Suppression of Cancer Cell Migration and Invasion by Protein Phosphatase 2A through Dephosphorylation of μ- and m-Calpains

The μ- and m-calpains are major members of the calpain family that play an essential role in regulating cell motility. We have recently discovered that nicotine-activated protein kinase C ι enhances calpain phosphorylation in association with enhanced calpain activity and accelerated migration and invasion of human lung cancer cells. Here we found that specific disruption of protein phosphatase 2A (PP2A) activity by expression of SV40 small tumor antigen up-regulates phosphorylation of μ- and m-calpains whereas C2-ceramide, a potent PP2A activator, reduces nicotine-induced calpain phosphorylation, suggesting that PP2A may function as a physiological calpain phosphatase. PP2A co-localizes and interacts with μ- and m-calpains. Purified, active PP2A directly dephosphorylates μ- and m-calpains in vitro. Overexpression of the PP2A catalytic subunit (PP2A/C) suppresses nicotine-stimulated phosphorylation of μ- and m-calpains, which is associated with inhibition of calpain activity, wound healing, cell migration, and invasion. By contrast, depletion of PP2A/C by RNA interference enhances calpain phosphorylation, calpain activity, cell migration, and invasion. Importantly, C2-ceramide-induced suppression of calpain phosphorylation results in decreased secretion of μ- and m-calpains from lung cancer cells into culture medium, which may have potential clinic relevance in controlling metastasis of lung cancer. These findings reveal a novel role for PP2A as a physiological calpain phosphatase that not only directly dephosphorylates but also inactivates μ- and m-calpains, leading to suppression of migration and invasion of human lung cancer cells. The μ- and m-calpains are major members of the calpain family that play an essential role in regulating cell motility. We have recently discovered that nicotine-activated protein kinase C ι enhances calpain phosphorylation in association with enhanced calpain activity and accelerated migration and invasion of human lung cancer cells. Here we found that specific disruption of protein phosphatase 2A (PP2A) activity by expression of SV40 small tumor antigen up-regulates phosphorylation of μ- and m-calpains whereas C2-ceramide, a potent PP2A activator, reduces nicotine-induced calpain phosphorylation, suggesting that PP2A may function as a physiological calpain phosphatase. PP2A co-localizes and interacts with μ- and m-calpains. Purified, active PP2A directly dephosphorylates μ- and m-calpains in vitro. Overexpression of the PP2A catalytic subunit (PP2A/C) suppresses nicotine-stimulated phosphorylation of μ- and m-calpains, which is associated with inhibition of calpain activity, wound healing, cell migration, and invasion. By contrast, depletion of PP2A/C by RNA interference enhances calpain phosphorylation, calpain activity, cell migration, and invasion. Importantly, C2-ceramide-induced suppression of calpain phosphorylation results in decreased secretion of μ- and m-calpains from lung cancer cells into culture medium, which may have potential clinic relevance in controlling metastasis of lung cancer. These findings reveal a novel role for PP2A as a physiological calpain phosphatase that not only directly dephosphorylates but also inactivates μ- and m-calpains, leading to suppression of migration and invasion of human lung cancer cells. The process of tumor cell invasion and metastasis is conventionally understood as the migration of individual cells that detach from the primary tumor, enter lymphatic vessels or the bloodstream, and seed in distant organs (1Friedl P. Wolf K. Nature Rev. Cancer. 2003; 3: 362-374Crossref PubMed Scopus (2470) Google Scholar). Cancer cells disseminate from the primary tumor either as individual cells, using amoeboid- or mesenchymal-type movement, or as cell sheets, stands, and clusters using collective migration. Cancer cell migration is typically regulated by integrins, matrix-degrading enzymes (i.e. metalloproteases, calpains, etc.), cell-cell adhesion molecules, and cell-cell communication (1Friedl P. Wolf K. Nature Rev. Cancer. 2003; 3: 362-374Crossref PubMed Scopus (2470) Google Scholar). Tumor invasion is a complex process that involves cellular migration and interaction with the microenvironment at an ectopic site (2Mamoune A. Luo J. Lauffenburger D.A. Wells A. Cancer Res. 2003; 63: 4632-4640PubMed Google Scholar). The extracellular matrix forms a dense molecular mesh-work so that cells may fail to penetrate without proteolytic degradation of the matrix molecules (3Heino, J., Kahari, V. M., (2002) Cell Invasion, Med. Intell. Unit 33, pp. 1-117 Landes Bioscience, Eurekah.comGoogle Scholar). Thus, the proteolytic ability in cells is critical in the processes of cell migration and invasion. Proteolytic enzymes, such as metalloproteases or cysteine proteases (i.e. calpains), dissolve tiny holes in the sheath-like covering (basement membrane) surrounding the blood vessels to allow cancer cells to invade (4Albini A. Iwamoto Y. Kleinman H.K. Martin G.R. Aaronson G.R. Kozlowski J.M. McEwan R.N. Cancer Res. 1987; 47: 3239-3245PubMed Google Scholar, 5Repesh L.A. Invasion Metastasis. 1989; 9: 192-208PubMed Google Scholar). Once the tumor cells enter the stroma, they can easily gain access to lymphatic and blood vessels for further dissemination (6Gomez D.E. Skilton G. Alonso D.F. Kazanietz M. Oncol. Rep. 1999; 6: 1363-1370PubMed Google Scholar). Understanding the mechanisms that regulate migration and invasion of tumor cells is important for development of novel therapies to control metastasis. Mounting evidence indicates that the calpain family of proteases plays an essential role in regulating cell migration and invasion, which potentially contribute to the metastasis of a variety of cancers, including lung cancer (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 9Franco S. Huttenlocher A. J. Cell Sci. 2005; 118: 3829-3838Crossref PubMed Scopus (398) Google Scholar). The mammalian calpain superfamily consists of 16 known genes. Fourteen of these genes encode proteins that contain cysteine protease domains; the other two genes encode smaller regulatory proteins that associate with some of the catalytic subunits to form heterodimeric proteases (9Franco S. Huttenlocher A. J. Cell Sci. 2005; 118: 3829-3838Crossref PubMed Scopus (398) Google Scholar). However, μ- and m-calpains are the major species in the calpain family that are ubiquitously and constitutively expressed in mammalian cells. A distinguishing feature of calpain activity is its ability to confer limited cleavage of protein substrates into stable fragments rather than complete proteolytic digestion (10Carragher N.O. Frame M.C. Int. J. Biochem. Cell Biol. 2002; 34: 1539-1543Crossref PubMed Scopus (120) Google Scholar). Thus, calpain-mediated proteolysis represents a major pathway of post-translational modification that influences various aspects of cell physiology, including apoptosis, proliferation, migration, and invasion (10Carragher N.O. Frame M.C. Int. J. Biochem. Cell Biol. 2002; 34: 1539-1543Crossref PubMed Scopus (120) Google Scholar, 11Sorimachi H. Ishiura S. Suzuki K. Biochem. J. 1997; 328: 721-732Crossref PubMed Scopus (620) Google Scholar). Calpain cleavage of focal adhesion components, including focal adhesion kinase, paxillin, talin, and possibly others, promotes the disassembly of these complexes, which leads to reduced cell adhesion and increased cell motility (12Carragher N.O. Levkau B. Ross R. Raines E.W. J. Cell Biol. 1999; 7: 619-630Crossref Scopus (211) Google Scholar, 13Carragher N.O. Fincham V.J. Riley D. Frame M.C. J. Biol. Chem. 2001; 276: 4270-4275Abstract Full Text Full Text PDF PubMed Scopus (121) Google Scholar). Recent reports indicate that, in addition to Ca2+ binding, phosphorylation of calpain can also enhance its activity to accelerate cell migration and invasion (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 14Glading A. Uberall F. Keyse S.M. Lauffenburger D.A. Wells A. J. Biol. Chem. 2001; 276: 23341-23348Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar). Epidermal growth factor, nicotine, and nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone have been found to induce calpain phosphorylation through activation of MAPKs 2The abbreviations used are: MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; SCLC, small cell lung cancer; t-Boc-LM-CMAC, t-butoxycarbonyl-Leu-Met-chloromethyl-aminocoumarin; PP2A/C, protein phosphatase 2A catalytic subunit; small t, SV40 small tumor antigen; siRNA, small interfering RNA; RNAi, RNA interference; PBS, phosphate-buffered saline; FBS, fetal bovine serum; HA, hemagglutinin; FITC, fluorescein isothiocyanate. ERK1/2 and/or protein kinase c ι, which is associated with increased calpain activity as well as cell motility (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 14Glading A. Uberall F. Keyse S.M. Lauffenburger D.A. Wells A. J. Biol. Chem. 2001; 276: 23341-23348Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar). However, whether a physiological phosphatase is involved in calpain dephosphorylation remains unclear. PP2A is a major protein serine/threonine phosphatase that participates in many cellular signaling pathways in mammalian cells (15Mumby M.C. Walter G. Physiol. Rev. 1993; 73: 673-699Crossref PubMed Scopus (627) Google Scholar). It is a heterotrimer consisting of a 36-kDa catalytic subunit (PP2A/C), a 65-kDa structural A subunit (PP2A/A), and a variable regulatory subunit (PP2A/B, which can vary in size from 50 to 130 kDa). The AC catalytic complex alone has phosphatase activity, while the distinct B-subunits can recruit PP2A/C to distinct subcellular locations and then define a specific substrate target (16Cegielska A. Shaffer S. Derua R. Goris J. Virshup D. Mol. Cell. Biol. 1994; 14: 4616-4623Crossref PubMed Scopus (100) Google Scholar, 17Sontag E. Nunbhakdi-Craig V. Bloom G. Mumby M. J. Cell Biol. 1995; 128: 1131-1144Crossref PubMed Scopus (296) Google Scholar, 18McCright B. Rivers A. Audlin S. Virshup D. J. Biol. Chem. 1996; 271: 22081-22089Abstract Full Text Full Text PDF PubMed Scopus (327) Google Scholar). Recent reports indicate that PP2A can potently restrict migration of various types of cells, including lung carcinoma cells (19Young M. Kolesiak K. Meisinger J. Int. J. Cancer. 2002; 100: 276-282Crossref PubMed Scopus (36) Google Scholar, 20Young M. Liu S. Meisinger J. Int. J. Cancer. 2003; 103: 38-44Crossref PubMed Scopus (25) Google Scholar, 21Pullar C. Chen J. Isseroff R. J. Biol. Chem. 2003; 278: 22555-22562Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar). However, the downstream targets for PP2A in negative regulation of cell motility have not totally been identified. Here we provided strong evidence that PP2A functions as a physiological calpain phosphatase to directly dephosphorylate both μ- and m-calpains, which leads to decreased calpain activity and suppression of migration and invasion of human lung cancer cells. Materials—Anti-μ-calpain, m-calpain, PP2A/C, fluorescein isothiocyanate (FITC)-conjugated anti-goat, and rhodamine-conjugated anti-rabbit IgG antibodies from from and PP2A from calpain substrate from The cell migration and cell invasion from antigen from The provided by of small antigen in provided by Mumby of used from Cell and Cell and human lung cancer cells from cells in with fetal bovine and and cells in with fetal bovine and with fetal bovine then with and with for with or C2-ceramide, cells with and in μ- or using a μ- or The to to a and to at of μ- or by The then by using a μ- or and using an from as (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar). of μ- or in cells with and with for μ- or using an The in and in of phosphatase 50 bovine PP2A and the at for The by the addition of The for Calpain phosphorylation by of Calpain in at in a and with for The cells then with or in the of for then a as (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar). Calpain with using as J. D. J. in Scholar, K. A. K. Biochem. 1995; PubMed Scopus Google Scholar). cells with and in the 50 and with of and The for at at for complete of cell μ- and m-calpains in of and into well and to in a and the in a 50 and at μ- or cleavage of can in the of in a The of in the can easily from of its K. A. K. Biochem. 1995; PubMed Scopus Google Scholar). Cell and Invasion with or as Cell migration using a cell migration the not cell or that through the with and then and a at Cell invasion using the cell invasion in an invasion which is a with cell culture The contain an size which a of is The extracellular matrix the cells from Invasion cells through the extracellular matrix and to the of the The with cells the in the with cell and for at with a at and the of into a culture and to to in complete Cell by a that the as L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar). then with to cell and in in the or of or for various to a with a and a at with with PBS, with and and with and with human μ- or and human PP2A/C primary antibodies for with and rhodamine-conjugated anti-rabbit antibodies for with and a and with the for subcellular of protein individual and from the using from of protein of PP2A by RNA PP2A/C into cells by using to the A control to known as a negative The of PP2A/C expression by using a PP2A/C for specific of the PP2A/C of from in culture as (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar). cells in with and with in the or of of for at for to the cells. The further at for to the cell the the at for in an with a The with and then in of A 50 and with for and then to of μ- or in the from cell culture by of PP2A by of in of μ- and in with of Calpain of and Invasion of Cancer findings and of have that phosphorylation of μ- and m-calpains through activation of MAPKs ERK1/2 and/or protein kinase C ι calpain activity and cell motility (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 14Glading A. Uberall F. Keyse S.M. Lauffenburger D.A. Wells A. J. Biol. Chem. 2001; 276: 23341-23348Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar). both μ- and m-calpains are with serine/threonine protein phosphatase 2A (PP2A) in both small cell lung cancer cells (i.e. and and cell lung cancer cells (i.e. and PP2A may as a physiological phosphatase to regulate calpain It is well known that the SV40 small tumor antigen can with the 36-kDa catalytic C and the A subunits of which can PP2A activity E. S. C. D. M. Mumby M. Cell. 1993; Full Text PDF PubMed Scopus Google Scholar). whether inhibition of PP2A activity calpain phosphorylation, the antigen into