Apoptosis Signal-regulating Kinase 1 (ASK1) Induces Neuronal Differentiation and Survival of PC12 Cells

Abstract

Apoptosis signal-regulating kinase 1 (ASK1) is a ubiquitously expressed mitogen-activated protein kinase kinase kinase that activates the c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase signaling cascades. We report here that expression of constitutively active ASK1 (ASK1ΔN) induces neurite outgrowth in the rat pheochromocytoma cell line PC12. We found that p38 and to a lesser extent JNK, but not ERK, were activated by the expression of ASK1ΔN in PC12 cells. ASK1ΔN-induced neurite outgrowth was strongly inhibited by treatment with the p38 inhibitor SB203580 but not with the MEK inhibitors, suggesting that activation of p38, rather than of ERK, is required for the neurite-inducing activity of ASK1 in PC12 cells. We also observed that ASK1ΔN induced expression of several neuron-specific proteins and phosphorylation of neurofilament proteins, confirming that PC12 cells differentiated into mature neuronal cells by ASK1. Moreover, ASK1ΔN-expressing PC12 cells survived in serum-starved condition. ASK1 thus appears to mediate signals leading to both differentiation and survival of PC12 cells. Together with previous reports indicating that ASK1 functions as a pro-apoptotic signaling intermediate, these results suggest that ASK1 has a broad range of biological activities depending on cell types and/or cellular context. Apoptosis signal-regulating kinase 1 (ASK1) is a ubiquitously expressed mitogen-activated protein kinase kinase kinase that activates the c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase signaling cascades. We report here that expression of constitutively active ASK1 (ASK1ΔN) induces neurite outgrowth in the rat pheochromocytoma cell line PC12. We found that p38 and to a lesser extent JNK, but not ERK, were activated by the expression of ASK1ΔN in PC12 cells. ASK1ΔN-induced neurite outgrowth was strongly inhibited by treatment with the p38 inhibitor SB203580 but not with the MEK inhibitors, suggesting that activation of p38, rather than of ERK, is required for the neurite-inducing activity of ASK1 in PC12 cells. We also observed that ASK1ΔN induced expression of several neuron-specific proteins and phosphorylation of neurofilament proteins, confirming that PC12 cells differentiated into mature neuronal cells by ASK1. Moreover, ASK1ΔN-expressing PC12 cells survived in serum-starved condition. ASK1 thus appears to mediate signals leading to both differentiation and survival of PC12 cells. Together with previous reports indicating that ASK1 functions as a pro-apoptotic signaling intermediate, these results suggest that ASK1 has a broad range of biological activities depending on cell types and/or cellular context. nerve growth factor apoptosis signal-regulating kinase 1 extracellular signal-regulating kinase horse serum c-Jun N-terminal kinase mitogen-activated kinase superior cervical ganglia tetracycline mitogen-activated protein MAPK/ERK kinase stress-activated protein kinase bone morphogenetic protein tumor necrosis factor Dulbecco's modified Eagle's medium fetal calf serum hemagglutinin phosphate-buffered saline wild type multiplicity of infection β-tubulin isoform III adenovirus neurofilament light neurofilament medium neurofilament heavy hygromycin The rat pheochromocytoma cell line PC12 is a useful model of neuronal differentiation and death (1.Greene L.A. Tischler A.S. Proc. Natl. Acad. Sci. U. S. A. 1976; 73: 2424-2428Crossref PubMed Scopus (4803) Google Scholar). On treatment with nerve growth factor (NGF),1 PC12 cells differentiate with sympathetic neuron-like characteristics including neurite outgrowth. Upon binding of NGF, the cell surface receptor tyrosine kinase is activated, and the activated kinase in turn activates the small GTP-binding protein Ras followed by sequential phosphorylation