Protein tyrosine kinase-6 is post-translationally regulated by arginine methylation and ubiquitination.

Protein tyrosine kinase 6 (PTK6) has context-specific, kinase-dependent and -independent functions in normal cells and cancer. In prostate cells, nuclear PTK6 suppresses growth, while active membrane-associated PTK6 promotes oncogenic signaling. Unlike SRC-family kinases, PTK6 is not modified by lipidation to promote membrane association. Although arginine residues in the PTK6 SH2 domain were previously linked to lipid binding, we found they are instead critical for protein stability and arginine methylation. Mutation of R131/R136 or R132 impaired PTK6 ubiquitination and its association with a Cullin-1-RING ubiquitin ligase complex, and its half-life increased from one hour to over 24 h. We show that PTK6 is targeted by PRMT1 and mutation of PTK6 R131/R136 or R132, or treatment with the type 1 PRMT inhibitor GSK3368715, leads to decreased arginine methylation, increased PTK6 protein stability and impaired PTK6 association with its substrates. In prostate cancer cells, ectopic expression of mutant PTK6 R131/R136 or R132 leads to reduced proliferation, anchorage-independent growth, and cell migration and invasion, when compared with wild type PTK6, even though higher levels of mutant protein are expressed. These results indicate that arginine methylation is a key regulatory switch for PTK6 signaling and protein turnover and may be central for the execution of its diverse context-specific functions. Mutation of PTK6 arginine residues has been reported in some cancers, which may contribute to disease-specific PTK6 expression and signaling.