The Benzo[c]phenanthridine Alkaloid, Sanguinarine, Is a Selective, Cell-active Inhibitor of Mitogen-activated Protein Kinase Phosphatase-1

Abstract

Mitogen-activated protein kinase phosphatase (MKP)1 -1 is a dual specificity phosphatase that is overexpressed in many human tumors and protects cells from apoptosis by the anticancer agent cisplatin (1), UV irradiation (2), and proteasome inhibitors (3). Over the past five years, reports have become more numerous describing high levels of MKP-1 in human tumors. For example, high levels of MKP-1 have been found in prostate (4), gastric (5), breast (6), and pancreatic cancer (7). In ovarian cancer samples, MKP-1 expression was correlated with decreased progression-free survival (8). High levels of MKP-1 expression were also found in the early phases of prostate, colon, and bladder carcinogenesis (9). Evidence that MKP-1 may actually support the transformed phenotype comes from a recent study by Liao et al. (7) who showed that PANC-1 human pancreatic cancer cells stably transfected with a full-length MKP-1 antisense construct had longer doubling times, decreased ability to form colonies in soft agar, and were unable to form tumors in nude mice. The precise mechanism by which loss of MKP-1 expression affects tumorigenicity, however, remains elusive. Several reports have implicated JNK/SAPK and p38 as the primary mediators of MKP-1 mediated cytoprotection (1-2). On the other hand, the data presented by Liao et al. (7) argue that the primary mechanism by which MKP-1 supports the transformed phenotype is mediated by ERK, but not JNK, as suppression of MKP-1 expression by antisense did not affect basal levels of phospho-JNK or phospho-p38, but instead increased basal ERK phosphorylation and prolonged ERK phosphorylation after epidermal growth factor stimulation in PANC-1 cells.The availability of a cell-active selective MKP-1 inhibitor would be a valuable tool for dissecting the complex regulatory processes involved in the attenuation of ERK, JNK, and p38 activation and for defining the contributions of MKP-1 and its cellular targets to the maintenance of the transformed phenotype. In light of recent findings, inhibitors of MKP-1 might also find applications as novel target-based antineoplastic therapies, either alone or in combination with clinically used antineoplastic agents (1-3).The search for MKP-1 inhibitors has been challenging for several reasons. In contrast to MKP-3, whose crystal structure has been reported and found to possess high structural similarity to the related VHR in its catalytic domain (10), no structural information is available for MKP-1. This may in part be due to difficulties in producing large amounts of recombinant enzyme and the need of MKPs to interact with their physiolog-

β-asarone from Acorus gramineus alleviates depression by modulating MKP-1

“…Overexpression of MKP-1 prevented ERK activity (low expression of p-ERK1/2) and downregulated the expression of BDNF. MKP-1 is not only directly expressed in response to stress, but is also a key negative regulator of the ERK signaling pathway, contributing to the expression of depressive symptoms (Vogt et al, 2005;Duric et al, 2010). BDNF is well-known for its effects on axon outgrowth and branching (Cohen-Cory, 2002).…”

Redox regulation of MAPK phosphatase 1 controls monocyte migration and macrophage recruitment

“…MKP-1 activity was determined with a modification of the commercially available MalachiteGreen-based PTP assay (Millipore). To assess MKP-1-specific PTP activity, lysates were analyzed in the absence and presence of 40 μM sanguinarine, a specific inhibitor of MKP-1 (49). Sanguinarine-sensitive PTP activity was attributed to MKP-1.…”

Implementation of high-content assay for inhibitors of mitogen-activated protein kinase phosphatases

“…The resulting KS values can assume a value between 0 (identical distributions) and 1 (completely different distributions). In previous reports, we had experimented with a two-dimensional implementation of the KS statistic and shown it dramatically reduced assay variability and the number of false positives compared with measurements based on well averages [33,39]. At the time, an appealing feature of the two-dimensional variation of the KS method was that it condensed all of the information content in each well into a single numerical value by ranging over data in an (x,y) plane in search of a maximum cumulative difference between two twodimensional data distributions [40,41].…”

“…The differential in Erk phosphorylation in MKPexpressing and non-expressing cells then serves as a measure of phosphatase activity. The HCS embodiment of the assay has been used for compound credentialing studies [31] and a small scale library screen [32]. The assay identified sanguinarine as a small molecule inhibitor of MKP-1 but not MKP-3.…”