Yeast Mpk1 cell wall integrity mitogen-activated protein kinase regulates nucleocytoplasmic shuttling of the Swi6 transcriptional regulator.
The yeast SBF transcription factor is a heterodimer comprised of Swi4 and Swi6 that has a well defined role in cell cycle-specific transcription. SBF serves a second function in the transcriptional response to cell wall stress in which activated Mpk1 mitogen-activated protein kinase of the cell wall integrity signaling pathway forms a complex with Swi4, the DNA binding subunit of SBF, conferring upon Swi4 the ability to bind DNA and activate transcription of FKS2. Although Mpk1-Swi4 complex formation and transcriptional activation of FKS2 does not require Mpk1 catalytic activity, Swi6 is phosphorylated by Mpk1 and must be present in the Mpk1-Swi4 complex for transcriptional activation of FKS2. Here, we find that Mpk1 regulates Swi6 nucleocytoplasmic shuttling in a biphasic manner. First, formation of the Mpk1-Swi4 complex recruits Swi6 to the nucleus for transcriptional activation. Second, Mpk1 negatively regulates Swi6 by phosphorylation on Ser238, which inhibits nuclear entry. Ser238 neighbors a nuclear localization signal (NLS) whose function is blocked by phosphorylation at Ser238 in a manner similar to the regulation by Cdc28 of another Swi6 NLS, revealing a mechanism for the integration of multiple signals to a single endpoint. Finally, the Kap120 beta-importin binds the Mpk1-regulated Swi6 NLS but not the Cdc28-regulated NLS.
Kim
Ki-Young
KY
Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA.
Truman
Andrew W
AW
Caesar
Stefanie
S
Schlenstedt
Gabriel
G
Levin
David E
DE
D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000378:metabolism*; D002473:Cell Wall / Q000201:enzymology / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D015151:Immunoblotting; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
C479560:KAP120 protein, S cerevisiae; D028884:Karyopherins; D008565:Membrane Proteins; D019913:Nuclear Localization Signals; C075111:SWI6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D012694:Serine; D005964:Glucosyltransferases; C095724:GSC2 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; C072724:SLT2 protein, S cerevisiae