Prostate-derived Sterile 20-like Kinase 2 (PSK2) Regulates Apoptotic Morphology via C-Jun N-terminal Kinase and Rho Kinase-1

Abstract

We have reported previously that human prostate-derived sterile 20-like kinase (PSK) 1 alters actin cytoskeletal organization and binds to microtubules, regulating their organization and stability. We have shown a structurally related protein kinase PSK2, which lacks a microtubule-binding site, activated c-Jun N-terminal kinase (JNK), and induced apoptotic morphological changes that include cell contraction, membrane blebbing, and apoptotic body formation. Apoptotic stimuli increased the catalytic activity of endogenous PSK2 and JNK, and dominant negative JNK or a physiological inhibitor of JNK blocked these apoptotic morphological responses to PSK2, demonstrating a requirement for JNK. PSK2 also stimulated the cleavage of Rho kinase-1 (ROCK-I), and the activity of ROCK-I was required for PSK2 to induce cell contraction and membrane blebbing. The activation of caspases was also needed for the induction of membrane blebbing by PSK2, which was itself a substrate for caspase 3. PSK2 therefore regulates apoptotic morphology associated with the execution phase of apoptosis, which involves dynamic reorganization of the actin cytoskeleton, via downstream targets that include JNK and ROCK-I. Our findings suggest that PSKs form a subgroup of sterile 20 (STE20)-like kinases that regulate different cytoskeletal processes.

Rho kinase in the regulation of cell death and survival

“…This caspase 3-mediated ROCK1 activation is both necessary and sufficient for the formation of membrane blebs through increasing MLC phosphorylation and actomyosin contraction [16,119]. The importance of this pathway in bleb formation was then confirmed by other studies in a variety of cell types, independent of apoptotic stimuli [23,70,86,104,127,155]. In addition, ROCK1-mediated blebbing facilitates cellular fragmentation and/or apoptotic cell clearance as discussed below.…”

“…Caspase 3 is believed to be responsible for activating ROCK1 in apoptotic cells, as evidenced by the absence of ROCK1 cleavage in caspase 3-deficient MCF-7 breast carcinoma cells and the presence of ROCK1 cleavage after restoring procaspase 3 expression [119]. In addition, ROCK1 cleavage by caspase 3 can be inhibited by caspase inhibitors in a variety of apoptotic cells [16,23,70,86,104,119,127,139,140,155]. However, caspase 3-independent cleavage of ROCK1 was observed in extracellular ATP-induced and P2X7 ATP receptor-mediated apoptosis [91] and in cancer cells subjected to combined BGC9331 (a thymidylate synthase inhibitor) and SN-38 (a topoisomerase I inhibitor) treatment [17].…”

Revival of apoptotic cells that display early‐stage dynamic membrane blebbing

“…cFLIP, IAP, and Bcl-2 do not contribute to the revival of apoptotic cells and to the decrease of activated caspase 3 after 2DED2DD induction. Immunoblot analysis was performed using extracts of 2DED2DD-stably transfected cells 2,4,6,8,12,24, and 48 h after tetracycline induction. Extracts from cells cultured without tetracycline are also shown.…”

Prostate-derived Sterile 20-like Kinases (PSKs/TAOKs) Phosphorylate Tau Protein and Are Activated in Tangle-bearing Neurons in Alzheimer Disease

“…Plasmids and Reagents-pRK5-Myc PSK1-␣/␤(1-349) (catalytically active), pRK5-Myc-PSK1-␣/␤(1-349) (K57A; kinasedeficient mutant), pRK5-Myc-PSK2(1-416) (catalytically active), and pRK5-Myc-PSK2(1-416) (K57A; kinase-deficient mutant) were made using methods described previously (7)(8)(9). pcDNA3.1-human tau was obtained from Prof. B. Anderton (King's College London).…”

“…Six p21-activated kinases, which have a C-terminal catalytic domain and an N-terminal Cdc42/Rac-interacting and -binding domain, and 22 germinal center kinase-like kinases, which possess an N-terminal kinase domain but no Cdc42/Rac-interacting and -binding domain (4 -6). Prostate-derived STE20-like kinases (PSKs; also referred to as thousand and one amino acid kinases) have been classified as members of the germinal center kinase VIII subfamily of STE20 kinases and include PSK1-␣ and PSK1-␤ (splice variants with identical N-terminal kinase domains; TAOK2 isoforms 2 and 1, respectively), PSK2 (TAOK1), and PSK3 (TAOK3) (2,(7)(8)(9)(10). Most STE20s activate one or more mitogen-activated protein kinase (MAPK) signaling pathways, and PSK1-␣ or PSK2 can stimulate c-Jun N-terminal kinase (JNK) and p38 MAPK (7-9, 11, 12).…”