and activation of three members of the mitogen-activated protein kinase (MAPK) superfamily, MAPK kinase kinase (MAPKKK)/Raf, MAPK kinase (MAPKK)/MEK, and MAPK/extracellular signal-regulated kinase (ERK) (2.Chao M.V. Cell. 1992; 68: 995-997Abstract Full Text PDF PubMed Scopus (267) Google Scholar, 3.Wood K.W. Sarnecki C. Roberts T.M. Blenis J. Cell. 1992; 68: 1041-1050Abstract Full Text PDF PubMed Scopus (656) Google Scholar, 4.Nishida E. Gotoh Y. Trends Biochem. Sci. 1993; 18: 128-131Abstract Full Text PDF PubMed Scopus (958) Google Scholar). Activation of the ERK pathway is thought to play roles during NGF-induced neuronal differentiation, since constitutively active MEK induced neurite outgrowth and selective blockade of the ERK pathway using dominant-negative MEK or the MEK inhibitor PD98059 resulted in inhibition of NGF-induced neurite outgrowth (5.Cowley S. Paterson H. Kemp P. Marshall C.J. Cell. 1994; 77: 841-852Abstract Full Text PDF PubMed Scopus (1844) Google Scholar, 6.Fukuda M. Gotoh Y. Tachibana T. Dell K. Hattori S. Yoneda Y. Nishida E. Oncogene. 1995; 11: 239-244PubMed Google Scholar, 7.Pang L. Sawada T. Decker S.J. Saltiel A.R. J. Biol. Chem. 1995; 270: 13585-13588Abstract Full Text Full Text PDF PubMed Scopus (895) Google Scholar). It has also been suggested that persistence of ERK activation is critical for differentiation of PC12 cells, since transient activation of ERK induced by agents such as EGF is insufficient to induce neurite outgrowth (8.Qui M.S. Green S.H. Neuron. 1992; 9: 705-717Abstract Full Text PDF PubMed Scopus (359) Google Scholar, 9.Traverse S. Gomez N. Paterson H. Marshall C. Cohen P. Biochem. J. 1992; 288: 351-355Crossref PubMed Scopus (802) Google Scholar, 10.Marshall C.J. Cell. 1995; 80: 179-185Abstract Full Text PDF PubMed Scopus (4213) Google Scholar). However, a contradictory finding was recently reported, in which an interfering mutant of the small G protein Rap1 which blocks the sustained phase of ERK activation did not inhibit NGF-induced neurite outgrowth, suggesting that sustained activation of ERK is not necessarily required for NGF-induced neuronal differentiation (11.York R.D. Yao H. Dillon T. Ellig C.L. Eckert S.P. McCleskey E.W. Stork P.J.S. Nature. 1998; 392: 622-626Crossref PubMed Scopus (755) Google Scholar). In another study, NGF-induced neurite outgrowth of PC12D cells, a subline of PC12 cells, was shown to be resistant to the addition of PD98059 (12.Sano M. Kitajima S. Brain Res. 1998; 785: 299-308Crossref PubMed Scopus (37) Google Scholar). Furthermore, neuronal differentiation of PC12 cells by treatment with bone morphogenetic protein (BMP)-2 was induced in the absence of ERK activation (13.Iwasaki S. Hattori A. Sato M. Tsujimoto M. Kohno M. J. Biol. Chem. 1996; 271: 17360-17365Abstract Full Text Full Text PDF PubMed Scopus (75) Google Scholar). These studies strongly suggest that signaling pathways other than the ERK cascade also contribute to neuronal differentiation of PC12 cells. Candidates for signaling pathways regulating neuronal cell death and differentiation include two different recently identified MAPK cascades that converge on c-Jun N-terminal kinase (JNK; also known as SAPK, stress-activated protein kinase) and p38 MAP kinase. Whereas the ERK signaling cascade is generally involved in the control of cell proliferation and differentiation, JNK and p38 are preferentially activated by cytotoxic stressors such as UV radiation, x-rays, heat shock and osmotic shock, and by proinflammatory cytokines such as tumor necrosis factor (TNF) and interleukin-1 (14.Raingeaud J. Gupta S. Rogers J.S. Dickens M. Han J. Ulevitch R.J. Davis R.J. J. Biol. Chem. 1995; 270: 7420-7426Abstract Full Text Full Text PDF PubMed Scopus (2030) Google Scholar, 15.Verheij M. Bose R. Lin X.H. Yao B. Jarvis W.D. Grant S. Birrer M.J. Szabo E. Zon L.I. Kyriakis J.M. Haimovitz-Friedman A. Fuks Z. Kolesnick R.N. Nature. 