The Human Cathelicidin LL-37 Modulates the Activities of the P2X7 Receptor in a Structure-dependent Manner

Abstract

Extracellular ATP, released at sites of inflammation or tissue damage, activates the P2X7 receptor, which in turn triggers a range of responses also including cell proliferation. In this study the ability of the human cathelicidin LL-37 to stimulate fibroblast growth was inhibited by commonly used P2X7 blockers. We investigated the structural requirements of the growth-promoting activity of LL-37 and found that it did not depend on helix sense (the all-d analog was active) but did require a strong helix-forming propensity in aqueous solution (a scrambled analog and primate LL-37 orthologs devoid of this property were inactive). The involvement of P2X7 was analyzed using P2X7-expressing HEK293 cells. LL-37 induced proliferation of these cells, triggered Ca2+ influx, promoted ethidium bromide uptake, and synergized with benzoyl ATP to enhance the pore and channel functions of P2X7. The activity of LL-37 had an absolute requirement for P2X7 expression as it was blocked by the P2X7 inhibitor KN-62, was absent in cells lacking P2X7, and was restored by P2X7 transfection. Of particular interest, LL-37 led to pore-forming activity in cells expressing a truncated P2X7 receptor unable to generate the non-selective pore typical of the full-length receptor. Our results indicate that P2X7 is involved in the proliferative cell response to LL-37 and that the structural/aggregational properties of LL-37 determine its capacity to modulate the activation state of P2X7. Extracellular ATP, released at sites of inflammation or tissue damage, activates the P2X7 receptor, which in turn triggers a range of responses also including cell proliferation. In this study the ability of the human cathelicidin LL-37 to stimulate fibroblast growth was inhibited by commonly used P2X7 blockers. We investigated the structural requirements of the growth-promoting activity of LL-37 and found that it did not depend on helix sense (the all-d analog was active) but did require a strong helix-forming propensity in aqueous solution (a scrambled analog and primate LL-37 orthologs devoid of this property were inactive). The involvement of P2X7 was analyzed using P2X7-expressing HEK293 cells. LL-37 induced proliferation of these cells, triggered Ca2+ influx, promoted ethidium bromide uptake, and synergized with benzoyl ATP to enhance the pore and channel functions of P2X7. The activity of LL-37 had an absolute requirement for P2X7 expression as it was blocked by the P2X7 inhibitor KN-62, was absent in cells lacking P2X7, and was restored by P2X7 transfection. Of particular interest, LL-37 led to pore-forming activity in cells expressing a truncated P2X7 receptor unable to generate the non-selective pore typical of the full-length receptor. Our results indicate that P2X7 is involved in the proliferative cell response to LL-37 and that the structural/aggregational properties of LL-37 determine its capacity to modulate the activation state of P2X7. P2X7 is an ATP-activated ion channel expressed by lymphocytes, dendritic cells, macrophages/microglia, and non-hematopoietic cells, including human primary fibroblasts (1Solini A. Chiozzi P. Morelli A. Fellin R. Di Virgilio F. J. Cell Sci. 1999; 112: 297-305Crossref PubMed Google Scholar). Activation of P2X7 causes massive calcium entry often followed by cell death (2Ferrari D. Chiozzi P. Falzoni S. Dal Susino M. Collo G. Buell G. Di Virgilio F. Neuropharmacology. 1997; 36: 1295-1301Crossref PubMed Scopus (244) Google Scholar). Cytotoxicity is likely due to the opening of a large, non-selective pore either intrinsic to or associated with P2X7, which permeabilizes the plasma membrane to molecules of mass up to 900 Da (3Steinberg T.H. Newman A.S. Swanson J.A. Silverstein S.C. J. Biol. Chem. 1987; 262: 8884-8888Abstract Full Text PDF PubMed Google Scholar). Its triggering has been shown to enhance proliferation of lymphocytes (4Baricordi O.R. Melchiorri L. Adinolfi E. Falzoni S. Chiozzi P. Buell G. Di Virgilio F. J. Biol. Chem. 1999; 274: 33206-33208Abstract Full Text Full Text PDF PubMed Scopus (177) Google Scholar), microglial cells (5Bianco F. Ceruti S. Colombo A. Fumagalli M. Ferrari D. Pizzirani C. Matteoli M. Di Virgilio F. Abbracchio M.P. Verderio C. J. Neurochem. 