Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins: IV. The viruses

Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins: IX. V-type position effect

By the use of a simplistic concept of the structure of heterochromatin, one can derive a formulation for the mechanism by which the phenomenon of V-type position effect can repress genic activity. This notion would explain how the Bar locus and other position effect examples cause genic repression. The mechanism, when extended, may also explain the process of cancer induction by hereditary means. In its most concise form the theory states that heterochromatin has a stabilized structure through special proteins, such as phosphorylated species that allows it the capacity to induce new domains of a "pseudo-heterochromatic" conformation to juxta-positional euchromatic segments for short distances by virtue of electrostatic and hydrogen bond forces.

Theoretical mechanism for synthesis of carcinogen induced embryonic proteins: VIII. Transcriptional theory

In this paper an extension of prior writings on the mechanism by which changes in genic expression is presented. The previous development of these ideas led to a unifying concept of alterations in heterochromatin due to a variety of carcinogenic agents as a pivital process leading to potential re-expressions of genes (1). The following deals just with structural features of chromatin before continuing to finer control levels of gene expression, especially in reference to cancer cells. The DNA methylation status is presented as being an important step in an intermediate stage of chromatin expression along with protein acetylation, phosphorylation and methylation as other means of modifying chromatin status.

Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins. VI. Radiation

The following is an attempt to devise a theory of specific induction processes required of the neoplastic transformation using the non-specific carcinogenic agent - radiation. A variety of biological considerations including comparative radiosensitivity, radiation effects on chromatin and enzymes, radiomimetic chemical induction of chromosomal anomalies, lethality and the tRNA function are also presented. These topics serve as background for elaborating a scheme of how a specific array of genes could become decontrolled. A concept derived involves the fixation of despiralized genic areas which are induced by hypomethylated DNA caused by anomalous DNA methylation. This process could be a potentially critical part of the irradiation-induced carcinogenic event. The concept of fixation of chromatin in an informational sense leads to a mechanism requiring a classic mutation, modified by a repair process that ultimately leads to an epigenetic event. More specifically it would appear that a critical target to induce the neoplastic response from a cell with irradiation could be the DNA responsible for the template sites (or at least a secondary area that indirectly could cause inactivation of this site) of the genes for DNA methylation. This would not necessarily be the only genic change required but one can derive gene derepressions from this type of molecular lesion. A similar scheme for gene repression has not been devised in this writing beyond the simplistic, although not unwarranted, viewpoint of direct DNA damage.

Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins. V. The steroids

Since the induction of neoplastic cells by steroids has been well documented, an attempt is made to formulate a mechanism for explaining the resultant embryonic features of such tumour cells. Special emphasis is given to estrogen receptor complexes and their effect on chromatin proteins. Specifically a mechanism is presented for estradiol-17-beta and its ability to alter the gene expression (derepression) of mammary gland epithelial cells. In this model we explore the possible effects of small differences in receptor or repressor proteins associated with estrogens to translate quantitative steroid administration into qualitative cellular responses.