1: EMBO J. 2003 Oct 15;22(20):5522-9. 

Groucho suppresses Pax2 transactivation by inhibition of JNK-mediated
phosphorylation.

Cai Y, Brophy PD, Levitan I, Stifani S, Dressler GR.

Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA.

Pax proteins are DNA-binding transcription factors that regulate embryonic
development through the activation and repression of downstream target genes.
The Pax2 gene is absolutely required for kidney development and for patterning
specific regions of the nervous system such as the eye, ear and hindbrain. The
Pax2/5/8 family of proteins contains both transcription activation and
repression domains. The activation domain of Pax2 is phosphorylated by the c-Jun
N-terminal kinase (JNK) to enhance Pax2-dependent transcription. In this report,
we demonstrate that the Groucho/TLE family protein, Grg4, interacts with Pax2 to
suppress transactivation. Grg4 is able to specifically inhibit phosphorylation
of the Pax2 activation domain, even in the presence of activated JNK.
Furthermore, the Grg4 interaction and suppression of phosphorylation depends on
Pax2 binding to its target DNA sequence and is independent of histone
deacetylation. These data suggest a new model for Groucho mediated suppression
of transcription through the specific inhibition of modifications in the
activation domain of a transactivator.

PMID: 14532124 [PubMed - indexed for MEDLINE]


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2: J Biol Chem. 2003 Nov 28;278(48):48422-33. Epub 2003 Sep 10. 

In vitro development of mouse embryonic stem cells lacking JNK/stress-activated
protein kinase-associated protein 1 (JSAP1) scaffold protein revealed its
requirement during early embryonic neurogenesis.

Xu P, Yoshioka K, Yoshimura D, Tominaga Y, Nishioka T, Ito M, Nakabeppu Y.

Division of Neurofunctional Genomics, Department of Immunobiology and
Neuroscience, Medical Institute of Bioregulation, Kyushu University and CREST,
Japan Science and Technology Corp., Fukuoka 812-8582, Japan.

The Jsap1 gene encodes a scaffold protein for c-Jun N-terminal kinase cascades.
We established c-Jun N-terminal kinase (JNK)/stress-activated protein
kinase-associated protein 1 (JSAP1)-null mouse embryonic stem cell lines by
homologous recombination. The JSAP1-null embryonic stem cells were viable,
however, exhibited hyperplasia of the ectoderm during embryoid body formation,
and spontaneously differentiated into neurons more efficiently than did wild
type. The expression of components of c-Jun N-terminal kinase cascades and a
subset of marker mRNAs during early embryogenesis was altered in the JSAP1-null
mutants. Retinoic acid dramatically increased the expression of JSAP1 and JNK3,
which were co-precipitated with anti-JNK3 in the neuroectoderm of wild type but
not JSAP1-null embryoid bodies. In the neurons differentiated from the wild type
embryoid bodies, JSAP1 was localized in the soma, neurites, and growth cone-like
structure of the neurites, and neurite outgrowth from the JSAP1-null embryoid
bodies was apparently less efficient than from wild type. JSAP1 and c-Jun
N-terminal kinase 3 were coexpressed in the embryonic ectoderm of E7.5 mouse
embryo, whereas Wnt1 and Pax2 were coexpressed with JSAP1 at the
midbrain-hindbrain junction in E12.5 mouse embryo, thus suggesting that JSAP1 is
required for early embryonic neurogenesis.

PMID: 12968026 [PubMed - indexed for MEDLINE]


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3: Genes Dev. 2003 May 15;17(10):1271-80. 

JNK initiates a cytokine cascade that causes Pax2 expression and closure of the
optic fissure.

Weston CR, Wong A, Hall JP, Goad ME, Flavell RA, Davis RJ.

Howard Hughes Medical Institute and Program in Molecular Medicine, University of
Massachusetts Medical School, Worcester, Massachusetts 01605, USA.

The c-Jun NH(2)-terminal kinase (JNK) group of mitogen-activated protein kinases
is stimulated in response to a wide array of cellular stresses and
proinflammatory cytokines. Mice lacking individual members of the Jnk family
(Jnk1, Jnk2, and Jnk3) are viable and survive without overt structural
abnormalities. Here we show that mice with a compound deficiency in Jnk
expression can survive to birth, but fail to close the optic fissure (retinal
coloboma). We demonstrate that JNK initiates a cytokine cascade of bone
morphogenetic protein-4 (BMP4) and sonic hedgehog (Shh) that induces the
expression of the paired-like homeobox transcription factor Pax2 and closure of
the optic fissure. Interestingly, the role of JNK to regulate BMP4 expression
during optic fissure closure is conserved in Drosophila during dorsal closure, a
related morphogenetic process that requires JNK-regulated expression of the BMP4
ortholog Decapentaplegic (Dpp).

PMID: 12756228 [PubMed - indexed for MEDLINE]


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4: J Biol Chem. 2002 Jan 11;277(2):1217-22. Epub 2001 Nov 7. 

Phosphorylation of Pax2 by the c-Jun N-terminal kinase and enhanced
Pax2-dependent transcription activation.

Cai Y, Lechner MS, Nihalani D, Prindle MJ, Holzman LB, Dressler GR.

Departments of Pathology and Medicine, University of Michigan, Ann Arbor,
Michigan 48109, USA.

The Pax gene family encodes DNA-binding proteins that can both activate and
repress transcription of specific target genes during embryonic development. Pax
proteins are required for pattern formation and cell differentiation in a broad
spectrum of developing tissues. Consistent with its expression in the
intermediate mesoderm, the optic cup and stalk, and the otic vesicle, Pax2, a
member of the Pax2/5/8 subfamily, is essential for the development of the renal
epithelia, the optic cup, and the inner ear. In addition to a DNA binding
domain, the Pax2 protein contains a carboxyl-terminal transactivation domain
rich in serine, threonine, and tyrosine. In this report, we demonstrate that the
Pax2 transactivation domain is phosphorylated by the c-Jun N-terminal kinase,
but not the ERK1/2 or p38 MAP kinases and that phosphorylation is coincident
with increased transactivation of a Pax2-dependent reporter gene. Activation of
JNK by either upstream kinase MEKK1 or DLK or by expression of Wnt signaling
proteins significantly enhances Pax2 phosphorylation in cells. In vitro kinase
assays using immunoprecipitated JNK or constitutively active, recombinant JNK
show phosphorylation of GST-Pax2 fusion proteins. In transfected cells,
phosphorylation of Pax2 correlates with increased transactivation of a
Pax2-dependent reporter gene, suggesting that serine/threonine phosphorylation
of the transactivation domain is important for Pax2 activity. Pax2 can form a
complex with the JNK scaffolding protein JIP1, and this interaction is enhanced
by activation of the JNK signaling module with the upstream kinase DLK. The data
demonstrate that Pax2 is a new target for the JNK signaling module and point to
a novel mechanism for mediating Pax-dependent transcription regulation.

PMID: 11700324 [PubMed - indexed for MEDLINE]


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