cells. cells with expression of small antigen enhances phosphorylation of both μ- and m-calpains and whether expression of small antigen the proteolytic activity of calpains, t-Boc-LM-CMAC, a calpain used for of calpain activity in cells as (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar). of by active can induce of the of the in the cells and can in increased (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar). The antigen into cells. cells with for indicate that expression of small antigen enhances calpain activity further the of small antigen activity for individual μ- calpain using as can calpain activity in are in which has been the are in a a in the of the active μ- or is to fragments small to of the and μ- or is also The are and with The μ- or activity in a reveal that expression of small antigen enhances of both μ- and m-calpains suggesting that phosphorylation may both μ- and m-calpains. the of small antigen cell a wound as with control cells, wound is accelerated in cells small antigen expression of small antigen enhances both migration and invasion of human lung cancer cells These findings that PP2A may function as a physiological calpain phosphatase to induce calpain dephosphorylation in lung cancer cell motility lung cancer cell (i.e. and also and results not These results the that calpain phosphorylation may a process that is regulated by calpain (i.e. ERK1/2 and protein kinase C (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 14Glading A. Uberall F. Keyse S.M. Lauffenburger D.A. Wells A. J. Biol. Chem. 2001; 276: 23341-23348Abstract Full Text Full Text PDF PubMed Scopus (186) Google and (i.e. Thus, protein phosphorylation of μ- and m-calpains may in cells specific inhibition of PP2A activity by small antigen up-regulates calpain phosphorylation Calpain in with of Calpain and Invasion of Cancer is a potent of PP2A B. S. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, M. Deng X. J. Biol. Chem. 2006; 281: Full Text Full Text PDF PubMed Scopus (121) Google is that may induce calpain dephosphorylation through activation of cells with and with in the or of of indicate that suppresses nicotine-induced phosphorylation of μ- and m-calpains in a Importantly, of cells with nicotine-stimulated calpain activity, wound healing, and cell migration and invasion These findings that PP2A may the calpain phosphorylation PP2A and with μ- and a potential role for PP2A as a physiological calpain subcellular of PP2A/C and calpain by A human μ- or m-calpain, PP2A/C and or anti-rabbit antibodies used so that cells without in μ- or is with PP2A/C in the of cells. whether PP2A enhances an association PP2A and cells with of for A using an μ- or The μ- or PP2A/C (i.e. by using a PP2A/C reveal that of cells with promotes PP2A/C to associate with μ- or in a Thus, PP2A/C may potentially function as a physiological phosphatase for both μ- and m-calpains to regulate in human lung cancer cells. PP2A and μ- and in with of and Invasion of Cancer is the known protein phosphatase expressed in mammalian cells (15Mumby M.C. Walter G. Physiol. Rev. 1993; 73: 673-699Crossref PubMed Scopus (627) Google Scholar). whether PP2A can directly dephosphorylate cells with and with for μ- or using an μ- or The μ- or used as substrate and with active PP2A at for that PP2A the from μ- or m-calpain, suggesting that PP2A can directly dephosphorylate μ- or in further whether PP2A can dephosphorylate in a into cells. The of PP2A/C by using an cells PP2A/C or control cells with and with for indicate that of potently nicotine-induced phosphorylation of both μ- and m-calpains of PP2A/C not only suppresses nicotine-stimulated calpain activity but also wound healing, migration, and invasion of human lung cancer cells of PP2A/C by Calpain and in and Invasion of Cancer that PP2A functions as a physiological calpain phosphatase to dephosphorylate which may to decreased calpain whether PP2A is essential for calpain cells with PP2A/C as that the PP2A/C and reduces PP2A/C expression in cells whereas control has Importantly, specific disruption of PP2A/C expression by not only results in phosphorylation of both μ- and m-calpains but also further enhances nicotine-stimulated calpain phosphorylation in association with increased calpain activity, accelerated wound healing, cell migration, and invasion These findings that PP2A may essential for dephosphorylation of to regulate motility of human lung cancer cells. of with of μ- and from Cancer has been to a of cell migration and invasion to focal and many focal including focal adhesion kinase, and Huttenlocher A. Lauffenburger D.A. J. Cell Sci. PubMed Google Scholar). secretion of from of cells into extracellular matrix is critical for the of calpain cell motility. We have discovered that or nitrosamine calpain phosphorylation promotes secretion of μ- and m-calpains from lung cancer cells into culture through a pathway (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar). whether C2-ceramide-induced dephosphorylation of cells with in the or of of for The as indicates that nicotine-induced secretion of both μ- and m-calpains in a Calpain activity is for of the cell and to of cells wound and tumor invasion H. J. C. S. D. Wells A. Mol. Cell. Biol. 2006; PubMed Scopus Google Scholar). inhibition of calpain activity by a or disruption of calpain expression by in decreased cell migration and/or invasion (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, A. S. R. D. M. A. