Curcumin Suppresses AP1 Transcription Factor-dependent Differentiation and Activates Apoptosis in Human Epidermal Keratinocytes

Abstract

The diet-derived cancer preventive agent, curcumin, inhibits skin cancer cell proliferation and tumor formation. However, its effect on normal human keratinocyte differentiation, proliferation, and apoptosis has not been adequately studied. Involucrin (hINV) is a marker of keratinocyte differentiation and a useful model for the study of chemopreventive agent action. We show that curcumin suppresses the differentiation agent-dependent activation of hINV gene expression and that an AP1 transcription factor DNA binding site in the hINV gene is required for this regulation. A protein kinase C, Ras, MEKK1, MEK3 signaling cascade controls hINV expression by regulating AP1 factor level. Curcumin treatment inhibits the novel protein kinase C-, Ras-, and MEKK1-dependent activation of hINV promoter activity and reduces the differentiation agent-dependent increase in AP1 factor level and DNA binding. This reduction requires proteasome function. In addition, curcumin treatment reduces cell number, which is associated with a reduced cyclin and cdk1 levels. Curcumin treatment also suppresses the Bcl-xL level, leading to reduced mitochondrial membrane potential and increased cleavage of procaspases and poly(ADP-ribose) polymerase. These studies provide important insights regarding the mechanism whereby curcumin acts as a chemopreventive agent in normal human epidermis. The diet-derived cancer preventive agent, curcumin, inhibits skin cancer cell proliferation and tumor formation. However, its effect on normal human keratinocyte differentiation, proliferation, and apoptosis has not been adequately studied. Involucrin (hINV) is a marker of keratinocyte differentiation and a useful model for the study of chemopreventive agent action. We show that curcumin suppresses the differentiation agent-dependent activation of hINV gene expression and that an AP1 transcription factor DNA binding site in the hINV gene is required for this regulation. A protein kinase C, Ras, MEKK1, MEK3 signaling cascade controls hINV expression by regulating AP1 factor level. Curcumin treatment inhibits the novel protein kinase C-, Ras-, and MEKK1-dependent activation of hINV promoter activity and reduces the differentiation agent-dependent increase in AP1 factor level and DNA binding. This reduction requires proteasome function. In addition, curcumin treatment reduces cell number, which is associated with a reduced cyclin and cdk1 levels. Curcumin treatment also suppresses the Bcl-xL level, leading to reduced mitochondrial membrane potential and increased cleavage of procaspases and poly(ADP-ribose) polymerase. These studies provide important insights regarding the mechanism whereby curcumin acts as a chemopreventive agent in normal human epidermis. Curcumin, diferuloylmethane, is a naturally occurring dietary agent, derived from the roots of Curcuma longa Linn, which has potent anti-cancer properties (1Aggarwal B.B. Kumar A. Bharti A.C. Anticancer Res. 2003; 23: 363-398PubMed Google Scholar, 2Stoner G.D. Mukhtar H. J. Cell. Biochem. Suppl. 1995; 22: 169-180Crossref PubMed Scopus (583) Google Scholar). Dietary or topical application of curcumin inhibits tumor development in 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate (TPA) 2The abbreviations used are: TPA, 12-O-tetradecanoylphorbol-13-acetate; KSFM, keratinocyte serum-free medium; hINV, human involucrin; MEK, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase; MEKK, MEK kinase; ERK, extracellular signal-regulated kinase; PKC, protein kinase C; C/EBP, CAAT/enhancer-binding protein; cdk, cyclin-dependent kinase.2The abbreviations used are: TPA, 12-O-tetradecanoylphorbol-13-acetate; KSFM, keratinocyte serum-free medium; hINV, human involucrin; MEK, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase; MEKK, MEK kinase; ERK, extracellular signal-regulated kinase; PKC, protein kinase C; C/EBP, CAAT/enhancer-binding protein; cdk, cyclin-dependent kinase.-induced mouse skin carcinogenesis (3Huang M.T. Ma W. Yen P. Xie J.G. Han J. Frenkel K. Grunberger D. Conney A.H. Carcinogenesis. 1997; 18: 83-88Crossref PubMed Scopus (151) Google Scholar, 4Singletary K. MacDonald C. Iovinelli M. Fisher C. Wallig M. Carcinogenesis. 1998; 19: 1039-1043Crossref PubMed Scopus (124) Google Scholar, 5Krishnaswamy K. Goud V.K. Sesikeran B. Mukundan M.A. Krishna T.P. Nutr. Cancer. 