REVIEW
Osteoclasts, mononuclear phagocytes, and c-Fos:
new insight into osteoimmunology
Koichi Matsuo and Neelanjan Ray1
Department of Microbiology and Immunology, School of Medicine, Keio University, Tokyo, Japan
1Medical Scholars Program, Vanderbilt University School of Medicine, Nashville, TN, USA(Received for publication on February 16, 2004)

Abstract. Osteoimmunology is the emerging concept that certain molecules link the skeletal and immune systems. The transcription factor c-Fos, a component of activator protein-1 (AP-1), is essential for
osteoclast differentiation. Mice lacking c-Fos are osteopetrotic owing to impaired osteoclast development. Recent studies suggest that in contrast to this positive role in osteoclastogenesis, c-Fos expression inhibits differentiation and activation of mononuclear phagocytes. Here, we focus on the contrasting roles of c-Fos in the bone and immune lineages. Both osteoclasts and mononuclear phagocytes
are derived from common myeloid precursors. Osteoclasts resorb bone, whereas macrophages andmyeloid dendritic cells phagocytose microbial pathogens, initiating innate and adaptive immunity.
Differentiation of the common precursors into either bone or immune lineage is determined by ligand
binding to cell-surface receptors, particularly receptor activator of NF-kB (RANK) for osteoclasts, or
Toll-like receptors (TLRs) for mononuclear phagocytes. Both RANK and TLRs activate the dimerictranscription factors NF-kB and AP-1. Yet, c-Fos/AP-1 plays a positive role in osteoclasts but a negative role in macrophages and dendritic cells. Further study is necessary to clarify this dual role of c-Fos.
(Keio J Med 53 (2): 78–84, June 2004)
Key words: AP-1, c-Fos, osteoclast, macrophage, dendritic cellhighly conserved ‘‘basic leucine zipper’’ (bZip) structure. The basic region is responsible for DNA-binding,and the leucine-zipper is for heterodimerization, typically with the Jun proteins, c-Jun, JunB and JunD. The
bZip structure is located in the middle of Fos proteins, but at the C-terminus of Jun proteins (Fig. 1). The
resultant dimeric transcription factor complexes arecollectively termed AP-1, and the consensus sequenceof their binding sites is 5 0 -TGA(G/C)TCA-3 0 . c-Fos istransiently induced in response to various stimuli, andexpressed in cell types ranging from neurons to keratinocytes. Thus it was surprising that mice lacking thistranscription factor showed an overt phenotype only inbone, namely osteopetrosis.5–7 But in fact, recent ﬁndings indicate that c-Fos is likely a key regulator in the
immune system as well.

Introduction
Rheumatoid arthritis and other inﬂammatory bonediseases illustrate the close link between bone biology
and immunology. Synovial inﬂammation, for example,
results in joint destruction mediated by pathologicalinteraction between T cells and osteoclasts.1,2 Patientswith inﬂammatory bowel disease such as Crohn’s disease are at high risk for osteoporotic vertebral fractures.3 Only recently, however, has it come to light thatcertain molecules actually regulate both the skeletal andimmune systems. These ﬁndings rationalize the emerging concept of osteoimmunology.4 In this review, we
describe the contrasting roles of the transcription factor
c-Fos in osteoclasts and mononuclear phagocytes.
c-Fos was originally identiﬁed as the cellular homologof the retroviral gene, v-Fos, which induces osteosarcomas in mice. Both in humans and in mice, three additional Fos proteins, Fra1, Fra2 and FosB have been
identiﬁed (Fig. 1). Fos family members each carry the

Osteoclast and Macrophage-Dendritic Cell Lineages
Differentiation into osteoclasts or mononuclear

Reprint request to: Dr. Koichi Matsuo, Department of Microbiology and Immunology, School of Medicine, Keio University, Shinanomachi 35,
Shinjuku-ku, Tokyo 160-8582, Japan, e-mail: matsuo@sc.itc.keio.ac.jp78Keio J Med 2004; 53 (2): 78–84

c-Fos
Fra1
Fra2
FosB

79

c-Jun
JunB
JunD
C

bZIP

C

N

N

AP-1
Fig. 1c-Fos and other AP-1 family members.

