Talin1 phosphorylation activates β1 integrins: a novel mechanism to promote prostate cancer bone metastasis

Abstract

Talins are adaptor proteins that regulate focal adhesion signaling by conjugating integrins to the cytoskeleton. Talins directly bind integrins and are essential for integrin activation. We previously showed that β1 integrins are activated in metastatic prostate cancer (PCa) cells, increasing PCa metastasis to lymph nodes and bone. However, how β1 integrins are activated in PCa cells is unknown. In this study, we identified a novel mechanism of β1 integrin activation. Using knockdown experiments, we first demonstrated talin1, but not talin2, is important in β1 integrin activation. We next showed that talin1 S425 phosphorylation, but not total talin1 expression, correlates with metastatic potential of PCa cells. Expressing a non-phosphorylatable mutant, talin1S425A, in talin1-silenced PC3-MM2 and C4-2B4 PCa cells, decreased activation of β1 integrins, integrin-mediated adhesion, motility, and increased the sensitivity of the cells to anoikis. In contrast, re-expression of the phosphorylation-mimicking mutant talin1S425D led to increased β1 integrin activation and generated biologic effects opposite to talin1S425A expression. In the highly metastatic PC3-MM2 cells, expression of a non-phosphorylatable mutant, talin1S425A, in talin1-silenced PC3-MM2 cells, abolished their ability to colonize in the bone following intracardiac injection, while re-expression of phosphorylation-mimicking mutant talin1S425D restored their ability to metastasize to bone. Immunohistochemical staining demonstrated that talin S425 phosphorylation is significantly increased in human bone metastases when compared to normal tissues, primary tumors, or lymph node metastases. We further showed that p35 expression, an activator of Cdk5, and Cdk5 activity were increased in metastatic tumor cells, and that Cdk5 kinase activity is responsible for talin1 phosphorylation and subsequent β1 integrin activation. Together, our study reveals Cdk5-mediated phosphorylation of talin1 leading to β1 integrin activation is a novel mechanism that increases metastatic potential of PCa cells.

The tale of two talins – two isoforms to fine‐tune integrin signalling

“…Phosphorylation of S446 is believed to be important in the regulation of the calpain cleavage between the head and the rod domain and is important for regulating FA turnover 71, 117, a process that has recently been shown to be essential for adhesion development and rigidity sensing 118. In addition, S425, which is also in the linker, is phosphorylated by CDK5, and this phosphorylation has been shown to enhance talin activity and increase integrin activation 119.…”

β1 and β3 integrins in breast, prostate and pancreatic cancer: A novel implication (Review)

“…However, when combined with their ligands, this integrin promotes the survival of cancer cells by activating different cell signaling proteins, including phosphoinositide 3-kinase/RAC-α serine/threonine protein kinase (AKT), FAKs and SFKs (1,13). While in certain tumors, β1 integrin may also induce anoikis resistance of cancer cells in suspension by phosphorylating FAKs and AKT (14,15). Additionally, β1 integrin may promote the proliferation of cells by phosphorylating FAKs and regulating SRC/mitogen-activated protein kinase (MAPK) to facilitate the expression of v-myc avian myelocytomatosis viral oncogene homolog (c-Myc) and cyclin D1 in cancer cells (16,17).…”

Cadherin-11 endocytosis through binding to clathrin promotes cadherin-11-mediated migration in prostate cancer cells

“…Endocytosis of adhesion proteins has been shown to play a role in the disassembly of adhesion complexes (Alarcos et al, 2015;Bockus et al, 2015;Jin et al, 2015;Kowalczyk and Nanes, 2012;Mosesson et al, 2008;Xiao et al, 2005); however, the mechanism by which Cad11 is internalized is unknown. In this study, we identified proteins that interact with the cytoplasmic domain of Cad11 and found that clathrin is one of the Cad11-interacting proteins.…”