The Importance of 3D Models in Initiation Mechanisms

In the talk given by Dr. Joan Brugge, she discusses progression, drug resistance, and the different aspects in which 3-D models aid in the investigation of cancer biology. Her laboratory has provided wonderful and crucial insights into the understanding and treatment of cancer.

Dr. Brugge covered small different 'contexts' in which three-dimensional cultures can help in cancer research and protein biochemistry. One of the interests in her laboratory was to research the cellular processes and pathways that mediate alterations that occur during the initiation and progression of breast cancer.

They had a vast understanding of the cellular pathways that regulated cancer, but they did not have an extensive understanding of what was driving all the different histologic and phenotypic changes in tumors themselves. She illustrated – in some slides – the cross-section of normal breast cells with glandular tissues, and tissues of breast cancer patients with hyperplasia, carcinoma in situ, and invasive carcinoma. They observed that normal cells have escaped the controls that normally limited their proliferation in normal tissue, but cells maintained their normal glandular structure. The cells were just larger in size and the lumen was observed to be empty.

However, in carcinoma in situ, they observed a notable feature – the cells were able to proliferate and survive in the center of these structures. They noticed that in the carcinoma in situ cells especially, the nuclei and cytoplasm were uniform in shape and the outer cells were still polarized. In other 'hybrid' carcinoma in situs, they saw a remarkable variation in the size and morphology of the nuclei and the cytoplasm, and they seemed to have lost their polarity. Their main question was: What is driving these differences and what in the cellular pathway is driving these differences? They realized that to answer these questions, they needed to culture cells in a condition which cells could be in 'spatial' organization.

They knew that with the classic tissue culture models – the standard monolayer tissue cultures – they would not be able to manipulate their cells and observe tumorigenic behavior. Dr. Brugge, inspired by cell culture model of epithelial ‘acini' done by H. Kleinman and M. Bissel, started to work with epithelial cells because they had similar behavior and organization to mammary cells. That is also when she decided that she wanted to work with 3-D cells to analyze alterations of cellular behavior. She observed that the MCF-10A cell line was the best-suited cell to study this behavior because this cell line had properties such as growth arrest, basal polarity, and hollow lumen.

They studied the morphogenesis of these epithelial cells and found – through three-dimensional assays – that the cells underwent a morphological switch in a few days, and there was no orientation of the Golgi relative to the nuclei. But after a few more days (about 4 to 5 days in culture), the outer cells, in particular, developed an access of apicobasal polarity. Basically, there was no polarization in the inner cells, but in the outer cells were polarized. They also learned more specific details in the EGF (epidermal growth factor). They proposed that because there was no integration of inner cells and no secretion of extracellular matrix proteins in the inner cells, these cells were deprived of proliferation and survival signals that were activated by EGF, and that created a 'proliferation arrest'. Inner cells then underwent apoptosis, consequently creating a hollow lumen. This finding would not be possible without three-dimensional models for the analysis of tumorigenic behavior and apicobasal polarity. These findings show the importance of the study of lipids, proteins, and membrane structures, which is what we covered in biochemistry lectures.

In our lectures, we covered the principles of integral membrane proteins, for example. We covered that these proteins span the entire membrane they are asymmetric. We also studied sphingolipids which are predominantly hydrophobic transmembrane segments, with amino acid clusters at non-polar/polar interfaces. We also studied the physical properties of membranes and their flexible and dynamic structures.

The study of membranes, proteins, lipids, help biochemists to understand membrane conformations which can lead to a better understanding of function. Like Dr. Brugge and her study in outer cell polarization, she could not have studied these structures without crucial knowledge in membrane structures and how polarity changes conformation, which leads to a change in function. Membranes define the boundaries of cells and their organelles such as nuclei and Golgi, as mentioned by Dr. Brugge. In our lecture, we learned that membranes provide compartmentalization within the cell, keeping proteolytic enzymes away from important cellular proteins. For example, in Dr. Brugee's research, she observed how protein synthesis in inner cells affects cell structure, making it hollow or not. They realized that proteins that were not being secreted in the extracellular matrix of inner cells were causing inner cells to undergo cell death, and cells to become hollow.

That demonstrates the importance of proteomics – the study of proteins – that we also covered in class. We studied in our lecture that the proteome consists of all proteins expressed in a cell during a specific state and that the proteome is dynamic and diverse. We also learned that the proteome depends on cell type, developmental stage, environment/stimuli, as well as metabolic status. If proteome is not well studied, research like Dr. Brugge's would not have such marvelous findings. Previous studies of proteome and cell cycles can help researchers in the development of even better technologies for cancer research, as well as further findings of the biochemistry of cancers. Dr. Brugge's research is innovative and superb. It creates an even more exciting future for cancer research.

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