2006; 99: 745-758Crossref PubMed Scopus (125) Google Scholar), and adventitial fibroblasts (6Gerasimovskaya E.V. Ahmad S. White C.W. Jones P.L. Carpenter T.C. Stenmark K.R. J. Biol. Chem. 2002; 277: 44638-44650Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar). In the immune system, ATP released by infected or stressed cells at sites of inflammation acts as a danger or alert signal. Among the many cellular receptors activated by extracellular ATP, P2X7 has been implicated in inhibition of infection by intracellular pathogens (7Darville T. Welter-Stahl L. Cruz C. Sater A.A. Andrews Jr., C.W. Ojcius D.M. J. Immunol. 2007; 179: 3707-3714Crossref PubMed Scopus (57) Google Scholar), in the processing and release of cytokines such as IL-1β, and in the modulation of cell death via apoptotic and necrotic pathways (8Lister M.F. Sharkey J. Sawatzky D.A. Hodgkiss J.P. Davidson D.J. Rossi A.G. Finlayson K. J. Inflamm. (Lond.). 2007; 4: 5Crossref Scopus (210) Google Scholar). As such, it appears to be an important player in inflammation. Antimicrobial host defense peptides have long been recognized as vital components of the innate immune system that provide an endogenous first line of defense against microbial infection by wielding a direct toxic activity against a wide range of microorganisms (9Zasloff M. Nature. 2002; 415: 389-395Crossref PubMed Scopus (6994) Google Scholar). This role has more recently broadened from that of endogenous antibiotics to multifunctional modulators of defense responses (10Zanetti M. J. Leukoc. Biol. 2004; 75: 39-48Crossref PubMed Scopus (853) Google Scholar) and early warning signals, or “alarmins” (11Oppenheim J.J. Yang D. Curr. Opin. Immunol. 2005; 17: 359-365Crossref PubMed Scopus (663) Google Scholar). Two evolutionarily distinct families of such peptides in particular, the defensins and the cathelicidins, are found in mammals and are either constitutively expressed or readily inducible upon infection, inflammation, or injury (12Frohm M. Agerberth B. Ahangari G. Stahle-Backdahl M. Liden S. Wigzell H. Gudmundsson G.H. J. Biol. Chem. 1997; 272: 15258-15263Abstract Full Text Full Text PDF PubMed Scopus (681) Google Scholar, 13Dorschner R.A. Pestonjamasp V.K. Tamakuwala S. Ohtake T. Rudisill J. Nizet V. Agerberth B. Gudmundsson G.H. Gallo R.L. J. Investig. Dermatol. 2001; 117: 91-97Abstract Full Text Full Text PDF PubMed Scopus (482) Google Scholar). They are diverse in length, sequence, and secondary structure, but all tend to adopt amphipathic conformations and are cationic at physiological pH L. M. Curr. Sci. 2005; PubMed Scopus Google Scholar). for ability to to the and to membrane to microbial is the cathelicidin in and is in the of K. 1997; PubMed Google Scholar), in lymphocytes and B. J. J. B. F. L. R. H. Wigzell H. Gudmundsson G.H. PubMed Google Scholar), and in cells from (12Frohm M. Agerberth B. Ahangari G. Stahle-Backdahl M. Liden S. Wigzell H. Gudmundsson G.H. J. Biol. Chem. 1997; 272: 15258-15263Abstract Full Text Full Text PDF PubMed Scopus (681) Google Scholar) and of M. B. G. Stahle-Backdahl M. 1999; PubMed Google Scholar). a in A. L. A. PubMed Scopus Google Scholar), but more it also in J. Gudmundsson G.H. Agerberth B. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, A. L. L. S. S. A. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). it a commonly used in in it has been shown to in of infection and A. R. C. F. C. F. A. B. M. V. M. G. 2006; PubMed Scopus Google Scholar). This likely the ability of LL-37 to of innate in to its direct of of the of LL-37 that it is for human cells, and lymphocytes F. K. A. M. H. H. 2002; PubMed Scopus Google Scholar, J. J.J. J. PubMed Scopus Google Scholar). is involved in by R. G. C. F. S. T. K. P. M. C. A. P. A. P. C. Gallo R.L. M. R. J. Investig. PubMed Scopus Google Scholar) and of human M.F. G. G. Stahle-Backdahl M. J. Investig. Dermatol. Full Text Full Text PDF PubMed Scopus Google Scholar). and cell proliferation by LL-37 be via activation of used KN-62, ethidium HEK293 cells, human intracellular Ca2+ J. J.J. J. PubMed Scopus Google Scholar, R. G. C. F. S. T. K. P. M. C. A. P. A. P. C. Gallo R.L. M. R. J. Investig. PubMed Scopus Google Scholar), the on the growth receptor and receptors M.F. B. E. G. M. J. 2005; PubMed Scopus Google Scholar, S. K. H. K. M. H. Yang L. S. A. M. K. J. Immunol. 