1996; 380: 75-79Crossref PubMed Scopus (1707) Google Scholar, 16.Kyriakis J.M. Avruch J. BioEssays. 1996; 18: PubMed Scopus Google Scholar). activation of the JNK and/or p38 pathway has been observed in to of in differentiated PC12 cells and other neuronal cells, suggesting the of JNK and p38 in neuronal death Z. Dickens M. J. Davis R.J. 1995; 270: PubMed Scopus Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, A. A. Kyriakis J. J. J. 1998; 18: PubMed Google Scholar, H. E. Y. Green M. Cell. Biol. PubMed Scopus Google Scholar). the JNK pathway was inhibited using a c-Jun neuronal death by factor was that the JNK pathway is a of neuronal death induced by factor Moreover, the a of the JNK M. Davis R.J. P. Nature. PubMed Scopus Google and in which is by a dominant-negative mutant A. M. PubMed Scopus Google were to in apoptosis of the of JNK activity for neuronal mutant the were shown to be and of apoptosis in suggesting that and apoptosis during Davis R.J. P. Neuron. Full Text Full Text PDF PubMed Scopus Google Scholar). On the other several of suggested that the JNK and p38 pathways are involved in neuronal of PC12 cells induced by expression of constitutively active of the and was by activation of JNK but not of ERK B. L. J. Cell. Biol. 1996; PubMed Google Scholar). of constitutively activated which the of the or of c-Jun induced neuronal differentiation of PC12 cells of signals S. R. J. 1998; PubMed Scopus Google Scholar). a protein kinase inhibitor and of neurite outgrowth in PC12 cells, induced activation of a JNK isoform R. M. H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In p38 was recently shown to be activated in to and to be required for NGF-induced differentiation of PC12 cells J. J.M. Z. Cell. Biol. 1998; 18: PubMed Google Scholar, T. Nishida E. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). was that p38 was activated by treatment with in PC12 cells and that activation of p38 be to induce neuronal differentiation of PC12 cells S. M. K. R. Tsujimoto M. Kohno M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). These suggested that the JNK and p38 pathways mediate biological signals not for neuronal cell death but also for neuronal Apoptosis signal-regulating kinase 1 (ASK1) is a ubiquitously expressed that activates the and signaling cascades H. Nishida E. K. P. M. T. M. K. K. Gotoh Y. PubMed Scopus Google Scholar). of ASK1 in cells in serum induced and in cells expression of a mutant of ASK1 inhibited suggesting that ASK1 a in the of apoptosis H. Nishida E. K. P. M. T. M. K. K. Gotoh Y. PubMed Scopus Google Scholar, M. H. M. K. K. Sawada Y. M. K. H. J. 1998; PubMed Scopus Google Scholar, M. H. J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). We recently found that of ASK1 induced death of PC12 cells and rat sympathetic Moreover, dominant-negative ASK1 the neuronal death induced by these cells T. M. K. L. K. H. Cell. Biol. PubMed Scopus Google Scholar). ASK1 was activated treatment with or and a mutant of ASK1 and JNK activation and suggesting that ASK1 is a in apoptosis as H. Nishida E. K. P. M. T. M. K. K. Gotoh Y. PubMed Scopus Google H. M. Y. K. H. M. K. H. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, H. H. 1998; PubMed Scopus Google Scholar). the of JNK and p38 in neuronal death and differentiation as is of ASK1 signals leading to death or differentiation of PC12 cells. We report here that transient or expression of constitutively active ASK1 (ASK1ΔN) induces neurite outgrowth in PC12 cells. We found that p38 and to a lesser extent JNK, but not ERK, were activated by expression of ASK1ΔN in PC12 cells. using MEK and a p38 inhibitor suggested a of activation of p38, rather than of ERK, to the neurite-inducing activity of ASK1 in PC12 cells. We also found that ASK1ΔN induced expression of several neuron-specific proteins and phosphorylation of neurofilament proteins, confirming that