phagocytes can be considered a lineage bifurcation,
similar to differentiation into either T versus B cells, orCD4þ versus CD8þ T cells. The common myeloid precursors commit to either the osteoclast or mononuclear
phagocyte lineage, depending upon stimuli received
from the external environment (Fig. 2).8–10 Generationof myeloid precursors is dependent on the presence ofmacrophage-colony-stimulating factor (M-CSF) and thetranscription factor PU.1, and mice devoid of either
factor lack both osteoclasts and macrophages. Myeloid
dendritic cells, the most potent antigen presenting cells(APCs) are central in eliciting T cell response. These
dendritic cells also differentiate from the same myeloid
precursors in the presence of granulocyte-macrophagecolony-stimulating factor (GM-CSF) and interleukin-4(IL-4).11,12 Myeloid precursors can be isolated not only
from bone marrow, but also from other sites, including
the spleen and peritoneal cavity.13
Osteoclast differentiation is associated with activationof genes encoding tartrate-resistant acid phosphatase(TRAP), calcitonin receptor, cathepsin K, b3 -integrin,and ATP-dependent proton pump subunits. Once committed, mononuclear osteoclasts fuse with each other,
forming multinucleated osteoclasts. They then polarize
and adhere to bone matrix, induce actin ring formation,
acidify bone surface and release osteolytic enzymes(Fig. 2).10 In contrast, macrophage differentiation isindicated by induction of various genes encoding cellsurface molecules, including F4/80, Mac-1 (CD11b),
MOMA-2, and MHC class II molecules, and enzymes
such as inducible nitric oxide synthase (iNOS). Dendritic cell differentiation is indicated by expression of
MHC class II molecules as well as CD11c (Fig. 2). Signals from cell surface receptors determine which set ofgenes the myeloid precursors will eventually express.

T cellRANKL
Dendritic cell

CD11c+
MHC class II+

GM-CSF

Macrophage

PAMPs
TLR

M-CSF
myeloidprecursor

hematopoietic
stem cell

RANK

TRAP+
+
Calcitonin R

F4/80+
CD11b (Mac-1)+
MHC class II+

Osteoclast

M-CSF
RANKL

cell fusionbonestromal cell / osteoblast
Fig. 2 Differentiation into osteoclasts or mononuclear phagocytes. PAMPs: pathogen associated molecular patterns, Calcitonin R: calcitoninreceptor.

80

Matsuo K and Ray N: c-Fos in osteoimmunology

LPS

RANKL
RANK

TLR4

LBP
CD14
MyD88

TRAF2

IRAK

TRAF6

Table 1 Immunological Phenotypes of Mice with Osteopetrosis Dueto Impaired Osteoclast Differentiation

TRAF6

Deﬁciency
c-Fos*
NF-kB (p50, p52)*

P

TRAF5

TAK1 (MAPKKK)

RANK*
RANKL

JNK, ERK, p38, Akt...
AP-1

Fos

Jun

NF-κB

microphthalmia (mi)PU.1

p50 p65 (RelA)
p52 RelBc-Rel

op/op (M-CSF)
TRAF6*

Immunological phenotypes
elevated IL-12 production in macrophages36
impaired cytokine production; impaired Bcell, thymus, and spleen development39,40
lack of lymph nodes but Peyer’s patches
present; impaired B-cell development41,42
lack of lymph nodes but Peyer’s patches
present; defects in early differentiation of T
and B cells43
mast cell defects44
lack of macrophages45; reduced lymphoidmyloid progenitors46
reduced macrophages47
lack of IL-1, CD40 and LPS signaling; lack oflymph nodes; lack of dendritic cellmaturation48–50* indicates cell-autonomous differentiation block.
NFATc1TRAP
calcitonin receptor

NO
TNF-α
IL-1, IL-6, IL-12

Fig. 3 RANK and TLR signals both activate NF-kB and AP-1, butwith different target gene expression. IRAK: IL-1 receptor-associatedkinase, Akt: protein kinase B.

RANK and TLRs
RANKL14–17 (encoded by Tnfsf11) is expressed as atrimer on osteoblasts. The RANKL receptor, RANK14(encoded by Tnfrsf11a), which is mainly expressed in
the myeloid lineages, belongs to the tumor necrosis
factor (TNF) receptor superfamily. RANKL-RANK
interaction initiates a signal cascade involving recruitment of intracellular tumor necrosis factor receptorassociated factors (TRAFs) such as TRAF2, TRAF5,
and TRAF618 (Fig. 3). Genetic experiments in mice
have revealed that RANKL, RANK, TRAF6 and thetranscription factors c-Fos and NF-kB (double knockout for p50 and p52) are essential for precursors tocommit into the osteoclast lineage (Table 1). Micelacking any of these molecules are osteopetrotic due tolack of bone resorption. It is worth noting that RANK
is necessary for lymph node formation as well (Table1). In the presence of M-CSF, the RANK pathway can
activate all three groups of mitogen-activated protein(MAP) kinases: c-Jun-N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38.
TRAF6 associates with transforming growth factor-bactivated kinase 1 (TAK1), which activates JNK and
AP-1, as well as inducing nuclear translocation of NFkB through IkB degradation (Fig. 3).19 The only component of AP-1 known to be necessary for osteoclast

