Stress-induced release of Oct-1 from the nuclear envelope is mediated by JNK phosphorylation of lamin B1.

The nuclear lamina can bind and sequester transcription factors (TFs), a function lost if the lamina is abnormal, with missing or mutant lamin proteins. We now show that TF sequestration is not all-or-nothing, but a dynamic physiological response to external signals. We show that the binding of the ubiquitous TF, Oct-1, to lamin B1 was reversed under conditions of cellular stress caused, inter alia, by the chemical methylating agent methylmethanesulfonate (MMS). A search for lamin B1 post-translational modifications that might mediate changes in Oct-1 binding using kinase inhibitors uncovered a role for c-Jun N-terminal kinase (JNK). Phosphoproteomic and site-directed mutagenesis analyses of lamin B1 isolated from control and MMS-treated nuclei identified T575 as a JNK site phosphorylated after stress. A new phospho-T575 specific anti-peptide antibody confirmed increased interphase cellular T575 phosphorylation after cell exposure to certain stress conditions, enabling us to conclude that lamin B1 acts as an interphase kinase target, releasing Oct-1 to execute a protective response to stress.

Mutations in the gene for the E1beta subunit: a novel cause of pyruvate dehydrogenase deficiency.

We describe two unrelated patients with pyruvate dehydrogenase (PDH) deficiency attributable to mutations in the gene encoding the E1beta subunit of the complex. This is a previously unrecognised form of PDH deficiency, which most commonly results from mutations in the X-linked gene for the E1alpha subunit. Both patients had reduced immunoreactive E1beta protein and both had missense mutations in the E1beta gene. Activity of the PDH complex was restored in cultured fibroblasts from both patients by transfection and expression of the normal E1beta coding sequence.