PC12 cells differentiated into mature neuronal cells by expression of Moreover, found that ASK1ΔN-expressing PC12 cells survived in serum-starved condition. these suggest that ASK1 mediate signals leading to both differentiation and survival of PC12 cells. cells were the PC12 cells were in Dulbecco's modified Eagle's medium with fetal calf serum horse serum and G in a to the hemagglutinin was and to p38 MAP kinase and were to ERK was MAP kinase medium and were and to neurofilament heavy which a in the of M.J. J. PubMed Google Scholar, M.J. J. PubMed Google was which and and III were and were and was ASK1 and were as M. H. M. K. K. Sawada Y. M. K. H. J. 1998; PubMed Scopus Google Scholar). infection of to PC12 cells be a multiplicity of infection of as by not The hygromycin and the were into and and and The for ASK1ΔN was into The was into PC12 cells using to the The cells were with hygromycin and several were was with expression for with and the were and for the expression of proteins by The cells were in with and 1 cells were in cell with type and to in with and for were with phosphate-buffered saline and with and a adenovirus or cells were with and in for an In the of cells, 1 cells were in type cell and to in with and were with and with and of the of cells, the of cells with a than cell was and with the of cells were in a and and cell were by the expression of neuronal proteins, cells were in the with the of to and by The protein of the was using a and the of protein were on and with in and for 1 the were with The were using the cells were in type cell and to in with and The cells were with and with of an cell were in by the of as the roles by ASK1 in neuronal cells, the of expression of a constitutively active mutant of ASK1 M. H. M. K. K. Sawada Y. M. K. H. J. 1998; PubMed Scopus Google in PC12 cells. cells were with hemagglutinin ASK1ΔN or in medium horse serum infection of to cells was an of as by not using a expression of ASK1ΔN was in an infection 1 cells to not the neurite-inducing activity of cells or with were for and by The cells with of of 1 cells neurite 1 cells with a neurite than cell were the of cells by infection in an 1 with the that infection with a adenovirus a mutant of ASK1 M. H. M. K. K. Sawada Y. M. K. H. J. 1998; PubMed Scopus Google or to induce neurite outgrowth in PC12 cells not these that the neurite outgrowth induced by infection with is on the kinase activity of ASK1. the roles of ASK1 in PC12 cells, a cell line ASK1ΔN in which the expression of ASK1ΔN is the control of a the of the expression of ASK1ΔN was on and as as by not the of in the expression of ASK1ΔN was in the of and the of ASK1ΔN expression was by the of of cells or not ASK1ΔN the of The ASK1ΔN-expressing cells of to cells with We the and of on the of neurite outgrowth in cells. the of of cells with or of the of cells to in with the expression of ASK1ΔN protein by and the of the of cells in a with or However, was the medium the of cells but was and a of to ASK1ΔN-induced neurite outgrowth was found to be not ASK1 activates the JNK and p38 MAP kinase pathways in cells H. Nishida E. K. P. M. T. M. K. K. Gotoh Y. PubMed Scopus Google Scholar). the signaling leading to the of neurite outgrowth by which MAP kinase cascade is activated in PC12 cells by the expression of the activation of ERK, JNK, and p38, using that the active of these We the of ASK1ΔN expression on activation of in cells the of with previous report for cells H. Nishida E. K. P. M. T. M. K. K. Gotoh Y. PubMed Scopus Google an activation of p38 was with expression of the was with signals to and of JNK were in the of cells, indicating the of signaling leading to JNK in cell in to p38, JNK was activated by activation of JNK was an of ASK1ΔN was expressed or We in ERK activation induced by ASK1ΔN on the with the not We the of ASK1ΔN on JNK and p38 in cells In the of and as in in to the