Microtubule affinity-regulating kinase 2 functions downstream of the PAR-3/PAR-6/atypical PKC complex in regulating hippocampal neuronal polarity

doi:10.1073/pnas.0509955103

Microtubule affinity-regulating kinase 2 functions downstream of the PAR-3/PAR-6/atypical PKC complex in regulating hippocampal neuronal polarity

*Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institute for Biological Sciences, and
^†Graduate School of Chinese Academy of Sciences, Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai 200031, China;
^§Departments of Cell Biology and Physiology and Internal Medicine, Howard Hughes Medical Institute, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110; and
^‡Cellzome AG, Meyerhofstrasse 1, D-69117 Heidelberg, Germany

Edited by Yuh Nung Jan, University of California School of Medicine, San Francisco, CA, and approved April 12, 2006 (received for review November 17, 2005)

Abstract

The PAR-3/PAR-6/atypical PKC (aPKC) complex is required for axon–dendrite specification of hippocampal neurons. However, the downstream effectors of this complex are not well defined. In this article, we report a role for microtubule affinity-regulating kinase (MARK)/PAR-1 in axon–dendrite specification. Knocking down MARK2 expression with small interfering RNAs induced formation of multiple axon-like neurites and promoted axon outgrowth. Ectopic expression of MARK2 caused phosphorylation of tau (S262) and led to loss of axons, and this phenotype was rescued by expression of PAR-3, PAR-6, and aPKC. In contrast, the polarity defects caused by an MARK2 mutant (T595A), which is not responsive to aPKC, were not rescued by the PAR-3/PAR-6/aPKC complex. Moreover, polarity was abrogated in neurons overexpressing a mutant of MARK2 with a deleted kinase domain but an intact aPKC-binding domain. Finally, suppression of MARK2 rescued the polarity defects induced by a dominant-negative aPKC mutant. These results suggest that MARK2 is involved in neuronal polarization and functions downstream of the PAR-3/PAR-6/aPKC complex. We propose that aPKC in complex with PAR-3/PAR-6 negatively regulates MARK(s), which in turn causes dephosphorylation of microtubule-associated proteins, such as tau, leading to the assembly of microtubules and elongation of axons.

Footnotes

^¶To whom correspondence should be addressed. E-mail: zgluo{at}ion.ac.cn
Author contributions: Y.M.C. and Z.G.L. designed research; Y.M.C., Q.J.W., H.S.H., P.C.Y., and J.Z. performed research; G.D. and H.P.-W. contributed new reagents/analytic tools; Y.M.C. and Z.G.L. analyzed data; and Z.G.L. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Abbreviations:

MAP,

microtubule-associated protein;

MT,

microtubule;

GSK3β,

glycogen synthase kinase 3β;

aPKC,

atypical PKC;

PAR,

partitioning-defective protein;

MARK,

microtubule affinity-regulating kinase;

siRNA,

small interfering RNA;

HEK,

human embryonic kidney;

DIVn,

n days in vitro;

aPKC-N,

amino-terminal PB1 domain of aPKC.