Analysis of Normal and Neoplastic Tissue NHC Proteins by High-Resolution Two-Dimensional Gradient Electrophoresis and Silver Staining

“Cancer” represents behavior of an abnormal cell phenotype characterized by uncontrolled cell division, invasiveness, metastasis, and inheritance in daughter cells. Transmissibility and stability of cancer most likely reflects presence of an inheritable DNA alteration (mutation) and/or expression or derepression of single genes, related groups, or both. A large number of recent studies have focused upon a proposed link between alterations of DNA (broadly termed mutagenesis) and eventual appearance of cancers. This “genetic” basis for carcinogenesis has been proposed to possibly result from a broad spectrum of alterations ranging from error-accumulation through gene redundancy and/or expression of oncogenes. No question remains as to the relation between certain types of DNA damage and induction of tumors. ⁴⁴ However, significant gaps still exist between demonstration of DNA damage and manifestation of the malignant phenotype. For example, not all carcinogens have been shown to interact with DNA. ²⁹ Also, the target size for neoplastic transformation appears to be 20- to 25-fold larger than that for mutation. ^{50 , 100} Further, selected cancers are able to express normal phenotypes under special conditions. ^{62 , 73} Although evidence indicates that alteration of DNA plays a major role in carcinogenesis, it is important to establish that part played by non-DNA factors, i.e., “epigenetic” effects. This is particularly appropriate since intriguing, although controversial evidence indicates that enhanced expression of normal cell proteins, or derepression of others may play a role in establishment and maintenance of malignant phenotype. ^{28 , 60} Epigenetic theories of carcinogenesis have derived from studies of normal differentiation and a major characteristic of most cancers — abnormality in control of normal gene expression. Generally, mutational events are not involved in differentiation; sequential expression of different genes effected by chromatin organization rearrangements. Examples of derepression and repression occur in human cervical and gastric carcinomas ³⁹ where the normally repressed condensed X chromosome decondenses and reactivates, and occur during hepatocarcinogenesis by loss of expression of genes for a-2-euglobulin production ⁹¹ and tryptophan oxygenase. ³³ Reexpression of “oncofetal” proteins by malignant cells and during carcinogen exposure represents another example of such phenomenon. Should disruption of normal gene expression be a critical, initial event in malignancy, then detection of changes in macromolecules regulating specific genes (chromosomal proteins) might provide insight into malignant phenotype-inductive sequence. Chromosomal proteins (histone and nonhistone [NHC]) control both structural and functional properties of eukaryotic genomes. ^{31 , 56} Histones are involved in genome packaging and are nonspecific repressors of DNA-dependent RNA synthesis. ^{32 , 49} Components of NHC proteins also control genomic maintenance but more importantly, catalyze defined gene sequence transcription. ^{35 , 48 , 57 , 70} Changes, therefore, in NHC proteins or NHC protein subgroups during carcinogenesis, could be “hallmarks” for malignant conversion and might play key roles in the process. The potential for chromosomal proteins as neoplastic transformation markers has been recently reviewed. ⁹² Functional and structural properties of chromosomal proteins in cells and changes occurring in malignancy have been recently reviewed, ^{40 , 79 , 80} and were subjects of previous reviews, ^{11 , 94} and monographs. ^{24 , 25 , 93}