The TLK1–MK5 Axis Regulates Motility, Invasion, and Metastasis of Prostate Cancer Cells

SIMPLE SUMMARY: Recent work by us and others have illustrated the critical importance of MK5/PRAK in the invasive and motility properties of several cancer cell lines and some mouse models. In our earlier work, we also uncovered that TLK1 modulates the activity of MK5 by phosphorylating S354 and two additional sites (S160 and S386). We have now expanded on the possible mechanisms of the TLK1 > MK5 axis mediated pro-motility and invasive activity and report that this may be due to reorganization of the actin fibers at lamellipodia and the focal adhesions network, in conjunction with increased expression of some MMPs. Pharmacological or genetic manipulation of prostate cancer (PCa) cell lines, LNCaP and PC3, results in drastic loss of in vitro motility and invasive capacity of these cells concomitant with alterations of their general morphology and reorganization of the focal adhesions distribution. In addition, PC3 used in tail-vein experimental metastases studies shows that the use of GLPG0259 (MK5 inhibitor) or J54 (TLK1 inhibitor) results in a drastic reduction of metastatic lung nodules, both macroscopically and histologically. ABSTRACT: Background: Metastatic dissemination of prostate cancer (PCa) accounts for the majority of PCa-related deaths. However, the exact mechanism of PCa cell spread is still unknown. We uncovered a novel interaction between two unrelated promotility factors, tousled-like kinase 1 (TLK1) and MAPK-activated protein kinase 5 (MK5), that initiates a signaling cascade promoting metastasis. In PCa, TLK1–MK5 signaling might be crucial, as androgen deprivation therapy (ADT) leads to increased expression of both TLK1 and MK5 in metastatic patients, but in this work, we directly investigated the motility, invasive, and metastatic capacity of PCa cells following impairment of the TLK1 > MK5 axis. Results: We conducted scratch wound repair and transwell invasion assays with LNCaP and PC3 cells to determine if TLK1 and MK5 can regulate motility and invasion. Both genetic depletion and pharmacologic inhibition of TLK1 and MK5 resulted in reduced migration and invasion through a Matrigel plug. We further elucidated the potential mechanisms underlying these effects and found that this is likely due to the reorganization of the actin fibers at lamellipodia and the focal adhesions network, in conjunction with increased expression of some MMPs that can affect penetration through the ECM. PC3, a highly metastatic cell line when assayed in xenografts, was further tested in a tail-vein injection/lung metastasis model, and we showed that, following inoculation, treatment with GLPG0259 (MK5 specific inhibitor) or J54 (TLK1 inhibitor) resulted in the lung tumor nodules being greatly diminished in number, and for J54, also in size. Conclusion: Our data support that the TLK1–MK5 axis is functionally involved in driving PCa cell metastasis and clinical aggressiveness; hence, disruption of this axis may inhibit the metastatic capacity of PCa.