Proteins that bind A-type lamins: integrating isolated clues.

What do such diverse molecules as DNA, actin, retinoblastoma protein and protein kinase Calpha all have in common? They and additional partners bind 'A-type' lamins, which form stable filaments in animal cell nuclei. Mutations in A-type lamins cause a bewildering range of tissue-specific diseases, termed 'laminopathies', including Emery-Dreifuss muscular dystrophy and the devastating Hutchinson-Gilford progeria syndrome, which mimics premature aging. Considered individually and collectively, partners for A-type lamins form four loose groups: architectural partners, chromatin partners, gene-regulatory partners and signaling partners. We describe 16 partners in detail, summarize their binding sites in A-type lamins, and sketch portraits of ternary complexes and functional pathways that might depend on lamins in vivo. On the basis of our limited current knowledge, we propose lamin-associated complexes with multiple components relevant to nuclear structure (e.g. emerin, nesprin 1alpha, actin) or signaling and gene regulation (e.g. LAP2alpha, retinoblastoma, E2F-DP heterodimers, genes) as 'food for thought'. Testing these ideas will deepen our understanding of nuclear function and human disease.