名古屋学芸大学健康･栄養研究所年報

第２号

２００８年

《Original Article》

Hoxc6 is overexpressed in gastrointestinal carcinoids and interacts with
JunD to regulate tumor growth
Kotoyo Fujiki＊ and Daniel C. Chung＊＊

Abstract
Background and Aims: The molecular alterations that underlie carcinoid tumor pathogenesis remain poorly
defined. The homeobox gene Hoxc6 was highly upregulated in human gastrointestinal carcinoid tumors, andwe sought to define its pathogenic role.
Methods: The functional and physical properties of Hoxc6 were investigated by establishing carcinoid cells
that stably overexpressed Hoxc6 or were deficient in Hoxc6. Cellular proliferation assays, luciferase reporter
assays, western blotting, and immunoprecipitation were performed.
Results:

Expression of Hoxc6 in cultured human BON1 carcinoid cells enhanced their proliferation, andknock-down of Hoxc6 inhibited their growth. Hoxc6 activated the oncogenic AP-1 signaling pathway through aphysical interaction with JunD. Mutations in the homeodomain of Hoxc6 blocked this interaction and inhibited
proliferation of carcinoid cells.
Conclusions: A novel molecular pathway has been identified that links Hoxc6 with oncogenic signaling
through the AP-1 pathway in carcinoid tumorigenesis.
Keywords: Hoxc6, carcinoid, AP-1, neuroendocrine tumor
Abbreviations:

Hoxc6-V1, Hoxc6 variant 1; Hoxc6-V2, Hoxc6 variant 2; AP-1, activator protein-1; MEN1,

multiple endocrine neoplasia 1
Acknowledgements: Stephen and Caroline Kaufer Fund for Neuroendocrine Tumor Research and Caring for
Carcinoid Foundation.

and excess levels can result in the clinical carcinoid

Introduction

syndrome 2. Gastrointestinal carcinoids are often

Carcinoid tumors are neuroendocrine neoplasms

classified together with neuroendocrine tumors ofthat can arise in multiple organ sites but are mostthe pancreas, as they share many clinical and bio-

1

commonly localized to the gastrointestinal tract .

logical features. However, key insights into their

They are typically slow-growing, well-differentiatedunderlying molecular pathogenesis are lacking.
Individuals with the Multiple Endocrine Neoplasia

tumors that secrete 5-hydroxytryptamine (serotonin),＊ Department of Nutrition, Nagoya University of Arts and Sciences, Aichi, Japan＊＊ Gastrointestinal Unit, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA

17Type 1 syndrome are at high risk for the development

ous DNA microarray studies indicated that Hoxc6of neuroendocrine tumors of the pancreas and pitu-

mRNA was strongly upregulated in gastrointestinal

itary, as well as parathyroid gland hyperplasia andcarcinoid tumors but not in closely related pancreatic

gastric carcinoids. The MEN1 tumor suppressor geneneuroendocrine tumors (in press). We now verify

that underlies the syndrome was cloned in 1997 3.

these findings and demonstrate that expression of

MEN1 also plays a role in sporadic pancreatic neu-

Hoxc6 stimulated the growth of carcinoid cells inroendocrine tumors and gastrointestinal carcinoids,

vitro. Hoxc6 enhanced signaling through the AP-1

but only a subset of these sporadic tumors harbors

pathway, and this was mediated by a novel interac-

4tion between Hoxc6 and the JunD component of

MEN1 mutations . The MEN1 gene product, menin,
5

has diverse functions , and most recently has beenAP-1. These findings link a developmental regulator

demonstrated to regulate gene transcription throughto an oncogenic signaling pathway. In addition tointeractions with a histone methyltransferase com-

providing an important new insight into the patho-

plex 6, 7. Some of the targets of menin include thegenesis of carcinoid tumors, these studies point to6

a molecular pathway that may be a novel target for.

therapy in carcinoids.

homeobox genes Hoxc6 and Hoxc8 as well as thecell cycle inhibitors p18 and p27

8, 9Homeobox (Hox) genes belong to the homeoprotein
family of transcription factors that are developmental

Materials and methods

regulators of growth, patterning, and differentiation.

