[CANCER RESEARCH 63, 4792– 4795, August 15, 2003]
Advances in Brief
BP75, Bromodomain-containing Mr 75,000 Protein, Binds Dishevelled-1 and
Enhances Wnt Signaling by Inactivating Glycogen Synthase Kinase-3␤1
Sunhong Kim, Jiwoon Lee, Jeehye Park, and Jongkyeong Chung2
National Creative Research Initiatives Center for Cell Growth Regulation and Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Yusong,
Taejon 305-701, Republic of Korea
Abstract
To identify novel regulators of Wnt signaling, we performed yeast
two-hybrid analyses with Dvl-1 and identified BP75 as a candidate. Here,
we demonstrated that BP75 directly interacts with Dvl-1 in mammalian
cells and enhances TCF-dependent gene expression induced by Dvl-1. In
support of these results, BP75 in cooperation with Dvl-1 was found to
facilitate dephosphorylation at Tyr216 of glycogen synthase kinase-3␤ and
consequently inhibit its kinase activity. Furthermore, the nuclear translocation and formation of vesicular structures of ␤-catenin were induced
by BP75 and Dvl-1 in a synergistic manner. Collectively, these results
provided us a novel mechanism in Wnt signaling where BP75 plays
important regulatory roles between glycogen synthase kinase-3␤ and Dvl.
Introduction
The Wnt family of signaling molecules plays a variety of important
roles in the development of various cancers in humans. The molecular
mechanisms underlying the Wnt pathway have been unveiled in the
past decade, and a general mechanism has been proposed as follows:
the secreted Wnt proteins bind to a family of seven-transmembrane
receptors, Frizzled (1). Activation of the receptor leads to the membrane translocation and hyperphosphorylation of Dvl3 protein (2). In
the absence of Wnt, GSK-3␤ phosphorylates axin, APC, and ␤-catenin, leading to the stabilization of axin and destruction of ␤-catenin
(3). Blocking of GSK-3␤ by Dvl induces the stabilization and accumulation of ␤-catenin in the cytosol and subsequent nuclear translocation of ␤-catenin, where it binds transcription factors, such as
TCF/LEF (4).
The Wnt signaling pathway unveiled thus far, however, has several
vague points. One of the most obscure points in Wnt signaling is how
Dvl prevents GSK-3␤ from phosphorylating critical substrates, such
as ␤-catenin and axin. In the aspect of the regulation of GSK-3␤, there
is evidence that Wnt signaling inactivates GSK-3␤ via protein kinase
C (5). In addition, it was recently demonstrated that frequently rearranged in advanced T-cell lymphomas 1 could bind to Dvl and
GSK-3␤ and prevent GSK-3␤ from phosphorylating axin and ␤-catenin (6, 7). But, these data do not preclude the possibility that a yet
unknown mechanism is involved.
To further understand the regulation of GSK-3␤ by Dvl, we performed yeast two-hybrid analyses with the DIX domain of Dvl-1 as
bait. We showed that BP75 binds to Dvl-1 and enhances ␤-cateninReceived 2/2/03; revised 6/11/03; accepted 7/1/03.
The costs of publication of this article were defrayed in part by the payment of page
charges. This article must therefore be hereby marked advertisement in accordance with
18 U.S.C. Section 1734 solely to indicate this fact.
1
Supported by the Ministry of Science and Technology of Korea and the BK21
Program of the Ministry of Education of Korea.
2
To whom requests for reprints should be addressed, at National Creative Research
Initiatives Center for Cell Growth Regulation and Department of Biological Sciences,
Korea Advanced Institute of Science and Technology, Yusong, Taejon 305-701, Republic
of Korea. Phone: 82-42-869-2620; Fax: 82-42-869-8260; E-mail: [email protected].
3
The abbreviations used are: Dvl, Dishevelled; GST, glutathione S-transferase; PTPBL, protein phosphatase BAS like; GSK, glycogen synthase kinase; APC, adenomatous
polyposis coli; HEK, human embryonic kidney; PDZ, PSD-95/Discs-Large/ZO-1.
and TCF4-dependent transcription synergistically with Dvl-1. Interestingly, BP75 and Dvl-1 cooperatively induced the dephosphorylation at Tyr216 of GSK-3␤ and thus inhibited its kinase activity.
