The regulation of TCF transcription factors by MAP kinase cascades

A dual role for ERK-1/2 in the regulation of plasmin activity and cell migration in metastatic NSCLC-H1299 cells

Occupational and environmental exposure of various toxins or cigarette smoke causes non-small cell lung carcinoma (NSCLC); a devastating disease with a very low survival rate after metastasis. Increased activity of plasmin is a hallmark in NSCLC metastasis. It is accepted that metastatic cells exhibit higher plasmin activity than cells from primary tumors. Mechanisms behind this elevation, however, are barely understood. We compared plasmin activity and cell migration of A549 cells derived from a primary lung tumor with metastatic H1299 lung cells isolated from lymph nodes. Surprisingly, we found higher plasmin activity and migration for A549 cells. mRNA levels of the plasminogen activator inhibitor-1 (PAI-1) were higher in H1299 cells and activity of extracellular-regulated kinases-1/2 (ERK-1/2) was increased. An inhibitor of ERK-1/2 decreased PAI-1 mRNA levels and increased plasmin activity or cell migration in H1299 cells. Transforming growth factor-β (TGF-β) decreased plasmin activity and migration in A549 cells but enhanced both in H1299 cells. The cytokine massively increased PAI-1 and decreased urokinase plasminogen activator (uPA) levels in A549 cells but strongly induced uPA and only weakly PAI- 1 expression in H1299 cells. Consequently, TGF-β enhanced plasmin activity and cell migration in H1299. Additionally, TGF-β activated ERK-1/2 stronger in H1299 than in A549 cells. Accordingly, an ERK-1/2 inhibitor completely reversed the effects of TGF-β on uPA expression, plasmin activity and migration in H1299 cells. Hence, we provide first data indicating TGF-β-promoted increased plasmin activity and suggest that blocking TGF-β-promoted ERK-1/2 activity might be a straightforward approach to inhibit NSCLC metastasis.

Net expression inhibits the growth of pancreatic ductal adenocarcinoma cell PL45 in vitro and in vivo

Pancreatic ductal adenocarcinoma has a poor prognosis due to late diagnosis and a lack of effective therapeutic options. Thus, it is important to better understand its molecular mechanisms and to develop more effective treatments for the disease. The ternary complex factor Net, which exerts its strong inhibitory function on transcription of proto-oncogene gene c-fos by forming ternary complexes with a second transcription factor, has been suspected of being involved in pancreatic cancer and other tumors biology. In this study, we found that the majority of pancreatic ductal adenocarcinoma tissues and cell lines had weak or no expression of Net, whereas significantly high level of Net expression occurred in paired adjacent normal tissues we studied. Furthermore, using in vitro and in vivo model systems, we found that overexpression of Net inhibited cell growth and survival and induced cell apoptosis in human pancreatic ductal adenocarcinoma cell PL45; the mechanisms by which Net inhibited the cell cycle progression were mainly through P21-Cyclin D1/CDK4 Pathway. Our data thus suggested that Net might play an important role in pancreatic carcinogenesis, possibly by acting as a tumor suppressor gene.

Expression of apoptosis signal-regulating kinase 1 in mouse spinal cord under chronic mechanical compression: possible involvement of the stress-activated mitogen-activated protein kinase pathways in spinal cord cell apoptosis

STUDY DESIGN

To examine apoptosis signal cascade in neurons and oligodendrocytes under the chronic spinal cord compression of tiptoe-walking Yoshimura (TWY) mouse, which is model of progressive cervical cord compression.

OBJECTIVE

To clarify the biologic mechanisms of apoptosis, which may produce destructive changes in the spinal cord under chronic mechanical compression, with a resulting irreversible neurologic deficit.

SUMMARY OF BACKGROUND DATA

The stress-activated mitogen-activated protein kinase pathways including ASK1 transmitted apoptosis signals after acute spinal cord injury. Apoptosis in acute spinal cord injury induced both secondary degeneration around the site of injury and chronic demyelination. Chronic spinal cord compression showed myelin destruction, loss of axons, and oligodendrocytes in white matter, and loss of neurons in gray matter. Apoptosis associated with chronic spinal cord compression contributes to these changes. However, the biologic mechanisms of apoptosis in the spinal cord under chronic mechanical compression remain unclear.

METHODS

We examined the expression of phosphorylated-apoptosis signal-regulating kinase 1 (ASK1), phosphorylated-c-Jun N-terminal kinase (JNK), phosphorylated-p38 mitogen-activated protein kinase (p38), and activated caspase-3 immunohistologically in TWY mice, an animal model of progressive cervical spinal cord compression, since the ASK1-JNK and -p38 signaling cascades participate in the signaling pathway leading to apoptosis in neural tissue and neuronal culture.

RESULTS

Double immunohistochemistry for phosphorylated-ASK1, phosphorylated-JNK, phosphorylated-p38, activated-caspase3, and cell-specific markers confirmed the presence of apoptosis signals in both neurons and oligodendrocytes in compressed spinal cord cells.

CONCLUSION

We found that mitogen-activated protein kinase pathways including ASK1, JNK, and p38 were activated in destructive spinal cord under chronic compression.