Stable cell lines

There are 4 clusters of Hox genes (HOXA-D), andHox proteins contain a homeodomain that consists

BON1 cells (a human pancreatic carcinoid cellof three helices separated by a short loop. Helix IIIline) were utilized to generate cells stably overex-(the C-terminal helix) contacts A/T-rich domains ofpressing Hoxc6-Variant1, Hoxc6-Variant 2, or an

10

DNA in the regulatory regions of many genes .

siRNA to Hoxc6. These stable cells are designatedBecause most homeobox proteins have similar DNA

BON-Flag control, BON-Hoxc6-V1, BON-Hoxc6-binding specificity in vitro, the timing of expression

V2, BON-si Hoxc6, and two independent clones ofas well as the interactions between Hox proteinseach construct was analyzed. The pCMV FLAG-tag

and other transcriptional regulators are likely to be

expression vector (Invitrogen) with the coding region

critical for their functional specificity. Deregulatedof the human Hoxc6 variant 1 (V1) (NM_004503) or

expression of Hox genes has been reported in many

variant 2 (V2) (NM_153693) inserted between thetumors, including lung, breast, ovarian, sarcoma,

BamHI and XhoI sites was transfected into BON1

and leukemia . The specific mechanisms by whichcells. The cDNA of Hoxc6 V1 and V2 were a kindHox genes contribute to the tumorigenic phenotype

gift of Dr. Carlos Moreno (Emory University, At-

are incompletely described. In some cases, theylanta) 13. The N191Q mutation in Hoxc6 V1 andmay function as transcription factors that stimulate

N109Q mutation in Hoxc6 V2 (AAC -> CAG) inthe expression of growth factors, such as Hoxb7-

the homeodomain 14 was introduced using the Quik

mediated upregulation of fibroblast growth factor in

Change IIXL Site-Directed Mutagenesis Kit (Strata-

melanomas 11. Overexpression of Hoxc6 is observedgene). The siRNA against Hoxc6 was made using

in human prostate cancer, where it functions to in-

pSR-neo vectors (Oligoengine, Seattle, WA). The

10hibit apoptosis

12, 13oligonucleotides were inserted between the BglII.

and HindIII sites to produce short hairpin RNA.

Because of the link between the Hoxc6 and6

Hoxc8 gene clusters and the MEN1 gene , we were

Two different sequences derived from human Hoxc6

curious whether expression of these Hox genes was

mRNA (5’-GGGAAAAUUACAAAAAGAG-3’, 5’-altered in human neuroendocrine tumors. Previ-

GCGAAUGAAUUCGCACAGU-3’), common to18

Hoxc6 is overexpressed in gastrointestinal carcinoids and interacts with JunD to regulate tumor growthboth variant 1 and variant 2, were selected. For con-

Nuclear extracts were prepared using the NE-trol siRNA, we used the sequence 5’-GCGCGCTTT-PER Nuclear and Cytoplasmic Extraction ReagentsGTAGGATTCG-3’ that does not correspond to any(PIERCE). 300 µg of nuclear proteins were incubat-

known human gene. The stable transfected cells

ed with ANTI-FLAG M2 beads (Sigma) overnight

were selected in 200 µg/ml geneticin (GIBCO) forat 4°C. The beads were washed 3 times with RIPA

14 days, and clones were screened for Hoxc6 stablebuffer (Boston BioProducts) for 5 min, and wereexpression by Western Blotting using ANTI-FLAG

boiled in NuPAGE SDS Sample Buffer (Invitrogen)

M2 (Sigma) and for Hoxc6 silencing by q-PCR.

for 10 min. The samples were run on NuPAGE

The cells were maintained in a 1:1 mixture of F12

4-12% Bis-Tris Gels (Invitrogen) and detected byand DMEM (Cellgro) with 10% fetal bovine serum

Western blotting using antibodies against JunD

(Cellgro) supplemented with 1% penicillin/strepto-(sc-74, Santa Cruz) and Flag (ANTI-FLAG M2,

mycin (Invitrogen) in 5% CO2 at 37°C.

Sigma). The expression levels of JunD and Hoxc6(FLAG) in the samples were confirmed by Western

Proliferation assay

Blotting using 10 µg of nuclear protein.

