Functional PAK-2 knockout and replacement with a caspase cleavage-deficient mutant in mice reveals differential requirements of full-length PAK-2 and caspase-activated PAK-2p34

Abstract

p21-Activated protein kinase 2 (PAK-2) has both anti- and pro-apoptotic functions depending on its mechanism of activation. Activation of full-length PAK-2 by the monomeric GTPases Cdc42 or Rac stimulates cell survival, whereas caspase activation of PAK-2 to the PAK-2p34 fragment is involved in the apoptotic response. In this study we use functional knockout of PAK-2 and gene replacement with the caspase cleavage-deficient PAK-2D212N mutant to differentiate the biological functions of full-length PAK-2 and caspase-activated PAK-2p34. Knockout of PAK-2 results in embryonic lethality at early stages before organ development, whereas replacement with the caspase cleavage-deficient PAK-2D212N results in viable and healthy mice, indicating that early embryonic lethality is caused by deficiency of full-length PAK-2 rather than lack of caspase activation to the PAK-2p34 fragment. However, deficiency of caspase activation of PAK-2 decreased spontaneous cell death of primary mouse embryonic fibroblasts and increased cell growth at high cell density. In contrast, stress-induced cell death by treatment with the anti-cancer drug cisplatin was not reduced by deficiency of caspase activation of PAK-2, but switched from an apoptotic to a nonapoptotic, caspase-independent mechanism. Homozygous PAK-2D212N primary mouse embryonic fibroblasts that lack the ability to generate the proapoptotic PAK-2p34 show less activation of the effector caspase 3, 6, and 7, indicating that caspase activation of PAK-2 amplifies the apoptotic response through a positive feedback loop resulting in more activation of effector caspases.

Proapoptotic Effects of the Chemokine, CXCL 10 Are Mediated by the Noncognate Receptor TLR4 in Hepatocytes

“…Recently, blocking of JNK has been identified to inhibit the CXCL10‐induced cleavage of caspase‐3 and PAK‐2 in β‐cells,24 suggesting that JNK is an upstream mediator of caspase‐3 and PAK‐2. Interestingly, CXCL10 also induced prolonged Akt and JNK activation in caspase‐8‐deficient hepatocytes, but did not affect the activity of the proapoptotic factors, caspase‐3 and PAK‐2p34, confirming that caspase‐8 is an upstream protease involved in caspase‐3 and PAK‐2 cleavage32 in response to CXCL10.…”

Dual Site Phosphorylation of Caspase-7 by PAK2 Blocks Apoptotic Activity by Two Distinct Mechanisms

“…Interestingly, PAK2 plays a dual role in the context of apoptosis: active full-length PAK2 stimulates cell survival (Jakobi et al, 2001; Marlin et al, 2009) while cleavage of the autoinhibitory domain results in propagation of the pro-apoptotic response (Lee et al, 1997; Rudel and Bokoch, 1997). This duality is dictated by the relationship of PAK2 with caspase cleavage (Marlin et al, 2011). PAK2 is cleaved by the executioner caspase-3 at D212, which separates the PAK2 kinase domain and autoinhibitory domains (Walter et al, 1998).…”

Prostasin may contribute to chemoresistance, repress cancer cells in ovarian cancer, and is involved in the signaling pathways of CASP/PAK2-p34/actin

“…22 Recombinant expression of PAK-2p34 induced morphological changes characteristic of apoptotic cell death in a variety of cell lines and induced apoptotic cell death. 23, 24 In addition, accumulation of PAK2-p34 by ubiquitin inhibits degradation results in a dramatic increase in cell death. 25 Therefore, PAK2-p34 is involved in cellular death regulation and execution of programmed cell death, and caspase activation stimulated by apoptotic stimuli appears to turn the antiapoptotic activity of PAK2 into a proapoptotic activity of PAK2-p34.…”

“…Aberrant activity/level of PAK2 or PAK2-p34 has been linked with human cancer, Alzheimer's, and Parkinson's disease. 23 …”