2005; PubMed Scopus Google Scholar, Di A. B. C. K. R. Gallo R.L. J. Immunol. 2005; PubMed Scopus Google Scholar). that LL-37 in H. M. J. Immunol. 2006; PubMed Scopus Google Scholar) and release in A. M. M. J. Immunol. 2004; PubMed Scopus Google Scholar) activation of P2X7. In this study found that P2X7 was also involved in the growth-promoting activity of LL-37 as shown using fibroblasts and human cells with human P2X7 the of LL-37 with P2X7, found that LL-37 triggered Ca2+ and ethidium bromide in HEK293 cells expressing P2X7 but not in cells. it the responses in cells. Activation of P2X7 by LL-37 was on the helix-forming propensity of LL-37 in aqueous solution and was of helix LL-37 restored pore-forming activity in cells expressing a truncated P2X7 receptor that is by unable to generate the non-selective pore typical of full-length P2X7. Our results indicate that expression of the P2X7 receptor is for cell activation and that of LL-37 are by P2X7 for and were from and and were from and were from ATP, ATP, KN-62, ethidium bromide and were from and were from Cell and were from were of were in and were by on a or were as A. L. L. S. S. A. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar, A. B. R. M. G. J. PubMed Scopus Google Scholar). The of the peptides was by mass using an were by the at of and scrambled LL-37 and the at of and for and by the The of peptides was using the on was by at using a and cells. were in pH in or in in pH are the of at with the of was from the at to Yang PubMed Scopus Google Scholar). Cell cells were at as in HEK293 cells were from the and in were with and HEK293 with full-length or P2X7 receptor lacking was with to the was in the of of Cell and cells were in at a of and for at in The cell was with and the was for this of cells were found to as by L. B. B. M. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). cells were in in the or of determine cell was to the and cells were for an were with and the at was Cell proliferation in the of was expressed as of the to cells. HEK293 cells expressing human P2X7 or cells were in in a at a of and at in cells were for the The was with in the of and cells were in with a as and with the Cell proliferation was as a of the cells as a plasma membrane cells were for at in in the or of at The activity of a in and cell was using the Cytotoxicity activity in the was expressed as of cellular of human expression was by HEK293 cells expressing truncated P2X7 with of a The was used as against human P2X7 was by cells with of a from scrambled was used as were using the cells were a and for at expression of and P2X7 were by were in a of of and to were on a or a for P2X7 The receptor was used at a of and the against human was used at a of in pH The primary was by to at a of was by The of was expressed as which is the of the the of and bromide and are commonly used of of the plasma membrane to mass aqueous was by HEK293 cells in solution pH in the of the of the was to membrane in plasma membrane were at the of was by cells in a solution pH and and cells at in the or of P2X7 blockers. were with for at with cells were in for were analyzed with a with the Cell using a ion as the of was was from cells using the to the with to of was for at with of and was in a of including of and of at were with the at at and at on the of the of the P2X7 and were as for P2X7, and and for and were analyzed in a and were with a Ca2+ cells were at for in solution in the of Virgilio F. D. A. J. T. J. Biol. Chem. 1987; 262: Full Text PDF PubMed Google Scholar, Virgilio F. T.H. Silverstein S.C. Cell PubMed Scopus Google Scholar). were in the and were in a by using a Ca2+ were using the at an of are as The of LL-37 on the of LL-37 to in investigated the ability of LL-37 to fibroblast proliferation using cells were for with LL-37 at to to proliferation M.F. B. E. G. M. J. 2005; PubMed Scopus Google Scholar, F. H. K. K. K. H. J. Investig. Dermatol. 