The stable cells were plated in 96-well plates
Statistical analysis(1,500–3,000 cells per well). Proliferation of cells
was measured by a colorimetric assay using theStatistical differences were analyzed by the stu-

CellTiter 96 aqueous one solution cell proliferation

dent’s t-test, and p-values <0.05 were consideredassay kit (Promega) on day 1, 3, and 7 after plat-statistically significant.

ing.
Results

Luciferase reporter assay

Hoxc6 stimulates cellular proliferation of BON1

One day after plating the cells in a 12 well plate,cells in vitro

0.25 µg of an AP-1 luciferase reporter construct that
contains 4 consensus AP-1 binding sites and 5 ng

Because Hoxc6 was significantly upregulatedof the pRL-CMV Renilla vector (Promega) werein carcinoids, we focused our attention on thisco-transfected using Lipofectamine 2000 (Invitro-gene. To determine the functional consequences ofgen). Luciferase activity was measured with the

Hoxc6 expression in BON1 carcinoid cells, stable

Dual Luciferase Reporter Assay System (Promega)cell lines were generated in which either Hoxc6-V1

48 hours after transfection.

or Hoxc6-V2 was overexpressed (Figure 1). Two
independent clones of each construct were analyzed.

Western Blotting and Immunoprecipitation

In vitro growth assays revealed that overexpression

Cells were lysed in chilled lysis buffer (Cellof variant 1 was associated with a 74% (clone #3,

Signaling) supplemented with proteinase inhibitor

p<0.01) to 92% (clone #17, p<0.01) increase in cell

(PSC, Roche). 15-20 ug protein lysate were re-number compared to control transfected cells at 7

solved on 4-12% NuPAGE Bis-Tris polyacrylamide

days (Figure 2). Similarly, overexpression of variant

gels (Invitrogen) and transferred to polyvinylidene

2 was associated with a 68% (clone #3, p<0.01) todifluoride membranes (Millipore). Nuclear extracts

109% (clone #2, p<0.01) increase in cell number

were isolated using NE-PER kit (Pierce). The blots(Figure 2).

were probed with Flag and b-Actin (Sigma) antibod-

To verify this effect, BON1 cells were gener-

ies. Immunoreactive proteins were visualized using

ated that stably expressed an siRNA to endogenous

Western Lighting Chemiluminescence Reagent Plus

Hoxc6. Wild-type BON1 cells express low levels of(Perkin Elmer Life Sciences).

Hoxc6. The siRNA sequence utilized is common to19

Figure 1 Hoxc6 expression in BON1 carcinoid cells
Stable cell lines were generated in which either Flag tagged Hoxc6 variant 1 or Hoxc6 variant 2 was expressed. Two indepedentclones of each construct were analyzed. Expression was confirmed by western blotting for Flag. Vector = BON1 cells stably
expressing an empty Flag vector.

Figure 2 Hoxc6 stimulates proliferation of BON1 cells in vitro
Proliferation of BON1 cells stably expressing Hoxc6 variant 1 (Hoxc6V1#3, Hoxc6V1#17), Hoxc6 variant 2 (Hoxc6V2#2,
Hoxc6V2#3), or siRNA to Hoxc6 (siHoxc6#1, siHoxc6#3) was measured by a colorimetric assay on days 1, 3, and 7 after plating.

both variants and therefore targets both Hoxc6 tran-

18% of baseline and levels of Hoxc6-V2 to 14% of

scripts. The silencing efficiency of two independentbaseline. When compared to BON1 cells expressing

siRNA constructs to Hoxc6 is shown in Figure 3.

a control siRNA, there was a 43% decrease in the

In BON-siHoxc6#1 cells, levels of Hoxc6-V1 were

number of BON-siHoxc6#1 cells and 49% decrease

suppressed to 16% of baseline and Hoxc6-V2 levelsin the number of BON-siHoxc6#3 cells at 7 days

to 18% of baseline. Similarly, in BON-siHoxc6#3(Figure 2). Thus, Hoxc6 can regulate the prolifera-cells, levels of Hoxc6-V1 were suppressed levels totion of BON1 carcinoid cells in vitro.

20

Hoxc6 is overexpressed in gastrointestinal carcinoids and interacts with JunD to regulate tumor growth

Figure 3 The silencing efficiency of Hoxc6 knock down stable cell lines
Vectors expressing si RNA against Hoxc6 were stably transfected in BON1 cells. The silencing efficiency of Hoxc6 knock
down stable cell lines was shown by quantitative PCR for Hoxc6 variant 1 and variant 2. The results are normalized to values
from cells expressing a control siRNA.

