Understanding Breast Cancer and Biotechnology: Case Study
This case study explores the research scientists at the Liggins Institute have done into the link between increased autocrine hGH and breast cancer.
>> Understanding Breast Cancer
>> Gene Expression: What is Going On to Create This Phenotype?
>> The Experimental Model
>> What Did the Scientists Find?
>> Meeting Human Need: Personalised Treatments Derived From Genetic Information
Understanding Breast Cancer
Scientists at the Liggins Institute wanted to know if increased levels of autocrine hGH were linked in some way to the development of breast cancer. To find this out they used cultured human breast cells to study the effect of differing levels of hGH on the development of breast cancer.
Cell Culture
You may be surprised to learn that human body cells are able to grow outside of our bodies if they are given the right conditions(e.g. specific pH, temperature and growth factors) and the nutrients they need to stay alive. It’s not as easy as it sounds as the right conditions require a controlled laboratory environment, especially to prevent infection by bacteria or fungi. Cells grown outside of the whole organism are said to be growing“in vitro”. This literally means“in glass”.(Cells inside an organism are said to be“in vivo” or“in life”).
Human cells, including cancer cells, can be cultured outside the human body in plastic flasks kept in incubators. Cells grown this way are called a cell culture. Cell cultures allow scientists to test the effect of chemicals on the cells and to investigate the normal physiology or biochemistry of cells. There are many genes that scientists have noted are expressed differently in cancer cells.
Once a gene has been identified it can be introduced to a cell line and the subsequent effects on the cells studied by growing these cells in cell culture. The gene must first be cloned and inserted into a plasmid vector and then amplified in bacteria. The vector is then transferred into mammalian cells using cell transfection technologies such as liposomes. These cells are incubated at human body temperatures and supplied with nutrients. By comparing the gene expression in these cells with control cells scientists can determine the changes in the cells that have been caused by the inserted gene. An alternative approach to look at the effects of a single gene is to inhibit the function of the gene or protein if the cells already express it.
The scientists found that when hGH is being secreted from breast cancer cells,(i.e. autocrine hGH), it increases cell growth rates and the cells are more invasive(Fig 5 and 6).
Next, the scientists wanted to find out about the molecules that are regulated by hGH that were causing the cells to grow faster and more aggressively. Their suspicion was that the autocrine hGH was affecting the expression of genes in the breast cancer cells.
Gene Expression: What is Going on to Create This Phenotype?
When studying disease, scientists want to find out how gene expression is being affected in the cells(e.g. genes being switched on/off or increasing/decreasing the level of gene expression). The phenotypic response that we see in organisms, such as the development of breast cancer, is almost always the result of a group of genes being expressed together, rather than just one gene. Scientists have been able to study gene expression one gene at a time for many years using a biotechnological process called the polymerase chain reaction(PCR). PCR is used to amplify(make multiple copies of) DNA.
In gene expression studies, PCR is used to amplify specific genes to find out whether that gene is being expressed in the tissue being studied. If genes are being expressed then mRNA will be produced. This mRNA is extracted from the cells and a process called reverse transcriptase is used to make a short section of DNA that is complementary to the mRNA - called cDNA. The cDNA is slightly different from the original DNA because it does not contain introns(a segment of a DNA or RNA molecule which does not code for proteins and interrupts the sequence of genes). The amount of cDNA produced will depend on the amount of mRNA which is determined by how active the gene is.
The cDNA is then amplified and analysed to establish how much mRNA was in the original sample. This gives an indication of how active the gene was. PCR only allows the study of one gene at a time, which makes the process very slow. The development of a new biotechnology, microarrays, has had a major impact on research into gene expression because it allows scientists to study thousands of genes all at the same time – giving the ability to study a genetic profile. Using a microarray we can identify which specific genes a cell is using at a particular point in time. This means that we can compare which genes are turned on or off in different conditions(e.g. when cancer is present compared to when cancer is absent).
What is a Microarray?
A microarray is a small glass slide that contains tiny fragments of known DNA sequences in different spots on a slide. This is also known as a gene or DNA chip. A human genome microarray will contain small fragments of each of the genes in the genome. These are called probes. Each spot on the slide contains multiple copies of the same probe.
Understanding Breast Cancer and Biotechnology: Case Study
Understanding Breast Cancer
Gene Expression: What is Going on to Create This Phenotype?