Materials and Methods
Yeast Two-Hybrid Analysis. The cDNA for the DIX domain of mouse
Dvl-1 was cloned into pEG202 plasmid, and the construct was introduced
into the yeast strain EGY48 using a conventional lithium acetate transformation protocol. The transformants were used to screen a HeLa cDNA
library as described (8). In addition to library screening, we performed
several rounds of yeast two-hybrid assays to confirm the interaction between Dvl-1 and BP75.
Cell Culture and Transfection. HEK 293T and COS-1 cells were grown
in DMEM supplemented with 10% fetal bovine serum. Transient transfection
in HEK 293T cells was performed at 50% confluency by a conventional
calcium phosphate method. COS-1 cells were transfected by LipoFectamine
Plus reagents (Invitrogen) according to the manufacturer’s instructions.
Immunoprecipitations and Immunoblot Analyses. For immunoprecipitation, the cells were washed in ice-cold PBS, and then lysed in EBC buffer (9).
12CA5 anti-HA monoclonal antibodies were incubated in clarified lysates for
4 h at 4°C, and protein G beads (Amersham-Pharmacia) were added for
another 1 h. For GST pull-down assays, glutathione-Sepharose beads (Amersham-Pharmacia) were added to clarify lysates. Precipitated beads were
washed twice with EBC buffer. Immunoblotting was carried out according to
a standard protocol. Anti-phosphospecific-Y216 GSK-3␤ antibody was purchased from Upstate Biotechnology, Inc.
Luciferase Assay. Luciferase assays were performed using a dual luciferase reporter assay kit (Promega) according to the manufacturer’s instructions.
GSK-3␤ Kinase Assay. After 36 h of transfection, cells were washed with
PBS and lysed in EBC buffer. HA-tagged GSK-3␤ was precipitated using
anti-HA antibody coupled to protein G-Sepharose beads. GSK-3␤ activities
were assayed as described previously (10).
Immunocytochemistry for ␤-Catenin. COS-1 cells were grown on glass
coverslips and transfected with Myc-␤-catenin, HA-BP75, or GST-Dvl-1.
Anti-␤-catenin antibody (Upstate Biotechnology, Inc.) and FITC-conjugated
antimouse antibody (Sigma) were used for cell staining according to the
manufacturer’s instructions. The samples were observed by a laser scanning
confocal microscope (Carl Zeiss).
Results
BP75 Interacts with Dvl in Vivo. To identify the proteins that
interact with Dvl-1, we carried out yeast two-hybrid analyses with the
DIX domain (amino acids 1– 85) of mouse Dvl-1 (Fig. 1A). Among
1.2 ⫻ 106 transformants, 20 candidates were found to interact with the
DIX domain, and among these, three independent cDNAs were derived from the same mRNA. Comparison of the amino acid sequences
of their predicted protein products with database entries revealed that
the clones were human orthologues of mouse BP75. Indeed, the
interaction between Dvl-1 and BP75 (a generous gift from Dr. W.
Hendriks, University of Nijmegen, the Netherlands) was further confirmed from the supplementary experiments using yeast two-hybrid
analyses (data not shown).
To obtain in vivo evidences for the interaction between BP75 and
4792
BP75 ENHANCES WNT SIGNALING
Fig. 1. BP75 binds to Dvl-1 and augments Dvl-1-induced hTCF4 activity. A, graphical
views of Dvl-1 and its deletion mutant used in the experiments. Evolutionarily conserved
domains, namely DIX, PDZ, and DEP, are indicated. Numbers refer to the amino acid
positions of mouse Dvl-1. In B and C, HEK 293T cells were transiently transfected with
pME18S-HA-BP75, pEBG-GST-Dvl-1, pEBG-GST-⌬N-Dvl-1 (amino acids 201– 695),
or empty vector (control) as indicated. After 36 h of transfection, the cells were lysed for
GST pull down (B) and anti-HA immunoprecipitation (C) assays. The precipitated
proteins were subjected to immunoblot analyses (top and middle panels). The immunoblots for the 1/10 amount of the total immunoprecipitated proteins were presented as a
control (bottom panels). The results shown are representative of three independent
experiments. In D and E, HEK 293T cells were transiently transfected with TOPFLASH
and pRL-TK Renilla reporter plasmids. D, pME18S-HA-BP75, pEBG-GST-Dvl-1, and/or
pEBG-GST-⌬N-Dvl-1 were cotransfected as indicated. In E, pME18S-HA-BP75, pEBGGST-Dvl-1, pcDNA3-Myc-TCF4, and/or pcDNA3-Myc-⌬N-TCF4 were cotransfected as
indicated. Dual luciferase assays were performed. The values in the graphs represent the
mean of three independent cell preparations ⫾ SD.
