Mitotic Phosphorylation of the Lamin B Receptor by a Serine/Arginine Kinase and p34cdc2

doi:10.1074/jbc.272.10.6208

Mitotic Phosphorylation of the Lamin B Receptor by a Serine/Arginine Kinase and p34^cdc2*

From the ^‡ Laboratory of Biochemistry, School of Chemistry, The Aristotelian University of Thessaloniki, Thessaloniki 54 006, Greece,
^§ Programme of Cell Biology, European Molecular Biology Laboratory, 69 017 Heidelberg, Germany, and
** Department of Basic Sciences, Faculty of Medicine, The University of Crete, Heraclion 71 110, Crete, Greece

^‡‡ To whom correspondence should be addressed:
Laboratory of Biochemistry, School of Chemistry, Aristotelian University of Thessaloniki, 54 006 Thessaloniki, Greece.
Tel.: 30 31 997726; Fax: 30 31 997689; E mail: giannako{at}ccf.auth.gr

↵^¶ Present address: Dept. of Neurosciences, Montreal General Hospital, Montreal H3G 1A4, Canada.

Abstract

The lamin B receptor (LBR) is an integral protein of the inner nuclear membrane that is modified at interphase by a nuclear envelope-bound protein kinase. This enzyme (RS kinase) specifically phosphorylates arginine-serine dipeptide motifs located at the NH₂-terminal domain of LBR and regulates its interactions with other nuclear envelope proteins. To compare the phosphorylation state of LBR during interphase and mitosis, we performed phosphopeptide mapping of in vitro and in vivo ³²P-labeled LBR and analyzed a series of recombinant proteins and synthetic peptides. Our results show that LBR undergoes two types of mitotic phosphorylation mediated by the RS and the p34^cdc2 protein kinases, respectively. The RS kinase modifies similar sites at interphase and mitosis (i.e. Ser⁷⁶, Ser⁷⁸, Ser⁸⁰, Ser⁸², Ser⁸⁴), whereas p34^cdc2 mainly phosphorylates Ser⁷¹. These findings clarify the phosphorylation state of LBR during the cell cycle and provide new information for understanding the mechanisms responsible for nuclear envelope assembly and disassembly.

Footnotes

↵^∥ Recipient of a research bursary granted by the Commission of the European Communities in the framework of the BIOMED 1 program. Present address: Institut fur Biochemie I, University of Heidelberg, D-69120 Heidelberg, Germany.
↵* This work was supported in part by a grant from the German-Greek Cooperation in Science and Technology. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

This article is dedicated to the memory of Prof. Nikolaos Alexandrou.
↵¹ The abbreviations used are:

LBR

lamin B receptor

wtNt

wild type NH2 terminus

GST

glutathione S-transferase

SF

splicing factor

PAGE

polyacrylamide gel electrophoresis

SRPK1

SR protein kinase 1.
↵² G. Simos and S. D. Georgatos, unpublished observations.
↵³ E. Nikolakaki, S. D. Georgatos, and T. Giannakouros, unpublished observations.
- Received September 15, 1996.
- Revision received November 5, 1996.