Disease relevance of BUB1

• Genomic instability at the BUB1 locus in colorectal cancer, but not in non-small cell lung cancer [1].
• So far the lesions of deletion are in the kinetochore localization domain of the hBUB1 gene that may explain why the deletion lesions in the BUB1 gene cause aneuploidy in lymphoma and lymphoma cells [2].
• These studies have revealed mutation of the mitotic checkpoint regulators BUB1 and BUBR1 and amplification of STK15 in a subset of CIN colon cancers [3].
• All cell lines as well as 9 FA, 9 FC, and 1 aneuploid papillary carcinoma were screened for mutations of BUB1 by SSCP and direct sequencing [4].
• Gene expression levels of the MAD2 and BUB1 mitotic spindle checkpoint genes were assessed in 37 Barrett's patients (with histology ranging from metaplasia to adenocarcinoma) by real-time RT-PCR [5].

High impact information on BUB1

• We show here that a murine homolog of the yeast mitotic checkpoint gene BUB1 localizes to the kinetochore during mitosis [6].
• Moreover, in some cancers displaying CIN the loss of this checkpoint was associated with the mutational inactivation of a human homologue of the yeast BUB1 gene; BUB1 controls mitotic checkpoints and chromosome segregation in yeast [7].
• The normal mitotic checkpoints of cells displaying microsatellite instability become defective upon transfer of mutant hBUB1 alleles from either of two CIN cancers [7].
• Therefore, Bub1-mediated phosphorylation of Cdc20 is required for proper checkpoint signaling [8].
• We speculate that inhibition of APC/C(Cdc20) by Bub1 in a catalytic fashion may partly account for the exquisite sensitivity of the spindle checkpoint [8].

Chemical compound and disease context of BUB1

• The hBUB1 gene of three lung cancer cell lines contained a thymine-to-cytosine substitution in codon 430 of exon 12, which did not result in an amino-acid substitution [9].
• A polymorphism in codon 93 of exon 4, a guanine-to-thymine substitution, in hBUB1 was found in one lung cancer cell line and one primary lung tumor [9].
• The hBUB1 gene of one adenocarcinoma tumor contained a somatic missense mutation, a cytosine-to-guanine substitution in codon 51 of exon 5 that resulted in a histidine-to-aspartic acid amino acid substitution [9].

Biological context of BUB1

• We have now used antisense and ribozyme-mediated temporary inhibition of BUB1 to study the consequences of mitotic checkpoint failure on the development of aneuploidy [10].
• The BUB1 locus was evaluated in 32 colorectal cancer (CRC) and 20 non-small cell lung cancer (NSCLC) primary tumors using a panel of seven microsatellite repeats for 2q, two CA repeats in BUB1, and gene mutation analysis [1].
• Inhibition of BUB1 results in genomic instability and anchorage-independent growth of normal human fibroblasts [10].
• Moreover, Zwint-1 is required for stable association of CENP-F and dynamitin but not BUB1 with the kinetochore [11].
• We show that full-length RAE1 and BUB1 proteins interact in mammalian cells and accumulate both at the kinetochores of prometaphase chromosomes [12].

Anatomical context of BUB1

• Numerical centrosome abnormalities or mutations in genes associated with the mitotic spindle checkpoint (BUB1 and MAD2) are two important mechanisms that can induce abnormal mitosis resulting in aneuploid daughter cells [13].
• Specifically, when Bub1 is inhibited by RNA interference, or aurora kinase activity is inhibited with the small molecule ZM447439, cells arrest transiently in mitosis following exposure to spindle toxins that prevent microtubule polymerisation [14].
• Here we show that HeLa cells depleted for Bub1 by RNA interference are defective in checkpoint signaling [8].
• Using a supervised analysis of the data, the authors found that the best discriminators for molecularly distinguishing between melanoma, benign nevi, and lymph nodes were MLANA, CD63, and BUB1 [15].
• Spindle checkpoint protein Bub1 corrects mitotic aberrancy induced by human T-cell leukemia virus type I Tax [16].

Associations of BUB1 with chemical compounds

• This multiprotein complex exhibits a kinase activity with a requirement for lysine 821 in the BUB1 kinase motif, resulting in BUB1 autophosphorylation and phosphorylation of associated MAD1 [17].
• We show that Plk1 binds to budding uninhibited by benzimidazole 1 (Bub1) in mitotic human cells [18].
• Consistent with this, we also show that Bub1 is rapidly phosphorylated following brief treatments with nocodazole or taxol [19].
• A thymine/cytosine polymorphism at 8 bp upstream of the 5' splice acceptor site of exon 10 was observed in Raji cell line and two AML specimens without a resultant change in the expression of hBUB1 [20].

Enzymatic interactions of BUB1

• Upon checkpoint activation, Bub1 itself is hyperphosphorylated and its kinase activity toward Cdc20 is stimulated [8].
• We have found that the spindle checkpoint kinase Bub1p becomes phosphorylated by Cdc2p during spindle damage in mitotic cells [21].
• Bub1 is ubiquitinated by immunopurified APC/C(Cdh1) in vitro [22].

Regulatory relationships of BUB1

• Furthermore, we show that both Bub1 and aurora kinase activity are required to promote binding of the MCC to the APC/C [14].
• Our data support the hypothesis that Bub1 compromise triggers p53-dependent senescence, which limits the production of aneuploid and potentially cancerous cells [23].

Other interactions of BUB1

• These results suggest that inactivation of the mitotic checkpoint genes BUB1, BUBR1, and BUB3 by epigenetic silencing does not seem to play a role in gastric carcinogenesis [24].
• Human cells contain two related protein kinases, hBUB1 and hBUBR1, that appear to have evolved from a single ancestral BUB1 gene [25].
• These observations provide a simple explanation of why BubR1 and Mad2 are essential for checkpoint function following spindle destruction, yet Bub1 and aurora B kinase activity are not [14].
• We suggest therefore that the checkpoint is composed of two arms, one dependent on Bub1, the other on aurora B [14].
• We examined the contribution of mitotic checkpoint dysfunction and mutations of BUB1 or BUBR1, components of the spindle assembly checkpoint pathway, to chromosomal instability in thyroid cancer [4].

Analytical, diagnostic and therapeutic context of BUB1

• To assess the role of these mechanisms, we used fluorescence in situ hybridization techniques to determine aneuploidy and centrosome copy number and PCR-SSCP to identify gene mutations of BUB1 and MAD2 in marrow cells of 25 patients [13].
• Expression analysis by Northern blot of breast cell lines showed variable expression of hBUB1 and hBUB1B genes [26].
• In the present study, an antibody was generated against BUB1 and its expression was studied in gastric cancer tissue sections (n = 80) by immunohistochemistry [27].
• One hundred and two lung cancer (50 small cell lung cancers and 52 non-small cell lung cancers) and 4 mesothelioma cell line DNAs were analyzed by Southern blot analysis, but no rearrangements or deletions of hBUB1 and hBUBR1 were detected [28].
• In addition, genomic PCR products of Bub1 exon 8, 10, 12, 15 and kinase domain from 9 oral cancer cell lines were analyzed by polymerase chain reaction-single-stand conformation polymorphism (PCR-SSCP) [29].

References