Dvl-1 in mammalian cells, we cotransfected HEK 293T cells with the
expression plasmids encoding wild-type Dvl-1, ⌬N-Dvl-1 (amino
acids 201– 695; Fig. 1A), and/or BP75 as described in “Materials and
Methods.” When Dvl-1 was pulled down by glutathione-Sepharose
beads, BP75 was specifically coprecipitated with wild-type Dvl-1
(Fig. 1B). In addition, BP75 and wild-type Dvl-1 were specifically
coprecipitated by BP75-specific immunoprecipitation (Fig. 1C), confirming the data obtained in the yeast two-hybrid analysis.
BP75 Enhances TCF4-dependent Transcription by a Dvldependent Mechanism. It has been well established that Dvl can
signal through ␤-catenin and TCF/LEF-1 (4). Moreover, overexpression of Dvl in the absence of Wnt leads to hyperphosphorylation of
Dvl and accumulation of ␤-catenin and thus mimics activation of Wnt
signaling (11). Therefore, to investigate whether BP75, which was
identified as a binding partner of Dvl-1, affects Wnt signaling, we
used a luciferase assay system based on TOPFLASH reporter containing multiple TCF4-binding sequences. As shown in Fig. 1D, Dvl-1
induced luciferase activity (Fig. 1D, Lane 2), but BP75 alone did not
significantly activate the ␤-catenin-dependent transcription activity
(Fig. 1D, Lane 3). Interestingly, however, coexpressed BP75 and
Dvl-1 strongly induced the transcription activity, ⬃5-fold higher than
Dvl-1 alone (Fig. 1D, Lane 4). When ⌬N-Dvl-1 was coexpressed with
BP75, as expected, the luciferase activity was not augmented (Fig.
1D, Lane 5). These results confirmed that BP75 functionally interacts
with Dvl-1 via the DIX domain of Dvl-1 and also demonstrated that
BP75 can enhance Wnt signaling in a Dvl-1-dependent manner.
To further confirm that BP75 can enhance Wnt-dependent transcription, we used a TCF4 mutant (⌬N-TCF4), which lacks the
NH2-terminal 30 amino acids and thus cannot bind to ␤-catenin (3, 4).
When wild-type TCF4 was coexpressed with Dvl-1 and BP75, the
synergistic activation of the transcriptional activity of Dvl-1 by BP75
was maintained (Fig. 1E, Lanes 1– 4) as in Fig. 1D. However, ⌬NTCF4 could not mediate the luciferase activity induced by Dvl-1 and
BP75 (Fig. 1E, Lane 5), confirming that BP75 can enhance Wnt
signaling in a ␤-catenin- and TCF4-dependent manner.
BP75 Enhances Wnt Signaling by Negatively Regulating
GSK-3␤ Activity. As mentioned, GSK-3␤ phosphorylates ␤-catenin
and leads to the destruction of ␤-catenin by specific E3-dependent
poly-ubiquitination (3, 4). To determine whether there is a relationship between BP75 and GSK-3␤, we coexpressed BP75 with GSK-3␤
in a dose-dependent manner. GSK-3␤ reduced the luciferase activity
induced by Dvl-1 to below the control level (Fig. 2A). As we increased the amount of BP75 expression, the luciferase activity reduced by GSK-3␤ expression was recovered (Fig. 2A, Lanes 4 – 6) in
a dose-dependent manner, indicating that BP75 regulates GSK-3␤
activity in vivo.
Next, we performed kinase assays for GSK-3␤ to determine
whether BP75 inhibits the phosphotransferase activity of GSK-3␤.
GSK-3␤ was immunoprecipitated and subjected to phosphotransferase assay. As expected, Dvl-1 expression inhibited the phosphotransferase activity of GSK-3␤ (Fig. 2B, Lane 2). Furthermore, inconsistent with the reporter assays (Figs. 1, D and E and 2A), BP75
enhanced the Dvl-1-mediated inhibition of GSK-3␤ activity (Fig. 2B,
Lane 3), but it was unable to down-regulate GSK-3␤ when ⌬N-Dvl-1
was coexpressed (Fig. 2B, Lane 4). These data strongly suggested that
the mechanism by which BP75 enhances Wnt signaling is correlated
with the inactivation of GSK-3␤.
