Protein phosphatase-2A regulates protein tyrosine phosphatase activity in Lewis lung carcinoma tumor variants

Role of Akt/Protein Kinase B in Cancer Metastasis

Metastasis is a critical step in the process of carcinogenesis and a vast majority of cancer-related mortalities result from metastatic disease that is resistant to current therapies. Cell migration and invasion are the first steps of the metastasis process, which mainly occurs by two important biological mechanisms, i.e., cytoskeletal remodelling and epithelial to mesenchymal transition (EMT). Akt (also known as protein kinase B) is a central signalling molecule of the PI3K-Akt signalling pathway. Aberrant activation of this pathway has been identified in a wide range of cancers. Several studies have revealed that Akt actively engages with the migratory process in motile cells, including metastatic cancer cells. The downstream signalling mechanism of Akt in cell migration depends upon the tumour type, sites, and intracellular localisation of activated Akt. In this review, we focus on the role of Akt in the regulation of two events that control cell migration and invasion in various cancers including head and neck squamous cell carcinoma (HNSCC) and the status of PI3K-Akt pathway inhibitors in clinical trials in metastatic cancers.

An Insight into the Anti-Angiogenic and Anti-Metastatic Effects of Oridonin: Current Knowledge and Future Potential

Cancer is one of the leading causes of death worldwide, with a mortality rate of more than 9 million deaths reported in 2018. Conventional anti-cancer therapy can greatly improve survival however treatment resistance is still a major problem especially in metastatic disease. Targeted anti-cancer therapy is increasingly used with conventional therapy to improve patients' outcomes in advanced and metastatic tumors. However, due to the complexity of cancer biology and metastasis, it is urgent to develop new agents and evaluate the anti-cancer efficacy of available treatments. Many phytochemicals from medicinal plants have been reported to possess anti-cancer properties. One such compound is known as oridonin, a bioactive component of Rabdosia rubescens. Several studies have demonstrated that oridonin inhibits angiogenesis in various types of cancer, including breast, pancreatic, lung, colon and skin cancer. Oridonin's anti-cancer effects are mediated through the modulation of several signaling pathways which include upregulation of oncogenes and pro-angiogenic growth factors. Furthermore, oridonin also inhibits cell migration, invasion and metastasis via suppressing epithelial-to-mesenchymal transition and blocking downstream signaling targets in the cancer metastasis process. This review summarizes the recent applications of oridonin as an anti-angiogenic and anti-metastatic drug both in vitro and in vivo, and its potential mechanisms of action.

Role of mTOR signaling in tumor cell motility, invasion and metastasis

Tumor cell migration and invasion play fundamental roles in cancer metastasis. The mammalian target of rapamycin (mTOR), a highly conserved and ubiquitously expressed serine/threonine (Ser/Thr) kinase, is a central regulator of cell growth, proliferation, differentiation and survival. Recent studies have shown that mTOR also plays a critical role in the regulation of tumor cell motility, invasion and cancer metastasis. Current knowledge indicates that mTOR functions as two distinct complexes, mTORC1 and mTORC2. mTORC1 phosphorylates p70 S6 kinase (S6K1) and eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1), and regulates cell growth, proliferation, survival and motility. mTORC2 phosphorylates Akt, protein kinase C α (PKCα) and the focal adhesion proteins, and controls the activities of the small GTPases (RhoA, Cdc42 and Rac1), and regulates cell survival and the actin cytoskeleton. Here we briefly review recent knowledge of mTOR complexes and the role of mTOR signaling in tumor cell migration and invasion. We also discuss recent efforts about the mechanism by which rapamycin, a specific inhibitor of mTOR, inhibits cell migration, invasion and cancer metastasis.

shRNA-mediated down-regulation of paxillin reduces cell invasion in human colon adenocarcinoma cell line SW480

AIM: To investigate the effect of short hairpin RNA (shRNA)-mediated down-regulation of paxillin expression on cell invasion in human colorectal adenocarcinoma cell line SW480 in vitro.

METHODS: shRNA targeting the paxillin gene was constructed and transfected into SW480 cells. SW480 cells were divided into three groups: untransfected cells, cells transfected with a control shRNA, and those transfected with a paxillin-specific shRNA. After transfection, the invasion of cells was analyzed by Transwell migration assay.

RESULTS: The expression of paxillin was inhibited in SW480 cells after the transfection of paxillin-specific shRNA. The numbers of cells passing the Transwell membrane were significantly lower in cells transfected with the paxillin-specific shRNA than in untransfected cells and those transfected with control shRNA (23.33 ± 6.12 vs 62.00 ± 6.26, 55.00 ± 13.04, F = 30.976, P < 0.05).

CONCLUSION: Down-regulation of paxillin gene expression reduces cell invasion in human colon adenocarcinoma cell line SW480 in vitro.

