What is normal? Part 1 of 2
Monday, January 5, 2015
We are going to start off 2015 with a bang! I asked my close friend and collaborator, Dr. Martha Stampfer, to write about anything that struck a chord with her, and she has written a multi part entry that explains the motivation for our recently published Cell Cycle paper. So here it goes, Martha uncensored part 1... - ML
Understanding what is an abnormal biological process assumes knowledge of what is normal, for comparison. Understanding the mechanisms by which a normal human epithelial cell transforms to malignancy requires knowing the state of the starting point – the normal human epithelial cell. If unquestionably abnormal cells are called “normal”, and used as normal controls for comparison to cancer cells, or as a starting point to investigate “early stage” carcinogenesis, significant errors can enter the literature.
I’ve worked on methods to grow normal human mammary epithelial cells (HMEC) since 1976, along with ways to transform these cells to immortality and malignancy. By normal, I mean cells taken from normal tissues that retain a normal genotype and are capable of phenotypic expression similar to normal HMEC in vivo. Obviously, growth in cell culture, 2D or even 3D, is not going to fully recapitulate normal in vivo behavior, or accurately represent whole body processes that influence cancer progression – future advances in microfluidic and chip-on-chip systems will hopefully improve in-vivo-like modeling. However, it’s still critical to use normal cells to study what is normal. Normal HMEC in vivo have a finite lifespan, intact RB and p53 pathways, and are vulnerable to oncogene-induced senescence (OIS). Multiple lineages (e.g., myoepithelial, luminal, progenitors) are present.
Unfortunately, I see the literature riddled with papers where highly abnormal cells, contrary to obvious biology, are called normal, “normal”, or untransformed. Most egregious is the extremely common tendency (found in top journals) of referring to immortally transformed cells, such as MCF10A, or hTERT immortalized HMEC, as normal or untransformed. Besides containing genomic/epigenomic errors, such cell lines have inactivated all the major tumor suppressor mechanisms present in normal HMEC (stasis, OIS, replicative senescence), so that a single additional error (e.g., an activated oncogene like Ras or erbB2) can confer malignant properties. There are many published papers showing how a variety of different single errors can malignantly transform immortal, non-malignant HMEC. However, in many cases, the immortally transformed cells are called normal or untransformed, and in most cases, the fact that the results obtained are completely dependent upon these highly aberrant cells having already inactivated the major tumor suppressor mechanisms - is not mentioned. But, similarly exposed normal cells would become senescent or die – that is the point of the elaborate tumor suppressor mechanisms that have evolved to prevent cancer in large long-lived organisms such as humans. If a single error could transform a normal human epithelial cell to malignancy, humanity wouldn't exist.
This widespread error serves to direct attention away from studying early stage carcinogenesis, and the process of immortalization. I’ve hypothesized for many years that immortalization (overcoming replicative senescence) is the rate-limiting step in human carcinoma progression, and possibly an excellent stage for therapeutic intervention to prevent cancer development. Our recent paper discusses this further, while presenting a method to facilitate interrogation of the HMEC immortalization process.
James C Garbe, Lukas Vrba, Klara Sputova, Laura Fuchs, Petr Novak, Arthur R Brothman, Mark Jackson, Koei Chin, Mark A LaBarge, George Watts, Bernard W Futscher & Martha R Stampfer
DOI:10.4161/15384101.2014.954456