Retinoids arrest breast cancer cell proliferation: retinoic acid selectively reduces the duration of receptor tyrosine kinase signaling

Retinoic acid (RA) induces cell cycle arrest of hormone-dependent human breast cancer (HBC) cells. Previously, we demonstrated that RA-induced growth arrest of T-47D HBC cells required the activity of the RA-induced protein kinase, protein kinase Calpha (PKCalpha) [J. Cell Physiol. 172 (1997) 306]. Here, we demonstrate that RA treatment of T-47D cells interfered with growth factor signaling to downstream, cytoplasmic and nuclear targets. RA treatment did not inhibit epidermal growth factor (EGF) receptor activation but resulted in rapid inactivation. The lack of sustained EGFR activation was associated with transient rather than sustained association of the EGFR with the Shc adaptor proteins and activation of Erk 1/2 and with compromised induction of expression of immediate early response genes. Inhibiting the activity of PKCalpha, a retinoic acid-induced target gene, prevented the effects of RA on cell proliferation and EGF signaling. Constitutive expression of PKCalpha, in the absence of RA, decreased cell proliferation and decreased EGF signaling. RA treatment increased steady-state levels of the protein tyrosine phosphatase PTP-1C and all measured effects of RA on EGF receptor function were reversed by the tyrosine phosphate inhibitor orthovanadate. These results indicate that RA-induced target genes, particularly PKCalpha, prevent sustained growth factor signaling, uncoupling activated receptor tyrosine kinases and nuclear targets that are required for cell cycle progression.

The role of c-Jun N-terminal kinase in the Aβ-mediated impairment of LTP and regulation of synaptic transmission in the hippocampus

The effects of the beta-amyloid peptide (Abeta) fragment 25-35 were investigated on hippocampal synaptic transmission and long-term potentiation (LTP) in vitro. Abeta([25-35]) was found to impair both post-tetanic potentiation (PTP) and LTP in the hippocampal CA1. The anthra[1,9-cd]pyrazol-6(2H)-one, SP600125, was used to inhibit c-Jun N-terminal kinase (JNK) activity, which is believed to mediate cell death. Prior application of SP600125 attenuated the Abeta([25-35])-mediated impairment of PTP and LTP, when measured from the pre-drug baseline. In the presence of SP600125 alone, we observed an increase in baseline synaptic transmission and reduction in paired-pulse facilitation, consistent with an increase in synaptic transmission. There was no alteration in the level of PTP and LTP obtained, when measured from the pre-drug baseline. In the presence of both SP600125 and Abeta, however, PTP was greatly enhanced compared with controls. We therefore suggest that the activation of the JNK signalling pathway mediates the effects of Abeta on synaptic plasticity. Our data also indicate that endogenous JNK activity may regulate neurotransmitter release in the hippocampal CA1 in vitro.

Metabolic stabilization of MAP kinase phosphatase-2 in senescence of human fibroblasts

Cellular senescence is characterized by impaired cell proliferation. We have previously shown that, relative to the young counterpart, senescent WI-38 human fibroblasts display a decreased abundance of active phosphorylated ERK (p-ERK) in the nucleus. We have tested the hypothesis that this is due to elevated levels of nuclear MAP kinase phosphatase (MKP) activity in senescent cells. Our results indicate that the activity and abundance of MKP-2 is increased in senescent fibroblasts, compared to their young counterparts. Further analysis indicates that it is MKP-2 protein, but not MKP-2 mRNA level, that is increased in senescent cells. This increase is the result of the increased stability of MKP-2 protein against proteolytic degradation. The degradation of MKPs was impaired by proteasome inhibitors both in young and old WI-38 cells, indicating that proteasome activity is involved in the degradation of MKPs. Finally, our results indicate that proteasome activity, in general, is diminished in senescent fibroblasts. Taken together, these data indicate that the increased level and activity of MKP-2 in senescent WI-38 cells are the consequence of impaired proteosomal degradation, and this increase is likely to play a significant role in the decreased levels of p-ERK in the nucleus of senescent cells.

Lack of Elk-1 phosphorylation and dysregulation of the extracellular regulated kinase signaling pathway in senescent human fibroblast

Replicative senescence is characterized by numerous phenotypic alterations including the loss of proliferative capacity in response to mitogens and numerous changes in gene expression including impaired serum inducibility of the immediate-early genes c-fos and erg-1. Transcription of c-fos in response to mitogens depends on the activation of a multiprotein complex formed on the c-fos serum response element (SRE), which includes the transcription factors SRF (serum response factor) and TCF (ternary complex factor). Our data indicate that at least two defects are responsible for the decreased c-fos transcription in senescent cells, one caused by diminished DNA binding activity of the SRF and another resulting from impaired activation of the TCF, Elk-1. In nuclei isolated from serum stimulated senescent cells the activating phosphorylation of p62(TCF)/Elk-1, which is catalyzed by the members of the extracellular-regulated kinase (ERK) family was strikingly diminished and correlated with a decrease in the abundance of activated ERK proteins. In contrast, in total cell lysates ERK phosphorylation and ERK activity (normalized to total protein) reached similar levels following stimulation of early- and late-passage cells. Interestingly, senescent cells consistently exhibited higher ERK protein abundance. Thus, the proportion of phosphorylated (active) ERK molecules in stimulated senescent cells was lower than in early passage cells. The accumulation of unphosphorylated ERK molecules in senescent cells correlated with the diminished abundance of phosphorylated (active) MEK. These data indicate that in senescent cells there is a general dysregulation in the ERK signaling pathway, which results in the accumulation of inactive ERK molecules, decreased abundance of active ERK in the nucleus of senescent cells, and subsequent lack of activation of the transcription factor TCF(Elk-1). These impairments, together with the impaired DNA binding activity of SRF, could potentially account for the lack of c-fos expression in senescent cells and for multiple other molecular changes dependent upon this pathway.