Nerve growth factor cooperates with p185(HER2) in activating growth of human breast carcinoma cells

Nerve growth factor (NGF) is known to exert a mitogenic effect on human bre ast cancer cells through proto-TrkA activation. Reverse transcriptase-PCR a nalysis of proto-TrkA expression in human breast carcinoma specimens and ce ll lines revealed trkA transcript in 12 of 14 human breast carcinoma specim ens and in all of four cell lines tested, while cytofluorimetric and Wester n blot analysis indicated proto-TrkA expression in three of the four cell l ines, NGF stimulated growth in only two of the three positive cell Lines. I nhibition of NGF-induced MAPK activation by an antibody directed against th e extracellular domain of TrkA but not by an inhibitor of TrkA phosphorylat ion demonstrated the requirement of NGF binding but not of proto-TrkA kinas e activity for MAPK activation, suggesting the recruitment of another kinas e for transmission of the mitogenic signaling. Indeed, NGF induced tyrosine phosphorylation and stimulated kinase activity of p185(HER2), a kinase rec eptor of the HER family. A TrkA phosphorylation inhibitor did not affect th is activation. Moreover, the two receptors were coprecipitated by antibodie s directed against proto-TrkA and p185(HER2). Down-modulation of p185(HER2) expression in a breast carcinoma Line transfected with a construct contain ing an anti-p185(HER2) antibody sequence and expressing proto-TrkA impaired NGF-induced MAPK activation and proliferation. Together these data show th at in cells expressing low levels of TrkA such as breast carcinoma cells, N GF must recruit other overexpressed receptors such as p185(HER2) in order t o generate a biological signal that can induce breast cancer cell growth.