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J. Biol. Chem., Vol. 280, Issue 30, 27561-27568, July 29, 2005

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Phosphatidylinositol-4-phosphate 5-Kinase Regulates Fission Yeast Cell Integrity through a Phospholipase C-mediated Protein Kinase C-independent Pathway^*

Lu Deng, Reiko Sugiura, Kazuki Ohta, Kazuki Tada, Masahiro Suzuki, Masato Hirata¶, Shun-ichi Nakamura||, Hisato Shuntoh**, and Takayoshi Kuno

From the Division of Molecular Pharmacology and Pharmacogenomics, Department of Genome Sciences and ^||Division of Biochemistry, Department of Molecular and Cellular Biology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan, Laboratory of Molecular Pharmacogenomics, School of Pharmaceutical Sciences, Kinki University, Kowakae 3-4-1, Higashi-Osaka 577-8502, Japan, ^¶Laboratory of Molecular and Cellular Biochemistry, Faculty of Dental Science and Station for Collaborative Research, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan, and ^**Faculty of Health Science, Kobe University School of Medicine, 7-10-2 Tomogaoka, Suma-ku, Kobe 654-0142, Japan

Fission yeast its3-1 mutant is an allele of the essential gene its3⁺ that encodes a phosphatidylinositol-4-phosphate 5-kinase (PIP5K) that produces phosphatidylinositol 4,5-bisphosphate. We found that the its3-1 mutant is sensitive to micafungin, a (1,3)--D-glucan synthase inhibitor, suggesting a cell wall integrity defect. Consistently, its3-1 mutation caused synthetic lethality with a (1,3)--D-glucan synthase mutant, bgs1-i2, and its3-1 mutant cells showed aberrant localization of green fluorescent protein-Bgs1. Similar aberrant localization of green fluorescent protein-tagged Rgf1, a putative phosphatidylinositol 4,5-bisphosphate-binding guanine nucleotide exchange factor for Rho protein, in its3-1 mutants was observed, suggesting a defective Rgf1/Rho pathway. To unravel the molecular mechanism(s), putative downstream components of PIP5K signaling were analyzed. Unexpectedly, overexpression of phospholipase C (Plc1), but not that of protein kinase C (PKC; Pck1 and Pck2), suppressed the phenotypes of the its3-1 mutant. These findings indicate that PKCs are not involved in the suppression, and further analysis revealed that PKCs are not downstream of Plc1 in fission yeast. Also, the enzymatic activity of Plc1 is essential for the suppression of the phenotypes and for the viability of the its3-1 mutant. These findings suggest that Its3 PIP5K regulates cell integrity through a Plc1-mediated PKC-independent pathway, in addition to the Rho/PKC pathway.

Received for publication, March 10, 2005 , and in revised form, May 27, 2005.

^* This work was supported by 21st Century Center of Excellence Program and by research grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan and the Asahi Glass Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 81-78-382-5440; Fax: 81-78-382-5459; E-mail: tkuno{at}med.kobe-u.ac.jp.

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