formation is c-Fos. Interestingly, however, mice lacking
another Fos family protein, Fra2 appear to be osteoporotic (E.F. Wagner, personal communications).
Signaling by TLRs induces macrophage differentiation and activation. TLRs recognize pathogenassociated molecular patterns (PAMPs) from a wide
variety of microorganisms. For example, lipopolysaccharide (LPS), a cell wall component of Gramnegative bacteria, is recognized by TLR4 with the helpof LPS-binding protein (LBP) and CD14 (Fig. 3).20
LPS stimulation leads to production and release ofvarious inﬂammatory mediators including TNF-a, IL-1,
IL-6, IL-12, as well as nitric oxide (NO). TLR3, TLR5
and TLR9 recognize double-stranded RNA, ﬂagellin
and unmethylated CpG DNA, respectively. TLR1,
TLR2 and TLR6 can cooperate to recognize peptidoglycan and several other speciﬁc PAMPs. TLR1 to
TLR9 are all expressed in myeloid precursors.21 Typically, TLR signaling is mediated by adaptor molecules
such as MyD88 and TRAF6, which eventually activate
NF-kB and AP-1. This results in production of inﬂammatory cytokines (Fig. 3), and subsequent induction of
innate and adaptive responses. RANK and TLR signaling appear surprisingly similar in that both activate
NF-kB and AP-1, including c-Fos. Yet, this similarity must only be superﬁcial since RANK signaling
promotes osteoclastogenesis, while TLR signaling is
generally believed to inhibit osteoclast differentiation.13,21,22 Furthermore, overexpression of c-Fos has
been shown to inhibit maturation of a murine myeloblastic leukemia cell line into macrophages.23 How
exactly is c-Fos involved in RANK and TLR signaling
in myeloid cells?

Keio J Med 2004; 53 (2): 78–84

Roles of c-Fos in Bone Biology
The necessity of c-Fos in osteoclast differentiation isrevealed by the severe osteopetrotic phenotype of c-Fos
deﬁcient (Fos= ) mice.5,6 A similar cell-autonomous
differentiation block in the osteoclast lineage is also
demonstrated in other osteopetrotic mice (Table 1).
The critical target genes of c-Fos in osteoclast differentiation have been extensively analyzed by rescue
experiments. In these experiments, putative c-Fos target
genes were expressed in Fos= precursors via retroviral vectors or transgenes to determine whether they
could overcome this block in differentiation.
Retroviral gene transfer of any Fos family genes,
particularly Fra1 (also known as Fosl1, for Fos-like 1),
results in osteoclast formation in vitro, demonstrated
by expression of Acp5 (encoding TRAP) and Calc
(encoding calcitonin receptor), as well as bone resorption.24 The rescue of osteoclastogenesis in Fos= precursors by Fra1 has also been shown in vivo by crossing
Fra1 transgenic mice with Fos= mice.24 This was further conﬁrmed by using a knock-in technique, whichallows Fra1 to be expressed under the Fos promoter,at the Fos locus.25 In Fos= osteoclast precursors,
Fra1 expression is hardly detectible. Furthermore, Fra1
carries functional AP-1 sites in intron 1,26 suggestingthat Fra1 expression is dependent on c-Fos duringosteoclast differentiation. Unlike c-Fos, Fra1 has nodetectible transactivation domains. The activation potential of Fra1-containing AP-1 may actually be determined by the heterodimerizing partner. It is not knownat present whether Jun proteins are the partners of Fra1
during osteoclast formation or not.
Transcription factors of the nuclear factor of activated T cells (NFAT) family contain the Rel-homology
domain, a conserved DNA-binding domain distantly
related to that of NF-kB.27 NFATs were originallyidentiﬁed in T cells and are involved in regulation ofgenes encoding IL-2 and other cytokines. Mice lacking
NFATc1 die in utero due to impaired heart development.28,29 The critical role of NFATc1 in osteoclastogenesis has recently been demonstrated.30,31 Importantly, we as well as others have observed that
expression of NFATc1 is induced in Fosþ=þ , but not
Fos= precursors during osteoclast differentiation.32
The lack of NFATc1 expression in the absence of c-Fos
is the cause, not the consequence of the differentiation
block. Exogenously expressed NFAT can rescue expression of Acp5 and Calc, as well as bone-resorbing
activity in cells from Fos= precursors in vitro.32 These
data establish the RANK – c-Fos – NFATc1 transcriptional cascade, which is critical for osteoclastogenesis.
NFATc1 is usually localized in the cytosol in phosphorylated form. Dephosphorylation by calcineurin, aCa 2þ -dependent phosphatase, is required for NFATc1

