Transfection of human ovarian cancer cells with the HER-2/neu receptor tyrosine kinase induces a selective increase in PTP-H1, PTP-1B, and PTP-α expression

Protein tyrosine phosphorylation is a key regulator of cell growth regulation and, when aberrant, is linked with the process of oncogenic transformation. Since tyrosine phosphatases (PTP) reverse phosphorylation mediated by tyrosine kinases (PTK), it has been hypothesized, but insufficiently studied to date, that PTPs function as tumor suppressors. Alternatively, PTPs may augment signal transduction by repriming substrates. To begin to assess the role of PTPs in ovarian cancer cell growth regulation, PTP partial cDNAs were cloned from the OVCA 433 ovarian cancer cell line using RT/PCR and degenerate oligonucleotide primers for the PTP consensus domain. Thirteen partial cDNAs were isolated, the sequences of which, when compared to GenBank, suggested that they were derived from PTP family members. These included PTP-α, PTP-γ, LAR, PTP-δ, T-cell PTP, PTP-2A(1D), PTP-1B, PTP-1C, PTP-H1, PTP-PEST, PTP-Gallus, and two isolates which potentially represent novel PTPs. Steady-state expression analyses revealed that PTP-1B expression was undetectable in normal epithelium but was expressed in four of five ovarian cancer cell lines. In contrast, the expression of two SH₂-containing PTPs, PTP-1C and PTP-2A, was detected in the normal ovarian epithelium but lost from one or more ovarian cancer cell lines. Finally, PTP-1B, PTP-α, and PTP-H1 expression was increased following HER-2/neu transfection of ovarian cancer cell lines. These results suggest that both normal ovarian epithelial cells and ovarian cancer cells express multiple PTPs. Further, some PTPs are differentially expressed between normal ovarian epithelium and ovarian cancer cells. Intriguingly, the transfection and increased expression of the prognostically significant HER-2/neu PTK induced a selective increase in the expression of the PTP-α, PTP-1B, and PTP-H1 tyrosine phosphatases.