Fig 1. Staining of keratin 6B (green) with tubules (red) and DNA (blue) in U2 OS cells.

Fig 2. Summary of differential expression of keratin 13 (KRT13) in cancers from pathologist scored tissue samples on the Human Protein Atlas.

It's time for another HPA image of the week! This week's image was brought to us by citizen scientists in Project Discovery, and specifically by Altytwo Altryness who found this image playing Project Discovery and correctly identified the antibody as labeling intermediate filaments and displaying cell to cell variability.

The protein labeled in Fig 1. is an image of keratin 6B, type II (KRT6B) in U-2 OS cells, human epithelial osteosarcoma, which is the reference cell line for the HPA.

Keratin is a well known intermediate filament protein that form filaments roughly 10nm in diameter. Most famously found in your hair and nails Keratin even makes up a key part of many animal horns. **This should not be confused with carotene, the hydrocarbon in carrots and pumpkins that makes them orange.

There are a number of reasons keratin may show cell-to-cell variability. Keratin proteins are known to respond to cell stresses, including mechanical stress (Russell et al. 2004). Additionally, keratins are implicated in cellular differentiation, polarization, motility, cell size, protein synthesis and membrane traffic and signaling (Karantza V. 2011). More testing would be required to determine what the major contributor to the variability is in this case.

There are roughly 54 known keratin proteins in your cells, and they play a key role in protecting your cells from stressors. Although there are many diseases associated with various keratin proteins, one disease related to keratin 6B specifically is the hereditary disease known as pachyonychia congenita in which a person's nails become very thick, and blisters can form on the soles of the feet making walking difficult (McLean et al. 1995).

Keratin is frequently used as a diagnostic tool in cancers as many cancers show characteristic expression patterns of keratin (Karantza V. 2011). Information regarding the differential expression of a protein can be seen on the atlas as well. Though keratin 6B is not publicly on the atlas yet, another keratin protein, keratin 13 (KRT 13) is clearly differentially expressed in a number of cancers, particularly skin cancer as seen in Fig 2. This incredible feature of the atlas is definitely worth checking out, so have fun exploring the various tissue samples visible under the previous link.

We would like to again thank Altytwo Altryness and all the citizen scientists participating in Project Discovery for their contribution to science!