Alternative splicing and mutation status of CHEK2 in stage III breast cancer.
The DNA damage checkpoint kinase, CHK2, promotes growth arrest or apoptosis through phosphorylating targets such as Cdc25A, Cdc25C, BRCA1, and p53. Both germline and somatic loss-of-function CHEK2 mutations occur in human tumours, the former linked to the Li-Fraumeni syndrome, and the latter found in diverse types of sporadic malignancies. Here we examined the status of CHK2 by genetic and immunohistochemical analyses in 53 breast carcinomas previously characterized for TP53 status. We identified two CHEK2 mutants, 470T>C (Ile157Thr), and a novel mutation, 1368insA leading to a premature stop codon in exon 13. The truncated protein encoded by CHEK2 carrying the 1368insA was stable yet mislocalized to the cytoplasm in tumour sections and when ectopically expressed in cultured cells. Unexpectedly, we found CHEK2 to be subject to extensive alternative splicing, with some 90 splice variants detected in our tumour series. While all cancers expressed normal-length CHEK2 mRNA together with the spliced transcripts, we demonstrate and/or predict some of these splice variants to lack CHK2 function and/or localize aberrantly. We conclude that cytoplasmic sequestration may represent a novel mechanism to disable CHK2, and propose to further explore the significance of the complex splicing patterns of this tumour suppressor gene in oncogenesis.
Staalesen
Vidar
V
Department of Molecular Biology, University of Bergen, Bergen, Norway.
Falck
Jacob
J
Geisler
Stephanie
S
Bartkova
Jirina
J
Børresen-Dale
Anne-Lise
AL
Lukas
Jiri
J
Lillehaug
Johan Richard
JR
Bartek
Jiri
J
Lønning
Per Eystein
PE
D017398:Alternative Splicing; D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D064447:Checkpoint Kinase 2; D004252:DNA Mutational Analysis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism
D064447:Checkpoint Kinase 2; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases