Abstract 2424: TLK1-MK5 axis modulates actin filaments and focal adhesion components to promote PCa cell migration and invasion
Authors: Khalil Md Imtiaz , Singh Vibha , King Judy A. , De Benedetti Arrigo 
Published: June 2022

Abstract
Background: Metastatic dissemination of prostate cancer (PCa) accounts for 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), which 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. Moreover, TCGA analysis also revealed higher expression of both TLK1 and MK5 in metastatic tumors. Therefore, we hypothesize that TLK1-MK5 axis promotes PCa cell migration and invasion through actin reorganization as well as focal adhesion proteins modification and disruption of this interaction may help to keep the tumor localized.
Methods and Results: We conducted scratch wound repair and proliferation assays to determine if TLK1 and MK5 can regulate motility and proliferation. Both genetic depletion and pharmacologic inhibition of TLK1 and MK5 resulted in reduced migration of both non-malignant MEF and PCa cells without affecting cellular proliferation rate. Trans-well invasion assays also demonstrated reduced invasion of MK5−/− MEF cells in Matrigel and other ECMs. However, TLK1 overexpression alone in the MK5−/− MEF cells did not increase the wound healing and invasion which suggested that TLK1 cannot enhance cellular migration and invasion in absence of MK5. We confirmed TLK1 binding of MK5 by co-IP, His- and GST-pull down assays and established that TLK1 phosphorylates MK5 on three residues (S160, S354, S386) that results in the catalytic activation of MK5. While WB detected substantial amount of pMK5 S354 and TLK1 in all major PCa cell lines, anti-androgen treatment increases pMK5 S354 level in a dose-dependent manner and pharmacologic inhibition of TLK1 reduces pMK5 S354 level in LNCaP cells, which suggest TLK1 as an authentic pMK5 S354 kinase. IHC analysis of TRAMP mice and human PCa TMA also revealed higher pMK5 S354 level in metastatic lesions compared to the low-risk tumors. In addition, pMK5 S354 was found to colocalize with neuroendocrine marker chromogranin A, together of which may suggest pMK5 as a potential biomarker of PCa aggressiveness. The motility reduction of PCa cells upon MK5 inhibition is a consequence of impaired actin filamentation as we observed in LNCaP and PC3 cells. Our WB analysis demonstrated that MK5 inhibition by a repurposed inhibitor results in decreased FAK Y861, Paxillin Y118, HSP27 S78/82 phosphorylation, and ERK3 stabilization, which could lead to altered actin filamentation, focal adhesions, morphology, as well as motility and invasion.
Conclusion: Our data support that TLK1-MK5 axis is involved in driving PCa cell metastasis and clinical aggressiveness, hence, disruption of this axis may inhibit the metastasis of PCa.
Citation Format: Md Imtiaz Khalil, Vibha Singh, Judy A. King, Arrigo De Benedetti. TLK1-MK5 axis modulates actin filaments and focal adhesion components to promote PCa cell migration and invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2424.