Download Badrilla Palmitoylation in Cancer

THE IMPORTANCE OF S-PALMITOYLATION IN
TUMORIGENESIS
Summary
What is S-Palmitoylation?
S-palmitoylation is a reversible posttranslational protein modification, whereby
palmitic acid forms a thioester bond with
the sulphur atom of particular cysteine
residues in target proteins.
How is it relevant to oncology?
Oncology includes the study of tumour
formation. Dysregulation of Spalmitoylation affects cell homeostasis,
and can produce tumors. Both insufficient
and excessive S-palmitoylation can
contribute to tumorigenesis and cell
metastasis. A balance of S-palmitoylation
and depalmitoylation thus must be
achieved to maintain normal cell function.
What if it applies to my research?
The CAPTUREomeTM S-Palmitoylated
Protein Kit can be used to identify proteins
modified with S-palmitic acid in your
experimental system.
Figure 1: Schematic diagram
of a DHHC domain-containing
palmitoyltransferase.
DHHC-domain proteins catalyse the
addition of S-palmitic acid to
particular cysteine residues in target
proteins. The white ovals ‘DPG’ and
‘TTXE’ refer to other common amino
acid sequence motifs that appear
across the family as well. Image
created by Alex Bateman.
Read on to find out more!
1.
DHHC Proteins & Tumorigenesis
Proteins with an Aspartate-Histidine-Histidine-Cysteine amino acid sequence are called
DHHC domain proteins, and they catalyse the S-palmitoylation of other proteins within
the cell. Loss-of-function mutations in DHHC-domain proteins are linked to several
types of cancers: zinc finger DHHC-type 2 (ZDHHC2) expression was found to be
significantly reduced in advanced liver and gastric cancer. Li et al.1 (2014) found that
60% of their liver tissue samples taken from patients with hepatocellular carcinoma
presented with low ZDHHC2 expression; this corresponds with Yan et al.2 (2013)
1
findings, where 45% of their study presenting with gastric adenocarcinoma also
exhibited significantly less ZDHHC2 expression as compared to adjacent normal tissue
samples2(p<0.05). Without ZDHHC2, proteins involved in cell fusion and adhesion are
3, and since these cancers tend to
downregulated due
to a lack of S-palmitoylation
S-palmitoylation
acts as
a switch to…
present with a high degree of metastasis4, it can be concluded that ZDHHC2 is required
to enhance cell-cell interactions through S-palmitoylation, and a reduced expression of
this key enzyme contributes to the progression of cancer.
Conversely, other DHHC proteins associated with cancer, such as ZDHHC7 and ZDHHC21,
appear to exacerbate the condition through S-palmitoylation. These enzymes act on sex
steroid receptors to activate the MAP/ERK pathway of cell signalling (see Figure 2).
Figure 2: Schematic diagram of the MAP/ERK pathway activated by
fibroblast growth factor (FGF). Neural cell adhesion molecule (NCAM), usually
expressed only in neurons, also activates the MAP/ERK pathway either through indirect
stimulation of FGFR, or via the proto-oncogene protein Fyn (which in turn activates Ras
to initiate the rest of the MAP/ERK pathway.) NCAM is expressed in certain ovarian
carcinomas, where they lead to aggressive metastasis, and cancer proliferation is
thought to do with activation of the MAP/ERK pathway (Turner & Grose, 201016;
Ditlevsen et al., 200715). S-palmitoylation of NCAM thus results in overstimulation of
this pathway due to an upregulation of its expression on the membrane surface.
2
ZDHHC7 is thought to promote cancer progression via overactivation of the MAP/ERK
pathway, as well as S-palmitoylation of the neural cell adhesion molecule, which is
expressed in aggressive ovarian epithelial carcinomas5. Estrogen receptors are
upregulated in premalignant and malignant breast tumours, and this increase is
associated with the upregulation of other sex steroid receptors which overactivate the
MAP/ERK pathway. Future strategies in treating breast cancer may look at
targeting these DHHC-containing enzymes, or disrupting the S-palmitoylation
process, in order to reduce cancer cell metastasis and proliferation6,7.
2. Ras Palmitoylation in Cancer
Figure 3:
Diagram depicting Ras Spalmitoylation:
(1) Prior to palmitoylation, Ras can interact
with the Golgi and endoplasmic reticulum
(ER) reversibly through transient membrane
attachments.
(2) Palmitoyl acyltransferases (PATs) Spalmitoylates and traps Ras to these
organelles, allowing for packaging and
secretion of these proteins to take place.
(3) Ras is localized to where it is needed
(e.g the pathway in Figure 1).
