12-O-Tetradecanoylphorbol-13-acetate (TPA)-induced c-Jun N-terminal Kinase (JNK) Phosphatase Renders Immortalized or Transformed Epithelial Cells Refractory to TPA-inducible JNK Activity

Abstract

Members of the mitogen-activated protein kinase (MAPK) 1 superfamily are proline-directed serine/threonine protein kinases that play pivotal roles in transducing various extracellular signals to the nucleus. They consist of three major subfamilies: MAPK/extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK)/stress-activated protein kinase (SAPK), and p38/Mpk2. MAPK/ERK is activated mainly by growth factors and phorbol esters and is associated with cellular proliferation and differentiation (1-3). JNK/SAPK and p38/ Mpk2 are activated by various extracellular stimuli, including growth factors, phorbol esters, UV irradiation and ionizing radiation, heat shock, hyperosmolarity, and cytotoxic drugs (3-6). Activation of these protein kinases leads to various responses, including gene expression, cell proliferation, differentiation, cell cycle arrest, apoptosis, early development, etc., depending on the cell type (7-11).MAPKs phosphorylate diverse target proteins in the membrane or cytosol as well as a number of nuclear transcription factors, indicating their critical role in orchestrating many short and long term changes in cell function (11,12). This has been confirmed recently using specific chemical inhibitors or by expressing mutant versions of different MAPKs or their upstream activators. These studies show that ERKs play a pivotal role in mediating neuronal differentiation in PC12 cells, as well as growth factor-stimulated proliferation and oncogenic transformation in fibroblasts (13,14). Similar approaches have yielded results supporting the view that JNK/SAPK and p38/ Mpk2 are critical in processes mediating platelet aggregation and secretion, in generation of inflammatory cytokines, and in pathways leading to apoptotic death in a number of cell types (15-18).Full activation of MAPKs requires phosphorylation of critical tyrosine and threonine residues. Several upstream dual specificity kinases catalyzing this modification have now been identified (1, 2, 9). Once activated, MAPKs phosphorylate and regulate several cellular proteins, including other protein kinases, cytoskeletal elements, stathmin, phospholipase A 2 , and transcription factors, notably Myc, Jun,19,20). The broad range of substrates indicates a pivotal role for MAPKs in cellular signal transduction, suggesting that the extent and duration of their activation play a key role in controlling cell function.A precise balance of the activities of protein kinases and protein phosphatases (PPs) plays a major role in receptormediated signaling pathways and cell cycle control. Several components of the ERK1/ERK2 pathway are subjected to regulation by PPs such as PP1 and PP2A. Protein-tyrosine phosphatases (PTPs) also play an important role in the attenuation of signals generated by protein-tyrosine kinases involved in mitogenesis. The extent and duration of protein-tyrosine kinase-mediated tyrosine phosphorylation can be greatly enhanced by treatment with the PTP inhibitor, sodium orthovanadate, or its peroxy derivatives (21, 22). It h...

Gene Regulation of CYP4F11 in Human Keratinocyte HaCaT Cells

“…Moreover, this induction of CYP4F11 was shown to be mediated by the JNK pathway as indicated by the loss of cytokine induction of CYP4F11, as well as c-Jun phosphorylation in the presence of JNK inhibitor SP600125. TPA had no effect on CYP4F11 mRNA levels in HaCaT, which is consistent with previous findings that TPA did not induce JNK activity in HaCaT cells (Zhou et al, 2000). CYP4F11 expression was strongly induced by addition of the cytokines TNF-␣ and IL-1␤ but not TPA, indicating the efficacy of AP-1 sites in regulation of CYP4F11 mRNA expression.…”

Overexpression of EGR-1 modulates the activity of NF-κB and AP-1 in prostate carcinoma PC-3 and LNCaP cell lines

“…We found that cisplatin, but not TPA was able to diminish the expression and activity of EGR-1 compared with 10% FCS. NF-κB and AP-1 play a critical role in the transcriptional regulation of genes that have been shown to suppress apoptosis and induce cellular transformation, proliferation, invasion, metastasis, chemo-resistance, radio-resistance and inf lammation (26,27,37,38). We also know that TPA is a potent stimulator of AP-1 trans-criptional activity and an efficient inducer of c-fos and c-jun gene expression.…”

Requirement for ERK Activation in Cisplatin-induced Apoptosis

“…To address this possibility, cells were treated with CDDP in the presence of the phorbol ester TPA. Numerous studies have indicated that TPA is a strong activator of the ERK signaling pathway (7, 28 -30) at concentrations that do not alter JNK activities in HeLa cells (31,32). 2 Cells were pre-incubated with or without 50 nM TPA for 1 h, followed by addition of 20 M CDDP.…”