Hoxc6 enhances signaling through the AP-1 path-ing through the AP-1 pathway.

way
Regulation of JunD expression by Hoxc6

To determine the mechanism through which
Hoxc6 may control cellular proliferation, we tested

In BON1 cells stably overexpressing Hoxc6, there

the consequences of Hoxc6 overexpression on thewas a modest increase in JunD mRNA levels. In

AP-1 signaling pathway that is frequently activated

BON-Hoxc6-V1 cells, there was a 2.23 fold increasein human malignancies. An earlier report suggested(p<0.05) in JunD mRNA levels, but only a 1.56 foldthat Hoxb4 can enhance signaling through the AP-1

increase (p=0.09) in BON-Hoxc6-V2 cells. In cells

pathway by upregulating the expression of Jun-B

stably expressing Hoxc6 siRNA, there was a 35%

18

and Fra-1 in Rat-1 cells . AP-1 is a heterodimericdecrease (p=0.07) in JunD mRNA levels. Thesetranscription factor that is a downstream target offindings suggest that Hoxc6 may regulate the ex-multiple oncogenes including Ras, and it can regu-

pression of JunD, but that the level of induction islate the expression of many genes critical for cellularmodest.

19

growth . A consensus AP-1 luciferase reporter construct was introduced into BON1 cells that stably

Hoxc6 physically interacts with JunD through its

overexpressed either Hoxc6 variant 1 or variant 2.

homeodomain

Compared to control BON1 cells, there was a 2.1

The effects of Hoxc6 on expression of JunD were

to 3.0 fold (p<0.01) increase in AP-1 reporter activ-

relatively modest, and we were curious whether there

ity in BON-Hoxc6-V1 cells, and a 2.1 to 2.8 fold

may be additional mechanisms controlling AP-1

(p<0.01) increase in BON-Hoxc6-V2 cells (Figure

activity by Hoxc6. A physical interaction between

4a). This induction was observed in two independent

the yeast homeodomain protein Hex and c-Jun has

clones. Similarly, in BON1 cells with Hoxc6 stably

been previously described, and Helix III of the Hex

knocked-down, there was a 70% reduction (p<0.01)

homeodomain mediated this interaction 14. Because

in AP-1 reporter activity in BON-siHoxc6#1 cells

c-Jun was not involved in the functional activation ofand a 66% reduction (p<0.01) in BON-siHoxc6#3

AP-1 by Hoxc6, we determined whether Hoxc6 may

cells (Figure 4b). Thus, Hoxc6 can enhance signal-

instead interact with JunD. Immunoprecipitation

21

Figure 4a Hoxc6 enhances signaling through the AP-1 pathway
A consensus AP-1 luciferase reporter construct was introduced into BON1 cells stably expressing Hoxc6 variant 1 (Hoxc6V1#3,
Hoxc6V1#17), Hoxc6 variant 2 (Hoxc6V2#2, Hoxc6V2#3). The results shown are the ratio of AP-1 luciferase activity in thesecells relative to those expressing vector control.

Figure 4b
A consensus AP-1 luciferase reporter construct was introduced into BON1 cells stably expressing siRNA to Hoxc6 (siHoxc6#1,
siHoxc6#3). The results shown are the ratio of AP-1 luciferase activity in these cells relative to those expressing vector control.

of Hoxc6 from BON1 cells stably overexpressing

was introduced in the Hoxc6 construct. There is

Hoxc6 followed by immunoblotting with a JunD

a conserved asparagine residue in Helix III of Hex

antibody revealed a specific interaction between

that was previously demonstrated to be essential

endogenous JunD and both Hoxc6 variants (Figure

for its interaction with c-Jun 14. This asparagine

5).

residue was selectively mutated in both Hoxc6 vari-

To test whether this interaction was mediated byants (N191Q in variant 1, designated mHoxc6-V1,

Helix III of the homeodomain, a point mutation

and N109Q in variant 2, designated mHoxc6-V2).

22

Hoxc6 is overexpressed in gastrointestinal carcinoids and interacts with JunD to regulate tumor growth

Figure 5 Hoxc6 interacts with JunD through its homeodomain
Immunoprecipitation of Hoxc6 (Flag) from BON1 cells stably overexpressing Flag tagged-Hoxc6 followed by immunoblottingwith a JunD antibody. The mutant constructs have a N191Q mutation in Hoxc6-V1 and N109Q mutation in Hoxc6-V2 homeodomain (AAC -> CAG).