81

to translocate into the nucleus. It is worth noting that
NFATc1 and AP-1 can interact at the protein level andbind cooperatively to DNA at certain promoters,
including those of Acp5 and IL-2. In summary, RANK
activates osteoclastogenic target genes, through c-Fos
and NFATc1, resulting in differentiation of myeloid
precursors into osteoclasts.
Unlike Fra1 or NFAT, c-Fos target genes in theosteoclast lineage are not always positive regulatorsof osteoclastogenesis. Microarray analyses comparing
osteoclastogenic cultures of Fosþ=þ and Fos= precursors revealed that Fos= precursors did not express
interferon (IFN)-inducible genes. It turns out that transcription of IFN-b is downregulated in the absence of cFos. A functional AP-1 site was identiﬁed in the IFN-b
promoter, suggesting that IFN-b is a c-Fos target genein osteoclast precursors.33 Surprisingly, signals from the
IFN-b receptor cause reduction of c-Fos protein. Thus,
there exists a c-Fos negative-feedback loop, which ismediated by IFN-b. Since IFN-b production in response
to Newcastle disease virus is still intact in Fos= myeloid precursors, IFN-b seems to be a c-Fos target gene
speciﬁcally during osteoclast differentiation.33 It was
unexpected that IFN-b, an antiviral cytokine, would
have an important role in bone physiology as well.
Downregulation of c-Fos by cytokines seems to bea general regulatory mechanism for suppressing osteoclast differentiation. GM-CSF and IL-3 are cytokines
which both act directly on early osteoclast precursors,
irreversibly blocking RANKL-induced osteoclast differentiation by downregulating c-Fos transcripts. As aresult these cells become macrophages or dendritic
cells.11,34
Roles of c-Fos in the Immune System:
Macrophages and Dendritic Cells
In contrast to its role in bone biology, the role of cFos in the immune system remains unclear. Osteopetrosis in mice is often accompanied by various immunological phenotypes (Table 1), and Fos= mice are no
exception to this phenomenon. Research examining thefunctions of c-Fos in mononuclear phagocytes suggeststhat c-Fos induction may be important in both innate
and adaptive immune responses, as we shall see below.
c-Fos/AP-1 has been shown to negatively regulatetranscription of iNOS, which is responsible for production of the microbiocidal compound, NO (Fig. 4A).35
Stimulation by LPS, IFN-g, or a combination of the two
induces iNOS in macrophages. c-Fos is also upregulated
in these macrophages post-LPS stimulation. By using
an inducible c-Fos transgene (Mx-c-fos), Okada et al.
showed that c-Fos overexpression suppressed iNOS,
preventing NO production in macrophages after LPS

82

Matsuo K and Ray N: c-Fos in osteoimmunology

A

c-Fos

iNOS

TNF-α

IL-12

B
Fos+/+

c-Fos Tg

Fos-/-

LPS

NO
TNF-α
IL-12

nd
nd
nd

Fig. 4 c-Fos acts as a negative regulator in macrophages. (A) c-Fos
can suppress genes encoding iNOS, TNF-a, and IL-12. (B) Lack of cFos results in IL-12 overproduction in LPS-stimulated macrophages,
and overexpression of c-Fos causes decreased production of NO andTNF-a.

stimulation (Fig. 4B).35 Interestingly, production of
TNF-a was also signiﬁcantly reduced in these transgenic
macrophages overexpressing c-Fos. On the other hand,
peritoneal macrophages from mice lacking c-Fos did
not show an abnormal increase in NO production whenstimulated with LPS and IFN-g. In this context, it ispossible that other Fos family members are substituting
for c-Fos.35
The negative regulatory function of c-Fos on theiNOS promoter may be explained by the interaction
between c-Fos and nuclear factor-IL6 (NF-IL6), another basic leucine zipper family transcription factor.35
NF-IL6 can induce iNOS by binding to its promoter
region. Protein-protein interaction between c-Fos and
NF-IL6 may interfere with the DNA-binding activityof NF-IL6, resulting in inhibition of iNOS. The TNF-agene also possesses binding sites for NF-IL6, AP-1 andadditionally NF-kB. However, the mechanism of TNF-adownregulation due to c-Fos overexpression is not yet
known. Overproduction of NO and other inﬂammatory
mediators is implicated in inﬂammatory bowel disease,
experimental arthritis, and septic shock. A possible
physiological role of c-Fos may be to suppress unnecessary production of these inﬂammatory mediators.
IL-12, a heterodimeric cytokine composed of two
subunits (IL-12 p40 and IL-12 p35), is released bymacrophages and dendritic cells upon stimulation by
LPS. c-Fos appears to inhibit IL-12 production in both