It has been known that the kinase activity of GSK-3␤ is modulated
by the phosphorylation at an evolutionary conserved residue, Tyr216,
in the activation loop (12). Therefore, we tested whether BP75 regulates the phosphorylation status of Tyr216 of GSK-3␤. GSK-3␤ was
immunoprecipitated by anti-HA antibody, followed by immunoblot
analyses using anti-phosphospecific-Tyr216 antibody. Intriguingly,
Dvl-1 alone decreased the tyrosine phosphorylation of GSK-3␤, and
when BP75 and Dvl-1 were coexpressed, the phosphorylation at
Tyr216 was completely abrogated (Fig. 2C). As expected, coexpression of ⌬N-Dvl-1 and BP75 was, however, unable to block the
tyrosine phosphorylation of GSK-3␤ (Fig. 2C). This result clearly
demonstrated that BP75 enhances Wnt signaling through inactivation
of GSK-3␤.
BP75 Induces the Nuclear Translocation of ␤-catenin. Finally,
we investigated the change in the subcellular localization of ␤-catenin.
COS-1 cells were transfected with ␤-catenin, BP75, and/or Dvl-1 and
immunostained with anti-␤-catenin antibody. ␤-catenin was mainly
concentrated in cell-to-cell contact regions when Wnt signaling was
absent (Fig. 3A). However, ␤-catenin dramatically translocated to the
nucleus in most of the cells when we coexpressed Dvl-1 with ␤-catenin (Fig. 3B), whereas BP75 alone weakly induced the nuclear localization of ␤-catenin (Fig. 3C). Intriguingly, when ␤-catenin, Dvl-1,
and BP75 were expressed simultaneously, ␤-catenin was localized in
the cytoplasmic vesicle-like structures as well as the nucleus (Fig.
3D). Other groups have also observed the localization of Dvl or axin
in this vesicular structure (11, 13–17). These results again confirmed
4793
BP75 ENHANCES WNT SIGNALING
Fig. 2. BP75 blocks Wnt/␤-catenin signaling by inhibiting GSK-3␤. In A, HEK 293T
cells were transfected with TOPFLASH, pRL-TK Renilla reporter, pEBG-Dvl-1, and/or
pCMV5-GSK-3␤-HA as indicated, and pME18S-HA-BP75 was transfected in a dosedependent manner. After 24 h of transfection, the cells were subjected to dual luciferase
assays. The values in the graphs represent the mean of three independent cell preparations ⫾ SD In B, HEK 293T cells were transiently transfected with pCMV5-GSK-3␤-HA,
pEBG-Dvl-1, pEBG-GST-⌬N-Dvl-1, and/or pBOS-BP75-Myc as indicated. After 36 h of
transfection, the cells were lysed, and the lysates were subjected to GSK-3␤ phosphotransferase assays (top panel). Immunoblot analyses for GSK-3␤, Dvl-1, and BP75 were
completed from the same cell lysates (top middle panel, bottom middle panel, and bottom
panel, respectively). The values in the graphs represent the mean of three independent cell
preparations ⫾ SD. In C, HEK 293T cells transfected with pCMV5-GSK-3␤-HA, pEBGDvl-1, pEBG-GST-⌬N-Dvl-1, and/or pBOS-BP75-Myc were lysed, and the lysates were
subjected to immunoprecipitation using anti-HA antibody. After washing the immunocomplexes, immunoblot analyses with anti-phosphospecific-Tyr216 of GSK-3␤ antibody
were conducted (top panel). Anti-HA, -GST, and -Myc immunoblot analyses (top middle
panel, bottom middle panel, and bottom panel, respectively) were also completed from the
same cell lysates, showing that the same amounts of the proteins were used for each
experiment.
tion of how BP75 induces dephosphorylation at Tyr216 of GSK-3␤.
One possibility is that BP75 may transport a protein tyrosine phosphatase(s) to the protein complex consisting of Dvl, axin, APC,
GSK-3␤, and ␤-catenin, leading to the dephosphorylation of GSK-3␤.
