Reduced expression of lamin A/C results in modified cell signaling and metabolism coupled with changes in expression...

Nuclear lamins are intermediate filament proteins that define the shape and stability of nuclei in mammalian cells. In addition to this dominant structural role, recent studies have suggested that the lamin proteins also regulate fundamental aspects of nuclear function. In order to understand different roles played by lamin proteins, we used RNA interference to generate a series of HeLa cell lines to study loss-of-function phenotypes associated with depletion of lamin protein expression. In this study, we used genome-wide proteomic approaches to monitor global changes in protein expression in cells with <10% of normal lamin A/C expression. Of approximately 2000 protein spots analyzed by two-dimensional electrophoresis, only 38 showed significantly altered expression in lamin A/C depleted cells. Of these, 4 protein spots were up-regulated, and 34 were down-regulated. Significant changes were seen to involve the general reduction in expression of cytoskeletal proteins, consistent with altered functionality of the structural cellular networks. At the same time, alterations in expression of proteins involved in cellular metabolism correlated with altered patterns of metabolic activity. In order to link these two features, we used antibody microarrays to perform a focused analysis of expression of cell cycle regulatory proteins. This confirmed a general reduction in expression of proteins regulating cell cycle progression and alteration in signaling pathways that regulate the metabolic activity of cells. The cross-talk between signal transduction and the cytoskeleton emphasizes how structural and kinase-based networks are integrated in mammalian cells to fine-tune metabolic responses.