Integrin-linked kinase (ILK) and p38(MAPK) are protein kinases that transduce extracellular signals regulating cell migration and actin cytoskeletal organization. ILK-dependent regulation of p38(MAPK) is critical for mammalian kidney development and in smooth muscle cell migration, however, specific p38 isoforms has not been previously examined in ILK-regulated responses. Signaling by ILK and p38(MAPK) is often dysregulated in bladder cancer, and here we report a strong positive correlation between protein levels of ILK and p38beta, which is the predominant isoform found in bladder cancer cells, as well as in patient-matched normal bladder and tumor samples. Knockdown by RNA interference of either p38beta or ILK disrupts serum-induced, Rac1-dependent migration and actin cytoskeletal organization in bladder cancer cells. Surprisingly, ILK knockdown causes the selective reduction in p38beta cellular protein level, without inhibiting p38beta messenger RNA (mRNA) expression. The loss of p38beta protein in ILK-depleted cells is partially rescued by the 26S proteasomal inhibitor MG132. Using co-precipitation and bimolecular fluorescent complementation assays, we find that ILK selectively forms cytoplasmic complexes with p38beta. In situ proximity ligation assays further demonstrate that serum-stimulated assembly of endogenous ILK-p38beta complexes is sensitive to QLT-0267, a small molecule ILK kinase inhibitor. Finally, inhibition of ILK reduces the amplitude and period of serum-induced activation of heat shock protein 27 (Hsp27), a target of p38beta implicated in actin cytoskeletal reorganization. Our work identifies Hsp27 as a novel target of ILK-p38beta signaling complexes, playing a key role in bladder cancer cell migration.Oncogene advance online publication, 25 February 2013; doi:10.1038/onc.2013.20.
Yu, L., Yuan, X., Wang, D., Barakat, B. M., Williams, E., & Hannigan, G. (2014). Selective regulation of p38beta protein and signaling by integrin-linked kinase mediates bladder cancer cell migration. Oncogene, 33(6), 690 - 701. https://doi.org/10.1038/onc.2013.20