A candidate phosphatase is PTP-BL, which has been demonstrated to
bind BP75 both in vitro and in vivo (19). This idea is also supported
by the data that APC binds to the second PDZ domain of PTP-BL
(20). As we have demonstrated the physical interaction between Dvl
and BP75 (Fig. 1), we can propose a model where PTP-BL is recruited
to the protein complex consisting of BP75, APC, and Dvl, and there
it dephosphorylates GSK-3␤ at Tyr216. Additional studies will be
carried out to address this hypothesis.
We also demonstrated that BP75 affects the subcellular localization
of ␤-catenin. Coexpression of BP75 and Dvl-1 induced ␤-catenin not
only to localize in the nucleus but also to translocate to the cytoplasmic vesicular structures (Fig. 3). In previous studies, Dvl has been
detected in punctate vesicular structures (11, 13, 14), which may be
the same structures that we have observed. Moreover, it was reported
that axin, a negative regulator of Wnt signaling, was also localized at
the punctate intracellular vesicles along with Dvl and ␤-catenin (15–
17). These data strongly suggested that the cytosolic components of
Wnt signaling, such as Dvl, axin, and ␤-catenin, are colocalized in the
vesicular structures. Therefore, the ␤-catenin fluorescence signals
shown in the cytoplasmic vesicular structures in Fig. 3D can be the
consequence of stabilization of ␤-catenin by the synergistic effect of
BP75 and Dvl-1; otherwise, GSK-3␤ leads to the destruction of
␤-catenin.
Collectively, we conclude that BP75 is recruited to the Wnt signaling complex by Dvl and induces the dephosphorylation of the
Tyr216 residue of GSK-3␤, which in turn is unable to phosphorylate
its substrate. Consequently, ␤-catenin can be stabilized and translocated to the nucleus. Our novel findings on the role of BP75 provide
an explanation of how Dvl inhibits GSK-3␤ during Wnt signaling.
However, additional studies are required to determine the exact mechanism by which BP75 induces the dephosphorylation of GSK-3␤.
that BP75 exerts a positive role in the Wnt/␤-catenin-dependent
signaling pathway in a Dvl-dependent manner.
Discussion
The activity of GSK-3␤ is regulated by phosphorylation at various
serine and threonine residues, and the sole tyrosine phosphorylation at
Tyr216 plays a critical role in maintaining GSK-3␤ activity. A recent
report demonstrated that Zak1 tyrosine kinase phosphorylates
GSK-3␤ at Tyr216 in the slime mold Dictyostelium (18), whereas the
tyrosine kinase that phosphorylates GSK-3␤ has yet to be discovered
in mammals. Meanwhile, here, we showed that BP75 induces dephosphorylation of GSK-3␤ at Tyr216 and subsequent activation of Wnt
signaling-dependent transcription. This finding gives rise to the ques-
Fig. 3. BP75 regulates the subcellular localization of ␤-catenin. COS-1 cells were
transiently expressed with ␤-catenin alone (A), ␤-catenin and Dvl-1 (B), ␤-catenin and
BP75 (C), or ␤-catenin, Dvl-1, and BP75 (D). After 24 h of transfection, the cells were
fixed and subjected to immunocytochemistry as described in “Materials and Methods.”
The images shown are representative of four independent experiments.
4794
BP75 ENHANCES WNT SIGNALING
Acknowledgments
We thank Dr. W. Hendriks for kindly providing BP75, Dr. R. Nusse for Dvl,
and Dr. J. R. Woodgett for GSK-3␤ plasmids.
References
1. Bhanot, P., Brink, M., Samos, C. H., Hsieh, J. C., Wang, Y., Macke, J. P., Andrew,
D., Nathans, J., and Nusse, R. A new member of the frizzled family from Drosophila
functions as a Wingless receptor. Nature (Lond.), 382: 225–230, 1996.
2. Polakis, P. Wnt signaling and cancer. Genes Dev., 14: 1837–1851, 2000.
3. Cadigan, K. M., and Nusse, R. Wnt signaling: a common theme in animal development. Genes Dev., 11: 3286 –3305, 1997.
4. Eastman, Q., and Grosschedl, R. Regulation of LEF-1/TCF transcription factors by
Wnt and other signals. Curr. Opin. Cell Biol., 11: 233–240, 1999.
5. Cook, D., Fry, M. J., Hughes, K., Sumathipala, R., Woodgett, J. R., and Dale, T. C.
Wingless inactivates glycogen synthase kinase-3 via an intracellular signalling pathway which involves a protein kinase C. EMBO J., 15: 4526 – 4536, 1996.