Immunoprecipitation-western studies revealed thatHoxc6 and AP-1 were verified by expressing the mu-

both of these Hoxc6 mutants failed to interact withtant Hoxc6 that fails to interact with JunD. In BON1

JunD (Figure 5).

cells expressing either mHoxc6-V1 or mHoxc6-V2,

To verify that Hoxc6 formed a complex with AP-1

there was a 57% (p<0.01) to 51% (p<0.01) reductionthat physically bound to DNA, a DNA-precipitationof AP-1 reporter activity, respectively, indicating thatassay was performed. Nuclear extracts from BON1

this Hoxc6 mutant can inhibit AP-1 activity. The

cells overexpressing either Hoxc6-V1 or Hoxc6-V2

growth rate of BON1 cells that stably expressed

were incubated with a biotinylated AP-1 consensus

mHoxc6 was then measured. In cells expressing

element probe, and the AP-1 probe was precipitatedeither mHoxc6-V1 or mHoxc6-V2, there was a 55%

with streptavidin beads. Precipitated proteins wereto 50% (both p<0.01) reduction in cell number at 7

separated on an acrylamide gel, and immunoblot-

days, respectively (Figure 6). Thus, mutant forms

ting for Hoxc6 was performed. In control cells, noof Hoxc6 that cannot interact with JunD can inhibit

Hoxc6 was identified in the precipitated complex.

AP-1 activity as well as cellular growth.

However, an interaction between Hoxc6 and theAP-1 probe was identified in extracts from cells

Discussion

overexpressing either wild-type Hoxc6 variant 1 orvariant 2. In contrast, when cells expressed mutant

Intestinal carcinoid tumors remain a fascinating

Hoxc6 (mHoxc6-V1 or mHoxc6-V2), no interaction

clinical entity. Unfortunately, the therapeutic op-with the AP-1 complex was observed (Figure 5).

tions for advanced disease are very limited 20. The

Thus, Hoxc6 directly binds to the AP-1 complex

poor understanding of the molecular genetic altera-on DNA, and this interaction is mediated by thetions that underlie these tumors has hindered thehomeodomain of Hoxc6.

search for new therapies. Defining the key facetsof the molecular circuitry of these unique tumors is

Mutant Hoxc6 inhibits AP-1 activity and cellular

an important prerequisite to the rational design ofgrowthnovel targeted approaches. The current studies have

The functional effects of the interaction between

identified a new molecular pathway in carcinoid23

Figure 6 Mutant Hoxc6 inhibits cellular growth
Proliferation of BON1 cells stably expressing mutant Hoxc6 variant 1 or variant 2 was measured by a colorimetric assay on days 1,
3, and 7 after plating.

tumorigenesis that involves the Hoxc6 homeobox

overexpression of Hoxc6 has thus far been impli-

gene.

cated in the pathogenesis of prostate cancer 12, 13. In

HOX genes are critical regulators of cellular pro-prostate cancer, Hoxc6 appears to regulate neutral

liferation and differentiation during development. A

endopeptidase (NEP) and insulin-like growth factor

link between deregulated expression of HOX genes

binding protein-3 (IGFBP-3), both of which may inand cancer has been observed in many tumor types,

turn regulate apoptosis 13.

but no consistent mechanism of action has yet been

In carcinoid tumors, Hoxc6 appears to function

defined. Although HOX genes are homeodomain

in a novel manner as a potent enhancer of signal-transcription factors that recognize a consensus

ing through the AP-1 pathway, and this is mediated

TAAT motif, their functions in cancer appear to bethrough JunD. There are at least 2 distinct mecha-

10

far more diverse . Overexpression of homeobox
25, 26

nisms for this effect. First, Hoxc6 can modestly, andupregulate JunD. In addition, Hoxc6 can physicallysome of this may be mediated by the upregulation ofinteract with JunD to enhance transcriptional activa-

genes normally targeted during development, suchtion through AP-1, and this interaction is mediatedgenes can induce cellular transformation11

as fibroblast growth factor . However, other non-by the homeodomain of Hoxc6. This contrasts withtranscriptional functions have been defined as well.

the yeast Hex transcription factor. Hex also binds to

For example, Hox11 can control the G2 cell-cycle

AP-1 proteins through the homeodomain, but Hex

checkpoint through its physical interaction withfunctions to inhibit AP-1 activity. This inhibitory

27

activity is strengthened when a Hex binding site isprotein phosphatases PP2A and PP4 .
Our studies have identified a role for Hoxc6 inalso present in the promoter 14. Thus, homeobox

carcinoid tumorigenesis. In the developing mouseproteins may be important regulators of AP-1 activ-

embryo, Hoxc6 is expressed in the spinal cord,

ity, and Hoxc6 is an enhancer of AP-1 activity inprevertebrae, kidney, and selected compartments ofcarcinoid tumors.

