Title: ``Tissue Arrays and Protein Arrays: New Methods, New Challenges''
Speaker: Stephen M. Hewitt, MD, PhD
Place: Stanley Coulter (SC) 239; Tuesday, 4:30pm


Tissue arrays and protein arrays are new high throughput platforms to study protein expression within cells and tissue. Both methods allow an investigator to combine tens to hundreds of different samples onto a single platform, and probe them with antibodies against specific proteins. In the case of a tissue array, this is a microscope slide, and for a protein array the samples are arrayed out as dots on a membrane or glass slide. Traditionally, immunohistochemistry has been performed on tissue and western blots of protein extracts, which yields detailed, but low volumes of data. These new platforms are not without their limitations, but have revolutionized the understanding of the proteome. No longer is the goal a detailed understanding of a single cell line or tumor, rather an understanding of biologic processes by examining and comparing multiple independent samples.

With these new methods, come new challenges. The interaction of proteins in cellular processes has traditionally been described as activation and repression, lacking any concept of quantification. However, it is now possible to profile a large number of samples for many proteins at one time and ask questions about signal propagation and signal amplitude. New antibodies against phosphorylated proteins are now available, allowing investigation of activated levels of proteins, rather than just their mere presence. This puts thousands of pieces in the hands of the investigator.

As an example, we have profiled the Akt signaling cascade on a multi-tumor tissue array platform and characterized different patterns of signal propagation in different tumor types. Analysis relied on traditional statistical approaches, which are not easily interpreted by biologist. These new methodologies offer a new set of tools to understand biology at a level that has not been possible in the past. With this new wealth of data, new methods of analysis are essential.