macrophages and dendritic cells.36–38 Using Fos=murine peritoneal macrophages, Roy et al. demonstrated that absence of c-Fos results in overproductionof IL-12 in response to LPS stimulation.36 This overproduction of IL-12 observed in Fos= macrophages
can be mimicked in Fosþ=þ and Fosþ= macrophages
when they are treated with IFN-g prior to LPS stimulation. IFN-g priming in these cells enhances IL-12
production presumably through downregulation of cFos. This is consistent with the fact that production of
IL-12 in Fos= macrophages is not further increased
by IFN-g priming.36
Similar to IFN-g pre-treatment, IL-4 pre-treatment
of Fosþ=þ peritoneal macrophages results in increased
production of IL-12 in response to LPS stimulation,
also likely via decrease in c-Fos transcripts.37 The already high IL-12 production by Fos= macrophages in
response to LPS is not further affected by IL-4 pretreatment. This effect of IL-4 is abolished, however, if
c-Fos is constitutively overexpressed in macrophages.
Thus, both IFN-g and IL-4 can prime macrophages
similarly for IL-12 production by downregulating c-Fos.
IL-12 production promotes Th1 response, and therefore
suppression of c-Fos may be a mechanism by which the
immune system modulates Th1 versus Th2 responses.
Research examining immature human dendritic
cells indicates that phosphorylation of c-Fos may be amechanism by which these cells differentially initiate a
Th2 instead of Th1 response, depending upon the nature of stimulation received (Fig. 5).38 LPS and ﬂagellin
promote a Th1 response, illustrated by production of
IFN-g and IL-12 by the dendritic cells. Pam3cys andSEA, in contrast, promote a Th2 response as shown by
IL-5 and IL-13 production by the dendritic cells. c-Fos
acts as a negative regulator of IL-12 production in dendritic cells as it does in macrophages. Both Pam3cys
and SEA stimulation appear to stabilize c-Fos throughphosphorylation via the ERK1/2 pathway. This resultsin suppression of IL-12, favoring the Th2 response.38
Thus, the role of c-Fos goes beyond that of a simple
negative regulator to possibly being part of a mechanism for ﬁne-tuning adaptive immunity.
Emerging data indicates that c-Fos is likely involved
in differentiation and activation of immune cells. A
better understanding of the roles of c-Fos in the immune system may lead to more effective therapies forsuppressing an overactive immune response.
Conclusion
The research we have discussed demonstrates thebreadth of functions that the transcription factor c-Fos
has in both osteoclasts and mononuclear phagocytes.
c-Fos is among several molecules which are importantin osteoimmunology, others include IFN-b, IFN-g,

Keio J Med 2004; 53 (2): 78–84

83

LPS

Th1

TLR4

FLG

IL-12

IFN-γ

Fos
TLR5

Th2
IL-5
IL-13

IL-5

Fos-P
IL-12

?

IL-4
IL-10

SEA
Pam3

TLR2

Fig. 5 c-Fos phosphorylation in dendritic cells may result in preferential induction of Th2 response. FLG: ﬂagellin, SEA: schistosome egg
antigens, Pam3: Pam3Cys-Ser-Lys4, Fos-P: phosphorylated c-Fos.

RANKL, TRAF6, NFAT, and NF-kB. What makes cFos especially interesting is the contrasting roles it
plays. Overall, it appears to be a positive regulator in
the osteoclast lineage, but a negative regulator in macrophages and dendritic cells. A clearer understandingof this dual nature of c-Fos may shed more light on thecomplex interplay between the skeletal and immune
systems.
Acknowledgements: This work is supported in part by the Medical
Scholars Program, Vanderbilt University School of Medicine. We
thank C. Zhao, G. Sano, H. Ishikawa, and S. Koyasu for criticalreading of the manuscript.

8.

9.

10.
11.