Optimization of a cyclic peptide inhibitor of Ser/Thr phosphatase PPM1D (Wip1)

PPM1D (PP2Cδ or Wip1) was identified as a wild-type p53-induced Ser/Thr phosphatase that accumulates after DNA damage and classified into the PP2C family. It dephosphorylates and inactivates several proteins critical for cellular stress responses, including p38 MAPK, p53, and ATM. Furthermore, PPM1D is amplified and/or overexpressed in a number of human cancers. Thus, inhibition of its activity could constitute an important new strategy for therapeutic intervention to halt the progression of several different cancers. Previously, we reported the development of a cyclic thioether peptide with low micromolar inhibitory activity toward PPM1D. Here, we describe important improvements in the inhibitory activity of this class of cyclic peptides and also present a binding model based upon the results. We found that specific interaction of an aromatic ring at the X1 position and negative charge at the X5 and X6 positions significantly increased the inhibitory activity of the cyclic peptide, with the optimized molecule having a K(i) of 110 nM. To the best of our knowledge, this represents the highest inhibitory activity reported for an inhibitor of PPM1D. We further developed an inhibitor selective for PPM1D over PPM1A with a K(i) of 2.9 μM. Optimization of the cyclic peptide and mutagenesis experiments suggest that a highly basic loop unique to PPM1D is related to substrate specificity. We propose a new model for the catalytic site of PPM1D and inhibition by the cyclic peptides that will be useful both for the subsequent design of PPM1D inhibitors and for identification of new substrates.

mTOR signaling in cancer cell motility and tumor metastasis

Tumor cell migration is a key step in the formation of cancer metastasis. The mammalian target of rapamycin (mTOR), a highly conserved and ubiquitously expressed serinethreonine kinase, has been intensely studied for over a decade as a central regulator of cell growth, proliferation, differentiation, and survival. Recent data have shown that mTOR also plays a critical role in the regulation of tumor cell motility and cancer metastasis. Here, we briefly review recent advances regarding mTOR signaling in tumor cell motility. We also discuss recent findings about the mechanism by which rapamycin, a specific inhibitor of mTOR, inhibits cell motility in vitro and metastasis in vivo.

Rapamycin inhibits IGF-1 stimulated cell motility through PP2A pathway

Serine/threonine (Ser/Thr) protein phosphatase 2A (PP2A) has been implicated as a novel component of the mammalian target of rapamycin (mTOR) signaling pathway. Recently we have demonstrated that mTOR regulates cell motility in part through p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1) pathways. Little is known about the role of PP2A in the mTOR-mediated cell motility. Here we show that rapamycin inhibited the basal or insulin-like growth factor 1 (IGF-1)-induced motility of human Ewing sarcoma (Rh1) and rhabdomyosarcoma (Rh30) cells. Treatment of the cells with rapamycin activated PP2A activity, and concurrently inhibited IGF-1 stimulated phosphorylation of Erk1/2. Inhibition of Erk1/2 with PD98059 did not significantly affect the basal mobility of the cells, but dramatically inhibited IGF-1-induced cell motility. Furthermore, inhibition of PP2A with okadaic acid significantly attenuated the inhibitory effect of rapamycin on IGF-1-stimulated phosphorylation of Erk1/2 as well as cell motility. Consistently, expression of dominant negative PP2A conferred resistance to IGF-1-stimulated phosphorylation of Erk1/2 and cell motility. Expression of constitutively active MKK1 also attenuated rapamycin inhibition of IGF-1-stimulated phosphorylation of Erk1/2 and cell motility. The results suggest that rapamycin inhibits cell motility, in part by targeting PP2A-Erk1/2 pathway.

Dictyostelium discoideum paxillin regulates actin-based processes

Paxillin is a key player in integrating the actin cytoskeleton with adhesion, and thus is essential to numerous cellular processes, including proliferation, differentiation, and migration in animal cells. PaxB, the Dictyostelium discoideum orthologue of paxillin, has been shown to be important for adhesion and development, much like its mammalian counterpart. Here, we use the overproduction of PaxB to gain better insight into its role in regulating the actin cytoskeleton and adhesion. We find that PaxB-overexpressing (PaxBOE) cells can aggregate and form mounds normally, but are blocked in subsequent development. This arrest can be rescued by addition of wild-type cells, indicating a non-cell autonomous role for PaxB. PaxBOE cells also have alterations in several actin-based processes, including adhesion, endocytosis, motility, and chemotaxis. PaxBOE cells exhibit an EDTA-sensitive increase in cell-cell cohesion, suggesting that PaxB-mediated adhesion is Ca(2+) or Mg(2+) dependent. Interestingly, cells overexpressing paxB are less adhesive to the substratum. In addition, PaxBOE cells display decreased motility under starved conditions, decreased endocytosis, and are unable to efficiently chemotax up a folate gradient. Taken together, the data suggest that proper expression of PaxB is vital for the regulation of development and actin-dependent processes.

Paxillin comes of age

Paxillin is a multi-domain scaffold protein that localizes to the intracellular surface of sites of cell adhesion to the extracellular matrix. Through the interactions of its multiple protein-binding modules, many of which are regulated by phosphorylation, paxillin serves as a platform for the recruitment of numerous regulatory and structural proteins that together control the dynamic changes in cell adhesion, cytoskeletal reorganization and gene expression that are necessary for cell migration and survival. In particular, paxillin plays a central role in coordinating the spatial and temporal action of the Rho family of small GTPases, which regulate the actin cytoskeleton, by recruiting an array of GTPase activator, suppressor and effector proteins to cell adhesions. When paxillin was first described 18 years ago, the amazing complexity of cell-adhesion organization, dynamics and signaling was yet to be realized. Herein we highlight our current understanding of how the multiple protein interactions of paxillin contribute to the coordination of cell-adhesion function.

Paxillin: adapting to change

Molecular scaffold or adaptor proteins facilitate precise spatiotemporal regulation and integration of multiple signaling pathways to effect the optimal cellular response to changes in the immediate environment. Paxillin is a multidomain adaptor that recruits both structural and signaling molecules to focal adhesions, sites of integrin engagement with the extracellular matrix, where it performs a critical role in transducing adhesion and growth factor signals to elicit changes in cell migration and gene expression.