1998; 30: 163-166Crossref PubMed Scopus (60) Google Scholar, 6Gafner S. Lee S.K. Cuendet M. Barthelemy S. Vergnes L. Labidalle S. Mehta R.G. Boone C.W. Pezzuto J.M. Phytochemistry. 2004; 65: 2849-2859Crossref PubMed Scopus (123) Google Scholar, 7Huang M.T. Ma W. Lu Y.P. Chang R.L. Fisher C. Manchand P.S. Newmark H.L. Conney A.H. Carcinogenesis. 1995; 16: 2493-2497Crossref PubMed Scopus (188) Google Scholar, 8Limtrakul P. Anuchapreeda S. Lipigorngoson S. Dunn F.W. BMC. Cancer. 2001; 1: 1Crossref PubMed Scopus (71) Google Scholar, 9Limtrakul P. Lipigorngoson S. Namwong O. Apisariyakul A. Dunn F.W. Cancer Lett. 1997; 116: 197-203Crossref PubMed Scopus (171) Google Scholar). Administration of 0.2-1% curcumin in the mouse diet is sufficient to achieve this response (7Huang M.T. Ma W. Lu Y.P. Chang R.L. Fisher C. Manchand P.S. Newmark H.L. Conney A.H. Carcinogenesis. 1995; 16: 2493-2497Crossref PubMed Scopus (188) Google Scholar, 8Limtrakul P. Anuchapreeda S. Lipigorngoson S. Dunn F.W. BMC. Cancer. 2001; 1: 1Crossref PubMed Scopus (71) Google Scholar, 9Limtrakul P. Lipigorngoson S. Namwong O. Apisariyakul A. Dunn F.W. Cancer Lett. 1997; 116: 197-203Crossref PubMed Scopus (171) Google Scholar). Several studies suggest that curcumin influences AP1 factor expression. Curcumin treatment of HeLa cells results in altered AP1 factor expression and activity (10Prusty B.K. Das B.C. Int. J. Cancer. 2005; 113: 951-960Crossref PubMed Scopus (188) Google Scholar), and dietary curcumin reduces carcinogen-induced c-fos expression in the epidermis of 7,12-dimethylbenz(a)anthracene/TPA-treated Swiss albino and CD-1 mice (8Limtrakul P. Anuchapreeda S. Lipigorngoson S. Dunn F.W. BMC. Cancer. 2001; 1: 1Crossref PubMed Scopus (71) Google Scholar, 9Limtrakul P. Lipigorngoson S. Namwong O. Apisariyakul A. Dunn F.W. Cancer Lett. 1997; 116: 197-203Crossref PubMed Scopus (171) Google Scholar, 11Kakar S.S. Roy D. Cancer Lett. 1994; 87: 85-89Crossref PubMed Scopus (114) Google Scholar). Curcumin also reduces c-jun and c-fos expression in murine keratinocyte JB6 cells (12Lu Y.P. Chang R.L. Lou Y.R. Huang M.T. Newmark H.L. Reuhl K.R. Conney A.H. Carcinogenesis. 1994; 15: 2363-2370Crossref PubMed Scopus (120) Google Scholar) and influences the proliferation and survival of other cell lines derived from surface epithelia, including HaCaT cells (10Prusty B.K. Das B.C. Int. J. Cancer. 2005; 113: 951-960Crossref PubMed Scopus (188) Google Scholar, 13Cho J.W. Park K. Kweon G.R. Jang B.C. Baek W.K. Suh M.H. Kim C.W. Lee K.S. Suh S.I. Exp. Mol. Med. 2005; 37: 186-192Crossref PubMed Scopus (145) Google Scholar), MDA-1986 cells (14Yan C. Jamaluddin M.S. Aggarwal B. Myers J. Boyd D.D. Mol. Cancer Ther. 2005; 4: 233-241Crossref PubMed Scopus (1) Google Scholar), oral squamous cell carcinoma cells (15Rinaldi A.L. Morse M.A. Fields H.W. Rothas D.A. Pei P. Rodrigo K.A. Renner R.J. Mallery S.R. Cancer Res. 2002; 62: 5451-5456PubMed Google Scholar), NCTC-2544 transformed keratinocytes (16Grandjean-Laquerriere A. Gangloff S.C. Le Naour R. Trentesaux C. Hornebeck W. Guenounou M. Cytokine. 2002; 18: 168-177Crossref PubMed Scopus (87) Google Scholar), and transformed murine keratinocytes (17Santibanez J.F. Quintanilla M. Martinez J. Nutr. Cancer. 2000; 37: 49-54Crossref PubMed Scopus (34) Google Scholar). These studies suggest that curcumin can modulate tumor formation in vivo, as well as, the proliferation of epidermisderived established cell lines. However, few studies have examined the impact of curcumin treatment on the function of normal human keratinocytes (18Balasubramanian S. Eckert R.L. J. Biol. Chem. 2004; 279: 24007-24014Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, 19Eckert R.L. Crish J.F. Efimova T. Balasubramanian S. Mol. Nutr. Food Res. 2006; 50: 123-129Crossref PubMed Scopus (19) Google Scholar). In the present report, we examine the effect of curcumin on human keratinocyte differentiation using involucrin as a marker of differentiation. Involucrin is expressed in the suprabasal layers in epidermis (20Eckert R.L. Crish J.F. Robinson N.A. Physiol. Rev. 1997; 77: 397-424Crossref PubMed Scopus (342) Google Scholar, 21Eckert R.L. Crish J.F. Efimova T. Dashti S.R. Deucher A. Bone F. Adhikary G. Huang G. Gopalakrishnan R. Balasubramanian S. J. Invest. Dermatol. 2004; 123: 13-22Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar). Because of its of expression and the that involucrin expression well R.L. Crish J.F. Efimova T. Dashti S.R. Deucher A. Bone F. Adhikary G. Huang G. Gopalakrishnan R. Balasubramanian S. J. Invest. Dermatol. 