Correlation between the activation of Neu tyrosine kinase and promotion of foci formation induced by selected organochlorine compounds in the MCF‐7 model system

Several studies have shown that some organochlorine compounds act like estrogen in certain animals and in vitro cell culture systems, and therefore, there is a possibility that they could promote the process of tumorigenesis in breast cancer cells. In our previous study, two representative organochlorines, 1,1,1‐trichloro 2‐ o ‐chlorophenyl‐2′‐ p ‐chlorophenyl ethane ( o,p ′‐DDT) and β‐1,2,3,4,5,6‐hexachlorocyclohexane (β‐HCH), were found to directly activate the protein tyrosine kinase of Neu (c‐ erb B‐2 proto‐oncogene product) immunoprecipitates isolated from MCF‐7 breast cancer cells. In the current study, we also found that 2,4,5‐trichlorophenoxyacetic acid (2,4,5‐T) at 1 nM and α‐HCH isomers at 100 nM could also significantly activate protein tyrosine kinase of Neu immunoprecipitates in a cell‐free system. We also found that organochlorines result in an increase of Neu protein tyrosine kinase after intact cell treatment in estrogen‐depleted medium. This Neu kinase activation by β‐HCH (100 nM) was blocked when the cells were pretreated with Neu mRNA antisense oligonucleotide ( p < 0.07, Student's t ‐test). Endogenously added α‐, β‐, and γ‐HCH, o,p ′‐DDT, 2,2′‐dichlorobiphenyl (2,2′‐PCB), and 2,4,5‐T at 100 nM were found to promote foci formation in postconfluent cultures of this cell line. This stimulatory effect caused by 17β‐estradiol, o,p ′‐DDT, and β‐HCH on foci formation was inhibited by coincubation with Neu monoclonal antibody ( p < 0.05). Those two events induced by organochlorines (i.e., Neu kinase activation and foci formation) seemed causally correlated. © 1999 John Wiley & Sons, Inc. J Biochem Toxicol 13: 296–302, 1999