NH2-terminally truncated HER-2/neu protein: relationship with shedding of the extracellular domain and with prognostic factors in breast cancer.
We identified an NH2-terminally truncated HER-2/neu product of M(r) 95,000 with in vitro kinase activity by Western blotting and immunoprecipitations using domain-specific antibodies. p95 levels correlated with the extracellular domain (ECD) shed from different cells under varied conditions. Both ECD and p95 were at approximately 20-fold lower levels in SKOV3 ovarian carcinoma cells, as compared to BT474 breast carcinoma cells. Both were stimulated by treatment of cells with the phorbol ester tumor promoter phorbol 12-myristate 13-acetate and the lysosomotrophic agent chloroquine. The hydroxamate inhibitor of metalloproteases, TAPI, suppressed both p95 and ECD in a dose-dependent fashion, with maximal inhibition at < or = 10 microM in BT474 cells. Cancer tissues were analyzed by Western blotting and scored for p95HER-2/neu and for p185HER-2/neu expression. Breast and ovarian cancer tissues were both found to express p95HER-2/neu in addition to p185HER-2/neu. Of 161 breast cancer tissues, 22.4% expressed p95, 21.7% overexpressed p185, and 14.3% were p95 positive and overexpressed p185. A higher proportion of node-positive patients (23 of 78) than node-negative patients (9 of 63) expressed p95 in all tumors combined (P = 0.032). In the group that overexpressed p185, those that contained p95 were associated with node-positive patients (15 of 21), whereas those that were p95 negative were associated with node-negative patients (8 of 11; P = 0.017). Neither p95- nor p185-rich patients significantly correlated with tumor size or with hormone receptor status in this study. Our findings show that breast cancers, which express the HER-2/neu oncogene, are heterogeneous with respect to HER-2/neu protein products. p95HER-2/neu appears to distinguish tumors that have metastasized to the lymph nodes from those in node-negative patients.
Christianson
T A
TA
Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201, USA.
Doherty
J K
JK
Lin
Y J
YJ
Ramsey
E E
EE
Holmes
R
R
Keenan
E J
EJ
Clinton
G M
GM
D016475:3T3 Cells; D000818:Animals; D001943:Breast Neoplasms / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology; D004151:Dipeptides / Q000494:pharmacology; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005260:Female; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors; D051379:Mice; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000032:analysis / Q000737:chemistry*; D010766:Phosphorylation; D011379:Prognosis; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis / Q000737:chemistry*; D014407:Tumor Cells, Cultured
D004151:Dipeptides; D016326:Extracellular Matrix Proteins; D006877:Hydroxamic Acids; D008666:Metalloendopeptidases; D009363:Neoplasm Proteins; D020794:Receptor Protein-Tyrosine Kinases; D018719:Erb-b2 Receptor Tyrosine Kinases; C092152:N-((2-(hydroxyaminocarbonyl)methyl)-4-methylpentanoyl)-3-(2'-naphthyl)alanylalanine, 2-aminoethylamide