A NOVEL PUTATIVE PROTEIN-TYROSINE-PHOSPHATASE CONTAINS A BRO1-LIKE DOMAIN AND SUPPRESSES HA-RAS-MEDIATED TRANSFORMATION

To investigate a potential role of protein-tyrosine phosphatases (PTPa ses) in myocardial growth and signaling, a degenerate primer-based rev erse transcription-polymerase chain reaction approach was used to isol ate cDNAs for proteins that contain a PTPase catalytic domain. Among t he 16 cDNA clones isolated by reverse transcription-polymerase chain r eaction from total neonatal rat cardiomyocyte RNA, one, designated PTP -TD14, was unique. Subsequent isolation and sequencing of a full-lengt h PTP-TD14 cDNA confirmed that it encodes a novel 164-kDa protein, p16 4(PTP-TD14) The C-terminal region contains the PTP-like domain, wherea s the N-terminal region shows no homology to any known mammalian prote in. However, this region is homologous to a yeast protein, BRO1, that is involved in the mitogen-activated protein kinase signaling pathway. Like BRO1, p164(PTP-TD14) contains a proline-rich region with two put ative SH3-domain binding sites. By Northern blot analysis, PTP-TD14 is expressed as a 5.3-kilobase pair transcript, not only in neonatal hea rt but also in many adult rat tissues. When expressed in either COS-7 or NIH-3T3 cells, p164(PTP-TD14) localizes to the cytoplasm in associa tion with vesicle-like structures. Expression of p164(PTP-TD14) in NIH -3T3 cells inhibits Ha ras-mediated transformation more than 3-fold. T his inhibitory activity is localized to the C-terminal PTPase homology domain, since no inhibition of Ha-ras-mediated focus formation was ob served with a PTP-TD14 mutant, in which the putative catalytic activit y was presumably inactivated by a point mutation. These findings indic ate that PTP-TD14 encodes a novel protein that may be critically invol ved in regulating Ha-ras-dependent cell growth.