Genes Involved in Immortalization of Human Mammary Cells
Creators: name: University Of California Office Of The President
Publisher: name: University of California Office of the President
publisherIdentifier: https://ror.org/00dmfq477
publisherIdentifierScheme: ROR
Year: 2024

description: Normal human mammary cells have a limited lifespan. After a certain number of cell divisions, they are no longer capable of further proliferation. Most scientists now believe that this limited lifespan, referred to as cellular senescence, arose as a cancer prevention mechanism in long-lived organisms such as humans. This hypothesis is based on two lines of evidence. First, invasive human breast carcinomas (and most adult cancers) are thought to result from accumulation of multiple genetic errors - around 9 errors have been estimated for breast cancer development. The limited proliferative capacity of normal breast cells makes it highly unlikely that so many errors could accumulate in the absence of some means of overcoming cellular senescence. Second, the vast majority of human breast cancers (and most human cancers) express an enzymatic activity, called telomerase, which is associated with an unlimited proliferative capacity - or immortality. This activity is not found in non-tumor breast tissues. Cells derived from normal human breast tissues exhibit cellular senescence when cultured under laboratory conditions, whereas some cells from tumor tissues can express an unlimited proliferative potential in culture.
 
 
 
 
 
 
 
 Since it is thought that nearly all breast cancers have undergone changes that allow them to overcome normal cellular senescence, uncovering the underlying mechanisms that allow these cells to gain an extended or unlimited potential may serve both to increase our understanding of breast cancer progression, and to provide new targets for therapeutic intervention in breast carcinogenesis. This proposal is concerned with uncovering those mechanisms involved in loss of normal cellular senescence and thus potentially responsible for the progression of early stages of breast cancer.
 
 
 
 
 
 
 
 The vast majority of breast cancers originate from a type of cell called an epithelial cell. Our laboratory has pioneered the development and use of cultured human mammary epithelial cells (HMEC) in order to study the changes in growth control processes that occur during breast cancer progression. Using chemical carcinogens, we have been able to transform normal finite lifespan HMEC to immortality. However, we still do not know what molecular changes have permitted these transformed cells to overcome cellular senescence. The goal of this proposal is to identify the individual genes that normally prevent immortalization, based on the assumption that these genes are mutated in immortally transformed cells.
 
 
 
 
 
 
 
 To identify such genes, we will use a relatively new methodology that employs gene fragments that may act as genetic suppressor elements. Finite lifespan HMEC which are likely to need just one more mutation to become immortal will be exposed to gene fragments (packaged in viral vectors) that may be able to disrupt the normal functions of the immortalization suppressor genes. Since immortally transformed cells will maintain growth after the finite lifespan cells have stopped growing, immortalized cells can be easily detected. The virally inserted gene fragments can then be identified by molecular markers attached to the viral vectors. The significance of the isolated and sequenced gene fragments will then be gauged by comparing their expression in normal vs. transformed HMEC, as well as by functional tests in which the full-length gene is introduced into immortal HMEC. The discovery of genes that normally suppress immortalization may aid in the design of drugs that specifically target the immortalization growth defect, provide diagnostic information, and greatly facilitate further studies on HMEC immortalization