the ASK1ΔN-induced neurite outgrowth and the activation of expression of ASK1ΔN and a and activation of p38 was to On the other activation of JNK was of p38 JNK was activated in the cells in the of the of or activation of p38 and in with the expression of activation of JNK was of The activation of p38 by ASK1ΔN was in cells, which with or and for activation of was a in the expression of ASK1ΔN and expression of but not of activated p38 but not JNK or ERK and not These strongly suggest that ASK1ΔN preferentially activates the p38 pathway in PC12 cells. Furthermore, with the that ASK1ΔN-induced neurite outgrowth was found the of is that p38, rather than JNK or ERK, a in ASK1ΔN-induced neurite outgrowth in PC12 cells. It has been suggested that activation of the ERK pathway roles in NGF-induced neuronal did not activation of ERK in or cells, activity of ERK is required for ASK1ΔN-induced neurite outgrowth In cells, a of phosphorylation of ERK was observed in the of but phosphorylation was induced by expression of In the of of the MEK PD98059 and the phosphorylation of ERK was and inhibited by PD98059 and the of cells was the of ASK1ΔN in the or absence of the MEK inhibitors, PD98059 and were found to the of cells. the in ERK phosphorylation was PD98059 and in to ASK1ΔN-induced neurite outgrowth. These results suggest that the ERK pathway to ASK1ΔN-induced neurite outgrowth in PC12 cells. the of p38 for ASK1ΔN-induced neurite outgrowth, the of a inhibitor of p38, on the neurite-inducing activity of cells were induced to in the or absence of ASK1ΔN-induced neurite outgrowth was inhibited in the of SB203580 We that of SB203580 cytotoxic on cells not that the neurite-inducing activity of ASK1ΔN was inhibited in a by addition of the of SB203580 in the medium the expression of not of SB203580 inhibited ASK1ΔN-induced neurite outgrowth. However, these strongly suggest that p38 is required for the neurite outgrowth induced by that the neurite outgrowth induced by ASK1ΔN was by neuronal differentiation of PC12 cells, the expression of several neuron-specific proteins as of neuronal with NGF-induced differentiation, cells were in in the of and cells, the cell line of cells that the for a tetracycline were also the for with or of cells were and to using a of to neuron-specific isoform III is by of and in with the of neuronal differentiation L.I. A. PubMed Scopus Google Scholar). using a to a in the expression of treatment with in both and cells. cells but not cells in the of also a in the expression of indicating that the of was induced by the expression of ASK1ΔN and was not a of the results were using a to which is a of proteins and is known to be expressed in of L.I. A. L.I. J. Biol. PubMed Scopus Google Scholar). with a previous report E. J. P. J. Sci. 1995; PubMed Google expression of was in both cells by treatment with of ASK1ΔN also protein in cells. These results that ASK1ΔN-induced of cells was by of neuron-specific of as was the with NGF-induced We the expression of neurofilament proteins, which are of the neuronal are of three proteins, neurofilament light neurofilament medium and neurofilament heavy these three and including phosphorylation Res. Biol. 1998; PubMed Google Scholar). In and cells, a to as a of phosphorylation the observed and were thought to to and of In both cells, treatment with both the and of expression of ASK1ΔN in cells induced a of a in suggesting that ASK1ΔN induces phosphorylation of in that of phosphorylation as a in and cells. the cells were with NGF, expression of was as a broad suggesting that both protein and phosphorylation of expression of in the ASK1ΔN-expressing cells was also as a broad with suggesting that expression of ASK1ΔN strongly induces phosphorylation of the ASK1ΔN-induced phosphorylation of a that of M.J. J. PubMed Google Scholar, M.J. J. PubMed Google Scholar). The the in the of the ASK1ΔN-expressing