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Abstract:
A common thread interwoven throughout the literature of cancer biology is a wide-ranging abnormality of gene regulation, manifested by misprogramming of protein synthesis. This phenomenon encompasses virtually every means of identification of proteins, including antigens, hormones, growth factors, membrane components, and enzymes. Studies by the author and others of the activities of enzymes existing in multiple forms (termed isozymes) in a series of rat hepatomas ranging widely in growth rate, degree of differentiation, and other phenotypic properties has extended this concept and added to it a dimension of functional significance. Isozymes that are in high activity in adult liver and that are geared kinetically to catalyze specific hepatic functions are lost in varying degrees and generally depend on the growth rate and degree of differentiation. In fast growing, poorly differentiated hepatomas, these are replaced by high activities of isozymes that are normally low or absent in adult liver. In many instances, the isozymes that are expressed in poorly differentiated hepatomas are present also in fetal liver, thus pointing to reactivation of genes that were active in the fetus but were inactivated during normal embryonic development. The loss of isozymes that are under rigid host endocrine control, as well as other proteins that maintain the differentiated state, and the re-activation of genes coding for fetal or ectopic proteins are probably crucial factors in the initiation and maintenance of cellular proliferation.
Insights
Cancer biology involves abnormal gene regulation and protein synthesis. Studies show altered isozyme patterns in rat hepatomas, with fetal isozymes reappearing in poorly differentiated tumors, suggesting gene reactivation.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Biology
Background:
- Cancer biology is characterized by widespread abnormalities in gene regulation, leading to misprogrammed protein synthesis.
- This dysregulation affects various proteins, including antigens, hormones, growth factors, membrane components, and enzymes.
Purpose of the Study:
- To investigate the functional significance of isozyme alterations in rat hepatomas.
- To correlate changes in isozyme activity with tumor growth rate and differentiation.
Main Methods:
- Analysis of isozyme activities in a series of rat hepatomas with varying phenotypic properties.
- Comparison of isozyme profiles in hepatomas with those in adult and fetal liver.
Main Results:
- Loss of adult liver-specific isozymes in hepatomas, with the extent of loss correlating with growth rate and differentiation.
- Upregulation of fetal or normally low/absent isozymes in fast-growing, poorly differentiated hepatomas.
- Re-expression of fetal isozymes suggests reactivation of developmental genes.
Conclusions:
- Altered isozyme expression is a key feature of cancer biology, reflecting aberrant gene regulation.
- The loss of differentiated proteins and re-expression of fetal proteins are critical in cancer initiation and proliferation.
- Isozyme analysis provides functional insights into tumor biology and potential therapeutic targets.