2007; Full Text Full Text PDF PubMed Scopus Google Scholar). Cell in a the activity was at this the cell was to that induced by LL-37 was at due to a release of the at this The structural of the cell growth-promoting activity of LL-37 were investigated by in the all-d LL-37 a scrambled of LL-37 a and to and the cathelicidin B. R. L. L. A. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar) all-d LL-37 activity to that of the LL-37 at up to was or toxic in the range of used and properties of the peptides in a The results with all-d LL-37 against a for to cellular a of was by the of scrambled LL-37 or to cell proliferation. The peptides a helix-forming propensity in aqueous with and all-d on LL-37 and all-d LL-37 in physiological and in of the of J. Gudmundsson G.H. Agerberth B. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). this secondary in the of and scrambled LL-37 propensity to that the the of LL-37 in solution are important of its We investigated this by the proliferative of LL-37 orthologs from primate that in sequence, and also helix-forming propensity A. L. L. S. S. A. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). Among LL-37 and LL-37 LL-37 in that amphipathic not in the of but also in and in and in the of The results of proliferation that peptides that properties to LL-37 and proliferation of capacity was found to with the proliferative activity but not with direct membrane The Cell of LL-37 by of the receptor P2X7 has been to cellular responses to LL-37 H. M. J. Immunol. 2006; PubMed Scopus Google Scholar, A. M. M. J. Immunol. 2004; PubMed Scopus Google Scholar) and has been implicated in the growth of cell also including adventitial fibroblasts (4Baricordi O.R. Melchiorri L. Adinolfi E. Falzoni S. Chiozzi P. Buell G. Di Virgilio F. J. Biol. Chem. 1999; 274: 33206-33208Abstract Full Text Full Text PDF PubMed Scopus (177) Google Scholar, F. Ceruti S. Colombo A. Fumagalli M. Ferrari D. Pizzirani C. Matteoli M. Di Virgilio F. Abbracchio M.P. Verderio C. J. Neurochem. 2006; 99: 745-758Crossref PubMed Scopus (125) Google Scholar, E.V. Ahmad S. White C.W. Jones P.L. Carpenter T.C. Stenmark K.R. J. Biol. Chem. 2002; 277: 44638-44650Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar). the involvement of P2X7 in the activity of LL-37 first the expression of the P2X7 in cells by of cells. The was expressed in these cells and was not for up to with LL-37 the of cellular receptor that is to be activated by LL-37 J. J.J. J. PubMed Scopus Google Scholar), was not expressed in these cells not of receptors that are commonly used to P2X7, including KN-62, and C. A. J. PubMed Scopus Google Scholar, R.A. A. PubMed Scopus Google Scholar), were for the ability to cell proliferation. the growth of cells to the cell with LL-37 that P2X7 be the ability of the P2X7 to cellular of a that is to be a of P2X7 the inhibition of this response did not the typical inhibition for P2X7 As shown in at and induced in and of cells in the of cells were with ATP M. S. P. M. Di Virgilio F. J. Biol. Chem. Full Text PDF PubMed Google Scholar), or with the was by ATP and but was by The is in line with that is a for P2X7 M. J. 2001; Google Scholar). The results of this to the of LL-37 in cells expressing P2X7 to on the involvement of P2X7 in these human a cell line lacking endogenous P2X7, either expressing human P2X7 or The LL-37 had a growth-promoting at a of in but not in This was not by either the scrambled LL-37 or with a P2X7 P2X7 expression by and the growth-promoting of LL-37 and had growth was also inhibited by LL-37 and P2X7 Activation in ability of LL-37 to modulate the channel activity of P2X7 was by or with and with of were LL-37 in the of up to to and triggered a and LL-37 had a on the In the of extracellular the was that the was of extracellular ion and not to release from intracellular triggered by of LL-37 in and The a in cells lacking P2X7, in cells expressing this receptor it was of LL-37 to cells with in and is that with P2X7 and modulate its responses to physiological or such as ATP or D. Pizzirani C. Adinolfi E. S. B. L. Falzoni S. M. R. Di Virgilio F. J. Immunol. 