(4) Upon activation, Ras is depalmitoylated
by surrounding enzymes, allowing it to
transiently return to the cytosol and re-enter
the S-palmitoylation process. (Goodwin et
al. 10)
S-palmitoylation facilitates cell signalling in the human body; hence, inappropriate Spalmitoylation would result in overactivation of the signalling processes, which can
influence gene expression. Ras, found in all cell lineages, are highly involved in
intracellular
pathways
that
regulate
cell
proliferation;
palmitoylation
and
depalmitoylation of these proteins ensure correct localisation, and adjusts
activation and inactivation of their signals as well. The different Ras isoforms
localise to distinct domains either via a Golgi-dependent or Golgi-independent pathway
when S-palmitoylated8 (see Figure 3). Inappropriate Ras activation due to defective
depalmitoylation is present in up to 30% of cancer cases, resulting in uncontrolled
cell growth and proliferation9.
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Ras hyperactivation results in a chronic change in cell signalling, leading to
cancerous cell progression. Depalmitoylation ensures that the Ras proteins are no
longer effective, and are trafficked back to organelles for repalmitoylation or
recycling10.
Compartmentalisation of Ras proteins has also been proven to be essential in
maintaining normal cell function11; while S-palmitoylation serves to localise the
proteins to regions of the membrane containing separate effectors and activators,
other modifications are required to facilitate their movement to and from these
regions. Rocks et al.12 (2005) conducted fluorescence studies to observe the
movement of Ras proteins from Golgi to plasma membrane, and found that
depalmitoylation aided primarily in retrograde trafficking from the membrane to
the Golgi. This suggests that the reversibility of S-palmitoylation is crucial to
maintaining normal cell functions, and any dysregulation results in tumorigenesis.
3. Apoptosis & Palmitoylation
Cell apoptosis is essential in regulating cell numbers and maintaining proper cell
function. Receptors FasL, FasR and death receptor-4 form part of the deathinducing signaling complex (DISC) that activates this process; S-palmitoylation
allows them to carry out their functions at the plasma membrane13. In
tumorigenesis, DISC is down-regulated due to an increase in depalmitoylation. FasR
depalmitoylation is facilitated by acyl protein thioesterases 1 and 2; in Berg et al.
(2015) study of chronic lymphocytic leukaemia (CLL) cells14, a reduced DISC
palmitoylation
status
was
observed
(p<0.02),
and
was
associated
with
overexpression of thioesterases. This suggests that the depalmitoylation of these
death receptors reduced cell sensitivity to external signaling, contributing to tumour
growth and apoptosis resistance.
This emphasizes the importance of S-
palmitoylation in aiding normal cell signaling to prevent deviant cell growth.
In conclusion, a balance between S-palmitoylation and depalmitoylation is required
to maintain normal cell function; any dysregulation that affects this process beyond
normal homeostatic levels leads to tumorigenesis and aberrant cell proliferation,
exemplified by the increased incidences of cancers associated with inappropriate
amounts of S-palmitoylation. This reversible protein modification process is
essential for cell-cell interactions, signalling pathway activation and protein
compartmentalisation within the cell; without it, one can only imagine the
disruptive – or even non-existent- signalling processes that will emerge from a state
of no S-palmitoylation.
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KEY POINTS
u Normal cell signaling and function is achieved by a balance of protein Spalmitoylation and depalmitoylation
u Loss-of-function mutations in DHHC-domains are linked to several types of
cancer
u Inappropriate Ras activation due to dysregulated depalmitoylation is
present in up to 30% of cancer cases
u S-palmitoylation regulates cell apoptosis both by protein activation and
membrane localisation
1. LI, S., TANG, G., ZHOU, D.X., PAN, Y.F., TAN, Y.X.,
4: SHARMA, C., YANG, X.H. & HEMLER, M.E. 2008.
ZHANG, J., ZHANG, B., DING, Z.W., LIU, L.J., JIANG, T.Y.,
DHHC2 Affects Palmitoylation, Stability, and Functions
HU, H.P., DONG, L.W. & WANG, H.Y. 2014. Prognostic
significance of cytoskeleton-associated membrane
of Tetraspanins CD9 and CD151. Molecular Biology of
the Cell, 19(8), pp. 3415-3425.
protein 4 and its palmitoyl acyltransferase DHHC2 in
hepatocellular carcinoma. Cancer, 120(10), pp. 1520-
5: PONIMASKIN, E., DITYATEVA, G., RUONALA, M.O,
1531.
