induction of sexual development and virulence in the smut fungus Ustilago maydis depends on Crk1,
a novel MAPK protein.
Garrido E, Voss U, Muller P, Castillo-Lluva S, Kahmann R, Perez-Martin J.
Departamento de Biotecnologia Microbiana, Centro Nacional de Biotecnologia CSIC, Campus
MAP kinases (mitogen-activated protein kinases) are activated by dual phosphorylation on specific threonine and specific tyrosine residues that are separated by a single residue, and the TXY activation motif is a hallmark of MAP kinases. In the fungus Ustilago maydis, which causes corn smut disease, the Crk1 protein, a kinase previously described to have roles in morphogenesis, carries a TXY motif that aligns with the TXY of MAP kinases. In this work, we demonstrate that Crk1 is activated through a mechanism that requires the phosphorylation of this motif. Our data show that Fuz7, a MAPK kinase involved in mating and pathogenesis in U. maydis, is required to activate Crk1, most likely through phosphorylation of the TXY motif. Consistently, we found that Crk1 is also required for mating and virulence. We investigated the reasons for sterility and avirulence of crk1-deficient cells, and we found that Crk1 is required for transcription of prf1, a central regulator of mating and pathogenicity in U. maydis. Crk1 belongs to a wide conserved protein group, whose members have not been previously defined as MAP kinases, although they carry TXY motifs. On the basis of our data, we propose that all of these proteins constitute a new family of MAP kinases.
PMID: 15601825 [PubMed - indexed for MEDLINE
A major question in cell biology is how molecular specificity is achieved by different growth factor receptors that activate apparently identical signaling events. For the neurotrophin family, a distinguishing feature is the ability to maintain a prolonged duration of signal transduction. However, the mechanisms by which neurotrophin receptors assemble such a sustained signaling complex are not understood. Here we report that an unusual ankyrin-rich transmembrane protein (ARMS+kidins220) is closely associated with Trk receptor tyrosine kinases, and not the EGF receptor. This association requires interactions between transmembrane domains of Trk and ARMS. ARMS is rapidly tyrosine phosphorylated after binding of neurotrophins to Trk receptors and provides a docking site for the CrkL-C3G complex, resulting in Rap1-dependent sustained ERK activation. Accordingly, disruption of Trk-ARMS or the ARMS-CrkL interaction with dominant-negative ARMS mutants, or treatment with small interference RNA against ARMS substantially reduce neurotrophin-elicited signaling to ERK, but without any effect upon Ras or Akt activation. These findings suggest that ARMS acts as a major and neuronal-specific platform for prolonged MAP kinase signaling by neurotrophins
(PLCepsilon) is a novel PLC that has a CDC25 guanine
nucleotide exchange factor (GEF) domain and two Ras
association (RA) domains of which the second (RA2) is critical for Ras activation of the enzyme. In the present studies, we
examined hormonal stimulation to elucidate receptor-mediated pathways that
functionally regulate PLCepsilon. We demonstrate that
epidermal growth factor (EGF), a receptor tyrosine kinase
(RTK) agonist, and lysophosphatidic acid (LPA),
sphingosine-1-phosphate (S1P), and thrombin, G protein-coupled receptor
agonists, stimulate PLCepsilon overexpressed
in COS-7 cells. EGF stimulated PLCepsilon in an
RA2-dependent manner through Ras and Rap. In
contrast, LPA, S1P and thrombin stimulated PLCepsilon
by both RA2-independent and dependent mechanisms. To determine the G proteins
that mediate the effects of these GPCR agonists, we coexpressed
constitutively active G proteins with PLCepsilon and
found that Galpha12, Galpha13,