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Differential stability of Arabidopsis D‐type cyclins: CYCD3;1 is a highly unstable protein degraded by a proteasome‐dependent mechanism
Author(s) -
Planchais Séverine,
Samland Anne K.,
Murray James A. H.
Publication year - 2004
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.0960-7412.2004.02071.x
Subject(s) - mg132 , cell cycle , cycloheximide , biology , microbiology and biotechnology , proteasome inhibitor , cell division control protein 4 , cyclin a , protein degradation , leupeptin , cyclin dependent kinase , proteasome , biochemistry , protein biosynthesis , ubiquitin , ubiquitin ligase , cell , protease , gene , enzyme
Summary In Arabidopsis , the D‐type cyclin CYCD3 is rate‐limiting for transition of the G 1 /S boundary, and is transcriptionally upregulated at this point in cells re‐entering the cell cycle in response to plant hormones and sucrose. However, little is known about the regulation of plant cell‐cycle regulators at the protein level. We show here that CYCD3;1 is a phosphoprotein highly regulated at the level of protein abundance, whereas another D‐type cyclin CYCD2;1 is not. The level of CYCD3;1 protein falls rapidly on sucrose depletion, correlated with the arrest of cells in G 1 phase, suggesting a rapid turnover of CYCD3;1. Treatment of exponentially growing cells with the protein synthesis inhibitor cycloheximide (CHX) confirms that CYCD3;1 is normally a highly unstable protein, with a half‐life of approximately 7 min on CHX treatment. In both sucrose‐starved and exponentially growing cells, CYCD3;1 protein abundance increases in response to treatment with MG132 (carbobenzoxyl‐leucinyl‐leucinyl‐leucinal), a reversible proteasome inhibitor, but not in response to the cysteine protease inhibitor E‐64 or the calpain inhibitor ALLN ( N ‐acetyl‐leucyl‐leucyl‐norleucinal). The increase on MG132 treatment is because of de novo protein synthesis coupled with the blocking of CYCD3;1 degradation. Longer MG132 treatment leads to C‐terminal cleavage of CYCD3;1, accumulation of a hyperphosphorylated form and its subsequent disappearance. We conclude that CYCD3;1 is a highly unstable protein whose proteolysis is mediated by a proteasome‐dependent pathway, and whose levels are highly dependent on the rate of CYCD3;1 protein synthesis.