2004; 123: 13-22Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar), the involucrin gene an model for the whereby chemopreventive skin differentiation. We also examine the impact of curcumin treatment on keratinocyte proliferation and results suggest that curcumin treatment inhibits keratinocyte proliferation and activation of involucrin gene expression and keratinocyte The of differentiation is associated with reduced AP1 factor expression and DNA binding. A of studies is the that curcumin suppresses expression of AP1 in the mechanism of of curcumin from that of other chemopreventive (18Balasubramanian S. Eckert R.L. J. Biol. Chem. 2004; 279: 24007-24014Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, S. Efimova T. Eckert R.L. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, S. M.T. G.R. Eckert R.L. Carcinogenesis. 2005; PubMed Scopus Google Scholar). and and curcumin from and curcumin in and from serum-free and from The and from from for including and from from for involucrin in and for and from for and mouse for and cyclin from for and and a for from including and from and keratinocytes from human as J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). of normal human in used for to of KSFM, and the for The with of involucrin promoter for with of involucrin and of kinase expression The for and to the cells in of In the in to of DNA of by of expression with in the or of or the of curcumin an the cells and for activity using in and a of activity of using a of and human keratinocytes with in the or of cells with and in cell and of protein on and to The membrane in with the and to used to the binding. and and the and as J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). This the hINV gene and the site is and in in KSFM, for with in the or of and treatment agent The cells with and and the cell using a cell with or with of or the cells with in and with to S. Eckert R.L. 2005; PubMed Scopus Google Scholar). and and keratinocytes or with The cells with and in of and of with of or for to the by The and the with The in and on a for using a mouse keratinocyte in with curcumin to of cell the of cell in and of the proteasome for activity by of the cleavage Curcumin a of hINV examined the impact of curcumin treatment on the increase in hINV gene promoter activity using a that the of hINV and to the gene J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). with and for with in an increase in activity in the of cells with of curcumin in a curcumin reduction in promoter and promoter activity increased curcumin activity curcumin We the impact of curcumin treatment on hINV levels. that treatment increased hINV by of curcumin this These suggest that curcumin influences hINV by regulating hINV promoter Curcumin an AP1 the DNA binding site for curcumin we examined a of hINV promoter The of the hINV gene promoter is to J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar) in curcumin treatment the increase in and However, curcumin the activity of and that the is in the which the site the we the impact of curcumin treatment on activity of the AP1 and in treatment increased and and this response by curcumin We have that the site as a of transcription T. P. J.F. Eckert R.L. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google is not that of this site increased promoter activity not the In of the site in a of that the site is required for this regulation. Curcumin hINV hINV gene expression a signaling cascade that novel PKC, Ras, MEKK1, and which activity of the T. P. J.F. Eckert R.L. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, T. Eckert R.L. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, T. Deucher A. T. M. Eckert R.L. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). the mechanism of curcumin we the of curcumin to promoter activation by of the novel and Ras, and in expression of the novel an increase in promoter activity that by curcumin In addition, as in promoter treatment with or MEKK1, also by treatment with Curcumin AP1 using the hINV promoter suggest that the which is in the of hINV is required for regulation. the impact of curcumin treatment on AP1 factor we curcumin influences AP1 factor level AP1 factor binding to the from and or with of is important to that the of AP1 this site not in cells J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). in in the of the the of in reduced of with from and a level of binding to However, a increase in in from is of that this level to in that the protein