References
12.
1. Kong YY, Feige U, Sarosi I, Bolon B, Tafuri A, Morony S,
Capparelli C, Li J, Elliott R, McCabe S, et al: Activated T cells
regulate bone loss and joint destruction in adjuvant arthritis
through osteoprotegerin ligand. Nature 1999; 402: 304–309
2. Redlich K, Hayer S, Ricci R, David JP, Tohidast-Akrad M,
Kollias G, Steiner G, Smolen JS, Wagner EF, Schett G: Osteoclasts are essential for TNF-a-mediated joint destruction. J Clin
Invest 2002; 110: 1419–1427
3. Klaus J, Armbrecht G, Steinkamp M, Bruckel J, Rieber A,
Adler G, Reinshagen M, Felsenberg D, von Tirpitz C: Highprevalence of osteoporotic vertebral fractures in patients with
Crohn’s disease. Gut 2002; 51: 654–658
4. Arron JR, Choi Y: Bone versus immune system. Nature 2000;
408: 535–536
5. Wang ZQ, Ovitt C, Grigoriadis AE, Mohle-Steinlein U, RutherU, Wagner EF: Bone and haematopoietic defects in mice lacking
c-fos. Nature 1992; 360: 741–744
6. Johnson RS, Spiegelman BM, Papaioannou V: Pleiotropic effects
of a null mutation in the c-fos proto-oncogene. Cell 1992; 71:
577–586
7. Grigoriadis AE, Wang ZQ, Cecchini MG, Hofstetter W, Felix R,
Fleisch HA, Wagner EF: c-Fos: a key regulator of osteoclast-

13.

14.

15.

16.

macrophage lineage determination and bone remodeling. Science
1994; 266: 443–448
Lean JM, Matsuo K, Fox SW, Fuller K, Gibson FM, Draycott G,
Wani MR, Bayley KE, Wong BR, Choi Y, et al: Osteoclast lineage commitment of bone marrow precursors through expressionof membrane-bound TRANCE. Bone 2000; 27: 29–40
Arai F, Miyamoto T, Ohneda O, Inada T, Sudo T, Brasel K,
Miyata T, Anderson DM, Suda T: Commitment and differentiation of osteoclast precursor cells by the sequential expression ofc-Fms and receptor activator of nuclear factor kB (RANK)
receptors. J Exp Med 1999; 190: 1741–1754
Teitelbaum SL, Ross FP: Genetic regulation of osteoclast development and function. Nat Rev Genet 2003; 4: 638–649
Miyamoto T, Ohneda O, Arai F, Iwamoto K, Okada S, Takagi
K, Anderson DM, Suda T: Bifurcation of osteoclasts and dendritic cells from common progenitors. Blood 2001; 98: 2544–
2554.
Miyamoto T, Suda T: Differentiation and function of osteoclasts.
Keio J Med 2003; 52: 1–7
Hayashi S, Yamada T, Tsuneto M, Yamane T, Takahashi
M, Shultz LD, Yamazaki H: Distinct osteoclast precursors inthe bone marrow and extramedullary organs characterized byresponsiveness to toll-like receptor ligands and TNF-a. J Immunol 2003; 171: 5130–5139
Anderson DM, Maraskovsky E, Billingsley WL, Dougall WC,
Tometsko ME, Roux ER, Teepe MC, DuBose RF, Cosman D,
Galibert L: A homologue of the TNF receptor and its ligand
enhance T-cell growth and dendritic-cell function. Nature 1997;
390: 175–179
Wong BR, Rho J, Arron J, Robinson E, Orlinick J, Chao M,
Kalachikov S, Cayani E, Bartlett FS, 3rd, Frankel WN, et al:
TRANCE is a novel ligand of the tumor necrosis factor receptor
family that activates c-Jun N-terminal kinase in T cells. J Biol
Chem 1997; 272: 25190–25194
Yasuda H, Shima N, Nakagawa N, Yamaguchi K, Kinosaki
M, Mochizuki S, Tomoyasu A, Yano K, Goto M, Murakami A,
et al: Osteoclast differentiation factor is a ligand for osteoprotegerin/osteoclastogenesis-inhibitory factor and is identical to
TRANCE/RANKL. Proc Natl Acad Sci USA 1998; 95: 3597–
3602

