Crem signaling in testis
cAMP responsive element modulator
(CREM) is a member of the basic
domain-leucine zipper class of transcription factors which bind as homo- and heterodimers
to a regulatory palindromic DNA sequence, the cAMP response element (CRE). CRE is
localized in the promoter regions of cAMP responsive genes.
CREM-encoding gene features
multiple sites of alternative splicing. Some splice variants function as activators,
e.g., CREM tau (CREM-activators) and some as repressors,
e.g., ICER (CREM-repressors) of transcription.
CREM is absolutely required for male fertility. The absence
of CREM-dependent transcription in post-meiotic germ cells
results in an arrest of spermatid differentiation and apoptosis [1], [2], [3].
CREM is highly expressed in testis cells. Its mRNA level
is predominantly regulated by the follicle-stimulating hormone
(FSH). The most important signaling pathway, affecting
CREM activity and expression, is Adenylate
cyclase/ cAMP/ Protein kinase A,
cAMP-dependent (PKA (c-AMP-dependent)) -dependent pathway
that is activated by G-protein alpha-s-coupled receptors,
such as Follicle stimulating hormone receptor (FSHR).
CREM gene consists of CRE regions in the promoters and its
expression is regulated by another cAMP responsive element binding protein 1
(CREB1); CREM expression is
alternatively regulated by autoregulatory pathway [3], [4].
In contrast to somatic cells, CREM does not appear to be
phosphorylated in haploid male germ cells, and its activation is not dependent on
phosphorylation or interaction with its coactivator, CREB binding protein
(CBP). CREM activity is
regulated through interactions with a germ cell-specific transcriptional co-activator
Four and a half LIM domains 5
(ACT). The ability of
ACT to regulate CREM activity
is controlled by a germ cell-specific kinesin, Kinesin family member 17
(KIF17), which regulates subcellular localization of
ACT. KIF17 colocalizes with
ACT in haploid spermatids and mediates the transport of
ACT from the nucleus to the cytoplasm at specific stages of
spermatid maturation. KIF17 movement is modulated by
phosphorylation by PKA
(c-AMP-dependent). The ability of KIF17 to
shuttle between the nuclear and the cytoplasmic compartments and to transport
ACT are dependent on neither its motor domain nor on
microtubules [3], [5].
CREM repressors (e.g., ICER) activity is primarily
determined by their intracellular concentration [3], [6], [7].
CREM activators are critical factors in regulation of
transcriptional activity in the spermiogenic program. They are responsible for
transcription of many key genes in postmeiotic germ cells, such as Outer dense fiber of
sperm tails 1 (ODF1), Lactate dehydrogenase C
(LDHC), Angiotensin I converting enzyme
(peptidyl-dipeptidase A) 1 (ACE1), Histone linker H1 domain,
spermatid-specific 1 (HILS1), Transition protein 1
(Tnp1), Hexokinase 2 (HXK2),
Testis-specific serine kinase 2 (TSSK2). During
spermatogenesis CREM repressors inhibit transcription of
many genes such as FSHR [1], [4], [8], [9].
References:
- Sassone-Corsi P
CREM: a master-switch governing male germ cells differentiation and apoptosis.
Seminars in cell & developmental biology 1998 Aug;9(4):475-82
- Monaco L, Kotaja N, Fienga G, Hogeveen K, Kolthur US, Kimmins S, Brancorsini S, Macho B, Sassone-Corsi P
Specialized rules of gene transcription in male germ cells: the CREM paradigm.
International journal of andrology 2004 Dec;27(6):322-7
- Hogeveen KN, Sassone-Corsi P
Regulation of gene expression in post-meiotic male germ cells: CREM-signalling pathways and male fertility.
Human fertility (Cambridge, England) 2006 Jun;9(2):73-9
- Monaco L, Foulkes NS, Sassone-Corsi P
Pituitary follicle-stimulating hormone (FSH) induces CREM gene expression in Sertoli cells: involvement in long-term desensitization of the FSH receptor.
Proceedings of the National Academy of Sciences of the United States of America 1995 Nov 7;92(23):10673-7
- Kotaja N, Macho B, Sassone-Corsi P
Microtubule-independent and protein kinase A-mediated function of kinesin KIF17b controls the intracellular transport of activator of CREM in testis (ACT).
The Journal of biological chemistry 2005 Sep 9;280(36):31739-45
- Fimia GM, De Cesare D, Sassone-Corsi P
A family of LIM-only transcriptional coactivators: tissue-specific expression and selective activation of CREB and CREM.
Molecular and cellular biology 2000 Nov;20(22):8613-22
- Kimmins S, Kotaja N, Fienga G, Kolthur US, Brancorsini S, Hogeveen K, Monaco L, Sassone-Corsi P
A specific programme of gene transcription in male germ cells.
Reproductive biomedicine online 2004 May;8(5):496-500
- Delmas V, van der Hoorn F, Mellstrom B, Jegou B, Sassone-Corsi P
Induction of CREM activator proteins in spermatids: down-stream targets and implications for haploid germ cell differentiation.
Molecular endocrinology (Baltimore, Md.) 1993 Nov;7(11):1502-14
- Nagamori I, Yomogida K, Adams PD, Sassone-Corsi P, Nojima H
Transcription factors, cAMP-responsive element modulator (CREM) and Tisp40, act in concert in postmeiotic transcriptional regulation.
The Journal of biological chemistry 2006 Jun 2;281(22):15073-81
