Tumorigenic conversion of NIH 3T3 cells by transfection with Shope fibroma virus DNA

Tumorigenic poxviruses: growth factors in a viral context?

Shope fibroma virus (SFV) is one of the few poxviruses that induce cutaneous tumours, whereas myxoma virus, a closely related leporipoxvirus, does not. However, both have a virally encoded homologue of the epidermal growth factor (namely SFGF and MGF, respectively) that is considered to be crucial for poxvirus tumorigenesis. In this study, the role of viral growth factors in the context of infection with SFV, a tumorigenic leporipoxvirus, was investigated. An SFV mutant was engineered with the sfgf gene deleted and replaced with mgf. Macroscopic, histological and cytological examinations led to the conclusion that growth factors are indeed important for the development and maintenance of fibromas, provided that they are expressed in the proper viral context. However, they are not exchangeable and MGF cannot substitute for SFGF in the genesis of fibromas. It is likely that factors other than viral epidermal growth factor homologues influence the development of tumours.

The cell cycle: a review

The cell cycle is a complex process that involves numerous regulatory proteins that direct the cell through a specific sequence of events culminating in mitosis and the production of two daughter cells. Central to this process are the cyclin-dependent kinases (cdks), which complex with the cyclin proteins. These proteins regulate the cell's progression through the stages of the cell cycle and are in turn regulated by numerous proteins, including p53, p21, p16, and cdc25. Downstream targets of cyclin-cdk complexes include pRb and E2F. The cell cycle can be altered to the advantage of many viral agents, most notably polyomaviruses, papillomaviruses, and adenoviruses. The cell cycle often is dysregulated in neoplasia due to alterations either in oncogenes that indirectly affect the cell cycle or in tumor suppressor genes or oncogenes that directly impact cell cycle regulation, such as pRb, p53, p16, cyclin D1, or mdm-2. The cell cycle has become an intense subject of research in recent years. This research has led to the development of techniques useful for the determination of the effects of drugs and toxins on the cell cycle. Any drug or toxin with DNA damaging ability would be expected to alter cell cycle progression, and therefore, the cell cycle should be considered in the design of studies using such chemicals. With the appropriate techniques, cell cycle alterations may also be detected in tissue sections. Because of the ubiquitous nature of the cell cycle, it deserves consideration in the design and interpretation of studies in a wide variety of disciplines.