cells, suggesting that ASK1ΔN and/or the expression of ASK1ΔN also induces phosphorylation of cells with or and The cell was to using and The but not the expression of as a in cells. the cells were with NGF, expression of was as a broad suggesting that treatment with induces phosphorylation of to extent in cells. with the results for cells, expressed in cells was as a the of which was by the that expression of ASK1ΔN strongly induced phosphorylation of in cells. the of phosphorylation of induced by the ASK1ΔN-induced phosphorylation of a In cells, phosphorylation of was the of the expression of ASK1ΔN and the activation of p38, which were of other neuron-specific proteins required several of the of ASK1ΔN not phosphorylation of was a by expression of These results suggest that p38 activated by ASK1 or ASK1 these that ASK1ΔN-induced of PC12 cells was by the expression of neuron-specific proteins and phosphorylation of neurofilament These strongly suggest that ASK1ΔN-induced neurite outgrowth results neuronal differentiation of PC12 cells. induces not differentiation but also survival of the that ASK1 also survival signals in PC12 cells, the of ASK1ΔN expression on serum-starved cells. cells were in different of in medium for to of cells was different the of serum and In to the in the of cells the of ASK1ΔN-expressing cells or of was or in the medium for suggesting that ASK1ΔN-expressing cells were in serum-starved condition. It also that expression of ASK1ΔN is required to the survival since was in than the of the cells or not ASK1ΔN in the medium for ASK1ΔN-expressing cells in the medium to in the medium the cells not ASK1ΔN an and the We also found that and cells with but not with or survived in the medium not These suggest that activation of ASK1 is of survival in PC12 cells. ASK1 thus to mediate signals leading to both differentiation and survival of PC12 cells. We the of p38 for the survival by treatment with the of SB203580 on ASK1ΔN-induced differentiation, cells differentiated by ASK1ΔN of and for 1 The differentiated cells were in the or or absence of SB203580 in medium the for survival different the of the of cells was In the absence of the of differentiated cells was in the medium for confirming that ASK1ΔN-expressing cells were in serum-starved condition. In the of the of cells was indicating that SB203580 inhibited the survival by These suggest that activation of p38 is required not for ASK1ΔN-induced neurite outgrowth but also for survival and that p38 is an of ASK1 signaling in PC12 cells. In the study, that expression of ASK1ΔN induced neuronal differentiation of PC12 cells, which was by neurite outgrowth, of neuron-specific proteins, and phosphorylation of neurofilament In ASK1 to survival in PC12 cells. with the neurite outgrowth, and activation of p38 was induced by expression of ASK1ΔN In activation of ERK was induced by expression of and inhibition of activity of ERK did not the of ASK1ΔN-induced cells suggesting that ASK1ΔN-induced neurite outgrowth not the activation of that NGF-induced differentiation of PC12 cells activation of the ERK pathway and is to MEK L. Sawada T. Decker S.J. Saltiel A.R. J. Biol. Chem. 1995; 270: 13585-13588Abstract Full Text Full Text PDF PubMed Scopus (895) Google Scholar, 10.Marshall C.J. Cell. 1995; 80: 179-185Abstract Full Text PDF PubMed Scopus (4213) Google suggest that a of signaling pathways the neurite-inducing activity of ASK1 that activated in NGF-induced differentiation of PC12 cells. of a dominant-negative mutant of ASK1 did not inhibit the NGF-induced neurite in PC12 cells not a p38 inhibitor inhibited ASK1ΔN-induced neurite outgrowth suggesting that the activation of p38 is required for p38 was to be required for and differentiation of PC12 cells T. Nishida E. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, S. M. K. R. Tsujimoto M. Kohno M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). is activation of p38 is to induce neurite outgrowth and/or neuron-specific p38 appears to be a generally required in neuronal differentiation of PC12 cells. We that ASK1 activates both the JNK and p38 pathways in cell types including cells, and PC12 cells H. Nishida E. K. P. M. T. M. K. K. Gotoh Y. PubMed Scopus Google Scholar, T. M. K. L. K. H. Cell. Biol. PubMed Scopus Google Scholar). activation of JNK was in PC12 cells. Whereas activation of p38 was the of activation of JNK was the neurite outgrowth was induced the of is that the activation of JNK neuronal differentiation of PC12 cells. JNK and c-Jun been suggested to in death signaling of factor was recently that expression of constitutively active in PC12 cells induced activation of both JNK and p38 to a and that these cells apoptosis H. E. Y. Green M. Cell. Biol. PubMed Scopus Google and that a c-Jun mutant inhibit suggesting the of JNK in death signaling in PC12 cells. that expression of ASK1ΔN induced differentiation, but not in PC12 cells be to the absence of activation of In expression of ASK1ΔN in cells with the absence of but not with the of or resulted in a in the of cells a of The of ASK1 be by the in JNK activity in the absence of the extent of JNK activation induced by ASK1ΔN is insufficient to death of PC12 cells, the activation of JNK by ASK1 the neurite-inducing activity of the It also be that activation of the JNK and p38 pathways is required for ASK1ΔN-induced neurite outgrowth in PC12 cells. We found that expression of ASK1ΔN neuron-specific of and strongly induced phosphorylation of neurofilament proteins suggesting that neurite outgrowth induced by expression of ASK1ΔN resulted neuronal differentiation of PC12 cells. the extent of phosphorylation of induced by expression of ASK1ΔN was than that induced by treatment with of is thus a of ASK1ΔN-induced differentiation of PC12 cells. and are the proteins in the the of phosphorylation is not and are of the in types of mature and are in Res. Biol. 1998; PubMed Google Scholar). of the phosphorylation in and are in the of L. M.J. M. B. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, E. H. H. J. 1994; PubMed Scopus Google Scholar). several including kinase C.L. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google R.J. J. Biol. Chem. Full Text PDF PubMed Google and J. 1995; PubMed Scopus Google Scholar, H. Grant P. J. 1998; 18: PubMed Google and J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, J. PubMed Google been in the phosphorylation of and to the study, is of that MAP ERK and JNK are to H. Grant P. J. 1998; 18: PubMed Google Scholar, J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google since p38, another in ASK1ΔN-expressing PC12 cells. Together with the that the phosphorylation of was the activation of p38 is that p38, rather than JNK, activated by ASK1 other activated by ASK1 or ASK1 The that ASK1ΔN-expressing cells in serum-starved another of ASK1 We found that expression of ASK1ΔN induced apoptosis in PC12 cells and T. M. K. L. K. H. Cell. Biol. PubMed Scopus Google Scholar). these to of the study, suggest that the expression of ASK1ΔN the cell expression of ASK1ΔN induces differentiation and ASK1 activity induces apoptosis in PC12 cells. In observed that of ASK1ΔN induced apoptosis in PC12 cells not On the other is to the expression of ASK1ΔN in PC12 cells with that in PC12 cells or also the that ASK1 preferentially mediate apoptosis in PC12 cells and to the different cellular context. We are the in the activation of signaling pathways and PC12 cells. to the ASK1ΔN-induced neurite outgrowth, survival was inhibited by a p38 inhibitor suggesting that the activation of p38 roles in both differentiation and survival induced by ASK1. However, in the absence of in a that the of ASK1 be a using neuronal cells of roles of ASK1 in neuronal We K. Y. K. Y. A. Y. S. K. and T. for