Brk protects breast cancer cells from autophagic cell death induced by loss of anchorage.
Brk, a tyrosine kinase expressed in a majority of breast tumors, but not normal mammary tissue, promotes breast carcinoma cell proliferation. Normal epithelial cells are dependent on cell-cell or cell-matrix interactions for survival and undergo apoptosis after disruption of these interactions. Tumor cells are less sensitive to the induction of apoptosis and are predicted to have the potential to disseminate. We investigated whether Brk has further roles in breast tumor progression by relating its expression to tumor grade and demonstrating its role in the regulation of carcinoma cell survival under non-adherent conditions. Brk expression was determined by reverse transcription PCR on RNA extracted from surgical samples of human breast cancers. Breast carcinoma cell survival in suspension culture was examined when Brk protein levels were suppressed by RNA interference. Additionally, the effect of experimentally overexpressing Brk in otherwise Brk-negative breast carcinoma cells was assessed. Brk mRNA expression was notably higher in grade 3 breast tumors, as compared with lower tumor grades. In suspension culture, Brk suppression increased the rate of cell death, as compared with controls, and this cell death program exhibited characteristics of autophagy but not of apoptosis. Conversely, experimental expression of Brk in Brk-negative cells increased cell survival whereas kinase-inactive Brk did not. Therefore, Brk enhances breast carcinoma cell survival in suspension, suggesting a role for Brk in supporting breast cancer cell dissemination.
Harvey
Amanda J
AJ
Brunel Institute for Cancer Genetics and Pharmacogenomics, Biosciences, School of Health Sciences and Social Care, Brunel University, Kingston Lane, Uxbridge, Middlesex, United Kingdom. amanda.harvey@brunel.ac.uk
Pennington
Caroline J
CJ
Porter
Sarah
S
Burmi
Rajpal S
RS
Edwards
Dylan R
DR
Court
William
W
Eccles
Suzanne A
SA
Crompton
Mark R
MR
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001343:Autophagy; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D018270:Carcinoma, Ductal, Breast / Q000378:metabolism / Q000473:pathology*; D002448:Cell Adhesion; D049109:Cell Proliferation; D002470:Cell Survival; D002478:Cells, Cultured; D018450:Disease Progression; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D016133:Polymerase Chain Reaction; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D034622:RNA Interference; D012334:RNA, Neoplasm / Q000032:analysis
D009363:Neoplasm Proteins; D012334:RNA, Neoplasm; D011505:Protein-Tyrosine Kinases; C088375:PTK6 protein, human