binding by not by the DNA an transcription factor binding site studies that and the site J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). the impact of curcumin treatment on this we that and the site in cells and that treatment with curcumin in a reduction in this The reduction in in the of curcumin, by a reduction in AP1 factor expression. this we and the level of of the AP1 by This a increase in and in the cells and a of this increase in the of curcumin suppresses the increase in AP1 factor levels. keratinocytes with the for to of The on a and with AP1 and used to binding. of proteasome function reduces the of and levels. human keratinocytes for with or with curcumin in the or of for of and by results in of The of that of and in human keratinocytes requires proteasome function (18Balasubramanian S. Eckert R.L. J. Biol. Chem. 2004; 279: 24007-24014Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar). the reduction in AP1 factor level requires proteasome cells with curcumin or in the or of a proteasome results that the reduction in and level is by treatment with that the response requires proteasome activity and for curcumin cell from keratinocytes with or The for of in curcumin treatment a increase in the level of and This increase is and curcumin this increase to the in the level of protein in cell in an increase in as as of curcumin However, the increase with the increase in and in the increase in and in with a reduction in and protein levels. We also proteasome activity using a proteasome We a increase in proteasome of treatment with This increase in activity and with the in Curcumin the impact of curcumin treatment on keratinocyte cell in curcumin a reduction in cell a of cell increased in curcumin treatment in a reduction in this increase that is curcumin of We that treatment with results in of cell the and that with and of curcumin a reduction in cell curcumin The reduction associated with that a of the cells from the formation of and to the The mechanism of reduction in cell altered expression of cell or activation of cell we examined the impact of curcumin treatment on cell protein level. with the that curcumin cell curcumin treatment reduced the of cyclin cyclin cyclin and cyclin the cyclin-dependent cdk1 level the of and We that curcumin increase cyclin-dependent kinase levels. However, level not and we that curcumin treatment reduced the of and is important to that the of AP1 the site not in J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar) Curcumin the impact of curcumin treatment on In apoptosis is associated with of the and poly(ADP-ribose) cleavage M. C. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, M. R. C. J. Invest. Dermatol. Full Text Full Text PDF PubMed Scopus Google Scholar). in curcumin treatment reduced Bcl-xL level not level. In not Bcl-xL or levels. of keratinocytes with curcumin and in of Bcl-xL level, that the curcumin response is the impact on we the cells for with curcumin, TPA, or a of and with a that in and from in of mitochondrial potential in cells with These suggest that curcumin keratinocyte which is associated with an of cells DNA cells for with or curcumin and for cell as in treatment not increase the of curcumin treatment in a and formation of the to cleavage J.M. S. Biol. 2002; PubMed Scopus Google Scholar, J.M. S. Biochem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). the impact of curcumin treatment on cell from curcumin or and the level by in reduced level of procaspases and and poly(ADP-ribose) in treatment and poly(ADP-ribose) with the of curcumin or for and for the level of the by results in of Curcumin AP1 and AP1 to the hINV is the of a and studies suggest that curcumin is an of tumor cell proliferation and tumor (3Huang M.T. Ma W. Yen P. Xie J.G. Han J. Frenkel K. Grunberger D. Conney A.H. Carcinogenesis. 1997; 18: 83-88Crossref PubMed Scopus (151) Google Scholar, 4Singletary K. MacDonald C. Iovinelli M. Fisher C. Wallig M. Carcinogenesis. 1998; 19: 1039-1043Crossref PubMed Scopus (124) Google Scholar, 5Krishnaswamy K. Goud V.K. Sesikeran B. Mukundan M.A. Krishna T.P. Nutr. Cancer. 1998; 30: 163-166Crossref PubMed Scopus (60) Google Scholar, 6Gafner S. Lee S.K. Cuendet M. Barthelemy S. Vergnes L. Labidalle S. Mehta R.G. Boone C.W. Pezzuto J.M. Phytochemistry. 2004; 65: 2849-2859Crossref PubMed Scopus (123) Google Scholar, 7Huang M.T. Ma W. Lu Y.P. Chang R.L. Fisher C. Manchand P.S. Newmark H.L. Conney A.H. Carcinogenesis. 