Protective role for lipid modifications of Src-family kinases against chromosome missegregation

Abstract

Src-family tyrosine kinases, which are expressed in various cell types, play critical roles in cell signalling at the cytoplasmic side of the plasma membrane through their lipid modifications. Src-family kinases are cotranslationally myristoylated and posttranslationally palmitoylated in the amino-terminal region. The Src-family member Lyn contains a myristoylation site at glycine-2 and a palmitoylation site at cysteine-3, whereas c-Src has a myristoylation site at glycine-2 but not any palmitoylation sites. However, little is known about the role for lipid modifications of Src-family kinases in cell division. Here, we show that non-lipid-modified Lyn and c-Src, Lyn(G2A/C3A) and c-Src(G2A), are delocalized from membranes to the cytoplasm and the nucleus, which gives rise to a significant increase in the rate of chromosome missegregation, such as chromosome lagging and anaphase chromosome bridging, in a tyrosine kinase activity-dependent manner. Treatment with the Src inhibitor PP2 shows that the kinase activity of non-lipid-modified, non-membrane-bound Src during M phase is critical for giving rise to chromosome missegregation. Given that only a fraction of Src-family kinases fails in lipid modifications during biosynthesis, these results suggest that Src’s membrane anchorage through their lipid modifications from prophase to anaphase plays a protective role against induction of chromosome missegregation.

The tyrosine kinase v-Src causes mitotic slippage by phosphorylating an inhibitory tyrosine residue of Cdk1

“…Cells exhibit chromosome instability through abnormal chromosome segregation in the next cell cycle of tetraploid cells. v-Src-induced chromosome bridge formation also contributes to the chromosome instability (7,25,44). The chromosome instability generates genetic diversity, and cells capable of adapting to growth-suppressive conditions by anti-cancer drugs or cells gaining metastatic ability can be selected (7).…”

v-Src-driven transformation is due to chromosome abnormalities but not Src-mediated growth signaling

“…To synchronize cells at the G 1 /S boundary, a double thymidine block was performed as described 20 , 38 , 39 . In brief, cells treated with 4 mM thymidine for 16 h were incubated in thymidine-free complete medium for 9 h, and the cells were further treated with 4 mM thymidine for 16 h.…”

“…Cell lysates were prepared in SDS-sample buffer were separated by SDS-PAGE and electrotransferred onto polyvinylidene difluoride membranes (PVDF, Millipore). Immunodetection was performed as reported previously 20 , 34 , 36 , 43 . Sequential reprobing of membranes with a variety of antibodies was performed after the complete removal of primary and secondary antibodies from membranes in stripping buffer or inactivation of horseradish peroxidase by 0.1% NaN 3 , according to the manufacturer’s instructions.…”

Nutrient-Dependent Changes of Protein Palmitoylation: Impact on Nuclear Enzymes and Regulation of Gene Expression

“…The authors found that, upon palmitoylation, Rif1 reduced the silencing of chromatin by competing with Silent Information Regulator/Repressor Activator Protein 1 (SIR/RAP1) complex for telomeric DNA binding. Thereby, Rif1palmitoylation may influence telomere anchoring, nuclear organization, and heterochromatin silencing [91]. Collectively, experimental evidence indicates that protein palmitoylation can be modulated by metabolic signals and may represent a novel mechanism regulating chromatin structure and gene expression.…”