FUKATA, M., FUKATA, Y., KOBE, F., WOUTERS, F.S.,
DELLING, M., BREDT, D.S., SCHACHNER, M. & DITYATEV,
2. YAN, S-M., TANG, J-J., HUANG, C-Y., XI, S-Y., HUANG,
M-Y., LIANG, J-Z., JIANG, Y-X., LI, Y-H., ZHOU, Z-W.,
ERNBERG, I., WU, Q-L. & DU,Z-M. Reduced Expression
A.
2008.
Fibroblast
Growth
Factor-Regulated
Palmitoylation of the Neural Cell Adhesion Molecule
Determines Neuronal Morphogenesis. Journal of
Neuroscience, 28(36), pp. 8897-8907.
of ZDHHC2 Is Associated with Lymph Node Metastasis
and Poor Prognosis in Gastric Adenocarcinoma. PLoS
6:
One. 8(2), e56366. doi:10.1155/2014/832712
Palmitoylation: a protein S-acylation with implications
ANDERSON,
A.M.
&
RAGAN,
M.A.
2016.
for breast cancer. npj Breast Cancer, 2(1), 16028.
3: OYAMA, T., MIYOSHI, Y., KOYAMA, K., NAKAGAWA,
H., YAMORI, T., ITO, T., MATSUDA, H., ARAKAWA, H. &
NAKAMURA Y. 2000. Isolation of a novel gene on
doi:10.1038/npjbcancer.2016.28
7: PEDRAM, A., RAZANDI, M., DESCHENES, R.J. & LEVIN,
E.R.
2011.
DHHC-7
and
-21
are
8p21.3-22 whose expression is reduced significantly
palmitoylacyltransferases for sex steroid receptors.
in human colorectal cancers with liver metastasis.
Molecular Biology of the Cell, 23(1), pp. 188-199.
Genes Chromosome Cancer, 29(1), pp. 09-15
8: LAUDE, A. & PRIOR, I. 2008. Palmitoylation and
localisation of RAS isoforms are modulated by the
hypervariable linker domain. Journal of Cell Science,
121(4), pp. 421-427.
5
9: EISENBERG, S., LAUDE, A., BECKETT, A., MAGEEAN,
C.J., ARAN, V., HERNANDEZ-VALLADARES, M., HENIS,
Y.I. & PRIOR, I.A. 2013. The role of palmitoylation in
regulating Ras function and localization. Biochemical
Society Transactions, 41(1), pp. 79-83.
10: GOODWIN, J., DRAKE, K., ROGERS, C., WRIGHT, L.,
LIPPINCOTT-SCHWARTZ, J., PHILLIPS, M.R. &
KENWORTHY, A.K. 2005. Depalmitoylated Ras traffics
to and from the Golgi complex via a nonvesicular
pathway. Journal of Cell Biology, 170(2), pp. 261-272.
11: OMEROVIC, J., LAUDE, A. & PRIOR, I.A. 2007. Ras
proteins: paradigms for compartmentalised and
isoform specific signaling. Cell Molecular Life Science,
64(19-20), pp. 2575-2589.
12: ROCKS, O., PEYKER, A., KAHMS, M., VERVEER, P.J.,
KOERNER, C., LUMBIERRES, M., KUHLMANN, J.,
WALDMANN, H., WITTINGHOFER, A. & BASTIAENS, P.I.
2005. An Acylation Cycle Regulates Localization and
Activity of Palmitoylated Ras Isoforms. Science,
307(5716), pp. 1746-1752.
13: ROSSIN, A., DURIVAULT, J., CHAKHTOURA-FEGHALI,
T., LOUNNAS, N., GAGNOUX-PALACIOS, L. & HUEBER
A.O. 2015. Fas palmitoylation by the palmitoyl
acyltransferase DHHC7 regulates Fas stability. Cell
Death & Differentiation, 22(1), pp. 643-653.
14: BERG, V., RUSCH, M., VARTAK, N., JÜNGST, C.,
SCHAUSS, A., WALDMANN, H., HEDBERG, C., PALLASCH,
C.P., BASTIAENS, P.I.H., HALLEK, M., WENDTNER, C. &
FRENZEL, L.P. 2015. miRs-138 and -424 control
palmitoylation-dependent CD95-mediated cell death
by targeting acyl protein thioesterases 1 and 2 in CLL.
Blood, 125(19), pp. 2948-2957.
15: DITLEVSEN, D.K., POVLSEN, G.K., BEREZIN, V. &
BROCK, E. NCAM-Induced Intracellular Signalling
Revisited. Journal of Neuroscience Research. 86(4), pp.
727-743.
16: TURNER, N. & GROSE, RICHARD. Fibroblast growth
factor signaling: from development to cancer. Nature
Reviews Cancer. 10(2), pp. 116-129.
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