84
17. Lacey DL, Timms E, Tan HL, Kelley MJ, Dunstan CR, Burgess
T, Elliott R, Colombero A, Elliott G, Scully S, et al: Osteoprotegerin ligand is a cytokine that regulates osteoclast differentiation and activation. Cell 1998; 93: 165–176
18. Ye H, Arron JR, Lamothe B, Cirilli M, Kobayashi T, Shevde
NK, Segal D, Dzivenu OK, Vologodskaia M, Yim M, et al: Distinct molecular mechanism for initiating TRAF6 signalling. Nature 2002; 418: 443–447
19. Mizukami J, Takaesu G, Akatsuka H, Sakurai H, NinomiyaTsuji J, Matsumoto K, Sakurai N: Receptor activator of NF-kB
ligand (RANKL) activates TAK1 mitogen-activated protein
kinase kinase kinase through a signaling complex containing
RANK, TAB2, and TRAF6. Mol Cell Biol 2002; 22: 992–1000
20. Medzhitov R: Toll-like receptors and innate immunity. Nat Rev
Immunol 2001; 1: 135–145
21. Takami M, Kim N, Rho J, Choi Y: Stimulation by toll-like receptors inhibits osteoclast differentiation. J Immunol 2002; 169:
1516–1523
22. Abu-Amer Y, Ross FP, Edwards J, Teitelbaum SL:
Lipopolysaccharide-stimulated osteoclastogenesis is mediatedby tumor necrosis factor via its P55 receptor. J Clin Invest 1997;
100: 1557–1565
23. Obata S, Okada S, Ohkubo Y, Murasawa M, Hatano M, Sekiya
S, Tokuhisa T: Overexpression of the c-fos gene perturbs functional maturation of M1 cells into macrophages. Mol Immunol
2003; 39: 585–594
24. Matsuo K, Owens JM, Tonko M, Elliott C, Chambers TJ,
Wagner EF: Fosl1 is a transcriptional target of c-Fos duringosteoclast differentiation. Nat Genet 2000; 24: 184–187
25. Fleischmann A, Hafezi F, Elliott C, Reme CE, Ruther U,
Wagner EF: Fra-1 replaces c-Fos-dependent functions in mice.
Genes Dev 2000; 14: 2695–2700
26. Bergers G, Graninger P, Braselmann S, Wrighton C, Busslinger
M: Transcriptional activation of the fra-1 gene by AP-1 is mediated by regulatory sequences in the ﬁrst intron. Mol Cell Biol
1995; 15: 3748–3758
27. Hogan PG, Chen L, Nardone J, Rao A: Transcriptional regulation by calcium, calcineurin, and NFAT. Genes Dev. 2003; 17:2205–2232
28. de la Pompa JL, Timmerman LA, Takimoto H, Yoshida H, Elia
AJ, Samper E, Potter J, Wakeham A, Marengere L, Langille BL,
et al: Role of the NF-ATc transcription factor in morphogenesisof cardiac valves and septum. Nature 1998; 392: 182–186
29. Ranger AM, Grusby MJ, Hodge MR, Gravallese EM, de laBrousse FC, Hoey T, Mickanin C, Baldwin HS, Glimcher LH:
The transcription factor NF-ATc is essential for cardiac valve
formation. Nature 1998; 392: 186–190
30. Ishida N, Hayashi K, Hoshijima M, Ogawa T, Koga S, Miyatake
Y, Kumegawa M, Kimura T, Takeya T: Large scale gene expression analysis of osteoclastogenesis in vitro and elucidation of
NFAT2 as a key regulator. J Biol Chem 2002; 277: 41147–41156
31. Takayanagi H, Kim S, Koga T, Nishina H, Isshiki M, Yoshida H,
Saiura A, Isobe M, Yokochi T, Inoue J, et al: Induction andactivation of the transcription factor NFATc1 (NFAT2) integrate RANKL signaling in terminal differentiation of osteoclasts.
Dev Cell 2002; 3: 889–901
32. Matsuo K, Galson DL, Zhao C, Peng L, Laplace C, Wang KZ,
Bachler MA, Amano H, Aburatani H, Ishikawa H, Wagner EF:
Nuclear factor of activated T-cells (NFAT) rescues osteoclastogenesis in precursors lacking c-Fos. J Biol Chem 2004; 279:
26475–26480
33. Takayanagi H, Kim S, Matsuo K, Suzuki H, Suzuki T, Sato K,
Yokochi T, Oda H, Nakamura K, Ida N, et al: RANKL maintains bone homeostasis through c-Fos-dependent induction ofinterferon-b. Nature 2002; 416: 744–749
34. Khapli SM, Mangashetti LS, Yogesha SD, Wani MR: IL-3 acts

Matsuo K and Ray N: c-Fos in osteoimmunology

35.

36.

37.

38.

39.

40.

41.

42.

43.

44.
45.

46.

47.

48.

49.

