The protein kinase Akt/PKB regulates both prelamin A degradation and Lmna gene expression

The serine/threonine kinase Akt/PKB is a major signaling hub integrating metabolic, survival, growth and cell cycle regulatory signals. The definition of the phospho-motif cipher driving phosphorylation by Akt led to the identification of hundreds of putative substrates, and it is therefore pivotal to name those whose phosphorylation by Akt is of consequence to biological processes. The Lmna gene products lamin A/C and their precursor prelamin A (collectively called A-type lamins) are type V intermediate filaments proteins forming a filamentous meshwork, the lamina, underneath the inner nuclear membrane, for nuclear envelope structures organization and interphase chromatin anchoring. In our previous work we reported that A-type lamins are phosphorylated by Akt at S301 and S404 in physiological conditions, and are therefore bona fide substrates of Akt. We describe here that Akt phosphorylation at S404 targets the precursor prelamin A for degradation. We further demonstrate that Akt regulates also Lmna transcription. All together, our study unveils a previously unknown function of Akt in the control of prelamin A stability and expression. Moreover, given the large number of diseases related to prelamin A, our findings represent a further important step bridging basic A-type lamins physiology to therapeutic approaches for lamin A-linked disorders.