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, M. J. A. M. S. 2006; PubMed Scopus Google that are in the cellular that cell motility. calpain activity is in various tumor cells with cells J. E. J. M. H. K. E. A. 2002; 100: PubMed Scopus Google Scholar, B. Frame M. 2004; 6: PubMed Google and suppression of invasion of carcinoma cells in (2Mamoune A. Luo J. Lauffenburger D.A. Wells A. Cancer Res. 2003; 63: 4632-4640PubMed Google that calpain activity in tumor cells may potentially tumor metastasis in a by migration and invasion. Thus, the mechanisms leading to calpain or may of in novel for of calpain activity is regulated by the is activation by contain in and However, structural that by of the alone are to the active site catalytic (9Franco S. Huttenlocher A. J. Cell Sci. 2005; 118: 3829-3838Crossref PubMed Scopus (398) Google Scholar). the of to in not cells. other regulatory including phosphorylation may play a critical role in regulating calpain findings and of discovered that MAPKs ERK1/2 and protein kinase C ι function as physiological calpain that can directly and (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 14Glading A. Uberall F. Keyse S.M. Lauffenburger D.A. Wells A. J. Biol. Chem. 2001; 276: 23341-23348Abstract Full Text Full Text PDF PubMed Scopus (186) Google suggesting that protein calpain phosphorylation may important for calpain However, is whether calpain dephosphorylation by a protein phosphatase plays a role in regulating calpain activity and cell motility. PP2A is a protein serine/threonine phosphatase that is for of the cellular serine/threonine dephosphorylation PP2A can regulate cell motility inhibition of PP2A activity with migration of various tumor cells (19Young M. Kolesiak K. Meisinger J. Int. J. Cancer. 2002; 100: 276-282Crossref PubMed Scopus (36) Google Scholar, 20Young M. Liu S. Meisinger J. Int. J. Cancer. 2003; 103: 38-44Crossref PubMed Scopus (25) Google Scholar). that PP2A functions as a calpain phosphatase specific disruption of PP2A activity by expression of small antigen enhances phosphorylation of both μ- and m-calpains in association with increased calpain activity and cell motility PP2A not only co-localizes and interacts with both μ- and m-calpains but also directly dephosphorylates μ- and m-calpains in and its potential role as a calpain phosphatase. Importantly, of PP2A/C results in calpain decreased calpain activity, and reduced cell migration and invasion By contrast, specific of PP2A/C expression by calpain phosphorylation in association with accelerated cell motility These findings evidence that PP2A is a physiological calpain phosphatase in Thus, PP2A suppression of cell migration and invasion may in a novel by directly and the major calpain the μ- and m-calpains. The functions as a that cellular including apoptosis, cell cell cell and cellular E. Res. 2003; 47: PubMed Scopus Google Scholar). It is that can PP2A activity by to its catalytic B. S. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). Here we found that the PP2A not only promotes PP2A/C to associate with μ- or but also potently calpain dephosphorylation 2A and suggesting that μ- and m-calpains may function as downstream targets in the suppression of cell motility We have that or nitrosamine calpain phosphorylation promotes secretion of active μ- and m-calpains from lung cancer cells through a pathway which may have potential to substrates in the extracellular matrix (7Xu L. Deng X. J. Biol. Chem. 2004; 279: 53683-53690Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 8Xu L. Deng X. J. Biol. Chem. 2006; 281: 4457-4466Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar). potently nicotine-stimulated calpain secretion indicates that C2-ceramide-induced dephosphorylation of μ- and m-calpains by PP2A calpain which may contribute to of cell motility. findings have PP2A as a novel physiological calpain phosphatase that can directly dephosphorylate and the major calpain the μ- and m-calpains. calpain dephosphorylation through activation of PP2A results in decreased calpain activity and suppression of calpain leading to reduced migration and invasion of human lung cancer cells. Thus, activation of PP2A to dephosphorylate calpain by may have relevance for the of cancer metastasis. We of and Mumby of for the and small