This week HPA image of the week, I've decided to highlight two of my favorite things, the cell cycle and actin filaments!

The protein labeled in Fig 1. is an image of Cell division cycle 42 effector protein (Rho GTPase binding) 4 (CDC42EP4). In addition to being quite a mouthful, this protein resides in the cytoplasm and is associated with the actin filaments. In this image, CDC42EP4 is seen in U-2 OS human osteosarcoma cells.

As the name suggests, the CDC42EP4 is a protein associated with CDC42, which helps regulate the transition from G1 to S (in which DNA is replicated), and is essential for proper cell cycle progression (Yasuda S et al. 2006).

This protein is associated with actin filaments inside the cell. Actin filaments are a dynamic network of microfilaments that regulate cellular structure, provide avenues for cellular transport, and are crucial for cellular motility and cell division (Mitchison TJ & Cramer LP 1996). These filaments run throughout the cytoplasm and consist of a backbone of actin monomers in a 7nm double helix filament whose assembly and organization is regulated through interactions with a number of actin binding proteins (Heng YW & Koh CG 2010).

Rho GTPases, to which CDC42EP4 binds, are responsible for regulating a number of activities in the cell including this cell cycle progression. As such this group of proteins is linked to cancer progression, mental disabilities and a number of other disorders (Boettner B & Van Aelst L 2002). Due to its role in disease, this group of proteins has been a target of drug treatments, such as Clostridium difficile toxin B which can cause cell cycle arrest in G2 (Ando Y et al. 2007).

This image provides only a brief insight into the importance of actin and actin binding proteins in your cells. For more, check out this excellent resource on all things actin.

A big thanks to all the members of the subcellular atlas team working to generate these images!

Devin Sullivan