6. Li, L., Yuan, H., Weaver, C. D., Mao, J., Farr, G. H., III, Sussman, D. J., Jonkers, J.,
Kimelman, D., and Wu, D. Axin and Frat1 interact with Dvl and GSK, bridging Dvl
to GSK in Wnt-mediated regulation of LEF-1. EMBO J., 18: 4233– 4240, 1999.
7. Thomas, G. M., Frame, S., Goedert, M., Nathke, I., Polakis, P., and Cohen, P. A
GSK3-binding peptide from FRAT1 selectively inhibits the GSK3-catalysed phosphorylation of axin and ␤-catenin. FEBS Lett., 458: 247–251, 1999.
8. Koh, H., Lee, K. H., Kim, D., Kim, S., Kim, J. W., and Chung, J. Inhibition of Akt
and its anti-apoptotic activities by tumor necrosis factor-induced protein kinase
C-related kinase 2 (PRK2) cleavage. J. Biol. Chem., 275: 34451–34458, 2000.
9. Lee, D., Sohn, H., Kalpana, G. V., and Choe, J. Interaction of E1 and hSNF5 proteins
stimulates replication of human papillomavirus DNA. Nature (Lond.), 399: 487– 491,
1999.
10. Bijur, G. N., De Sarno, P., and Jope, R. S. Glycogen synthase kinase-3 beta facilitates
staurosporine- and heat shock-induced apoptosis. Protection by lithium. J. Biol.
Chem., 275: 7583–7590, 2000.
11. Yanagawa, S., van Leeuwen, F., Wodarz, A., Klingensmith, J., and Nusse, R. The
dishevelled protein is modified by wingless signaling in Drosophila. Genes Dev., 9:
1087–1097, 1995.
12. Hughes, K., Nikolakaki, E., Plyte, S. E., Totty, N. F., and Woodgett, J. R. Modulation
of the glycogen synthase kinase-3 family by tyrosine phosphorylation. EMBO J., 12:
803– 808, 1993.
13. Axelrod, J. D., Miller, J. R., Shulman, J. M., Moon, R. T., and Perrimon, N.
Differential recruitment of dishevelled provides signaling specificity in the planar cell
polarity and Wingless signaling pathways. Genes Dev., 12: 2610 –2622, 1998.
14. Yang-Snyder, J., Miller, J. R., Brown, J. D., Lai, C. J., and Moon, R. T. A frizzled
homolog functions in a vertebrate Wnt signaling pathway. Curr. Biol., 6: 1302–1306,
1996.
15. Kitagawa, M., Hatakeyama, S., Shirane, M., Matsumoto, M., Ishida, N., Hattori, K.,
Nakamichi, I., Kikuchi, A., Nakayama, K., and Nakayama, K. An F-box protein,
FWD1, mediates ubiquitin-dependent proteolysis of beta-catenin. EMBO J., 18:
2401–2410, 1999.
16. Fagotto, F., Jho, E., Zeng, L., Kurth, T., Joos, T., Kaufmann, C., and Costantini, F.
Domains of axin involved in protein-protein interactions, Wnt pathway inhibition, and
intracellular localization. J. Cell Biol., 145: 741–756, 1999.
17. Smalley, M. J., Sara, E., Paterson, H., Naylor, S., Cook, D., Jayatilake, H., Fryer,
L. G., Hutchinson, L., Fry, M. J., and Dale, T. C. Interaction of axin and Dvl-2
proteins regulates Dvl-2-stimulated TCF-dependent transcription. EMBO J., 18:
2823–2835, 1999.
18. Kim, L., Liu, J., and Kimmel, A. R. The novel tyrosine kinase ZAK1 activates GSK3
to direct cell fate specification. Cell, 99: 399 – 408, 1999.
19. Cuppen, E., van Ham, M., Pepers, B., Wieringa, B., and Hendriks, W. Identification
and molecular characterization of BP75, a novel bromodomain-containing protein.
FEBS Lett., 459: 291–298, 1999.
20. Erdmann, K. S., Kuhlmann, J., Lessmann, V., Herrmann, L., Eulenburg, V., Muller,
O., and Heumann, R. The Adenomatous Polyposis Coli-protein (APC) interacts with
the protein tyrosine phosphatase PTP-BL via an alternatively spliced PDZ domain.
Oncogene, 19: 3894 –3901, 2000.
4795