Protein Phosphatase 4 Is a Positive Regulator of Hematopoietic Progenitor Kinase 1

Guisheng Zhou,Jonathan S Boomer,Tse-Hua Tan

doi:10.1074/jbc.m410317200

Guisheng Zhou, Jonathan S Boomer + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m410317200

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Abstract

Hematopoietic progenitor kinase 1 (HPK1) is a hematopoietic specific mammalian Ste20-like protein kinase and has been implicated in many cellular signaling pathways including T cell receptor (TCR) signaling. However, little is known about the in vivo regulation of HPK1. We present evidence that HPK1 is positively regulated by protein phosphatase 4 (PP4; also called PPX and PPP4), a serine/threonine phosphatase. We found that PP4 interacted with HPK1 and that the proline-rich region of HPK1 was necessary and sufficient for this interaction. We also found that PP4 had phosphatase activity toward HPK1 in vivo and that co-transfection of PP4 with HPK1 resulted in specific kinase activation of HPK1. Moreover, we found that the PP4-induced HPK1 kinase activation was accompanied by an increase in protein expression of HPK1. Pulse-chase analysis showed that PP4 increased the half-life of HPK1. Further studies showed that HPK1 was subject to regulation by ubiquitination and ubiquitin-targeted degradation and that PP4 inhibited HPK1 ubiquitination. In addition, we found that TCR stimulation enhanced the PP4-HPK1 interaction and that wild-type PP4 enhanced, whereas a phosphatase-dead PP4 mutant inhibited, TCR-induced activation of HPK1 in Jurkat T cells. Combined with the observation that PP4 enhanced HPK1-induced JNK activation, our studies identify PP4 as a positive regulator for HPK1 and the HPK1-JNK signaling pathway.

Highlights

Hematopoietic progenitor kinase 1 (HPK11; named MAP4K1) belongs to the HPK1/GCk subgroup of mammalian Ste20-like kinases that activate the JNK pathway and is considered as a potential MAPK kinase kinase kinase [1, 2]
HPK1 Interacts with phosphatase 4 (PP4) through Its Proline-rich Region—We have previously found that PP4 acts as a positive regulator for the JNK pathway during TNF-␣ signaling and that PP4 probably exerts its effect on JNK in an indirect manner, since no direct PP4-JNK interaction was detected [46]
We found that HPK1 is one of the upstream activating kinases that interacted with PP4

Summary

Introduction

Hematopoietic progenitor kinase 1 (HPK11; named MAP4K1) belongs to the HPK1/GCk subgroup of mammalian Ste20-like kinases that activate the JNK pathway and is considered as a potential MAPK kinase kinase kinase [1, 2]. The HPK1/GCk subgroup of kinases includes germinal center kinase (GCK), GCK-like kinase (GLK), HPK/GCK-like kinase/NcK-interacting kinase, and kinase homologous to Ste20/Sps1/GCK-related [1] These kinases are characterized by an N-terminal kinase domain, a C-terminal regulatory region, and the lack of a Rac1/Cdc42-binding domain found in p21-activated kinases, the other subgroup of mammalian Ste20-like kinases [1, 3]. We have shown that the adaptor protein, the HPK1interacting protein of 55 kDa, is involved in the kinase activation of HPK1 by TCR stimulation [28]. We observed that TCR stimulation enhanced the PP4-HPK1 interaction and that PP4 was involved in the kinase activation of HPK1 by TCR stimulation These observations suggest that PP4 is a positive regulator for HPK1 and the HPK1-JNK signaling pathway

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