1.10 The H4K20 Histone Methyltransferases SETD8,
SUV420H1, and SUV420H2
Methylation of H4K20 is catalyzed by the SETD8, SUV420H1, and SUV420H2,
protein methyltransferases in humans [122].
Among the SET domain-containing methyltransferases, SETD8 (also known as
PR-SET7, SET8, or KMT5A) is the sole enzyme responsible for H4K20
monomethylation [123]. H4K20 methylation has been found to play a key role in
processes ranging from DNA damage repair, DNA replication, mitotic condensation,
to the regulation of gene expression [123]. In addition to H4K20, SETD8 has many
nonhistone substrates, including PCNA (PCNAK248me1) and the tumor suppressor
p53 (p53K382me1) [123]. Even though H4K20me is now broadly studied, its
function in gene expression is still not well defined, being associated with both
gene expression and repression [123]. The outcome of H4K20me may vary in relation
to the cellular and genomic context. SETD8 is overexpressed across a number of
cancers including bladder cancer, non-small cell and small cell lung carcinoma,
chronic myelogenous leukemia, hepatocellular carcinoma, and pancreatic cancers
[123], and it is playing a role in invasiveness and metastasis [123]. Additionally,
SETD8 has been reported to be involved in other processes including erythroid
maturation regulation [123], maintenance of adult skin and epidermal proliferation,
adipogenesis and metabolism, and intrauterine growth restriction (IUGR) process
[123]. In 2007, Reinberg et al. reported the first two SETD8 inhibitors: the dye-like
compounds H acid (68) and thymolphthalein (69) (Fig. 9) [124]. Identified through
the screening of a focused library against four MTs (SETD8, G9a, SETD7, PRMT1),
these compounds both displayed dual inhibition against SETD8 (IC 50 : 3.8 and
9.0 μM, respectively) and EZH2 (IC 50 : 3.0 and 25.2 μM, respectively). The cellular
activity of compound 68 could not be appreciated due to cell permeability issues.
Conversely, when tested in HeLa cells, compound 69 induced a dose-dependent
reduction of cell viability together with a marked global H4K20 demethylation,
without affecting other histone marks (not even H3K27me3). Additionally, this
compound dose- and time-dependently enriched the mitotic population, while abrogating the DNA stimulatory effect on SETD8 methyltransferase activity [124].
As the result of different studies aimed to identify epigenetic multiple ligands, Mai
et al. in 2012 reported bis(bromomethoxyphenol)- and bis(dibromomethoxyphenol)containing derivatives as SETD8 inhibitors [125]. Interestingly, compounds
MC1946 (70), MC1947 (71), MC1948 (72), and MC2569 (73) (Fig. 9) displayed
SETD8 selective inhibition with IC 50 values ranging from 2.6 to 10.2 μM. All these
compounds reduced H4K20me1 levels in U937 cells, after 24 h treatment at 50 μM,
and compound 71 induced 28% of granulocytic differentiation and massive cell death
in the same cell line [125].
One year later, the polyketide nahuoic acid A (74, Fig. 9), isolated from Streptomyces sp. cultures, was shown to inhibit SETD8 (IC 50 : 6.5 Æ 0.5 μM) competing
with SAM cofactor (K i : 2 Æ 0.3 μM) and without any significant effect on other
tested MTs [126]. More recently, compound 74 and its penta-acetate derivative have
been shown to inhibit cancer cell (U2OS, SUM159, MDA-MB-436) proliferation
[127]. Further structural manipulation of compound 74, as in its analogues nahuoic
144
G. Stazi et al.
SUV420H1, and SUV420H2
Methylation of H4K20 is catalyzed by the SETD8, SUV420H1, and SUV420H2,
protein methyltransferases in humans [122].
Among the SET domain-containing methyltransferases, SETD8 (also known as
PR-SET7, SET8, or KMT5A) is the sole enzyme responsible for H4K20
monomethylation [123]. H4K20 methylation has been found to play a key role in
processes ranging from DNA damage repair, DNA replication, mitotic condensation,
to the regulation of gene expression [123]. In addition to H4K20, SETD8 has many
nonhistone substrates, including PCNA (PCNAK248me1) and the tumor suppressor
p53 (p53K382me1) [123]. Even though H4K20me is now broadly studied, its
function in gene expression is still not well defined, being associated with both
gene expression and repression [123]. The outcome of H4K20me may vary in relation
to the cellular and genomic context. SETD8 is overexpressed across a number of
cancers including bladder cancer, non-small cell and small cell lung carcinoma,
chronic myelogenous leukemia, hepatocellular carcinoma, and pancreatic cancers
[123], and it is playing a role in invasiveness and metastasis [123]. Additionally,
SETD8 has been reported to be involved in other processes including erythroid
maturation regulation [123], maintenance of adult skin and epidermal proliferation,
adipogenesis and metabolism, and intrauterine growth restriction (IUGR) process
[123]. In 2007, Reinberg et al. reported the first two SETD8 inhibitors: the dye-like
compounds H acid (68) and thymolphthalein (69) (Fig. 9) [124]. Identified through
the screening of a focused library against four MTs (SETD8, G9a, SETD7, PRMT1),
these compounds both displayed dual inhibition against SETD8 (IC 50 : 3.8 and
9.0 μM, respectively) and EZH2 (IC 50 : 3.0 and 25.2 μM, respectively). The cellular
activity of compound 68 could not be appreciated due to cell permeability issues.
Conversely, when tested in HeLa cells, compound 69 induced a dose-dependent
reduction of cell viability together with a marked global H4K20 demethylation,
without affecting other histone marks (not even H3K27me3). Additionally, this
compound dose- and time-dependently enriched the mitotic population, while abrogating the DNA stimulatory effect on SETD8 methyltransferase activity [124].
As the result of different studies aimed to identify epigenetic multiple ligands, Mai
et al. in 2012 reported bis(bromomethoxyphenol)- and bis(dibromomethoxyphenol)containing derivatives as SETD8 inhibitors [125]. Interestingly, compounds
MC1946 (70), MC1947 (71), MC1948 (72), and MC2569 (73) (Fig. 9) displayed
SETD8 selective inhibition with IC 50 values ranging from 2.6 to 10.2 μM. All these
compounds reduced H4K20me1 levels in U937 cells, after 24 h treatment at 50 μM,
and compound 71 induced 28% of granulocytic differentiation and massive cell death
in the same cell line [125].
One year later, the polyketide nahuoic acid A (74, Fig. 9), isolated from Streptomyces sp. cultures, was shown to inhibit SETD8 (IC 50 : 6.5 Æ 0.5 μM) competing
with SAM cofactor (K i : 2 Æ 0.3 μM) and without any significant effect on other
tested MTs [126]. More recently, compound 74 and its penta-acetate derivative have
been shown to inhibit cancer cell (U2OS, SUM159, MDA-MB-436) proliferation
[127]. Further structural manipulation of compound 74, as in its analogues nahuoic
144
G. Stazi et al.