1995; 16: 2493-2497Crossref PubMed Scopus (188) Google Scholar, 8Limtrakul P. Anuchapreeda S. Lipigorngoson S. Dunn F.W. BMC. Cancer. 2001; 1: 1Crossref PubMed Scopus (71) Google Scholar, 9Limtrakul P. Lipigorngoson S. Namwong O. Apisariyakul A. Dunn F.W. Cancer Lett. 1997; 116: 197-203Crossref PubMed Scopus (171) Google Scholar). However, the effect of curcumin on normal keratinocyte cell function has not been adequately studied. the impact of curcumin on keratinocyte function is keratinocytes the cell present in the epidermis the study the impact of curcumin on keratinocyte differentiation, we a which is expressed in the suprabasal layers (20Eckert R.L. Crish J.F. Robinson N.A. Physiol. Rev. 1997; 77: 397-424Crossref PubMed Scopus (342) Google Scholar). Involucrin expression is increased activation of a novel PKC, Ras, MEKK1, and MEK3 cascade that activity in the T. P. J.F. Eckert R.L. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, T. Eckert R.L. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, T. Eckert R.L. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). of and reduction of activity to increased of and AP1 transcription These in to hINV gene to increase expression T. P. J.F. Eckert R.L. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, T. Eckert R.L. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). is a agent that hINV gene expression by this cascade J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). present study that curcumin inhibits the increase in hINV promoter activity and the increase in hINV expression. studies that curcumin inhibits promoter activation of the novel and Ras, and These suggest that curcumin with in the cascade of This cascade AP1 S. Efimova T. Eckert R.L. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, T. P. J.F. Eckert R.L. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). The AP1 transcription factor of and P. M. PubMed Scopus Google Scholar). These factor and factor that to the AP1 factor DNA to gene expression P. M. PubMed Scopus Google Scholar, P. A. M. 2001; PubMed Scopus Google Scholar). The hINV promoter in the a of AP1 that and J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). present studies show a reduction in binding of AP1 to this that curcumin to promoter activity by with AP1 In studies suggest that curcumin AP1 transcription factor with In treatment of AP1 with curcumin results in reduced binding to the AP1 factor to DNA Lee J. Biochem. Mol. Biol. 2005; Google Scholar, G. Lee J. Kim B. Park C. Cancer Lett. 2002; PubMed Scopus Google Scholar, Park S. Park C. Kim Biochem. Res. 2004; PubMed Scopus Google Scholar). However, this effect is not to present we a reduction in promoter activity in the of the for of AP1 factor with DNA in is Lee J. Biochem. Mol. Biol. 2005; Google Scholar, G. Lee J. Kim B. Park C. Cancer Lett. 2002; PubMed Scopus Google Scholar, Park S. Park C. Kim Biochem. Res. 2004; PubMed Scopus Google Scholar). A is that the reduction in promoter activity is by the of studies that as a with to increase hINV promoter F. Crish and R. L. this is a we that a is that the response is to a reduction in AP1 factor levels. This is on that curcumin treatment reduces and in and to with the hINV promoter site J.F. Crish J.F. C. Eckert R.L. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). These with the that of AP1 factor is important for the Curcumin has been to the AP1 factor level in other cell of murine keratinocyte JB6 cells with curcumin results in a reduction in c-jun Lee J. Biochem. Mol. Biol. 2005; Google Scholar), and in HeLa cells curcumin treatment an increase in level and a reduction in c-fos level (10Prusty B.K. Das B.C. Int. J. Cancer. 2005; 113: 951-960Crossref PubMed Scopus (188) Google Scholar). Curcumin treatment of cells reduces c-fos level H. K. M. T. T. A. K. H. M. S. 2003; 22: PubMed Scopus Google Scholar). Curcumin also inhibits the increase in c-jun and protein level in human cells Park S. Park C. Kim Biochem. Res. 2004; PubMed Scopus Google Scholar). studies in that curcumin treatment of human keratinocytes to a reduction in the level of AP1 including and This that curcumin treatment is to a of AP1 in Curcumin and present studies that treatment with a proteasome inhibits the of curcumin to AP1 factor that proteasome function is required for curcumin action. This is with that of AP1 factor level proteasome function C. F. P. G. C. M. 2001; PubMed Scopus Google Scholar, J. 2003; 116: PubMed Scopus Google Scholar). is that curcumin requires proteasome curcumin has been to the In curcumin treatment inhibits proteasome activity and P. A. A. Biochem. Res. 2006; PubMed Scopus Google Scholar, P. A. A. M. Res. 2006; PubMed Scopus Google Scholar). In proteasome function is also by curcumin J. Cancer. 