastases were found, and whole brain irradiation (44 Gy) was given. Eleven months after radiotherapy, he suffered from dizziness and abnormal gait. Enhanced CT of the head showed slight enlargement of the lateral ventricles and markedly low density of the white matter, but no evidence of intracranial tumor involvement. A magnetic resonance scan (axial T2-weighted) showed symmetric extensive hyperintensity in the white matter. Treatment-related leukoencephalopathy caused by the PE therapy and whole brain irradiation was diagnosed. He was alive 8 months after the appearance of neurological symptoms, without recurrence of lung cancer. A search of the literature revealed no previous report of leukoencephalopathy related to PE therapy.

An autoradiographic study of the renewal of mouse bronchiolar epithelium following bromobenzene exposure.

This study discusses mice bronchiolar epithelium following bromobenzene (BrBZ) exposure. Our study shows 3 cell types following BrBZ exposure: Clara cells, ciliated cells, and newly discovered BrBZ-resistant nonciliated cells. Through electron microscopic autoradiography, we were able to show the proliferative ability of BrBZ-resistant nonciliated cells. This finding suggests that BrBZ-resistant nonciliated cells may function as progenitor cells. In addition to discovering this new cell type, our results also demonstrate and confirm the proliferative ability of modified Clara cells.

Preneoplastic changes of xenotransplanted human distal airway epithelium induced by systemic administration of 4-nitroquinoline-1-oxide to host nude mice.

To elucidate a possible role of hematogenously transported carcinogens in pathogenesis of peripheral lung carcinoma in humans, we investigated whether the bronchiolar and alveolar epithelial cells of adult human lung xenografts in nude mice could be a target for the chemical carcinogen 4-nitroquinoline-1-oxide (4NQO) after its systemic administration to the host mice. Peripheral lung tissues from adult humans were transplanted s.c. into nude mice, and 4NQO (15 mg/kg) was administered s.c. to the host mice at a site distant from the xenografts at 2 and 3 weeks after transplantation. The human lung xenografts were maintained for from 20 to 52 weeks, and then serial sections were examined histologically and immunohistochemically. Three types of epithelial changes, i.e. epidermoid metaplasia, papillary hyperplasia of columnar and epidermoid cells, and atypical adenomatous hyperplasia, were induced in the 4NQO group, with a statistically significant difference for these combined epithelial lesions (P less than 0.01) and for epidermoid metaplasia (P less than 0.05) compared to the control group. Some epidermoid metaplasias showed significant nuclear atypia. In addition, almost all foci of epidermoid metaplasia and papillary hyperplasia contained cells positive for carcinoembryonic antigen, suggesting both types of the lesions were preneoplastic. The morphologic characteristics of the atypical adenomatous hyperplasia were very closely similar to those of the hitherto reported preneoplastic or putative neoplastic lesions in the human peripheral lung. Our results indicated that the alveolar and bronchiolar epithelial cells of human lung xenografts were affected by systemically applied 4NQO, and subsequently underwent transformation to a preneoplastic state.

Long-term maintenance of human distal airway epithelial cells in nude mice: a potentially useful model for the study of pulmonary carcinogenesis and lung cell biology.

We investigated whether the normal morphology of distal airway epithelial cells from adult human lungs could be maintained for long periods of time as xenografts in nude mice. Peripheral lung tissue obtained from normal regions of lungs resected for lung cancer was transplanted subcutaneously into nude mice. The implants were then retrieved at intervals from 2 to 26 weeks for light and electron microscopy, and for immunohistochemical examination. At 2 weeks, revascularization of the implants and replication of immature epithelial cells were observed. At 4 weeks and thereafter, the epithelium formed in the implants was almost mature and normal in appearance. Pseudostratified columnar epithelium composed of ciliated, mucus, and basal cells lined the larger airspaces, whereas the smaller airspaces including alveolar structures were generally lined with type II pneumocytes and occasionally with Clara cells. Normal alveoli with type I pneumocytes and capillary networks were rarely observed. The implants were maintained in the nude mice for as long as 26 weeks. Cytokinetic studies of the epithelial cells in the implants using immunocytochemical detection of incorporated bromodeoxyuridine revealed that an inverse relationship existed between the degree of maturation and the replicative capacity of the epithelial cells. It was also found that, even in the mature epithelium, a small fraction of the cells were undergoing DNA synthesis. Peripheral lung tissue xenografts in nude mice may provide an excellent in vivo model for the study of pulmonary carcinogenesis and also for the study of both the function and differentiation of human epithelial cells of the distal airways.