2004; PubMed Scopus Google Scholar). We LL-37 also this this cells were with in the or of a that induced a with induced a followed by a the and the were by a with LL-37 In the in the of LL-37 was with The P2X7 this by LL-37 the primate cathelicidin was in as of a it did not by did it the This is in with the cell proliferation shown in and the requirement for a for activation of P2X7 by LL-37 a of Ca2+ release from intracellular a response on activation of receptors LL-37 via of P2X7 activation is the of the plasma membrane to mass aqueous due to opening of a non-selective pore (3Steinberg T.H. Newman A.S. Swanson J.A. Silverstein S.C. J. Biol. Chem. 1987; 262: 8884-8888Abstract Full Text PDF PubMed Google Scholar). investigated LL-37 was to of the ethidium bromide by cells The was of and was as of induced by of at the of the triggered by LL-37 in for plasma membrane by this but in the of P2X7 expression was at at this is LL-37 pore opening triggered by with a of of and an of by and that induced by LL-37 to Ca2+ influx, had on triggered by results on Ca2+ and that LL-37 activation of the channel and pore functions of P2X7. by was not by the LL-37 up to that the not a LL-37 in HEK293 with P2X7 the of the receptor of a truncated of the P2X7 receptor from This receptor, which the is to an channel but to the non-selective pore A. F. E. R.A. Buell G. 272: PubMed Scopus Google Scholar). in by it was on HEK293 expressing full-length P2X7 in the of LL-37 not in cells expressing the full-length but also in expressing the truncated receptor of cells with of LL-37 a of in and results that the of P2X7 is not for LL-37 the by which LL-37 restored pore of truncated P2X7 receptor, inhibited by and using a were to expression by was with an is shown as defense peptides are multifunctional molecules that the host from by pathogens and endogenous defense responses (10Zanetti M. J. Leukoc. Biol. 2004; 75: 39-48Crossref PubMed Scopus (853) Google Scholar). the are in host defense and the of in diverse physiological or are in study as endogenous defense and as for the of on multifunctional host defense peptides have many including a of 2006; PubMed Scopus Google Scholar), but on a of the of with host cells as host defense peptides in distinct of the immune response and on cells. The of the human cathelicidin LL-37 have been to activation of LL-37 is for human or receptors F. K. A. M. H. H. 2002; PubMed Scopus Google Scholar, J. J.J. J. PubMed Scopus Google Scholar), and it proliferation of cells via activation of R. G. C. F. S. T. K. P. M. C. A. P. A. P. C. Gallo R.L. M. R. J. Investig. PubMed Scopus Google Scholar) and of via growth receptor and receptors M.F. B. E. G. M. J. 2005; PubMed Scopus Google Scholar, S. K. H. K. M. H. Yang L. S. A. M. K. J. Immunol. 2005; PubMed Scopus Google Scholar, Di A. B. C. K. R. Gallo R.L. J. Immunol. 2005; PubMed Scopus Google Scholar). responses to such as of release from A. M. M. J. Immunol. 2004; PubMed Scopus Google Scholar) and inhibition of in H. M. J. Immunol. 2006; PubMed Scopus Google Scholar), to be by the receptor P2X7. all these that LL-37 acts in a it is it by with cellular receptors in a or by receptor activity A. K.R. C. S. R.L. Gallo R.L. J. Immunol. 2007; PubMed Scopus Google Scholar). In this study have shown that the ability of LL-37 to cell proliferation was inhibited by P2X7 In line with these LL-37 the cellular of calcium and of induced by P2X7 in HEK293 cells, it the intracellular calcium induced in the of ATP by of the of The that P2X7 have a strong is In investigated this in the intracellular pathways involved (5Bianco F. Ceruti S. Colombo A. Fumagalli M. Ferrari D. Pizzirani C. Matteoli M. Di Virgilio F. Abbracchio M.P. Verderio C. J. Neurochem. 2006; 99: 745-758Crossref PubMed Scopus (125) Google Scholar, E. Ferrari D. C. M. P. R. Di Virgilio F. Biol. 2005; PubMed Scopus Google Scholar). The in Ca2+ and the of to an in cellular ATP are in this of LL-37 a strong helix-forming propensity that is from a of and for of J. Gudmundsson G.H. Agerberth B. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). This appears to be a in the of primate cathelicidin A. L. L. S. S. A. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). Our results indicate that the cell growth-promoting activity of LL-37 was on its primate LL-37 that helix-forming propensity to that of LL-37 had a the the to cell to calcium P2X7, and to pore in cells. was LL-37 the of M.F. A. 2004; PubMed Scopus Google Scholar) and membrane and of human lymphocytes A. L. L. S. S. A. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). a an intrinsic propensity to a in solution to with with of its ability to the membrane S. A. J. 2005; PubMed Scopus Google Scholar). these that the structural/aggregational properties of LL-37 its capacity to modulate the activation state of P2X7 by first its of with the cell was found and membrane that cell proliferation was not associated with membrane The involvement of of the membrane properties appears In P2X7 activity is to in the membrane as by the that the P2X7 is by a of in membrane E. J. 2007; PubMed Scopus Google Scholar). In line with this LL-37 has recently been to cell functions with the cell membrane A. K.R. C. S. R.L. Gallo R.L. J. Immunol. 2007; PubMed Scopus Google Scholar). Our P2X7, receptors were by LL-37 the that the induced by the at the membrane are for activation of structural is to a direct of LL-37 with P2X7 or with LL-37 We on LL-37 and on in of the amphipathic of receptor has by an and an that is of the intracellular the of P2X7, with P.L. J.A. J.J. R.A. J. Immunol. 2001; PubMed Scopus Google Scholar) and is involved in functions of the receptor also including pore In at the pore-forming activity the channel activity A. F. E. R.A. Buell G. 272: PubMed Scopus Google Scholar). Our results indicate that LL-37 to pore-forming activity in cells expressing a truncated P2X7, that the of the receptor is not for LL-37 activity and is not involved in LL-37 the that LL-37 a pore-forming to the truncated P2X7 that the of activation the not be for pore the opening of a pore is as the of P2X7 the of its and the of activation of such a non-selective plasma membrane are Two have been the pore is intrinsic to the receptor, which a Virgilio F. Ferrari D. Falzoni S. Chiozzi P. M. T.H. O.R. Google Scholar), or the pore is a membrane activated by the receptor via the R.A. 2002; PubMed Scopus Google Scholar). and P. A. J. 2006; PubMed Scopus Google Scholar) have shown that the plasma membrane channel triggered by P2X7 the that the pore is from the receptor. The ability of LL-37 to via the truncated P2X7 that the is not an absolute requirement for pore In the of a that LL-37 is to the as a to the the pore is intrinsic to the receptor, LL-37 the The results shown in and that pore by the truncated P2X7 receptor in the of LL-37 via a from that of the full-length P2X7 receptor. As in a of expression of at in uptake, that was likely not implicated in this In in this expression to the and in was by Virgilio F. Ferrari D. Falzoni S. Chiozzi P. M. T.H. O.R. Google Scholar). the capacity of LL-37 to host cell it be that the LL-37 and P2X7 the activity of all-d LL-37 that the of the membrane for to be of or helix has been that all-d peptides to of the receptor or of the cell receptor the activity of the full-length in a to that in D. J. Biol. 2004; PubMed Scopus Google Scholar, D. J. 2005; PubMed Scopus Google Scholar). This of be the membrane and is with the role of the membrane in with the receptor. P2X7 a for ATP with and the of ATP that are for in activation are not found in the extracellular this it has been that endogenous molecules are to the receptor to to physiological of ATP, as a danger for cells. has been shown to calcium pore and by P2X7 in microglial cells T. M. H. J. Neurochem. 2007; PubMed Scopus Google Scholar), and has a activity in S. R. S. M. 2006; PubMed Scopus Google Scholar). is that LL-37 such a role by with ATP for activation of the receptor at sites of inflammation or tissue This is by the that LL-37 is by human upon M.F. G. G. Stahle-Backdahl M. J. Investig. Dermatol. Full Text Full Text PDF PubMed Scopus Google Scholar), and the ATP is also likely to be in this as a of cellular LL-37 has been involved in that are important for tissue such as and by of a role of in of tissue from the that at the is in as with R. G. C. F. S. T. K. P. M. C. A. P. A. P. C. Gallo R.L. M. R. J. Investig. PubMed Scopus Google Scholar). In the study that LL-37 fibroblast proliferation. have a role in tissue the of and to and of extracellular which is for Our results that the fibroblast growth-promoting activity is a by which LL-37 to the