Interphase phosphorylation of lamin A

Abstract

Nuclear lamins form the major structural elements comprising the nuclear lamina. While loss of nuclear structural integrity has been implicated as a key factor in the lamin A gene mutations causing laminopathies, the normal regulation of lamin A/C (LA/C) assembly and organization in interphase cells is still undefined. We assumed phosphorylation to be a major determinant, identifying 21 prime interphase phosphorylation sites, with 8 high turnover sites. The roles of these latter sites were examined by site-directed mutagenesis, followed by detailed microscopic analysis, including fluorescence recovery after photobleaching, fluorescence correlation spectroscopy, and nuclear extraction techniques. Results reveal three phosphorylation regions, each with dominant sites, together controlling LA/C structure and dynamics. Interestingly, two of these interphase sites are hyperphosphorylated in mitotic cells and one is within the sequence missing in progerin of the Hutchinson Gilford Progeria Syndrome. A model is presented where different phosphorylation combinations will yield markedly different effects on the assembly, subunit turnover, and mobility of LA/C between and within the lamina, the nucleoplasm, and the cytoplasm of interphase cells.