50.

directly on osteoclast precursors and irreversibly inhibits receptor activator of NF-kappaB ligand-induced osteoclast differentiation by diverting the cells to macrophage lineage. J Immunol
2003; 171: 142–151
Okada S, Obata S, Hatano M, Tokuhisa T: Dominant-negative
effect of the c-fos family gene products on inducible NO synthase
expression in macrophages. Int Immunol 2003; 15: 1275–1282
Roy S, Charboneau R, Cain K, DeTurris S, Melnyk D, Barke
RA: Deﬁciency of the transcription factor c-fos increases
lipopolysaccharide-induced macrophage interleukin 12 production. Surgery 1999; 126: 239–247
Roy S, Charboneau R, Melnyk D, Barke RA: Interleukin-4
regulates macrophage interleukin-12 protein synthesis through ac-fos mediated mechanism. Surgery 2000; 128: 219–224
Agrawal S, Agrawal A, Doughty B, Gerwitz A, Blenis J, Van
Dyke T, Pulendran B: Cutting Edge: different toll-like receptor
agonists instruct dendritic cells to induce distinct Th responses
via differential modulation of extracellular signal-regulated
kinase-mitogen-activated protein kinase and c-Fos. J Immunol
2003; 171: 4984–4989
Franzoso G, Carlson L, Xing L, Poljak L, Shores EW, Brown
KD, Leonardi A, Tran T, Boyce BF, Siebenlist U: Requirement
for NF-kB in osteoclast and B-cell development. Genes Dev
1997; 11: 3482–3496
Iotsova V, Caamano J, Loy J, Yang Y, Lewin A, Bravo R:
Osteopetrosis in mice lacking NF-kB1 and NF-kB2. Nat Med
1997; 3: 1285–1289
Dougall WC, Glaccum M, Charrier K, Rohrbach K, Brasel K,
De Smedt T, Daro E, Smith J, Tometsko ME, Maliszewski CR,
et al: RANK is essential for osteoclast and lymph node development. Genes Dev 1999; 13: 2412–2424
Li J, Sarosi I, Yan XQ, Morony S, Capparelli C, Tan HL,
McCabe S, Elliott R, Scully S, Van G, et al: RANK is the intrinsic hematopoietic cell surface receptor that controls osteoclastogenesis and regulation of bone mass and calcium metabolism.
Proc Natl Acad Sci USA 2000; 97: 1566–1571
Kong YY, Yoshida H, Sarosi I, Tan HL, Timms E, Capparelli C,
Morony S, Oliveira-dos-Santos AJ, Van G, Itie A, et al: OPGL isa key regulator of osteoclastogenesis, lymphocyte development
and lymph-node organogenesis. Nature 1999; 397: 315–323
Nechushtan H, Razin E: The function of MITF and associatedproteins in mast cells. Mol Immunol 2002; 38: 1177–1180
Tondravi MM, McKercher SR, Anderson K, Erdmann JM,
Quiroz M, Maki R, Teitelbaum SL: Osteopetrosis in mice lacking
haematopoietic transcription factor PU.1. Nature 1997; 386: 81–84
Scott EW, Fisher RC, Olson MC, Kehrli EW, Simon MC, Singh
H: PU.1 functions in a cell-autonomous manner to control thedifferentiation of multipotential lymphoid-myeloid progenitors.
Immunity 1997; 6: 437–447
Yoshida H, Hayashi S, Kunisada T, Ogawa M, Nishikawa S,
Okamura H, Sudo T, Shultz LD: The murine mutation osteopetrosis is in the coding region of the macrophage colony stimulating factor gene. Nature 1990; 345: 442–444
Lomaga MA, Yeh WC, Sarosi I, Duncan GS, Furlonger C, Ho
A, Morony S, Capparelli C, Van G, Kaufman S, et al: TRAF6
deﬁciency results in osteopetrosis and defective interleukin-1,
CD40, and LPS signaling. Genes Dev 1999; 13: 1015–1024
Naito A, Azuma S, Tanaka S, Miyazaki T, Takaki S, Takatsu K,
Nakao K, Nakamura K, Katsuki M, Yamamoto T, et al: Severe
osteopetrosis, defective interleukin-1 signalling and lymph nodeorganogenesis in TRAF6-deﬁcient mice. Genes Cells 1999; 4:
353–362
Kobayashi T, Walsh PT, Walsh MC, Speirs KM, Chiffoleau E,
King CG, Hancock WW, Caamano JH, Hunter CA, Scott P,
Turka LA, Choi Y: TRAF6 is a critical factor for dendritic cellmaturation and development. Immunity 2003; 19: 353–363