2004; PubMed Scopus Google Scholar). In mouse curcumin suppresses proteasome which to apoptosis P. A. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar). In in HeLa curcumin treatment of M. M. Huang B. C. W. J. Mol. Biol. 2004; PubMed Scopus Google Scholar). studies suggest that the reduction in AP1 factor expression in keratinocytes requires proteasome function. This is with a that the reduction in factor level in keratinocytes requires proteasome function (18Balasubramanian S. Eckert R.L. J. Biol. Chem. 2004; 279: 24007-24014Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar). that proteasome as an in to the studies that of and is increased in the suggest that in including proteasome function is required for curcumin action. Curcumin has been to cell proliferation, and of cells in the of the cell S. G. Aggarwal B.B. 2005; PubMed Scopus Google Scholar). that curcumin treatment a reduction in keratinocyte cell and that this is associated with an increased of is in the of cells in the other cell the mechanism for the reduced cell number, we the impact on cell protein and marker expression. is by a of protein including the cyclin-dependent and activation the K. 2003; PubMed Scopus Google Scholar). cyclin associated with increased activity and increased cell In the and of and squamous cell carcinoma cell proliferation by curcumin is associated with reduced cyclin expression a mechanism that and A. S. C. M. Aggarwal B.B. 2002; PubMed Scopus Google Scholar). A reduction in cyclin level is in human cells and cells T. S. Das T. G. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar, S. P. Aggarwal B.B. Carcinogenesis. 2003; PubMed Scopus Google Scholar). studies with in that cyclin However, we also a reduction in cyclin cyclin and cyclin that in keratinocytes the response is and that curcumin of the cell In the human cancer cell curcumin treatment results in an increase in the level of the the cyclin-dependent kinase J. Huang Lu 2002; PubMed Scopus (120) Google Scholar). A in study is the of cyclin-dependent kinase levels. The of and This is to a reduction of the level of is associated with cell We this in the of the of cell proliferation, we that the reduction in a of the However, we not that cyclin that the cells of Curcumin on the reduction in keratinocyte cell to is a of cell that cell and and S. Huang J.M. 2003; 22: PubMed Scopus Google Scholar, G. Med. 2000; PubMed Scopus Google Scholar). This is associated with activation of which that for the of J.M. S. Biol. 2002; PubMed Scopus Google Scholar). In this is by a in the of Bcl-xL to to a reduction in Bcl-xL level or an increase in expression M. C. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, M. R. C. J. Invest. Dermatol. Full Text Full Text PDF PubMed Scopus Google Scholar). studies curcumin treatment results in reduced Bcl-xL expression. This is associated with of mitochondrial membrane reduced and of cells DNA These suggest that the keratinocytes studies that curcumin apoptosis in and cancer cells that is associated with reduced and Bcl-xL and and activation A. S. C. M. Aggarwal B.B. 2002; PubMed Scopus Google Scholar, A. C. D. P. Aggarwal B.B. 2001; PubMed Scopus Google Scholar). We that the reduction in the Bcl-xL protein results in a in the in of and that this to the of and of mitochondrial membrane of present studies that curcumin suppresses keratinocyte differentiation and proliferation and keratinocyte We have the response of keratinocytes to treatment with other chemopreventive In response to treatment with keratinocytes proliferation and (18Balasubramanian S. Eckert R.L. J. Biol. Chem. 2004; 279: 24007-24014Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, S. Efimova T. Eckert R.L. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). In an anti-cancer derived from suppresses keratinocyte proliferation and differentiation. The present studies that curcumin treatment suppresses keratinocyte proliferation and differentiation and These to the that chemopreventive However, differentiation, and curcumin These suggest that have for the treatment of surface cell and that this important is that the present studies examine the impact of curcumin treatment on normal human keratinocyte important in studies to using is an important skin and important to curcumin in