Role of the phosphatase PP4 in the activation of JNK-1 in prostate carcinoma cell lines PC-3 and LNCaP resulting in increased AP-1 and EGR-1 activity

The specific signaling connections between the mitogen-activated protein kinases (MAPK) such as c-Jun N-terminal kinase (JNK-1) and phosphatases PP4 and M3/6, affecting the family of early nuclear factors, is complex and remains poorly understood. JNK-1 regulates cellular differentiation, apoptosis and stress responsiveness by up-regulating early nuclear factors such as c-Jun, a member of the activating protein (AP-1) family, and the Early Growth Factor (EGR-1). C-Jun, when phosphorylated by c-Jun N-terminal kinase (JNK-1) associates with c-Fos to form the AP-1 transcription factor that activates gene expression. We have investigated the regulation of the JNK-1 kinase by co-transfecting phosphatases PP4 and M3/6 in prostate cancer cell lines PC-3 and LNCaP, which have been previously stimulated with human EGF or cisplatin. Co-transfections of plasmids expressing the JNK-1 and the serine/threonine phosphatases PP4 resulted in a significant increase in JNK-1 activity in both PC3 and LNCaP cells. In contrast, co-transfection of JNK-1 with the dual specific phosphatase serine/threonine M3/6 showed only a marginal effect in JNK-1 activity. The phosphatase M3/6 also failed in blocking the induction of JNK-1 activity observed in presence of PP4. The higher activity of JNK-1 was associated with increased activities of the factors c-Jun/AP-1 and EGR-1. This suggests that JNK-1 activity in PC-3 and LNCaP cells requires not only active PP4 for stable maintenance but also suggests that the relative degree of phosphorylation of multiple cellular components is the determinant of JNK-1 stability.

Identificação de genes codificadores de serina/treonina fosfatases em Dictyostelium discoideum e caracterização funcional da proteína fosfatase do tipo 4 (PP4) / Identification of phosphatases serine/treonine genes coders in Dictyostelium discoideum and functional characterization of phosphatases protein type 4 (PP4)

As serina/treonina fosfatases (PPs) são enzimas responsáveis pela desfosforilação de resíduos de fosfoserina e/ou fosfotreonina e estão subdivididas em duas famílias gênicas designadas PPP e PPM. A família PPP está dividida em cinco subfamílias, que compreendem as PPs do tipo 1 (PP1), 2A (PP2A), 2B (PP2B), 5 (PP5) e 7 (PP7), de acordo com a similaridade entre as sequências de aminoácidos das subunidades ou domínios destas enzimas. Novas PPs estão sendo descobertas em diferentes organismos e classificadas nestas famílias ou subfamílias com base na análise comparada de suas sequências. Uma delas é a proteína fosfatase do tipo 4 (PP4), descoberta originalmente em coelhos e cujas funções biológicas vêm sendo progressivamente elucidadas...

Changes in the pp1 and mRNA level and pp1 activity of ascites hepatomas at different cell growth rates

It is now well established that the type 1 alpha of serine / threonine protein phosphatases [PP1 alpha] may be implicated in malignant phenotype. Although the PP1 alpha mRNA level increased in livers at preneoplastic stages of hepatocarinogenesis and all of examined rat ascites hepatomas, unexpectedly, dramatically decreased in some of primary hepatomas. In order to elucidate the low level of PP1 alpha mRNA in some of primary hepatomas and investigate any correlation between cell growth rates and change [s] of both PP1 alpha mRNA and PP1 activity, the present experiments were done. The most important aspects of the present study are: 1] The PP1 alpha mRNA level may decreased in ascites hepatoma AH -109A cells harvested from a highly bloody ascites compared to ones harvested from a milky ascites. 2] The spontaneous PP1 activity in particulate fraction of AH-7974F showed a positive correlation with cell growth rate. 3] There was no correlation between proliferation rate of AH-7974F and the amount of PP1 alpha catalytic subunit as well as potential PP1 activity in particulate fraction. Therefore, it is suggested that the PP1 alpha mRNA level may decrease in the primary hepatomas with low proliferation rate which were under very bad nutritional conditions