The researchers describe that CPEB1 shortens a highly specific region of RNAs (RNAs are the molecules that carry gene information for protein synthesis). This region holds most of the signals that determine whether an RNA molecule is made into a protein or not. "CPEB1 "takes off the brakes" for hundreds of RNAs that stimulate cell desdifferentiation and proliferation, allowing them to be made into proteins; however, in addition to removing the brakes in the nucleus, this protein accompanies RNA to the cytoplasm, where it speeds up the production of these proteins", explains the senior author of the paper Raúl Méndez, head of the "Translational control of cell cycle and differentiation" group at IRB Barcelona.
Raúl Méndez is an expert on the CPBE protein family, a type of RNA-binding protein that has a positive and crucial role in early embryo development. "CPEB proteins are necessary during development and also during tissue regeneration via stem cells in adults, but if the programme governed by CPEBs is continually switched on, cells divide when they are not supposed to and form a tumor", explains Méndez. The CPEB family comprises four proteins, which compensate each other's normal function but which have specific activities in diseased states.
"This finding is positive from a therapeutic viewpoint because it means that if you remove CPEB1 from healthy cells, its function can be taken over by any other CPEB protein. In contrast, in tumors only CPEB1 has the capacity to shorten these regions, thus affecting only tumor cells", states Italian researcher Felice Alessio Bava, first author of the paper, and post-doctoral fellow with Méndez's group who, this year, has obtained his doctorate degree through the "la Caixa" International Fellowship Programme. This study provides further evidence of the potential of CPEB proteins as therapeutic targets.
In 2011, in a study published in Nature
Medicine, Méndez identified that CPEB4 "switches on" hundreds of genes linked to tumor growth. This new study explains that the overexpression of CPEB4 in tumors is because CPEB1 has also "released the brakes that keep CPEB4 at low levels in a healthy tissue". "The fact that these proteins control each other is also advantageous from a therapeutic point of view", asserts Méndez, "because partial inhibition, by a drug, would be amplified, thus allowing tumor cell reprogramming. The amplification should make it easier to find a viable compound".