Disease relevance of Ccnb2

• We show here that immunoprecipitates of either v-mos from Moloney murine sarcoma virus-transformed NIH 3T3 cells or c-mos from Xenopus eggs phosphorylate cyclin B2 in vitro [1].
• These truncated viral segments were placed immediately upstream of a reporter gene, a derivative of the influenza virus NS cDNA, either as monocistronic constructs or as dicistronic constructs in which the upstream cistron was the Xenopus laevis cyclin B2 cDNA [2].

High impact information on Ccnb2

• Previous studies from this laboratory have shown that purified MPF from Xenopus eggs contains cyclin B2 complexed with cdc2 kinase [1].
• Moreover, ablation of c-mos(xe) from oocytes by antisense oligonucleotide injection reduces the rate of cyclin B2 phosphorylation in oocyte extracts by 40% [1].
• The cyclin B2 component of MPF is a substrate for the c-mos(xe) proto-oncogene product [1].
• The licence to replicate is given by Cdc6 at the end of meiosis I, but the cytostatic factor (CSF) pathway, which maintains large amounts of active Cdc2/Cyclin B2, prevents the entry into S phase until fertilization [3].
• Using a polyclonal antibody raised against B2 cyclin from Xenopus laevis, we show that prophase-arrested Xenopus oocytes contain a stockpile of cyclin B2 protein [4].

Biological context of Ccnb2

• Using affinity-purified antiserum we have examined cyclin B2 levels in Xenopus oocytes at various stages of oogenesis [5].
• Microinjection of Xenopus oocytes with in vitro-synthesized RNAs encoding Xenopus cyclin B1 or cyclin B2 induces the progression of meiosis, characterized by germinal vesicle breakdown (GVBD) [6].
• In addition, during anaphase T201D Plx1 reduced preferentially the degradation of cyclin B2 and delayed the reduction in Cdc2 histone H1 kinase activity [7].
• These results demonstrate that in Xenopus laevis activation of Plx1 is sufficient for the activation of Cdc25C at the initiation of mitosis and that inactivation of Plx1 is required for complete degradation of cyclin B2 after anaphase and completion of cytokinesis [7].
• Together, these results strongly suggest that zygote-dependent deadenylation of cyclin A1 and cyclin B2 mRNAs is responsible for the downregulation of these proteins [8].

Anatomical context of Ccnb2

• Cyclin B1 is present at 4 x 10(8) molecules per oocyte in stage VI oocytes, and rises steadily during maturation, ultimately reaching similar levels to cyclin B2 in unfertilized eggs [9].

Associations of Ccnb2 with chemical compounds

• During progesterone-induced maturation, an increase in the synthesis of cyclin B2 is observed, although Western blotting experiments show that this new synthesis does not significantly increase the mass of cyclin over the maternal stockpile [4].
• It is suggested rather that the tyrosine phosphorylation of p34cdc2 plays a role in inhibiting cyclin B2 degradation [10].
• Addition of cycloheximide in MPF-injected stage IV oocytes induces neither the inhibition of histone H1 kinase activity nor the cyclin B2 degradation [10].
• Besides serine 53, a second cyk phosphorylation site in cyclin B2 was identified as threonine 41 [11].
• Recently, we have partially purified and characterized a specific cell cycle-regulated cyclin B2 kinase (cyk) from prophase oocytes of Xenopus laevis after an ATP-gamma-S activation step (R. Derua, I. Stevens, E. Waelkens, A. Fernandez, N. Lamb, W. Merlevede, and J. Goris, 1997, Exp. Cell Res. 230, 310-324) [11].

Other interactions of Ccnb2

• Microtubule-associated protein (MAP) kinase from Xenopus eggs phosphorylated cyclin B1 significantly at Ser-94 or Ser-96, whereas it was largely inactive against cyclin B2 [12].

Analytical, diagnostic and therapeutic context of Ccnb2

• Highly purified maturation-promoting factor (MPF) from Xenopus eggs contains both cyclin B1 and cyclin B2 as shown by Western blotting and immunoprecipitation using Xenopus anti-B-type cyclin antibodies [13].
• Site-directed mutagenesis of these sites indicated that phosphorylation of these sites in Xenopus cyclin B2 was not required for the hallmark functions of cyclin B2 [11].

References