28

lung, stomach, and intestine . In human tumors,

The AP-1 transcription factor regulates a diverse

24

Hoxc6 is overexpressed in gastrointestinal carcinoids and interacts with JunD to regulate tumor growth3.

set of cellular processes, and these effects are not

Chandrasekharappa SC, Guru SC, Manickam P, Olufe-

only cell-specific but also dependent upon the bal-mi SE, Collins FS, Emmert-Buck MR, Debelenko LV,ance of specific Fos and Jun proteins. In contrast toZhuang Z, Lubensky IA, Liotta LA, Crabtree JS, Wang
Y, Roe BA, Weisemann J, Boguski MS, Agarwal SK,

c-Jun, the precise functions of JunD remain incom-

Kester MB, Kim YS, Heppner C, Dong Q, Spiegel AM,

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Burns AL, Marx SJ. Positional cloning of the gene forenvironment, JunD can exhibit both pro-proliferative

multiple endocrine neoplasia-type 1. Science 1997;29

as well as growth inhibitory properties . The tu-

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Duerr EM, Chung DC. Molecular genetics of neuroen-interact with JunD, and it can suppress the growth

docrine tumors. Best Pract Res Clin Endocrinol Metabpromoting activity of JunD 30, 31. In contrast, Hoxc6

2007; 21: 1-14.
5.

appears to function in an opposing manner to regu-

Agarwal SK, Kennedy PA, Scacheri PC, Novotny EA,
Hickman AB, Cerrato A, Rice TS, Moore JB, Rao S, Ji

late JunD. The relationship between Hoxc6 andY, Mateo C, Libutti SK, Oliver B, Chandrasekharappa

menin in carcinoid tumors remains uncertain. Stud-SC, Burns AL, Collins FS, Spiegel AM, Marx SJ.

ies in murine embryonic tissue have demonstrated

Menin molecular interactions: insights into normal

6

a strong induction of Hoxc6 by menin . However,functions and tumorigenesis. Horm Metab Res 2005;

menin mRNA levels in carcinoid tumors and BON1

37: 369-74.
6.

cells were very low, and overexpression of menin in

Hughes CM, Rozenblatt-Rosen O, Milne TA, Copeland
TD, Levine SS, Lee JC, Hayes DN, Shanmugam KS,

BON1 cells did not induce Hoxc6 gene expression

Bhattacharjee A, Biondi CA, Kay GF, Hayward NK,(data not shown). Thus, menin does not appear to

Hess JL, Meyerson M. Menin associates with a tritho-

be an important regulator of Hoxc6 expression inrax family histone methyltransferase complex and withadult neuroendocrine tissues.

the hoxc8 locus. Mol Cell 2004; 13: 587-97.

The selective induction of Hoxc6 in carcinoid

7.

Yokoyama A, Somervaille TC, Smith KS, Rozenblatt-tumors but not pancreatic neuroendocrine tumors,

Rosen O, Meyerson M, Cleary ML. The menin tumor

normal pancreas, or normal intestine suggests thatsuppressor protein is an essential oncogenic cofactor
for MLL-associated leukemogenesis. Cell 2005; 123:

there are likely to be tissue-specific mechanisms

207-18.

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8.

tumor pathogenesis, Hoxc6 may also play a role

Karnik SK, Hughes CM, Gu X, Rozenblatt-Rosen O,
McLean GW, Xiong Y, Meyerson M, Kim SK. Meninin specifying the neuroendocrine phenotype. This

regulates pancreatic islet growth by promoting histone

selective upregulation also suggests that Hoxc6 may

methylation and expression of genes encoding p27Kip1

be an important therapeutic target. Potential strate-

and p18INK4c. Proc Natl Acad Sci U S A 2005; 102:

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14659-64.
9.

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Milne TA, Hughes CM, Lloyd R, Yang Z, RozenblattRosen O, Dou Y, Schnepp RW, Krankel C, Livolsi VA,

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Gibbs D, Hua X, Roeder RG, Meyerson M, Hess JL.

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